Some Reactive Intermediates in Organo-Phosphorus Chemistry

Home , Phosphoramidate

SOME REACTIVE INTERMEDIATES IN ORGANO-PHOSPHORUS CHEMISTRY

A Thesis

submitted, in partial fulfilment of the conditions

governing candidates for the degree of

DOCTOR OP PHILOSOPHY

THE UNIVERSITY OF NEW SOUTH WALES

Ian D. Jenkins, B.Sc.

July 1969 &'****» J v' * uii*»y>' (i)

SUMMARY

The decomposition of phenylphosphinic anhydride at room temperature to pentaphenylcyclopentaphosphine, phenylphosphine and phenylphosphonic anhydride has been shown to proceed with formation of the univalent phosphorus compound, phenylphosphinidene. Pentaphenylcyclopentaphosphine reacts with phenylphosphinic acid under mild conditions to give phenylphosphine and phenyl phosphonic anhydride; the reaction appears to involve the unstable phenylphosphinic anhydride as an intermediate. The pentaphosphine reacts with phosphorous and hypophosphorous acids to give a large number of products including phosphine and phenylphosphonic acid.

A convenient gravimetric method for the estimation of several trivalent phosphorus compounds, including phenylphosphine, by oxidation with tellurium tetrachloride, is reported.

Tris(dimethylamino)phosphine reacts with tetraphenylcyclopentadienone to give a stable, 1:1 zwitterionic adduct containing a P-O-C bond. Pyrolysis of this adduct affords hexamethylphosphoric triamide, and a hydrocarbon, , tentatively assigned the structure 1,2,3,4,5»6,6a-heptaphenyl-lObH-benz[e]-as-indacene.

The intermediacy of 5-carbena-1,2,3,4-tetraphenylcyclopenta-1,3- diene in this pyrolytic decomposition is discussed. Tris(dimethylamino )phosphine adds to 1,2,3,4-tetraphenylfulvene in a similar (ii)

fashion to give a stable 1:1 adduct.

Trimethylphosphite reacts with tetraphenylcyclopentadienone to give dimethyl-5-niethyl-2,3>4,5-tetraphenylcyclopenta-1,3-dien-

1-ol phosphate, the 2-ol phosphate isomer, and 1,2,3,4-tetraphenylfulvene. Evidence is presented for initial attack by trimethylphosphite on the carbonyl oxygen atom of the dienone to give a zwitterionic intermediate analogous to that obtained with the aminophosphine and this ketone.

Tetraphenylcyclopentadienone undergoes base-catalysed Michael- type addition of methyl phenylphosphinate, dimethyl phosphonate and diphenylphosphine oxide, with formation of a carbon-phosphorus bond.

Addition both a and p to the carbonyl group was observed, the more sterically demanding nucleophiles resulting in attack at the a position.

Several unusual features in the mass spectra of cyclopentadiene systems are discussed. (iii)

TABLE OF COBTEHTS

Page

INTRODUCTORY SECTION ...... 0 0 0 0 0 0 1

Part A. Phenylphosphinidene from Phenylphosphinic Anhydride 17

Part B. The Reaction of Pentaphenylcyclopentaphosphine

with Phenylphosphinic Acid ...... 0 9 0 0 0 0 26

Part C. Estimation of Phenylphosphine using Tellurium

Tetrachloride ...... 0 9 0 0 0 0 35

Part D. The Reaction of Tris(dimethylamino)phosphine

with Tetraphenylcyclopentadienone 0 9 9 0 0 0 38

Part E. The Reaction of Trimethylphosphite with

Tetraphenylcyclopentadienone ...... 0 9 0 0 0 9 60

Part F. The Reaction of P(lV) Nucleophiles with

Tetraphenylcyclopentadienone ...... 0 9 9 0 0 0 70

Part Gr. Mass Spectra of Cyclopentadiene Systems 0 9 9 0 0 0 173

EXPERIMENTAL SECTION ...... 9 9 0 0 0 0 88

Part A ••• 9 9 0 0 0 0 9 0 0 0 0 0 0 0 0 0 0 0 90

3 0 0 0 0 0 0 9 0 0 0 0 0 0 0 0 0 0 9 0 0 9 98

C 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 9 9 0 0 9 0 113

3 9 0 0 0 0 0 0 0 0 0 0 0 0 0 9 0 9 0 9 0 0 114

ill 0 9 0 0 0 9 0 0 0 0 9 9 0 0 9 0 0 0 9 9 0 140

F 0 0 0 0 0 9 0 9 0 9 0 9 0 0 9 0 0 0 9 0 9 149 (iv)

Page APPENDIX • •• ••• ••• • • • ••• • • # • • • 168

REFERENCES • •• ••• ••• • • • ••• ••• ••• 180

INDEX OF COMPOUNDS 190

ACKNOWLEDGEMENTS ... 192 INTRODUCTORY SECTION

The rapid growth of organophosphorus chemistry over the last two decades can be attributed to its theoretical interest (for example, the recent studies of pseudo-rotation in P(V) structures), its wide practical applications (pharmaceutical preparations, insecticides and fungicides, plasticisers and stabilisers, surface active compounds, extractants, catalysts, fire resistant polymers, lubricating oil additives and additives conferring flame resistance 2 on fabrics, synthetic resins etc.) and, more recently, to the biological significance of these compounds.

2-Aminoethylphosphonic acid (AEPA) was isolated from protozoa of the sheep’s rumen in 1959^ and is distributed throughout the lower phyla in Protozoa, Porifera and extensively in molluscs.

All known natural phosphonates appear to be closely related to or derived from AEPA. Although the biosynthesis of the C-Pbond, and indeed, its function in nature, has not yet been solved, the initial step is believed to be rearrangement of a phospho- enolpyruvate to the phosphonopyruvate. The breakdown of the phosphonates, involving cleavage of the very stable C-P bond, can be performed by a number of bacteria. In the organism Bacillus

Cereus, AEPA undergoes transamination with formation of 2

2-phosphonoacetaldehyde which is then broken down by another 4 enzyme to orthophosphate and acetaldehyde.

2-Phosphonoacetaldehyde appears to be stable in aqueous solution at high and low pH values, but at pH5 and 90° it breaks 5 down to acetaldehyde and phosphate." The breakdown of phosjhonic to phosphoric compounds via a metaphosphate-type intermediate has been the subject of intensive study for many years, because of the suspected role of metaphosphate in the reactions of the 6k biological phosphorylating agent, ATP. Conversion of 2-phosphonoacetaldehyde to acetaldehyde and phosphate at pH5 can bs visualised as proceeding via the hypothetical metaphosphate 'l).

0 - / HO —> HO C X H (1)

h3p°4 + CH^CHO

There is some analogy for this in the conversion of phosphono-amino

g- acids to phosphate in the presence of ninhydrin and a base. " Here also, a system of the type ”0-P(0)(0R)-X-Y=Z^ is the precursor to metaphosphate formation. Breakdown to metaphosphate is a sinple heterolytic fragmentation (X=Y-Z~ being eliminated) of the t^pe 7 reviewed by Grob and Schiess .

The original aim of this work was to study suspected inier- mediates of the metaphosphate type (l), as well as the lower valency - 3 -

forms (2) (metaphosphite, see ref. 8) and (3) (phosphinidenes).

(1) (2) (3)

These three species appear to be highly reactive and whenever they are suspected intermediates, polymeric compounds (RPO^)^,

(RPO)^ and (RP) can usually be isolated. These polymers are themselves quite reactive and attempts to ’trap' (1 - 3) are often complicated by reaction between the trapping agent and the polymers to give the same products expected for the monomeric units.

Although species of type (1) are probably formed in several of the reactions described in this thesis, the only attempt to generate (1) per se was by photolysis (u.v.) of 2-phenyl-1,3»2- dioxaphospholane which could theoretically break down to phenylmetaphosphonate (1, R = Ph) and ethylene. No reaction was observed however, when a Vfo solution of this ester was irradiated in ether for six hours.

The elimination of hydrogen chloride from a phosphinic chloride, RPH(0)C1, seemed to offer a ready route to (2). The phosphinic chloride was to be prepared from the corresponding amide, RPH(o)NR2. All attempts to prepare phenylphosphinic morpholinamide however, led to the isolation of the bis-morpholinium salt of phenylphosphonic anhydride and pentaphenylcyclopenta- - 4 -

phosphine. Moreover, phenylphosphinic anhydride was found to decompose at room temperature to give phenylphosphonic anhydride, pentaphenylcyclopentaphosphine and phenylphosphine. * It seemed more than likely that phenylphosphinidene (3, R = Ph) was involved in these decompositions and most of the work described in this thesis arose from attempts to prove the existence of this fascinating species.

Phosphinidenes are carbene analogues. Phenylphosphinidene has received the most attention of univalent phosphorus compounds, 11 but has been studied very little when compared with nitrenes. 1 2 Pluck and Issleib have claimed the existence of phenylphosphinidene and its dimer in (PhP)^ melts and solutions of these melts in 4 31 benzene or tetrahydrofuran. Their evidence was based on P n.m.r. spectra which showed small peaks at +47.2 (assigned to PhP-)»

+26.1 (assigned to PhP=PPh) p.p.m. as well as the main absorption at +2.0 p.p.m. (H^PO^ = 0.0 p.p.m.). The presence of such large amounts of phosphinidene (detectable by the relatively insensitive

0 -1 P n.m.r.) seems dubious, especially in view of the recent work of Schmidt et al.^ who observed no phosphinidene (m/e 108) in the mass spectrum of pentaphenylcyclopentaphosphine at low ionisation energies ( <10 e.v., 150°) and concluded that the fragments PhP and ^2^2 were f>orme

(and not by electron impact) however, since its intensity relative to Ph(rP[r+ decreased by a factor of 5 after minutes (150°, 20 e.v.). j j - 5 -

* This they attributed to the higher volatility of Ph^P^.

Schmidt et al. point out that some of the reactions attribut

able to phenylphosphinidene can also be described in terms of

diradicals. Irradiation of (PhP),- at low temperature resulted in

a red colour which slowly disappeared as the temperature was

raised. The sample was paramagnetic. The e.s.r. signal was

assigned to the open chain pentaphosphine diradical, PhP-(PPh)^-PPh. 14 The reaction of cyclopolyphosphines with 2,3-dimethyl-1,3-butadiene

(catalysed by u.v. light) to give the tetrahydrophosphorin (4) was

explained in terms of such diradical species. Heating (RP) with

dienes gives both (4) and the phospholene (5) and was presumed to

occur via the Ph^P^ ring. (A Fh^P^ ring has been isolated as a

dianion.^

(5) (4) 16 The exchange reactions that occur with cyclic phosphines,

viz.

(RP)5 + (R'P)n R4R'P5 + R3R'2P5 +.... rr,4P5

can be accounted for either in terms of the phosphinidene or the 1 3 open-chain diradical. Other reactions that may involve phenyl-

Perhaps the high field peaks observed by Pluck and Issleib are due to the trimeric, (PhP)^ and tetrameric, (PhP)^ species, respectively. - 6 -

phosphinidene are the formation of 1,2,3-triphenyl-1,2,3- triphosphaindane from dilithium phenylphosphide and o-bromo- 17 iodobenzene, and the dehalogenation of phenylphosphonous

dichloride with metals.

The structures of the cyclopolyphosphines themselves have only recently been elucidated. "Phosphorobenzene", (PhP)^ was

originally prepared by Kohler and Michaelis in 1877 (Ber. 1_0, 807).

It exists in at least four different forms: A (m.p. 150°),

B (m.p. 190°), C (m.p. 252-286°) and D (m.p. 260-285°).18’19 The 20 most commonly encountered form, A, is pentameric. Compound

B is hexameric and both the trigonal (m.p. 190-5°), and triclinic

(m.p. 185-9°) modifications have a chair conformation with equatorial phenyl groups. They appear to differ mainly in the 21 orientation of the phenyl rings. Compounds C and D have been assumed to be polymeric, but the value of n may not be very 18 22 high. * Compound A is converted to C by heating in piperidine at 80°C; heating C in diphenylether gives A; compound B is converted to A on heating, or on treatment with hydrochloric acid/ 18 benzene. The different polymeric forms do not always undergo the same reactions. The pentamer, for example, is reported to react with nickel carbonyl and with sulphur [to give apparently

(PhPS)^], whereas the hexamer reacts with neither of these substances.^ ®

The nature of (PhP)n in solution is not clear. Both (PhP)^ p p/ and (PhP)^ are reported to be tetrameric, (PhP)^, in solution. 1 - 7 -

For example, in the absence of ether, (PhP)^ reacts with Ni(CO)^

to give (PhP)t-.Ni(CO)^, while with ether as solvent,

(PhP)4.Ni(CO)3 is formed?3

In this thesis, the isolation of the pentamer, A (identified

by its m.p. and mass spectrum) from the decomposition of phenyl-

phosphinic anhydride is described. In addition, pentaphenylcyclo-

pentaphosphine was isolated from the oxidation of phenylphosphine by three quite different methods (cf. phenylstibine, PhSbH^, which loses hydrogen at room temperature giving phenylstibene,

PhSb:, and then polymeric (PhSb)n).^1 Thus, refluxing a mixture

of phenylphosphine and 2,2*-azobis-isobutyronitrile ('hzo-bisnitrile")

in benzene for nine hours gave the pentaphosphine, (PhP)^, 25 The azo-bisnitrile is a known free radical initiator and the most likely mechanism here is hydrogen abstraction from phenylphosphine by isobutyronitrile radicals, Me^CCN. This appears to occur 26 in the analogous oxidation of Ph^PH to Ph^P-PPh^. A second method of oxidation, refluxing phenylphosphine in carbon tetra chloride in the presence of a tertiary base, also gave the pentaphosphine (50i°) • Although a free radical process is possible, an ionic mechanism appears more likely:

+ - -HC1 , PhPH + CC1. —> PhPH-Cl + CC1. -- > PhPHCl + HCC1. --- » (PhP) 2 4 2 3 3 n

The use of carbon tetrachloride and a tertiary base to oxidise 28 dialkylphosphites has been described. ' A third method, the 8

reaction between phenylphosphine and tetraphenylcyclopentadienone

("dienone”) to give the pentaphosphine and 2,3»4,5-tetraphenylcyclopent-2-enone ("mono-enone") probably involves an ionic mechanism also, with initial attack by the phosphorus lone pair on the carbonyl oxygen atom being followed by proton transfer to the dienyl ring (by analogy with reactions described later in this thesis). The conversion of the resulting enolphosphinite (6) to the mono-enone (7) is purely speculative, but may proceed as shown:

■> + PhP: II H

(6) (7)

Schmidt * has reported that diethyluisulphide and benzil are both good traps for phenylphosphinidene. This thesis describes the successful application of benzil in the trapping of phenyl phosphinidene formed by decomposition of phenylphosphinic anhydride. Diethyldisulphide was found to be an unsatisfactory / trapping agent as both the pentaphosphine and phenylphosphine gave rise to the same product expected for the phosphinidene, diethyl- dithiophenylphosphonite. The use of tetraphenylcyclopentadienone as a potential trap for the phosphinidene gave no evidence of formation of a Diels-Alder type adduct (8)

(8) - 9 -

but in the course of this work it was found that phenylphosphinic acid (in the presence of a base such as morpholine or pyridine) rapidly reduced the dienone to the monoenone (7). This observation led to a general study of the reactions of the dienone with

P(lll)^ and P(lV) nucleophiles. It will be shown that the ambident

P(lV) nucleophiles in general undergo Michael addition with P-C bond formation, while the P(lll) nucleophiles attack the carbonyl oxygen atom to give P-O-C structures, one of which has been isolated as a stable, though reactive, solid. An explanation of these findings in terms of Pearson*s concept of hard and soft acids and bases3 is not immediately obvious as both R^P and R2P(o)" nucleophiles would be expected to be ’soft’, while the carbonyl carbon (and to a lesser extent its ’Michael equivalent’) might be considered a fairly ’hard acid’ site. The carbonyl oxygen would

+ — be expected to be a hard base if polarised in the sense R^C-O and

- + 21 a hard acid if polarised in the sense R2C-0, although Pearson classes the carbonyl oxygen as a soft acid. Pearson’s classific ation would be consistent with attack at oxygen by polarisable

P(lll) nucleophiles, but does not explain the Michael addition observed for (soft) R2P(o)”. 32 33 34 Prom recent reviews * and the work of Ramirez, it appears that attack by P(lll) on carbonyl oxygen is most likely to occur when the resulting negative charge at the carbonyl carbon atom is stabilised by electron withdrawal (e.g. trifluoromethyl substitu ents) or by delocalisation. Thus, hexafluoroacetone is reported to - 10

undergo attack at oxygen by R^p34>35 and ^ ^ but the evidence, although strong, is indirect, as no 1:1 adduct was isolated. A recent paper by Ramirez et al. 37 claims that initial attack by tris(dimethylamino)phosphine is on the carbonyl oxygen in aromatic aldehydes containing an electron withdrawing group, but in another recent paper, 34 he claims that the less nucleo philic (i.e. harder) triethyljphosphite reacts with pentafluoro- benzaldehyde to give a 1,4,2-dioxaphospholane (9) which undergoes a slow transformation at room temperature to the 1,3»2-dioxaphospholane (10).

0 — CHC^F.. / i 0 5 / C6P5 (EtO).P 1± (EtO).P 3 \ ' 3 \ CH — 0 C6P5 C6P5

(9) (10)

The formation of (9) would almost certainly involve initial attack by phosphorus at the carbonyl carbon.

Attack at carbonyl oxygen has also been claimed in the 3ft reaction of diphenylketene with triethylphosphite, and in the reaction of R2P-1TR'2 with R"2C0 to give R2P(0 )CR"2NR» .39

Pertinent to the work described in this thesis are the reactions of triethyljphosphite with 2,3~diphenyl.indenone^° and fluorenone,^ of tris(dimethylamino)phosphine with fluorenone,^2 and of triphenylphosphine with 3,4-dicyano-2,5-diphenylcyclopentadienone. 43 11

2,3-Diphenylindenone and triethylphosphite give small amounts of a 1:1 adduct formulated as (11).

(11)

Fluorenone and triethyljphosphite give the cyclic phosphorane

(12) which on heating is converted to the spirocyclic ketone (13) and a small amount (3$) of the alkene (14).

04) 12

Tributylphosphine gave the alkene (14) in higher yield (40$), but triphenylphosphine failed to react. No reaction was observed between xanthone or benzanthrone and P(lll) nucleophiles.^

Pluorenone reacts with the cyclic aminophosphine, 2-N- pyrrolidino-1,3-dimethyl-1,3,2-diazaphospholane, to give a 2:1 adduct analogous to (12). Tris(dimethylamino)phosphine, however,

is reported^ to convert fluorenone to the alkene (14) at room temperature in methylene dichloride solution over a period of

i 4-5 hours. The ~ P n.m.r. evidence obtained by Ramirez (a single peak at 6 -23.9 p.p.m., cf. (Me^N)^PO 6 -23.4) certainly indicates that deoxygenation by the aminophosphine has occurred under these mild conditions, but the isolation of (14) (in 50$ yield) involved a distillation of the phosphoramidate at 150°. It is suggested, by analogy with work described later in this thesis, that formation of (14) and of the phosphoramidate did not occur until the distil lation stage, and that the room temperature reaction may have been simply a formation of the zwitterion (15).

(15) 13 -

31 This suggestion requires a coincidence of the P chemical shifts of (15) and of P(o)(NMe9)y As he obtained no evidence for a 2:1 adduct, Ramirez invoked the formation of (15) followed by loss of P(0)(NTvTe0and formation of fluorenylidene to account for the product (14). However, cleavage of the C-0 bond in (15) and formation of a carbene at room temperature seems unlikely in view of the observed thermal stability of an analogous zwitterion formed between tetraphenylcyclopentadienone and the trisaminophos- phine (see Part D). Only one other stable 1:1 adduct formed from a monoketone and a P(lll) compound has been reported; 3>4-dicyano-

2,5-diphenylcyclopentadienone reacts with triphenylphosphine under very mild conditions (1 hour at room temperature in benzene) to 4 3 give the zwitterion (16).

P( Ph).

(16)

By contrast, triphenylphosphine failed to react with tetraphenylcyclopentadienone even under forcing conditions (16O0,

3 hours) (Part D). Presumably, an additional stabilisation in

(16) results from the strongly electron withdrawing cyano-groups - 14 -

and also from a greater degree of planarity (and hence aromaticity) of the cyano-dienide ring compared with the more crowded tetraphenyl- dienide ring.

In general, trialkylphosphites do not react with simple ketones. Acetone and cyclohexanone, for instance, don*t react o 44 except at ^ 200 under pressure. Benzophenone does not react with trimethylfchosphite, triphenylphosphite or triphenylphosphine at 160°. Tri(isopropyl)phosphite gave (l70°/72 hours) a mixture of products including (Pr^0)2P(0)CHPh2» Pt^CsCPhg, Ph^CHCHPhg and / i \ 44 (Pr 0)^P0. Initial attack at carbonyl oxygen was proposed.

Enolizable ketones react with aminophosphines to give enamines.^’^ The reaction of aminophosphines [and other P(lll) 47 nucleophiles] with di- and tri-ketones has been discussed elsewhere^- and will not be treated here. The products formed are usually of the phosphorane, P(v) type, e.g. (17), involving attack at carbonyl oxygen (ref. 47, Ramirez 1967).

Ph^/0 Ph>/0\ \+ PhCOCOPh + P(NMeo) P(NMe2)3 P(NMe2)3 2'3 / Ph^^o' Ph^^o_

(17) - 15 -

a,p-Unsaturated ketones undergo smooth Michael addition by triethyljphosphite in the presence of a suitable proton donor such 48 as phenol. Thus cyclopent-2-enone reacts as shown. Similarly,

p(or)3 -- pP(0)(0R)2 ------► ^ + PhOR PhOH I! 0

attack by trimethylphosphite and triphenylphosphine on trans- 49 dibenzoylethylene occurs at carbon to give a 1,4-addition product.

Most p-quinones appear to undergo attack at oxygen by trimethyl phosphite. Triphenylphosphine usually attacks at carbon except in 49 such compounds as p-chloranil, when attack is at oxygen.

The addition of P(lV) nucleophiles to a,p-unsaturated carbonyl compounds raises the question of a tautomeric equilibrium:

Vn. R2P-0H

This has been shown to lie almost wholly on the side of the P(lV) 50 structure except for R = CF^, when the P-OH form is stable. The hydrogen atom in PH(0) structures is normally acidic, although treatment of diarylphosphine oxides with ethanolic sodium 51 hydroxide liberates hydrogen, indicating hydridic nature in this instance. Apparently R2PH(o) can act as a nucleophile in the absence of bases. Thus diphenylphosphine oxide adds to 16 -

c:-j p-quinone in benzene to give the 1:1 adduct (18). Usually addition reactions such as this require the presence of catalytic

(18) amounts of base to give the anion R^PCo)", although the alternative

P(lll) form, R^P-O”, is the nucleophile in reactions with phos- 52 phinous halides.

It has been proposed that the P(lll) tautomer, R^POH, serves 53 as a reactive intermediate in the reactions of these compounds.

In the following discussion, apart from a few commonly accepted names [e.g. tris(dimethylamino)phosphine] the nomenclature is essentially that used by the Chemical Society in their Handbook for

Authors (Special Publication No. 14). Thus phenylphosphinic acid is PhPH(0)0H, while phenylphosphonic acid is PhP^XOH)^. The term

’phosphorous acid' is used to denote the substance HP(0)(0H)2 (which strictly is 'phosphonic' acid) and similarly, hypophosphorous acid denotes H^P^^H (which is actually 'phosphinic' acid). The suffix

"ite" indicates a P(lll) structure (i.e. only three groups attached to phosphorus) and the suffix "ate" a P(lV) structure (i.e. four groups attached to phosphorus). - 17 -

The following discussion is divided into two main sections.

The first, comprising parts A, B and C, is directly concerned with the reactive intermediate phenylphosphinidene. The second section

(parts D, E, P) is a study of the reactions of P(lll) and P(lV) nucleophiles with tetraphenylcyclopentadienone.

MThe danger is dogmatic thought; it plays the devil with religion and science is not immune from it." - Whitehead.

Part A Phenylphosphinidene from Phenylphosphinic Anhydride

Much of the work on the formation and decomposition of phenyl phosphinic anhydride was completed in 1965 and is reported in the 54 Q 10 Honours Thesis of I.D. Jenkins and in two publications."’

Part A is a discussion of these former results in the light of new work aimed at the detection of the suspected intermediate, phenylphosphinidene.

Phenylphosphinic anhydride (20) undergoes a facile decomposition at room temperature (half life at 50°C in chloroform was approximately

40 minutes) to phenylphosphonic anhydride (49$)* pentaphenylcyclopentaphosphine (13$) and phenylphosphine (13$). The following mechanisms (Scheme 1) are suggested: 18

0 0 D.C.C. ii n PhPH(0)0H ----—->■ Ph-P-O-P-Ph i i (19) H H (20) 0 0 II II Ph —fj3—0 — P—Ph OH OH (24) OH \ 40x PhP(0)(0H)2 PhP: Ph-Px%5-Ph /_>0

(21)

PhPH

Ph-P 0^ H (22)

A Ph\ 7Ph OH l /p-pv O^P-Ph Ph-p\ xP"Ph (H I P Ph-p- 0 I I ^ Ph H (23)

Scheme I - 19 -

The phenylphosphonic acid formed could be dehydrated by the phosphinic anhydride (20) to give phenylphosphonic anhydride (24) and phenylphosphinic acid (19). (Addition of phenylphosphonic acid, 2 moles, to the anhydride (20) blocked the reaction.) Phenyl- phosphinidene can either polymerise to give the pentaphosphine (23) or abstract hydrogen from the acid (19) or the anhydride (20) to give phenylphosphine. Evidence for hydrogen abstraction from (19) was obtained by carrying out a decomposition of the anhydride (20) in the presence of an excess of the acid (19). The yield of phenylphosphine increased markedly to 45 - 5i.e. 80-100$, based on the previous mechanisms. It was considered that this reaction was good evidence for the intermediacy of phenylphosphinidene.

However, later work has shown that this evidence is complicated by a reaction between the pentaphosphine (23) and phenylphosphinic acid to give phenylphosphine and phenylphosphonic anhydride (see Part B).

Assuming that phenylphosphinic anhydride, upon decomposition, gives equimolar amounts of PhP [in the form of the pentamer (23)] and phenylphosphine (i.e. the approximate ratio determined experi mentally) the stoichiometry of this reaction would be as shown in equation (i):

[PhPH(0)]20 --- > 0.4 PhPH2 + 0.08 (PhP)5 + 0.6 [PhP(0)(OH)]20 ...(i)

This equation can readily be derived from the previous mechanisms and the sequences discussed above. There is no real analogy for these proposed mechanisms, and Kirby and Warren"^ have altered the original 20 -

proposal to one involving fragmentation to phenylmetaphosphonate and the equivalent of phenylphosphine oxide, followed by recombin ation of these two species to give the intermediate (22). Initial fragmentation is unnecessary as the intermediate (22) is readily obtained by a rearrangement involving a 4-membered transition state as shown (Scheme 1). Four-membered transition states are not uncommon in phosphorus chemistry (cf. the Wittig reaction)1 and attack by the phosphorus lone pair on the phosphoryl oxygen is quite conceivable as triphenylphosphine deoxygenates phosphorus oxychloride to give triphenylphosphine oxide and phosphorus 55 trichloride:

Ph^P + P0C13 •V Ph3P0 + PC13

It is intriguing to postulate that the oxidation of phosphorous and hypophosphorous acids by Cr(Vl) (a surprisingly slow reaction) might occur via an intermediate analogous to (21). These oxidations 56 have recently been described^ in terms of initial formation of an anhydride, HO^POCrC^ , followed by a simple fragmentation of the

0 0 II II H+ 0 „ x .OH Eg- QnCr-O-P-H xr r P Cr(IV) + H3P04 I ,*l 0_ OH 21

type 0 Cr^P-OH. OH Decomposition of the anhydride (20) in the presence of benzil, in the dark at room temperature, results in the formation of the phosphorane (25). This is very strong evidence for the postulated

(25) intermediate, phenylphosphinidene. Neither pentaphenylcyclopentaphosphine nor phenylphosphine react with benzil to give (25) under these conditions. The unsuccessful use of diethyljdisulphide as a 10 trapping agent has been described elsewhere. Other unsuccessful trapping agents tried included (i) toluene - the slightest trace of dibenzyl (few p.p.m.) was detected by g.l.c.; PhPH^ and (PhP),- were formed as usual, (ii) t-butyl alcohol - the only product isolated was phenylphosphinic acid (iii) Azo-benzene - a reaction occurred when the anhydride and azobenzene were refluxed together in ethyl'acetate, but phenylphosphine was still formed and in addition, it was found that pentaphenylcyclopentaphosphine reacted with azo- 22

benzene under these conditions to give polymeric (PhP)^(PhN)n complexes. The reaction was not further investigated. (iv) Tetra- cyclone (see introduction), (v) Diphenylphosphine. The use of diphenylphosphine to trap the phosphinidene seemed to be a reasonable idea,(at least in theory). Hydrogen abstraction

PhP: + Ph2PH ----- > PhPH + Ph2P- to give PhPH and the diphenylphosphino radical could result in the formation of either triphenyldiphosphine or tetraphenyldiphosphine. 57 Diphenylphosphino radicals have been observed by e.s.r., and could well be more stable than phenylphosphinidene. The problem lay in the detection of triphenyldiphosphine and/or tetraphenyl diphosphine in the presence of large amounts of other reagents, especially diphenylphosphine. G.l.c. is a possibility, but problems could arise such as the disproportionation of the unsymmetrical diphosphine^ and the possible reaction between (PhP)^ and Ph2PH in the injection block of the g.l.c. An example of this latter type of reaction is the cleavage of (CP^P)^ by primary and secondary phosphines, 59 e.g.

Me2PH + (CF3P)4---- » CF3PH2 + Me^ + CF3P(PMe2)2

The actual method employed was aerial oxidation of the total mixture, but tetraphenyldiphosphine dioxide could not be detected by t.l.c.

To return to the decomposition of phenylphosphinic anhydride, it can be seen that approximately 20°/o of the phosphorus has not been - 23 ~

accounted for (phenylphosphine 13$, pentaphenylcyclopentaphosphine

13$, phenylphosphonic anhydride ~50$). From equation (i), the

theoretical yields would be 20$, 20$ and 60$, respectively. This

discrepancy could be due to the difficulty in isolation and

(quantitative) estimation of the air sensitive phosphines (crude

C A yields of the pentaphosphine (23) were as high as 16$). It was

shown in one experiment that after the isolation of the phosphonic

anhydride, PhPH^ and (PhP)^, some oxidisable phosphorus material

still remained in the filtrate (this was shown by the reduction of

tellurium tetrachloride to elemental tellurium - see Part C).

Other products such as polymeric phenylmetaphosphonate and phenyl-

metaphosphonite might also be present.

Polymeric phenylmetaphosphonite is apparently formed during

the restricted hydrolysis (i.e. with limited amounts of water) of 8d phenylphosphonous dichloride and of phenylphosphonous diamides.

Mizrakh and Evdakov have claimed that the species (PhPO)^ and

(PhPO)^ (which are thought to be cyclic anhydrides with P(lll)

oxidation state) are hydrolysed by water at 80-100° to give phenyl

phosphonic acid (63$) and attribute this oxidation to a

"disproportionation of phenylphosphinic acid". Almost certainly,

the oxidation they observed was due to partial hydrolysis to

phenylphosphinic anhydride (2o) [or higher anhydrides such as

PhPH(0)0P(Ph)0PH(0)Ph which might also decompose in an analogous

fashion to (20)], as phenylphosphinic acid does not undergo dis

proportionation until ^160°. - 24 -

Rearrangement of P(v) to P(lll) compounds is not common,^ the thermal breakdown of phosphinic acids to primary phosphines 61 and phosphonic acids being the best known example [equation (ii)].

rph(o)oh rph2 + rp(o)(oh)9 ...... (ii)

In view of the results obtained with phenylphosphinic anhydride, it is proposed that the disproportionation of phosphinic acids [equation

(ii)] takes place via a thermally formed anhydride, analogous to (20).

The formation of anhydrides in the thermal decomposition of 62 phosphorous and hypophosphorous acids was suspected by Joly in 1886 but only recently has any evidence been obtained for this. 61 Hossenlopp et al. have prepared pyrophosphorous acid, H^P^O^, from phosphorous acid and phosphorous trichloride. These workers tried to prepare higher polyphosphorous acids by treating H^P^O,. (and H^PO^) with dicyclohexylcarbodi-imide (DCC) but obtained only decomposition products; a yellow (P^H)^ compound (analogous to that formed during the decomposition of diphosphine), trimetaphosphate, and polyphosphoric acids, H0(P0^H)nH (n = 6 or 7). Apparently, thermal or mild dehydration (such as that achieved with DCC) of phosphorous acid anhydride leads to decomposition similar to that observed with (20).

The bis-sodium salt of pyrophosphorous acid is more stable than the free acid, but decomposes at ^290° to PH^, orthophosphate and tri- and tetra-metaphosphates.

A pyrophosphorous acid diester, (26) has been prepared from 64 the corresponding monoalkylphosphite and DCC. This is reported - 25 -

II II K’ + RO-P-O-P-OR ------> R* NPH(0)0R + ROPHO " R* NH0 I | 2 v 2 2 2 H H

(26) (27) to be highly reactive, giving a yellow precipitate on standing.

However, the compound must be considerably more stable than the anhydride (20) as it could be purified by molecular distillation.

Also, the diester (26), unlike the analogous phosphinic compound

(20), undergoes a normal anhydride cleavage by secondary amines to give a phosphonic amide (27). These latter compounds are thermally unstable and undergo slow decomposition at room temperature, turning orange and then brown. The products of this decomposition would be of considerable interest as the method described above was precisely that used in the attempted preparation of phenylphosphinic 54 morpholinamide, the original reaction which led to the discovery of phenylphosphinic anhydride and to the hypothesis that phenylphosphinidene was an intermediate in the (unusual) decomposition of this substance.

In conclusion, although most of the trapping agents were either unsuccessful or failed to discriminate between the phosphinidene and pentaphenylcyclopentaphosphine, the benzil reaction provides very convincing evidence for the intermediacy of phenylphosphinidene in the decomposition of phenylphosphinic anhydride.

It was mentioned earlier in Part A that phenylphosphinic acid - 26 -

was an unsatisfactory trapping agent as it reacted with pentaphenylcyclopentaphosphine. This reaction will now be discussed.

Part B The Reaction of Pentaphenylcyclopentaphosphine with

Phenylphosphinio Acid

Pentaphenylcyclopentaphosphine reacts with phenylphosphinic acid (when the reagents are melted together at 85-90° refluxed in a solvent such as benzene or acetonitrile) to produce phenylphosphine and phenylphosphonic anhydride. The experimental stoichiometry of the reaction (which accounts for 9&f° of the phosphorus) is shown in equation (iii):

0 0 n it 3PhPH(0)0H + 0.2 (PhP)c --- > 1.6 PhPH0 + 1.13 Ph-P-O-P-Ph ..(iii) j £ li OH OH

This was determined by varying the molar ratio until virtually complete consumption of reagents was obtained (see Table 2 ,

Experimental). Phenylphosphinic acid is quite stable under these conditions in the absence of the pentaphosphine.

Originally it was thought that the phenylphosphine might be arising by hydrogen abstraction, (28), from the acid by phenylphosphinidene (which could be considered to be in "equilibrium" with the cyclic phosphine (23) - cf. work of Fluck and Issleib) “ but such a simple process is precluded by the observed stoichiometry which requires that some of the phenylphosphine formed must arise, i PhPO + PhPH,

(28) not from the pentaphosphine, but from the phenylphosphinic acid

(Equation iii). This was further confirmed by replacing phenyl phosphinic by p-tolylphosphinic acid: heating a mixture of pentaphenylcyclopentaphosphine (0.3 mole, PhP) with p-tolylphosphinic acid (1 mole) gave a 48:52 mixture of p-tolylphosphine (~0.25 mole) and phenylphosphine (0.27 mole), as well as p-tolylphosphonic anhydride (0.36 mole). This demonstrates that, within the accuracy of the experiment, the (PhP)<- is converted to PhPH^, while at the same time, the tolylphosphinic acid is converted to tolylphosphine and tolylphosphonic anhydride. The similarity between these products and those obtained in the anhydride decomposition reactions (Part A) could well lead to the conclusion that the pentaphosphine is

'effectively' dehydrating the phosphinic acid and that the resulting phosphinic anhydride is decomposing to give the observed products.

Before attempting to write a mechanism in accord with equation

(iii), it is to be noted that the presence of 0.5 mole of base

(morpholine or triethylamine) per 1.0 mole acid, appeared to com pletely inhibit the reaction. Smaller amounts (0.1 mole) did not block the reaction. The formation of deuterated phenylphosphine,

PhPD^, from dp-phenylphosphinic acid, PhPD(0)0D, and the pentaphos phine demonstrated conclusively that hydrogen abstraction was from 28

P-H and/or P-OH (the original reactions were carried out in a

solvent and hydrogen abstraction from the solvent was a possibility).

Further, the pentaphosphine failed to react with methyl phenyl-

phosphinate, PhPH(0)0CH^ (even in the presence of u.v. light),

with dimethylphosphite and with diphenylphosphine oxide, i*e. the

acid function appeared to be necessary. It was also found that the

pentaphosphine reacted with water and with methanol in the presence

of an acid catalyst to give phenylphosphine and phenylphosphinic

acid (in the case of water) and phenylphosphine and methyliphenyl-

phosphinate in the case of methanol. No reaction was observed in

the absence of an acid andofair. Reaction was observed in air in

the absence of an acid, presumably because of prior oxidation of

the pentaphosphine to acidic material. Treatment of the pentaphos phine with formic acid/benzene gave virtually no phenylphosphine, but (PhP)^ could not be reclaimed from the oily mixture.

Trippett et al. have studied reactions of tetraphenyldiphosphine 65 66 with aromatic carboxylic acids J and alcohols but both of these reactions occurred under quite forcing conditions (180-200° or u.v. light) as opposed to the very mild conditions employed above. Their mechanism invoked initial formation of diphenylphosphino radicals.

From the evidence presented, reaction between the pentaphosphine and phenylphosphinic acid probably proceeds via an ionic mechanism in at least the first stages. Protonation of the cyclic phosphine followed by nucleophilic attack at a neighbouring phosphorus by phenylphosphinate anion would give the intermediate (29)» which - 29 -

Ph Ph / P 0 HUP \ 0 PhPhPhPhPh II kN P-Ph II I I I I I Ph-P-0 ▼ P Ph-P-O-P-P-P-P-P-H ( \ / P 1 Ph \ Ph H (29)

PhPH(0)0H V

0 Ph Ph Ph Ph 0 II i i i | || Ph-P-O-P-P-P-P-O-P-Ph + PhPHn 1 | ^ H H

PhPH(0)0H

| etc. V

0 0 0 Ph 0 0 ii II ii i ii II Ph-P-O-P-Ph + Ph-P-O-P-O-P-Ph + Ph-P-O-PHPh + PhPH2 I i 1 1 i H H H H H (31) (30)

0 H-0 II iv N PhPOp + (30) Ph-P-O-P-OrP-Ph Ph-P-OrP-Ph

H Ph 0—H

PhP02 + PhPH2

Scheme 11 - 30 -

could undergo fragmentation as suggested in scheme IT (although the intermediate (29) could "be attacked by phenylphosphinic acid at several other positions). This kind of sequence leads eventually to the structures (30), (31) * phenylphosphinic anhydride and phenylphosphine. The intermediates (30) and (31) could fragment as suggested to give phenylphosphine and phenylmetaphosphonate (which would lead to dehydration of phenylphosphinic acid followed by decomposition to phenylphosphonic anhydride as described in Part A).

The final outcome is the formation of phenylphosphine and phenylphosphonic anhydride, and the stoichiometry (derivable from scheme

II) of this reaction is as shown in equation (iv):

0 0 ll ll 3PhPH(0)0H + 0.24 (PhP)c --- > 1.8 PhPH_ + 1.2 PhPOPPh___ (iv) 0 2 I 1 OHOH

It can be seen that, to a first approximation, the experimentally observed stoichiometry [equation (iii)] is in close agreement with equation (iv) (although it must be emphasised that this offers no justification for the proposed mechanism, as equation (iv) is readily derivable in the absence of a mechanism).

The acid catalysed reactions of the pentaphosphine with water and with methanol could also occur via a mechanism such as that in scheme II. Intermediates analogous to (30) and (31) in the case of water would be PhP^)^ and PhPH(0)0H (i.e. the observed product). 67 Phenylphosphine oxide is known to eliminate water with formation of (PhP)^, but decomposition to phenylphosphine and phenylphosphinic - 31

acid is also possible under the conditions of the reaction. In the case of methanol, the corresponding intermediates would be

PhPH(OMe) and PhP(0Me)2> The latter ester could undergo an acid catalysed Arbuzov rearrangement to methylphenylphosphinate (the main product obtained) while the former intermediate could be oxidised (during 'work-up’) to methylphenylphosphinate. Esters of the type RPH(OR*) are unknown, so that their stability and reactions are speculative.

This discussion is only intended as a relatively simple rationalisation which is compatible with the experimental findings.

The reaction appears to be far more complex than is indicated above.

For example, it is not apparent why a reduction in the amount of pentaphenylcyclopentaphosphine from 0.24 mole [the amount required by equation (iv)] to 0.20 mole (and in one case 0.18 mole - see

Experimental, Table 2) should have virtually no effect on the yield of phenylphosphine. This lower stoichiometry requires that some water be liberated (from the phenylphosphinic acid) or alternatively, that the phenylphosphonic anhydride be accompanied by phenylphosphonic acid as shown in equation (v). This equation was derived by

3PhPH(0)0H + 0.2 (PhP)^ --- > 1.666'PhPH2 + 1.0 [PhP(0)0H]20 +

0.333'PhP(0)(OH)2 ..... (v) assuming that the molar ratio of reagents, 3:0.2, [of. equation (iii)] gave rise to unknown amounts of the three products indicated. The presence of some phenylphosphonic acid is not inconsistent with the experimental findings, as the crude isolated morpholinium salt (of - 32 -

the phosphonic ’anhydride’) had a melting point some 10-20° lower than the pure phosphonic anhydride salt.

The reaction of the pentaphosphine with phenylphosphinic acid was extended to phosphorous and hypophosphorous acids. Both of these reactions proved to be very complex and were not intensively studied. In summary, melting a mixture of phosphorous acid and the pentaphosphine gave rise to phosphine, phenylphosphine, phenylphosphonic acid, phosphoric acid and pyrophosphoric acid. The relative amounts of these products depended, not only on the molar ratio of reagents, but also on the presence or absence of a solvent, and the reaction time. The amount of phosphine formed was usually quite high, accounting for some 30-5of the phosphorous acid, e.g.

hp(o)(oh)9 + 0.09 (PhP)s--- > o.36 ph3 + 0.45 h4p2°7 + °*04 PhPH2

+ 0.4 PhP(0)(0H)2 and

HP(0)(0H)o + 0.12 (PhP)c---- >0.5 PH3 + 0.24 H^O^ + 0.02 PhPIl2

+ 0.36 PhP(0)(0H)2

(see also Table 3 , Experimental).

In addition to these products, a yellow amorphous powder was usually isolated. It had a mass spectrum not dissimilar to that

of pentaphenylcyclopentaphosphine but in addition had strong peaks at m/e 51°, 448. The strongest peak in the spectrum was at m/e 108, i.e. PhP. The substance is almost certainly a mixture, the main component having the composition (PhP)^OPp (m/e 51°). The peak - 33

corresponding to (PhP)^ (i.e. m/e 540) was quite weak. The 448 peak

corresponds to loss of P^ from (PhP)^0P,_, and is accompanied by a

metastable at ~393.7. Another strong metastable at ~ 234.5 could result from the transition 448 “>324 [i.e. (PhP)^O —> (PhP), + PhPO] but could also be attributed to 293 > 262 [i.e.

Ph3P? ~> Ph3P + P],

Hypophosphorous acid appeared to react with the pentaphosphine

in an analogous fashion, e.g.

H2P(0)0H + 0.12 (PhP)5 —-> 0.44 PH3 + 0.12 PhPH2 +

pyrophosphate + PhP(0)(0H)2 + two other uncharacterised acids.

The mechanism of the reaction of phosphorous and hypophosphorous acids with the pentaphosphine is presumably closely related to the phenyl phosphinic acid case.

To conclude this section, one final reaction which bears on the ionic mechanism proposed above, will be discussed. The original idea of hydrogen abstraction (28) from phenylphosphinic acid by phenylphosphinidene suggested a reaction between 2,2*-azobis-isobutyro- 25 nitrile, a known free-radical initiator, and phenylphosphinic acid.

When phenylphosphinic acid and the azo-bisnitrile (2 moles) were refluxed in benzene (5 hours under nitrogen), pentaphenylcyclopentaphosphine (11 $£) was isolated. The other major product appeared to be polymeric phenylmetaphosphonate, as addition of morpholine to - 34 -

the solution gave the phosphoramidate salt (32) (40$), together with the morpholinium salt of phenylphosphonic anhydride (19$).

Moreover, this reaction could be carried out in the presence of an excess of morpholine, clearly differentiating it from the base-inhibited pentaphosphine reaction. The following (free- radical) mechanism is suggested (scheme III) in which the first

• step is hydrogen abstraction by isobutyronitrile radicals, Me^CCN.

0 II . -H' Ph OH 0-- > PhP02

H hnr2 v 0 II + Ph - P - NR0 H NR, | d d s / \ hr2 = N 0 0- \___/ (32)

Scheme III

The phenylmetaphosphonate formed could either polymerise or react with phenylphosphinic acid to give phenylphosphonic anhydride and phenylphosphinic anhydride. Reaction with morpholine would give the phosphoramidate (32). (This substance is converted to the morpholinium salt of phenylphosphonic anhydride upon recrystallis ation from moist ethylacetate.) The pentaphosphine presumably arises from decomposition of phenylphosphinic anhydride. No phenylphosphine would be isolated as this substance reacts with the azo- bisnitrile to give pentaphenylcyclopentaphosphine. 35 -

Part C Estimation of Phenylphosphine with TeCl^

The reactions described in Parts A and B necessitated the development of a quick means of quantitatively determining small

quantities (5-500 mg) of the highly air sensitive phenylphosphine, both neat and in dilute solution in organic solvents. All the

initial work was done by comparative g.l.c. with standard phenyl phosphine solutions, but the method proved to be tedious and was

only approximate.

It was found that tellurium tetrachloride was reduced

essentially quantitatively at room temperature to elemental tellurium, which could be removed by filtration, and weighed. The determination, which was clean, rapid and reproducible, was carried out by simply adding an excess of TeCl^ dissolved in a solvent such as methanol, acetonitrile or acetone, to the phenylphosphine dissolved in benzene. The mixture was allowed to stand for ~ 5 minutes, filtered, and the tellurium dried under vacuum and weighed.

This method was extended to other P(lll) compounds and was found to be applicable to pentaphenylcyclopentaphosphine, triphenylphosphine and tris(dimethylamino)phosphine. The four P(lll) compounds mentioned all precipitated between 9? and 99i° of the theoretical amount of tellurium. The stoichiometry of the reaction is shown in equation (vi). Several P(lll) compounds,

RxPHy + ■5-S-j-tJC TeCl4 ---- » / --J Te + yHCl +

^(S-x) (vi) - 36 -

trimethylphosphite, tributylphosphine and phosphorous trichloride, failed to give near quantitative yields of tellurium. In the case of trimethylphosphite, the decreased yield of tellurium (80$) could well be due to an Arbuzov-type isomerisation to dimethyl- methylphosphonate induced by the TeCl^. Tributylphosphine appears to form complexes, as cautious addition of Bu^P to an excess of

TeCl^ in acetone resulted in a reddish colouration. No tellurium formed until the mixture was heated.

Tellurium tetrachloride was also reduced (99$) by the P(lV) compound phenylphosphinic acid, but the reaction was much slower and required heating. The reaction was found to be faster in methanol than in acetonitrile. Estimation of phenylphosphine and of pentaphenylcyclopentaphosphine in the presence of a large excess of phenylphosphinic acid would have been useful, but the technique was found to be unsatisfactory in this case. The large amount of heat generated at the site of reduction of the P(lll) compound was apparently sufficient to bring about reduction of a large amount of the phenylphosphinic acid as well. Phenylphosphinic acid gives

0.5 mole Te by virtue of the single oxidisable P-H [equation (vii)].

PhPH(0)0H + 0.5 TeCl^ ---> 0.5 Te + HC1 + PhPCl(0)0H...... (vii)

In the course of this investigation, two tellurium halide complexes were isolated. The first, a red complex prepared by dissolving elemental tellurium in a mixture of bromine and pyridine in methanol, analysed for TeBr^.C ^N^ and is assigned the - 37 -

- £\ r— —» — structure TeBr^ ,2C^H^NH by analogy with the known Cs^LTel^J complex. The second, a yellow complex, prepared from TeCl^ and morpholine hydrochloride in methanol/acetonitrile analysed for

TeC18•C16h4oN4°4' 69 Some Russian workers ' have reported complexes of the type

(HITR^^TeClg (R = n-octyl) and (HNR^)TeCl^_, and a morpholine complex has been^ assigned the structure [TeCl^(MR^

(HNR0 = morpholine), but complexes of TeCl^ associated with as many as 4 chloride ions do not appear to have been mentioned. The above yellow complex probably has a lattice made up of TeCl^- anions, chloride ions and morpholinium ions. - 38 -

Part D The Reaction of Tris(dimethylamino)phosphine with

Tetraphenylcyclopentadienone

Tris(dimethylamino)phosphine reacts with tetraphenylcyclo pentadienone (when the reagents are stirred together under nitrogen at room temperature for 3 days or refluxed in benzene for 1-2 hours) to give the zwitterion (33) in high yield. It can be isolated as

Ph^____ /Ph

Ph^Vj^Ph II 0 :P(NMe2)3

(33)

white or very pale straw-coloured crystals which are indefinitely stable in the absence of air and moisture. The crystals rapidly turn red upon exposure to air due to the regeneration of the dienone.

Dissolution in chloroform also gives the red dienone colour and n.m.r. indicates the slow formation of (MeoN)^P0 [cf. work of 4-2 Ramirez^ with (15) in methylene dichloride].

The structure of the zwitterion (33) was assigned on the basis of microanalyses, spectroscopic data and its chemical reactions.

There was no carbonyl or phosphoryl absorption in the infrared - 39 -

spectrum. Absorptions at 1060, 1000 and 973 cm" may be attributable

to P-O-G and P-N-C vibrations.

The n.m.r. spectrum in deuterochloroform gave a ratio of N-Me

protons to aromatic protons of 18:20. The spectrum in benzene

showed a doublet at 61,71 due to the N-Me protons. This is at quite high field [cf. P(NMe2)3, 62.55; PO(NMe2)3, 62.50; both in CgHg] and 31 is attributed to shielding by the negatively charged ring. P n.m.r.

in pyridine showed a broad multiplet at 6-31.8 p.p.m. (6 H-^PO^ = 0)

consistent with the structure (33) but incompatible with a dimeric

P(v) structure, which would be expected to have a large positive 71 chemical shift.

The zwitterion (33) does not appear to decompose until near

the m.p. and is quite stable at 120°. Though stable to aqueous

alkali, it is readily decomposed under acidic or neutral conditions.

Hydrogen bromide converts it to 5-bromo-1,2,3,4-tetraphenylcyclopenta-

1,3-diene (34; X = Br) in high yield, but sulphuric acid gives only a bisulphate salt of (33) from which the zwitterion can be regenerated by treatment with aqueous base.

(34) - 40 -

Methyl iodide reacts with (33) to give fiery-red crystals of

1 ,2,3,4-tetraphenylfulvene (36), which could arise by elimination

of hydrogen iodide from an initially formed iodo-methyldiene, or attack by iodide ion on a C-methyl hydrogen atom in (35) with

simultaneous expulsion of the phosphoric amide. The fulvene (36) reacts with the amino-phosphine to give a colourless adduct (37),

Ph\ /Ph Mel ‘Ph I" Me 0 —P(NMe2)3 2'3 (35)

-(Me2N)3P0,HI

Ph\_____ ^Ph

ii ch2

(36)

analogous to (33). Extension of this alkylation reaction to the preparation of substituted tetraphenylfulvenes seems quite feasible, but was not investigated. The zwitterion (33) reacts with dimethylamine in ethanol (but not in benzene) to give the dimethylamino-diene (34; X = NMe9). These transformations can all be rationalised in terms of initial protonation (or alkylation) of the dienide ring, followed by displacement of the phosphoric amide, and formation of the very stable phosphoryl bond.

Oxidation of (33) by air or hydrogen peroxide gives the dienone but only in ~50$ yield. Possibly breakdown of a peroxide

(38a) or (38b) would give rise to the phosphoramidate (1 mole), the dienone (1 mole), and ’nascent oxygen' (1 gm atom) which could bring about rapid oxidation of dienone (0.5 mole) to give cis- 72 dibenzoylstilbene formed from a peroxide such as (39)»

Ph\ •Ph

Ph ■Ph ph^\/^Ph 0 0 II K i 0 (m2n)3p —— n*

(38a) (38 b) (39)

The formation and stability of (33) may be rationalised as follows. Tris(dimethylamino)phosphine is a very nucleophilic substance with a very polarisable lone pair of electrons on the phosphorus atom. Polarisation of the dienone carbonyl group in

— + the sense R^C-O would be favoured by the extensive delocalisation possible for the negative charge, while formation of the phosphorus- - 42 -

oxygen bond would result in a phosphonium cation much stabilised by the attached nitrogen atoms. Stabilisation by nitrogen might + occur through resonance forms such as H^P=NMe^, and certainly the

P-TT bond in dialkylaminophosphonium compounds and in phosphoramid- ates is far more stable to hydrolysis than in P(lll) compounds; thus P(NMe2)^ is hydrolysed by water, while PC^NMe^)^ is stable to boiling aqueous alkali. 73 Another (controversial) factor that may influence attack by phosphorus at oxygen is d-orbital participation.

As bond formation between oxygen and phosphorus proceeds, the developing positive charge on phosphorus could contract the diffuse

3d orbitals^ and allow back donation by oxygen (as well as nitrogen), 74 thus facilitating formation of a strong P-0 bond, A developing negative charge on the oxygen atom is quickly transferred to the dienyl ring to give a potentially aromatic (6'7Telectron) system.

The bulk of the four phenyl groups could severely hinder formation of a planar 5-membered ring so that extensive delocalisation of the negative charge into the phenyl rings might well be as important as stabilisation arising from aromaticity in a cyclopentadienide ring

(which would require a propeller-like configuration of the phenyl groups around the ring).

The failure of triphenylphosphine to react with the dienone

(even under forcing conditions) to give an adduct analogous to (33) is presumably due to the decreased nucleophil.icity of this phosphine

(relative to the aminophosphine) and also to the lack of stabilisation of the phosphonium cation by the phenyl groups. Stabilisation of - 43 -

the positive charge on phosphorus is possibly the more important factor, as trimethylphosphite, which is even less nucleophilic than 75 triphenylphosphine, reacts with the dienone in a similar fashion to the aminophosphine [although the zwitterion analogous to (33) is unstable and cannot be isolated - see Part E],

Pyrolysis of the zwitterion (33) at 160-180° results in loss of the phosphoric amide, PO(NMe^)^, and formation of a colourless hydrocarbon, (80$). The molecular formula of this substance corresponds to a deoxy-dienone-dimer (hereafter called "the dimer") and was confirmed by high resolution mass-matching. Its n.m.r. spectrum (100 Me), which shows a single non-aromatic proton (singlet

65.232) and ca. 39 protons, excludes octaphenyl fulvalene as a possible structure. An odd feature in this n.m.r. spectrum is the division of the aromatic protons into a low field group (~35H) and a high field group (~4H), the high field group lying just out of the normal aromatic range (of 68-66.6 observed for all other aromatic compounds in this thesis) by approximately 0.2 p.p.m. As 76 steric compression usually gives rise to a downfield shift, perhaps this upfield shift is due to shielding of some of the aromatic protons by a neighbouring phenyl ring, i.e. the structure of the dimer is such that some of the aromatic protons are forced to lie within the shielding zone of a phenyl ring. [The structures proposed later for the dimer, (43-47), show a very close proximity of the phenyl groups in the 3,4- positions.]

The chemical shift of the single non-aromatic proton corresponds - 44 -

to a dienyl-hydrogen, cf. 1,2,3»4,5-pentaphenylcyclopentadiene (40),

65.07 and 1,1’-dihydrooctaphenylfulvalene (41), 64.999 p.p.m.

ph :>r"Ph H ^ H Phv^X/Ph

^Ph

(40) (41)

The dimer is a remarkably stable substance being unaffected by refluxing trifluoroacetic acid, by irradiation with ultraviolet light (in benzene solution) and by heating at 360°. It can be recovered in high yield after refluxing in potassium permanganate/ sodium periodate solution, or alkaline hydrogen peroxide. Catalytic hydrogenation had no effect and formation of a Diels-Alder adduct with maleic anhydride or tetracyanoethylene could not be induced.

When the dimer was stirred with powdered sodium in dimethoxyethane, an intensely coloured solution resulted, which, upon addition of methanol, gave a complex mixture of dihydro-dimer isomers and starting material. Ozonolysis decomposed the dimer, but very complex mixtures were again obtained.

Although oxidations under neutral and alkaline conditions were - 45 -

unsuccessful, oxidation was achieved under acidic conditions: potassium permanganate/acetic acid, chromium trioxide/acetic acid and chromium trioxide/trifluoroacetic acid. Oxidation with chromium trioxide in trifluoroacetic acid gave benzoic acid, phthalic anhydride and o-benzoylbenzoic acid. These products were identified by conversion of the acidic material from the oxidation to methyl esters which were examined by gas chromatography. The presence of o-benzoylbenzoic acid, which was confirmed by treatment of the ester mixture with oleum and isolation of anthraquinone (3.3$)» indicates that the structural unit (42) is present in the dimer.

(42)

With this limited chemical and physical evidence, five possible structures may be drawn (43-47). Structures containing a fulvenic double bond have been excluded on the basis of the u.v. spectrum which showed no absorption attributable to the long wavelength band

of the dimer render a fulvalene structure rather unlikely - 46 -

2,3,4,2’,3',4*-Hexaphenylfulvalene, for example, gives dark khaki 77 crystals.

It has not been possible to distinguish unequivocally between the five possibilities for the structure of the dimer. Prom a study

of models, strain could result from an interaction between the phenyl groups in the 3 and 4 positions. This interaction is least in (45) by virtue of the tetrahedral carbon atom at position 3. - 47 -

Structure (44) should differ from the remaining four, in that

there can be no conjugation between the two dienyl rings.

Structures (43)» (45)» (46) and (47) would be expected to exhibit a somewhat longer wavelength band in the u.v. than an isolated tetraphenylcyclopentadiene system. The u.v. spectrum of the dimer

does in fact exhibit a strong absorption at X 362 m^ (log e 4.13* max cyclohexane); cf. 1,2,3,4-tetraphenylcyclopenta-1,3-diene, X in six 343 (log 6 4.10, cyclohexane). An additional band at 310 m/j,

(log e 4.39) in the dimer, but absent in the diene, awaits inter pretation but might be attributed to a 1,2,3-triphenyl-1,3-diene chromophore; cf. 1,2,3-triphenyl-4-methylcyclopenta-1 ,3-diene, 7 8b 318 mft (log e 4.14, ethanol). Conversion of the dimer to a monobromoderivative (discussed later) followed by reduction with lithium aluminium hydride regenerates the dimer, but in addition, a small amount of an isomeric material (with an identical mass spectrum to that of the dimer) which lacks the long wavelength band at 362 m/j, in the u.v. is obtained. This also exhibits the unexplained absorption at 312 mfj. (log e 4.47, cyclohexane). On the basis of this u.v. data, the isomeric dimer is assigned structure (44). Of the remaining four possibilities, structure (43) is assigned to the dimer itself, mainly on the grounds that the single hydrogen in (43) has the least distance to move (cf. Rice and Teller’s principle of least motion)^ from its original position on the ortho substituted phenyl ring (50), as shown in the following proposed mechanism

(scheme IV). This assignment, on the basis of mechanism, has the - 48 -

Ph\_____/Ph Ph\____ /Ph

I i (Me2N)3P0 Phx'\^''Ph

0 + ^P(NMe2)3 (48)

Scheme IV - 49 -

necessary corollary that (43) is probably the most stable of the five possible isomers, as only one isomer (indeed one stereoisomer) is obtained from the pyrolysis of (33)» and this isomer cannot be rearranged either photochemically or under acid conditions. Also, in reactions of dimer-derivatives where (43) - (47) could conceivably be formed (discussed later) the same dimer is always obtained in major amount; the isomeric dimer assigned structure (44), although isolated on several occasions, was always a minor product.

A possible pathway for the formation of (43) - (47) is shown in scheme IV.

Initial formation of the carbene (48) could be followed by attack of this (electron deficient) species on the electron rich dienide ring of (33) to give the complex (49). Loss of PO(NIvTe^)^ followed by a 1,3-proton shift in (58) would give the proposed dimer structure (43). This attack of carbene on precursor appears to be a more likely process than dimerisation of (48) as dimerisation of carbenes is rare,^ Attempts to trap the carbene (48) were not very successful. Thus, pyrolysis of (33) in high boiling solvents

(diglyme, mesitylene) where hydride abstraction might be expected

to predominate over the sterically demanding processes of dimeris ation of (48), or attack of (48) on the precursor (33)> still gave the dimer as the principal product. Apparent hydride abstraction was

observed when the zwitterion (33) was heated with phenylphosphine

(or diphenylphosphine) at 160°. The products obtained were 1,2,3*4- tetraphenylcyclopenta-1,3-diene (52), dihydrofulvalene (4l), dimer, - 50 -

and pentaphenylcyclopentaphosphine (or tetraphenyldiphosphine isolated as the dioxide). However, a similar reaction

^Ph

PhPH- Ph^\^-ph (33) + + Dimer (43) + (PhP)^ Ph\^>V/Ph H H PhT kPh

(52) (41)

occurred between (33) and phenylphosphine in refluxing benzene solution; the diene (52) was obtained in high yield, but there was no detectable formation of dihydrofulvalene (41) or dimer (43).

This indicates that the diene (52) can be formed by attack of the phosphine on the zwitterion (33) without the necessity for prior formation of a carbene. In the higher temperature reaction, however, formation of all three hydrocarbons is readily explained in terms of the carbene intermediate, and this is further evidenced by a greatly increased yield of the dihydrofulvalene (to ~ 45$) when the amount of phosphine is reduced (to 1 mole of P-H). It is suggested that decomposition of the zwitterion (33) in the presence of an excess of the diene (52) might well give rise to the dihydrofulvalene (41) which would provide further support for the intermediacy of (48). 51

The attempted trapping of the carbene (48) by diethyl maleate

(a successful trap for the carbene from diazofluorene) and by

triphenylphosphine or tris(dimethylamino)phosphine was also

unsuccessful, the dimer being the major product isolated in each

case. It is difficult to see why a carbene, apparently too steric

ally hindered to react with diethyl maleate, should nevertheless

react with the zwitterion (33) or with itself. Perhaps (48) is a

relatively stable carbene and has a greater preference for centres

of high electron density (i.e. 33) due to the very electrophilic

carbon atom in the resonance structure (53).

Ph\____ /Ph Ph\ /Ph

Ph^^J^Ph Ph^^^Ph +

(53)

Irradiation of a benzene solution of the zwitterion (33) with

ultraviolet light afforded 1,2,3,4,5-pentaphenylcyclopentadiene (40),

in 27io yield. A similar irradiation of 5-diazo-1,2,3>4-tetraphenyl-

cyclopenta-1,3-diene (54) also afforded the pentaphenyldiene (40) but in low yield (8$). Pyrolysis of the diazodiene (54) however,

gave no trace of the dimer (43). 82 Durr and Scheppers, who have studied the photolysis of the

diazodiene (54), offer strong evidence for the formation of 52 -

1,2,3,4-tetraphenyl-5-carbena-cyclopenta-1,3-diene (48) in the form of C-H insertion reactions and stereospecific addition to double bonds. It would appear that photolysis of the zwitterions

(33) and (54) gives rise to the carbene (48), so that pyrolysis of these zwitterions might well proceed via a different pathway. This appears to be the case with diazo compounds where pyrolysis gives

O *5 biradical species containing nitrogen, (the products are often azines, ^C=N-N=C^ ) but it is difficult to see how else the phosphorus zwitterion (33) could form the dimer other than through an intermediate carbene.

It is intriguing to speculate that photolysis gives rise to a singlet carbene (48) (as evidenced by the stereospecific addition 81 to olefins) while the pyrolysis reaction (a process involving far less energy than photolysis) of (33) gives rise to the more stable triplet carbene. (Aryl carbenes, ' cyclopentadienylidene and 53 -

p (T fluorenylidene 7 are known to have triplet ground states.) Pyrolysis of the diazodiene (54) in the presence of pyridine and of triphenyl- 8 6 phosphine is reported to give pyridinium and triphenylphosphonium tetraphenylcyclopentadienylides, respectively, but the formation of these products does not require the intermediacy of the carbene (48).

The proposed dimer structures require the generation of an ortho substituted phenyl ring (scheme IV). The literature contains several 82 87 88 examples ’ ’ of such a process but these usually involve attack by a phenyl group on a neighbouring carbonium ion. One example which closely resembles the ring closure in scheme IV and gives rise to an ortho-substituted phenyl group is as follows.

Pyrolysis of the spiro compounds (57) and (58) [obtained in the 82 same way as (56)] is reported to give structures (59) arid (60)f

Me Me (57) (58)

170 170 } /Ph /Ph

Ph Me H Me Me Et Me H

(59) (60) - 54 -

respectively. In view of the

60.7, 3H (J = 7 Hz), these structures may be incorrect; the alter native structures (61) and (62), respectively are suggested for the following reasons.

The cyclopentadienyl hydrogen (H3) in structures (59) and (60)

is diallylic and would be expected to absorb ~ 64 p.p.m. - cf. tetraphenylcyclopentadiene (52), 64.0 and the cyclohexenyl compound

(55), 64.38. The observed shift in (59) and (60) of —' 65*1 p.p.m.

is closer to that expected for a proton which is both diallylic and benzylic - cf. pentaphenylcyclopentadiene (40), 65.07. Moreover, the dienyl hydrogen (H3) in (59) is split into a triplet with an unusually small (2 Hz) coupling constant - cf. the cyclohexenyl compound (55) where the dienyl hydrogen occurs as a doublet (J = 7 Hz).

A coupling constant of 2 Hz is perhaps not unreasonable in the revised structure (61).

/Ph

'H 'Me Me Et Me Me

(61) (62)

Rearrangement of (57) and (58) could occur by a free-radical 55 -

„ 82 process (invoked by Durr and Scheppers) but an ionic pathway analogous to that in scheme IV seems just as likely. Opening of the 3-membered ring would occur in such a way as to give the most stable carbonium ion (or radical), e.g.

(63)

The 1,3-hydrogen shift in (63) to give (62) is precisely the step required to form the proposed dimer structure (43) (see scheme IV).

A series of 1,2-hydrogen shifts is not possible in this instance

(i.e. 50 -*43> or 63 “►62) except via a radical process. A free radical mechanism for the formation of the dimer is shown in scheme V

Apart from the unlikelihood of the dimerisation step to give (64), the diradicals formed are allylic, and hence stabilised. The diradical (65) could readily rearrange to any of the structures

(43 - 47) by a series of 1,2-hydride shifts. Evidence for this type of process was obtained by heating 1,1’-dihydro-octaphenylfulvalene

(41) with palladium on charcoal (300°) (in the hope that a radical - 56 -

species such as (64) might be generated). The dimer, (43)» was isolated in 32$ yield (in addition to small amounts of the diene

(52) and another unidentified material). Treating the dihydrofulvalene (41) with dibenzoylperoxide or azobisisobutyronitrile in boiling benzene did not bring about this conversion.

Scheme V

The solitary non-aromatic proton of the dimer (43) exhibits typical allylic activity. It may be replaced by bromine or chlorine using the appropriate N-halosuccinimide, and selenium dioxide converts it to the corresponding alcohol (66; X = OH). - 57 -

(66)

The canary-yellow bromo-dimer (66; X = Br) reacted rapidly with methanol (< 5 min at 65°) to give a colourless methyl ether, which did not have the long wavelength band at ^ 360 m/j. present in the dimer* However, the u.v. spectrum was very similar to that of the isomeric dimer assigned structure (44), so that structure (67) appears most likely for the methyl ether. Pyrolysis of this

substance (67) resulted in regeneration of the dimer (43) with, presumably, elimination of formaldehyde, though this was not detected. The mass spectrum of (67) showed loss of both formaldehyde 58 -

and methoxyl (accompanied by appropriate metastable ion). Loss of formaldehyde could take place through a four- or five-centre transition state to give (44) or (43), respectively. The facile methanolysis reaction did not occur with the bromo-diene (34;

X = Br), but 5-bromo-1,2,3,4,5-pentaphenylcyclopenta-1,3-diene slowly formed the methyl ether. This supports the assignment of the bromine atom in (66; X = Br) which is both benzylic and allylic.

Rather oddly, the bromo-dimer did not undergo a facile hydrolysis.

When the bromo-dimer (66; X = Br) was stirred with tris-

(dimethylamino)phosphine in benzene, a brown precipitate was obtained which, upon treatment with ethanol, gave the dimer (43). This reaction is readily explained by attack of the phosphorus at bromine to give an ion pair (anion = 51) which is subsequently protonated.

A similar reduction has been observed with the bromo-diene (34; 86 X = Br) and triphenylphosphine.

In a final attempt to degrade the dimer into recognizable fragments, its eosin-sensitized photo-oxidation was examined. Two products were isolated, either of which could be obtained as the principal component by varying the solvent. Both had the molecular formula (mass spectra) and showed carbonyl absorption in the infrared at 1700 and 1665 cm , respectively. Reduction resulted in loss of the carbonyl absorption and formation of alcohols with the uptake of only two atoms of hydrogen (mass spectra, 1H n.m.r.); hence only one of the oxygen atoms is originally present as a car bonyl group. The second oxygen is presumably an ether linkage. As 59 -

only small amounts of material were available, no degradative work to further elucidate the structures of these photo-oxides, was carried out.

To conclude this section, it has been shown that tris(dimethyl amino)phosphine reacts with tetraphenylcyclopentadienone to give a stable, zwitterionic 1:1 adduct containing a P-O-C bond. Further pyrolytic decomposition of this adduct leads to a hydrocarbon whose structure has not been definitely established, although a highly probable structure, (43)* has been proposed. A preliminary X-ray investigation of this hydrocarbon has revealed that it is triclinic and that there are two molecules to the unit cell, which has a o volume of 2195-47 cu A. The space group is either P1 or P1 and the . o . o direct cell dimensions are a = 10.294 A, b = 18.695 A and c =

11.937 l.

A possible chemical proof of the structure (43) might lie in its conversion to the phenyldimer (66; X = Ph) followed by vigorous oxidation and the isolation of o-dibenzoylbenzene. The difficulty would be in establishing that the introduced phenyl group did, in fact, replace the hydrogen atom at position 10b. 60

Part E The Reaction of Trimethylphosphite with

Tetraphenylcyclopentadienone

The previous section (Part D) described the reaction of tris(dimethylamino)phosphine with the dienone to give the zwitter-

ionic 1:1 adduct (33). Extension of this reaction to other P(lll) compounds has shown that trimethylphosphite also reacts with the

dienone, and although a zwitterion analogous to (33) cannot be

isolated, such a species appears to be formed transiently in

solution.

Trimethylphosphite reacts with tetraphenylcyclopentadienone

(when the reagents are stirred together under nitrogen at 30° for

18 hours) to give dimethyl-5-niethyl-2,3,4,5-tetraphenylcyclopenta-

1 ,3-dien-1-ol phosphate (68), (~55$)» the isomeric enolphosphate

(69), (~ 41$), and small amounts (*^ 1$) of 1,2,3,4-tetraphenylfulvene (37). The yields quoted are estimated values based on n.m.r.;

the enol phosphate (68) was isolated as white crystals in 47$ yield,

but the isomeric material, (69) was only obtained as an oil

contaminated with (68). The enol phosphate structure (68) was

assigned on the basis of mass spectral and analytical data which

support the formula C^^^O^P; the infrared spectrum showed strong

absorption at 1280 (P=0) and 1035 cm""^ (P-O-C) but no carbonyl

absorption was present; the *H n.m.r. spectrum showed aromatic,

methoxyl and C-methyl protons in the ratio 20:6:3» respectively;

vigorous acid hydrolysis with 75$ sulphuric acid cleaved the enol

phosphate and gave a mixture of cis (71) and trans (72)

* Refers to the orientation of the 4,5-phenyl groups. - 61

5-methyl-2,3,4,5-tetraphenylcyclopent-2-enones. Separation of the two isomeric ketones by fractional crystallisation allowed their stereochemistry to be determined by n.m.r, spectroscopy; the trans-structiire was assigned to the compound with the highest field methyl group (due to shielding by the 4-phenyl group on the same side of the molecule).

Characterisation of the isomeric phosphate (69) was similarly achieved by infrared and n.m.r. spectroscopy and by hydrolysis to cis (73) and trans (74) 4-methyl-2,3,4,5-tetraphenylcyclopent-

2-enones (see Table 1).

The proposed mechanism for the reaction of trimethyljphosphite with the dienone is shown in scheme VI. Formation of the zwitterionic intermediate (70) followed by Arbuzov-type dealkylation

(which is presumably both intra- and inter-molecular) would give rise to the observed products.

The intermediate (70) may be formed by direct attack of phosphorus at oxygen or by initial attack at carbonyl carbon followed by rearrangement. In view of the previous discussion on attack at carbonyl oxygen (Part D) and the results obtained by others (treated briefly in the Introduction) especially Stockel,"^ the former seems the more likely possibility. Moreover, confirm atory evidence was obtained for initial attack at oxygen by carrying out the reaction in methanol. Reaction between trimethylphosphite and the dienone in this solvent was very fast 62 -

Ph^

Ph^ ^Ph II 0

P(OMe)*

Ph -Ph Ph

Ph Ph Ph

0. + 0 + s P(OMe). ^P(OMe).

(70)

Ph Ph^ /Ph Ph-v_____^Ph ch3 . /'Ph Ph Ph/>CPh Ph Q 0. v'P(0)(0Me)2 I H P(0)(0Me). P(0)(0Me), (68) (69)

h/»20 H/^HpO

Ph Ph\. .Ph Ph\ ^Ph

Ph't\/,CPh Ph-'V/^Ph Pf/\/^ph II ch3 II II 0 ch2 0

(71,72) (3 7) (73,74)

Scheme VI - 63 -

(<5 minutes at 65°) and the products obtained were 2,3»4,5- tetraphenylcyclopent-2-enone (7), (60$), dimethyl 1 ,3,4,5-tetraphenylcyclopent-1 ,3-dien-2-ol phosphate (75)» (10$) and methyl

2»3>4,5-tetraphenylcyclopenta-2,4-dienyl ether (76), (9$)* Enol phosphates (68) and (69) were not formed. Such behaviour is readily explicable in terms of protonation of (70) followed by either alcohol exchange [i.e. displacement by methoxide of the dienyl alcohol; an essentially irreversible step due to back- enolisation of this species to the mono-enone (7)] or dealkylation

(Scheme VII).

These two experiments, one in the presence of methanol, the other in its absence, virtually exclude prior attack at carbonyl carbon followed by rearrangement to oxygen. This latter possibility would be expected to yield products such as (77) when the reaction is carried out in a protic solvent, and products containing a carbon-phosphorus bond were not observed.

The use of a protic solvent to trap an unstable or transient

QQ species such as (70) in solution has been described previously '

(in the Perkow reaction, for example, triphenylphosphine reacts with phenacyl bromide in the presence of methanol to give acetophenone - good evidence for attack by phosphorus at the bromine atom). This technique was found to be successful in the reaction of tributylphosphine with the dienone. Although no reaction was observed in the absence of a solvent, (a reaction to 40 give 1,1’-dihydrooctaphenylfulvalene has been reported however, and presumably takes place at high temperatures, i.e,>160°), - 64 -

in the presence of methanol, tributylphosphine smoothly reduced the dienone to the mono-enone (7) in high yield (94$). A mechanism analogous to that in scheme VII seems likely. Since neither triphenylphosphine nor triphenylphosphite brought about this conversion, the formation of even very small (equilibrium) amounts of zwitterionic P-O-C adducts from these two P(lll) compounds seems very unlikely. Presumably steric and electronic factors are responsible for this lack of interaction with the dienone oxygen atom by Ph^P and (PhO)^P. Steric factors probably account also for the failure of the intermediate (70) to react with another molecule of ketone as expected; cf. the reaction of fluorenone with (EtO)^P to give a 2:1 adduct (12).

Ph\____.>Ph

Ph^Y^Ph 0 (7) + (MeO)4P+

Ph\ ^Ph Ph Ph's. I | H i i Ph •''V^Ph Ph •Ph ''Ph

ho" P(0)(0Me)2 H OMe P(0)(0Me)'

(77) (75) (76)

Scheme VII - 65 -

The n.m.r, spectra of the enol phosphates (68) and (69)

display a puzzling feature. The methoxyl protons of the isomer

(69) occur as a pair of doublets (A6 = 4 Hz) whereas in isomer

(68) they occur as a single sharp doublet. Rotational isomerism

in (69) is unlikely as no coalescence of the doublet pair was

observed at 160°; indeed, the chemical shift difference, Ab,

increases with increasing temperature (see Experimental), and

furthermore, the C-CH^ group appears as a sharp singlet. The

spectrum of the isomer (68) was unchanged at both high and low

temperatures and in a variety of solvents. Since the methoxyls 90 in both isomers are diastereotopic it is difficult to see why

the doubling of the peaks should only be observed in isomer (69) where the affected protons are furthest removed from the chiral centre. (A possible explanation of this effect is however,

offered in Part P.) A similar doubling (A 6 = 2 Hz) of the methoxyl resonances in the enol phosphate (75) was used as evidence for this structure over the alternative dimethyl 2,3,4,5-tetra-

phenylcyclopenta-1 ,3-dien-1-ol phosphate structure (see Part P).

*H n.m.r. data for the four diastereoisomeric ketones obtained

from the acid hydrolysis of enol phosphates (68) and (69) are

shown in Table 1.

Comparing (7l) and (72), (73) and (74) it can be seen that

the trans-structure in each case has the higher field methyl group

due to shielding by the phenyl group on the same side of the molecule. Strangely, quite the reverse holds for the benzylic 66 -

TABLE 1

n.m.r. spectra of Cyclopentenones

Ketone 6CH3 6H a 6H0 h Phx F-H (71) Y 1.72 (1.52) - 4.03 (3.85) Ph^s^-ch3 n Ph 0

Phu P U (72) 1.2 (1.15 4.2 (4.27) PhYx^ch3 n Ph 0

»h Phx F (73) 1.78 (1.78) 4.45 (4.40) - -H ii 0 Ph

F h Ph\ (74) ch3 1.08 (1.28) 4.73 (4.84) 1 „—H Ph^V3h 0

F h Ph\___ I (78)a 4.45 pH 4.9 phArDh 0 F>h Ph\ uM (7) 4.56 (4.53) 3.76 (3.83) Ph -H II 3h 0

(a) Ref. 78b

Chemical shifts (&) in p.p.m. downfield of internal Me,Si, CDCl^ solvent except for ketones (73) and (74) where CCl^was used. Values in brackets were measured in benzene. - 67 -

hydrogens, i.e.the trans-structure in each case has the lower field chemical shift for the single hydrogen atom. Comparing (78) and (7), the benzylic hydrogens (both a and p) are to higher field in the trans-compound (7) than the corresponding hydrogens in the cis-structure. These observations, although contradictory, are not sufficient to reverse the stereochemical assignments of

(71 )/(72) and (73)/(74) for the following reasons. First, the compounds assigned the trans-structures were formed in greater amount then the corresponding cis-isomers. (Epimerisation under the strongly acid hydrolysis conditions would be expected to give the more stable trans-isomers in higher proportion.) Secondly, the benzene shifts are more easily rationalised in terms of the proposed cis-trans assignments than if these assignments are reversed; for example, both H and CH^ groups in the cis-structure

(71 ) suffer an appreciable upfield shift in benzene, while in the trans-structure (72), where presumably both H and CH^ are already subject to a shielding influence by the 4-phenyl group, the benzene shift is either very small or in the opposite direction, i.e. downfield. This is generally true for the rest of the compounds in Table 1; the groups in a trans-structure never suffer an upfield shift in benzene greater than 0.05 p.p.m., and in fact the shifts are often downfield to the extent of ~0.2 p.p.m.

Thirdly, shielding by a neighbouring phenyl of methyl groups (by

0.5-0*7 p.p.m.) is much greater than (de)shielding of the benzylic hydrogens (<0.3 p.p.m.) in structures (72), (74), but is - 68 -

comparable with the large shielding (0.69 p.p.m.) of the (3- benzylic hydrogen in (7). The following argument is an attempt to explain this observation.

In structure (72), the 5-methyl group should severely hinder free rotation of the 5-phenyl group. Moreover, orientation of this phenyl group such that it can effectively shield the

4-hydrogen atom is greatly inhibited by interaction between the methyl group and the ortho-hydrogens. Presumably, in both (72) and (74) the benzylic hydrogen atom is barely shielded by the neighbouring phenyl ring, and may in fact lie in a deshielding zone.

The above section (Part E) completes the discussion of the reactions of P(lll) compounds with tetraphenylcyclopentadienone.

The evidence presented is most easily explicable in terms of initial attack of phosphorus at oxygen to give zwitterionic P-O-C adducts, the formation and stability of which are dependent upon the type of phosphorus substituent. The reaction is not a general one, as shown by the failure of both triphenylphosphine and triphenyllphosphite to form even small (equilibrium) amounts of 1:1 adducts. Similarly, replacement of the dienone by 2,5-dimethyl-

3,4-diphenylcyclopentadienone(79) did not afford an isolable adduct when this ketone was treated with tris(dimethylamino)- phosphine. When the mixture was refluxed, (79) was converted to - 69 -

a complex mixture of high molecular weight hydrocarbons

apparently comprising polymers of the deoxygenated ketone (80;

n = 2-4). Tris(dimethylamino)phosphine was also found to effect

Ph\____ ^Ph Ph^_____,/Ph I I P(NMe2)3 CH3'Y^CH3 160° V ch3/t^vch3 n 0

(79) (80)

deoxygenation of benzophenone, but the reaction was very slow,

and only small amounts of tetraphenylethylene and 1,1,2,2-tetra-

phenylethane were formed. These deoxygenation reactions are

probably complex, involving attack at both oxygen and carbonyl

carbon.

The next section (Part P) describes the reactions of P(lV)

nucleophiles with the dienone. These reactions bear virtually

no resemblance to the reactions of P(lll) nucleophiles with this

ketone, and are thus treated separately. - 70 -

Part F. The Reaction of P(lV) Nucleophiles with

Tetraphenylcyclopentadienone

The P(lV) nucleophiles employed in this work were methylphenylphosphinate, dimethylphosphonate, and diphenylphosphine

oxide. These reagents fail to react by themselves with the

dienone, but in the presence of a base, addition of the phosphorus

compound takes place, usually just on mixing the reagents together

in a solvent at room temperature.

When the dienone was treated with methylphenylphosphinate

in benzene, and dimethylamine passed over the solution, a canary yellow complex formed within 5 minutes. Similar yellow complexes were obtained when other bases such as morpholine, ammonia,

2,3i4,6,7,8,9»l0-octahydropyrimido-[l,2-a]azepine, and sodium

hydride were used instead of dimethylamine, and when methylphenyl

phosphinate was replaced by dime thy l(phos phonat e, although in this

latter case morpholine failed to give the initial yellow complex.

Analytical and n.m.r. data showed that these yellow

complexes were 1:1:1 adducts of the dienone, P(lV) nucleophile,

and base. E.s.r. experiments indicated the presence of paramag

netic species, though the signals were not always as strong nor

as well resolved as the example in fig. 1, which shows the

spectrum obtained when the dienone was treated with methylphenyl

phosphinate and gaseous ammonia in hexamethylphosphoramide as

solvent. Very similar spectra were obtained with the dienone,

- 72 -

methylphenylphosphinate and morpholine in benzene, and with dienone, dimethyljphosphonate and the azepine base in benzene.

These radicals await further investigation; they are not without 91 precedent, as Ramirez has reported that the complex formed from chloranil and triphenylphosphine gives a strong e.s.r. signal, recently attributed^ to the phenolic radicals (31 ) and (82).

The yellow complexes, with the exception of the complexes prepared from sodium hydride, were unstable in air, turning a dirty green on standing in a desiccator for a short time. Aerial oxidation regenerated the dienone (30$). Dissolution in chloro form gave deep-green solutions which turned red-brown on standing; addition of ethyl acetate to these solutions reprecipitated most of the yellow complex.

The *H n.m.r. spectrum of the dienone/morpholine/methylphenylphosphinate complex (complex A) was not well resolved - possibly a 31 result of paramagnetic broadening. P n.m.r. showed a broad peak at -40.03 p.p.m. (6 H^PO^ = ®)» PhpP(o)OEt, 6 -31.1 and - 73 -

71 PhP(0)Me(0H), 6 -40.1 p.p.m. A much sharper *H n.m.r. spectrum was obtained for the corresponding dienone/methylphenylphosphinate/

dimethylamine complex (complex B): aromatic multiplet (25H),

N-Me protons, singlet (6H), P-OMe protons, 2 doublets (3H), and a + broad peak for (2H). Addition of water to this n.m.r. sample

in CDCl^ resulted in the immediate formation of the phosphino- ketone (84). The infrared spectra of the two yellow complexes

(A and B) showed absorption at 2700 and 2400 cm” (NH^), rather

_-j weak phosphoryl absorption at 1200-1240 cm , strong absorption at -^1030 cm” (P-0-C) but no carbonyl absorption.

Prom the evidence presented, the structure (83) is assigned to the yellow complexes A and B, where HRR^ is morpholine and dimethylamine, respectively.

Phv PhPH(Q)0Me Ph^\/^Ph HNRo I! 0

(83)

H+or A

Ph- Ph Tph OMe Ph' ii 0

(85) (84) - 74 -

The alternative structure (85) does not explain the intense yellow colour of these substances - cf. the dienone/tris(dimethylamino )phosphine adduct (33), while its conversion to (84) upon addition of water would be unexpected. Moreover, the methoxyl group in (85) would give only a doublet in the *H n.m.r. spectrum, while the (diastereoisomeric) methoxyl in (83) could give rise to the twin doublet pattern observed for (B). The yellow colour of

(83) is a little strange, although solutions of 2,3,4,5-'tetraphenylcyclopent-2-enone in ethanol/sodium ethoxide were observed to be an orange colour, presumably due to enolates such as (86).

(86)

Other unusual features of the structure (83) are its para magnetic nature, the lability of the C-P bond (aerial regeneration of dienone), and the inability of dimethylaramonium or morpholinium cations to protonate the enolate oxygen at room temperature

(although this process, which is discussed later, does occur in refluxing benzene or on addition of H^O). Two possible - 75 -

explanations of the paramagnetism are offered; the first is the formation of a charge-transfer type complex (87), by donation of one electron from the P(lV) anion to the cyclopentadiene ring.

Donation of a second electron to the dienyl ring by the carbonyl group would result in a 67T-electron system (cf. Part D).

h2nr2

(87)

The second explanation involves the oxidation of the enolate (83) by another molecule of dienone to give the ion-radical combination

(88).

(88) - 76 -

One further piece of evidence for the enolate structure (83) was obtained by treating the dienone with the sodium salt of methylphenylphosphinate. Addition of acetic anhydride to the I resulting yellow complex brought about immediate decolourisation; chromatography of this mixture afforded the enol acetate (89)» though in rather low yield. Structure (99) is assigned on the basis of spectroscopic data and by comparison with the enol acetates

(90) and (90* The infrared spectrum of (89) showed strong absorption at 1775 (C=0) and 1230, 1170 cm“^ (P=0); the ultraviolet spectrum showed a long wavelength absorption at 335 also given by the enol acetate (90); n.m.r. of (89) showed a doublet of

doublets for the methoxyl protons and a doublet for the C-Me protons, indicating the presence of two diastereoisomers. The enol acetates (90) and (91) were prepared by acetylation of the corresponding ketones (7, 71) with isopropenyl acetate and an acid catalyst. Enol acetate (91) has a shorter wavelength - 77 -

absorption (320 m/j,) than the acetate (90) (335 mfi) • Further evidence for the structure (90) is the chemical shift (65.13) of the dienyl hydrogen atom; a slightly lower field shift would be expected if the hydrogen atom were a to the acetate group.

Unfortunately, the corresponding 4-methyl isomer of (91) could not be obtained as the ketone (73) failed to acetylate with isopropenyl acetate and an acid catalyst.

The dimethylamine/methylphenylphosphinate/dienone complex, (b), lost its yellow colour upon refluxing in benzene and gave a high yield (87$) of the phosphino-ketone (84). This ketone was readily converted to the morpholinium salt (92) by warming with morpholine.

(84) (92)

The structure (84) was assigned on the basis of analytical and mass-spectral data, which support the formula C^gH^O^P; infrared and ultraviolet spectroscopy indicate the presence of an a, (3- unsaturated ketone in a 5-membered ring; n.m.r. shows aromatic and methoxyl protons in the ratio 25-3» and a single hydrogen as - 78 -

a doublet (^Jp^ 14 Hz) at 65.82 p.p.m. The large coupling constant is attributed to splitting by phosphorus on the same side -J of the molecule (i.e. phenyl groups cis) and corresponds to a dihedral angle near 60 . The trans-structure would be expected to exhibit a much smaller coupling constant (cf. cis- and trans-monoenones, Table 1). The (3-position of the phosphino group on the 5-membered ring was established by pyrolysing the corres ponding morpholinium salt (92) in D^O at 200°. The product obtained was 4-deuterio 2,3,4,5-'tetraphenylcyclopent-2-enone (93), the identity of which was confirmed by mass spectral analysis and

*H n.m.r. comparison with the trans-monoenone (7).

*H n.m.r. of the morpholinium salt (92) also showed a single hydrogen as a doublet (^Jptr 14 Hz) at low field (55.49) and it is therefore assigned the same cis-stereochemistry as (84).

Conversion of (92) to the free acid followed by treatment with diazomethane gave an isomer of (84). *H n.m.r. of this isomer,

(84a), showed a single hydrogen as a doublet (3j 14.5 Hz) at - 79 -

low field (65.52), while the methoxyl doublet was shifted upfield by 0.25 p.p.m. from its position in the isomer (84). Presumably this is the diastereoisomer of (84) in which only the configuration of the phosphorus atom has been changed,

The ketone (84) was partially epimerised to the trans compound (94) under strong (70$ H^SO^) acid conditions; the

Ph P(0)(0Me)Ph H

(94) phosphinate ester function, although susceptible to hydrolysis by base, was quite stable to strong acid. n.m.r. of (94) showed a single hydrogen as a doublet 1*6 Hz) to higher field

(65.26) than in the corresponding cis-isomers (84) and (84a), indicating shielding by the 5-phenyl group on the same side of the molecule. Similarly, the low coupling constant is consistent with a trans-relationship between phosphorus and the lone hydrogen atom.

A mixture of all three of the diastereoisomeric ketones (84.

84a, 94) and in addition ketone (92), was obtained when the dienone was refluxed in benzene with methyl phenylphosphinate and morpholine. The great complexity of products in this case, compared with the essentially stereospecific formation of (84) from complex B, may be due to the presence of morpholine. (Any 80

dimethylamine formed from complex B would be lost almost immediately - b.p. 7°.)

It was mentioned at the beginning of this section that dimethyljphosphonate failed to give an initial yellow complex in the presence of morpholine. In contrast to the very rapid reaction observed with methyljphenylphosphinate and this base, decolourisation of the red dienone by dimethylphosphonate and morpholine took ^22 hours at room temperature in ethyl acetate or benzene.

A combination of crystallisation and chromatography pro cedures yielded the expected Michael-addition products (95) and

(96), but in addition to these, considerable quantities (~ 35$) of the enol-phosphates (97) and (75) were isolated. [in actual fact, the compounds (95) and (96) were not isolated as such, for under the conditions of the reaction they are partially converted to mono-morpholinium salts analogous to (97). Acidification of the reaction mixture allowed the isolation of one of the free phosphonic acid mono-esters which could be methylated with diazomethane to give (95) *3 Most of the structural work on the

Michael-addition products was carried out on the phosphonic acid mono-ester from (95) • This material analysed for C^qH^O^P; the infrared spectrum showed carbonyl (1700 cm" ) and phosphoryl -J (1180 cm”) absorptions; n.m.r. showed aromatic and methoxyl protons in the ratio 20:3, and a single hydrogen as a doublet

(^JpTT 15.5 Hz) at low field (65.48). By analogy with the phosphino- 81

ketone (84), this material is assigned the cis-structure. The corresponding dimethyl ester (95) is therefore also cis; n.m.r. of the diester showed a similar, single hydrogen atom as a doublet

(^JpH 16 Hz) at 65.34 p.p.m. The methoxyl groups in (95) are diastereotopic^ and occur as two widely spaced (A60.33 p.p.m.) doublets.

Ph^\/^Ph I! 0

HNR. (Me0)2P(0)H

Ph< Ph> ■P(0)(0Me): ■P(0)(0Me); Ph- ■H Ph- H II II 0 0

(95) (96)

Ph Ph

Ph Ph Ph h2nr2

P(0)(0Me)' P(0)(0Me)0~

(75) (HNRp = morpholine) (97)

The structure of the trans-diester (96) was assigned by comparison with structure (94) and on the basis of its 1H n.m.r. spectrum which showed the single hydrogen atom as a doublet

(^Jptr 4.7 Hz) to higher field (64.97) than in (95)» i.e. shielding 82

by the 4-phenyl group on the same side of the molecule. Structure

(96) also showed two widely spaced (A60.32 p.p.m.) doublets due to the diastereotopic methyl groups. Such a large diastereotopic effect is believed to be a result of restricted rotation about the C-P bond; Benezra and Ourisson"^ have shown that A 6 is a function of the size of the group on the carbon atom (3 to the phosphorus, and hence, of the degree of hindered rotation about the C-P bond. This effect can also be used to explain the diastereotopic effect present in the enol phosphate (69) but absent in the isomeric structure (68). The structure (69) might be expected to exhibit more hindrance to free rotation about the 2 C-0 and P-0 bonds, owing to the adjacent phenyl groups on sp carbons, than structure (68) where steric compression is relieved 3 by an a-sp carbon atom.

Warming the enol phosphate (75) with morpholine converts it to the morpholinium salt (97); acidification of (97) followed by treatment with diazomethane regenerates the diester (75)* The enol phosphate structure (75) was assigned on the basis of analytical and mass spectral data which support the formula _ -j C^H^yO^P; the infrared spectrum shows phosphoryl (1270 cm" ) and P-O-C absorptions (1060, 1030 cm- ), but there was no carbonyl absorption; the ultraviolet spectrum shows a long wavelength band at 33C m/i - cf. (92); *H n.m.r. shows two doublets (A6O.O3 p.p.m.) due to two (diastereotopic) methyl groups - cf. (69)* a single dienyl hydrogen atom ("65.09) as a doublet (5 Hz), and aromatic - 83 - hydrogens (20H). The chemical shift and coupling constant of the dienyl hydrogen atom virtually exclude the alternative structure 4 in which this hydrogen is placed a to the phosphate group, as coupling constants (1-3 Hz) in such systems are smaller than couplings (4-6 Hz). 1Finally, the enol phosphate (97) is converted to the mono-enone (7) in high yield by either acid hydrolysis (50$ sulphuric acid) or by pyrolysis at 200°.

The anomalous reaction between the dienone, dimethylphosphonate and morpholine, which fails to give an initial 1:1:1 complex, but results in both Michael addition and addition to the carbonyl oxygen atom, is not easily explicable. Presumably the difference in basicity of morpholine (pKa 8.33)^ and dimethylamine (pKa 10.73)^ is responsible for the failure to obtain an immediate 1:1:1 addition complex, but it is difficult to see why morpholine should be too weak a base to remove the proton from (Me0)2P(0)H and yet catalyse the addition of PhPH(0)0Me to the dienone.

An attempted rationalisation of the reaction is shown in

Scheme VIII. If it is assumed that with morpholine as base, the

base (MeOLP(O)H ----- ^ (Me0LP=0 ----- * (MeOLP-OH C. \ C. \ ^ (98)

Ph\ Phx. Ph _ Ph\ ■P(0)(0Me)2 (MeO)?POH (Me0)?P(0) _ Q Ph^\/^Ph ------Ph Ph II 0 O^P(0Me)20H

(99) (100) Scheme VIII - 84 -

concentration of dimethylphosphonate anion is very low, perhaps comparable with the concentration of dime thy ijphos phi te tautomer

(98), then the reversible nature of the Michael reaction^ would result in an equilibrium concentration of dienone and enolate

(100). Removal of (100) by protonation [a known slow step - cf. yellow complex (83)] would allow eventual conversion of all the dienone to the Michael addition product, unless of course, the remaining equilibrium concentration of dienone were undergoing an alternative reaction, such as attack by the P(lll) tautomer

(98) at the carbonyl oxygen atom (cf. Parts D,E) to give (99) and hence the enol phosphate. The only evidence for this suggestion is that when the reaction was carried out in refluxing benzene, decolourisation was effected in 2-3 minutes and the amount of enol phosphate formed appeared to be less than in the room temperature reaction [presumably due to the more rapid removal of (100) by protonation]. To test this tautomer-addition hypothesis, the 96 reaction was carried out in methanol, as this solvent is reported to catalyse the tautomerism of secondary phosphine oxides. No reaction was observed in methanol however, in the absence of morpholine. p-Toluenesulphonic acid was also found to be an ineffective catalyst, so that if in fact the enol phosphate arises by attack of the P(lll) tautomer (98) at oxygen, morpholine appears to play a necessary part in the reaction. Attack by the P(lll) tautomer of dialkylphosphites on the carbonyl oxygen of hexafluoro- 97 acetone has been reported^ but this reaction did not require the - 85 -

presence of a base.

The third P(lV) nucleophile, diphenylphosphine oxide, also underwent an anomalous reaction with the dienone. When dimethylamine was passed over a solution of the dienone and diphenyl phosphine oxide in benzene, a rapid change of colour, from red to brown, was observed. Upon refluxing, the solution regained its red dienone colour, but lost it again on cooling. Crystallisation of the now pale greenish-yellow solution gave the tertiary phosphine oxide (101).

Ph?P(0)H Ph^\^^ph s Me2NH II 0

(102) (101)

The structure (101 ) was assigned on the basis of analytical and mass spectral data; the infrared spectrum showed absorption _ -j at 1730 cm , attributable to saturated carbonyl in a 5-membered ring, and at 1200 cm (phosphoryl); the ultraviolet spectrum showed only cis-stilbenoid absorption at ~ 267 mp; *H n.m.r. showed ^ 30 aromatic hydrogens and a single hydrogen as a broad singlet (63.2). The benzylic hydrogen atom a to the carbonyl group is at rather high field (cf. bH^, Table 1) and is presumably - 86 -

strongly shielded by either the phenyl group or the diphenylphosphinoxy group on the opposite side of the carbonyl function.

The virtual absence of a 5-bond, homoallylic coupling in (101) is attributed to the relative configurations of the sp^ carbon atoms which govern the P-H dihedral angle. The tertiary phosphine oxide (101 ) is not thermally stable, gaining the red dienone colour on heating (also, the base peak in the mass spectrum was due to the dienone, m/e 384); the initially observed brown colour is attributable to a mixture of dienone and enolate (102).

Attack by diphenylphosphine oxide anion at the carbon atom a to the carbonyl group, to give the 1,4-addition product (101), is rather unusual. Presumably steric factors inhibit the more normal

Michael addition at the 3-carbon atom, as was observed with methylphenylphosphinate and dimethyljphosphonate anions.

A similar 1,4-addition has been observed by this author in previous work. 54 Treatment of the dienone with an equimolar mixture of phenylphosphinic acid and phenylphosphonous bis- morpholinamide in refluxing benzene for 0.5 hour gave a white, highly insoluble precipitate of the morpholinium salt (103).

\ HpN + 0 V /

(103) - 87 -

A Structure (103) exhibited carbonyl (1735 cm” ), phosphoryl

(1210 cm“ ) and morpholinium absorptions in the infrared, cis- stilbenoid absorption in the ultraviolet (—265 m^u), and the

n.m.r. spectrum showed aromatic and morpholinium hydrogens in

C the correct ratio, and a single hydrogen as a doublet ( Jpjj 2.5 Hz) at low field (64.78). The morpholinium salt (103) slowly decom posed in refluxing benzene to give 2,3,4,5-tetraphenylcyclopent-

2-enone - yet another instance of a very labile C-P bond.

In conclusion, it has been shown that tetraphenylcyclopentadienone undergoes base-catalysed, Michael-type addition by P(lV) nucleophiles with formation of a carbon-phosphorus bond.

Addition, both a and (3 to the carbonyl group was observed, the more sterically demanding nucleophiles resulting in attack at the a-position. In one anomalous case, the products of both Michael addition and addition to the carbonyl oxygen atom were obtained.

Attack at the carbonyl oxygen atom in this case was attributed, not to the P(lV) nucleophile, but to a tautomeric P(lll) species, as it has been shown in previous sections of this thesis that

P(lll) nucleophiles attack the oxygen atom of the dienone. EXPERIMENTAL SECTION

MAs the true method of knowledge is experiment, the true faculty of knowing must be the faculty that experiences."

William Blake. 88

Experimental Section

All operations involving phosphorus compounds were carried out in a fume cupboard under nitrogen, except where reactants and products were known to be stable to oxidation, odourless, and non-toxic. Nitrogen was of the commercial, oxygen-free variety and was further purified by passing it through a deoxygenating solution (sodium/benzophenone ketyl in diglyme) where particularly oxygen-sensitive compounds were involved.

Solvents. Ether refers to diethyl ether; 'petrol' refers to the light petroleum fraction, b.p. 60-80°; benzene was dried by azeotropic removal of water and stored over sodium wire, other solvents such as ethyl acetate and acetonitrile were dried over anhydrous calcium sulphate; ethanol refers to absolute alcohol

(except for u.v. spectra which were determined in 95i° alcohol).

Melting points (m.p.) were determined in soda-glass capillaries in an electrically heated metal block. Decomposition of the sample at the m.p. is denoted by (dec.); S.T. denotes determin ation of m.p. in an evacuated, sealed tube.

Spectra. Ultraviolet (u.v.) and visible spectra were determined on a Beckman DBG- (grating) spectrophotometer, and are reported in - 89 -

mjj. (log e). Infrared (i.r.) spectra (run as smears - for liquids,

or mulls in nujol) were determined either on a Perkin-Elmer

’Infracord’ or a Hilger-Watts 'Infrascan'. Proton magnetic

resonance (’H n.m.r.) spectra were measured on a Yarian A60 machine

and some (where stated) on a Yarian HA100 instrument. Chemical

shifts are 6-values measured downfield from tetramethylsilane;

coupling constants (j) are in Hz. Phosphorus magnetic resonance

0 A ( P n.m.r.) spectra were measured at 40.5 MHz on a Jeolco

JMM-4H-100 using 85$ phosphoric acid as external reference. E.s.r.

spectra were measured on a Yarian Y-4-502 E.P.R. spectrometer.

Mass spectra were measured on the AEI-MS9 instrument at

Sydney University. Mass-spectral data is tabulated in the Appendix

to this thesis.

Silica gel for chromatography purposes was Mallincrodt 100 mesh, unless otherwise stated.

Phenylphosphine was(quantitatively)estimated using the tellurium

tetrachloride method (Part C) when the amount involved was less

than 0.5 g, or when other inert material was present (e.g. solvents).

Abbreviations: HOC - dicyclohexylcarbodiimide; DME - 1,2-

dimethoxyethane; DMSO - dimethylsulphoxide; DME - dimethyl-

formamide; (PhP)j- - pentaphenylcyclopentaphosphine; TEP -

tetrahydrofuran; diglyme - diethylene glycol dimethyl ether;

HMPT - hexamethylphosphoric triamide. - 90 -

Formation and Decomposition of Phenylphosphinio Anhydride

The experimental procedure for the preparation of phenylphosphinic anhydride in solution, the kinetics of decomposition, and the unsuccessful use of diethylftisulphide as a trapping agent 10 for phenylphosphinidene have been described elsewhere. The anhydride may also be generated in the absence of a solvent.

Reaction between Phenylphosphinio Acid and DCC

Phenylphosphinio acid (2.0 g) and DCC (1.45 g» 0,5 mole) were stirred together in an evacuated flask (0.1 mm) at 80-90° for

2-3 hours. The phenylphosphine evolved was pumped into a cold trap and estimated with TeCl^ (0.205 g, 13$). The residue was treated with chloroform and the insoluble dicyclohexyl urea removed by filtration. Addition of morpholine gave the morpholini.um salt of phenylphosphonic anhydride (1.53 g, 48.5$). Evaporation of the filtrate and addition of ethanol gave (PhP)^ (0.19 g» 12.5$).

The residue was treated with excess tellurium tetrachloride (1.5 g) to give elemental tellurium [0.105 g, equivalent to 87 mg, 5.7$

(PhP)5, or 0.19 g PhPH(0)0H].

Decomposition of Phenylphosphinio Anhydride in the Presence of Benzil

Phenylphosphinio acid (2.0 g) in ethylacetate (8 ml) and benzene (12 ml) was treated with DCC (1.45 g> 0.5 mole) under nitrogen. The solution was shaken for three minutes and filtered - 91

into an evacuated flask containing benzil (2.95 g> 2 moles). The resulting clear, yellow solution was sealed under nitrogen and the flask, wrapped in aluminium foil, was set aside for 14 days.

T.l.c. on the solution after this time showed the presence of considerable quantities of the expected phosphorane, (25). The

Rp (0.65, SiO^/benzene) and blue fluorescence were identical to that of authentic material. Benzil itself had a weak green fluorescence, R^ 0,5. A solution of pentaphenylcyclopentaphosphine

(50 mg) and benzil (200 mg, 4 moles) in benzene (5.5 ml) and ethyljacetate (2 ml), allowed to stand under the same conditions as above, showed no trace of this phosphorane by t.l.c. When the solution was refluxed under nitrogen in the absence of light for

0.5 hour, there was still no formation of the phosphorane. A sample of the pentaphosphine and benzil in HMPT left standing in a lit (fluorescent lamp) fume cupboard for 3 weeks showed the presence of a small amount of the phosphorane by t.l.c. Phenyl- phosphine and benzil did not form the phosphorane when these reagents were refluxed in benzene/ethylacetate for 0.5 hour.

In a separate anhydride experiment (using the same quantities as in the 14-day experiment) a small amount of the phosphorane was isolated by chromatography. The anhydride decomposition was brought about by refluxing the solution for 0.5 hour. T.l.c. was the same as that obtained in the 14-day experiment. After standing overnight, the mixture was poured onto a dry, fat column of silica gel (Pluka, Kieselgel D5» 80 g) under a blanket of nitrogen and eluted with 40$ dry benzene/petrol. The initial fractions were - 92 -

concentrated and treated with acetonitrile to give a little of the phosphorane (27 rag, $) identical to authentic material by i.r. and t.l.c. Further elution of the column with benzene gave some benzoin (0.25 g» equivalent to 50 mg PhP or approximately

30$ of the normally isolated yield of the pentaphosphine) identified by i.r. It is considered that the phosphorane is formed in much higher yield than that isolated here, and that decomposition occurred during the chromatography stage. (A solution of the phosphorane in chloroform decomposed after standing in air for several hours.)

Decomposition of Phenylphosphinic Anhydride in the Presence of

(a) Piphenylphosphine

Phenylphosphinic acid (2.0 g) in ethyl acetate (14 ml) contain ing diphenylphosphine (4 ml,~1.5 mole) was treated with DCC

(1.45 g> 0*5 mole) under nitrogen. The solution was shaken, allowed to stand for 2 hours, and filtered under vacuum to remove the dicyclohexylurea. The flask containing the filtrate was sealed under nitrogen, wrapped in aluminium foil, and set aside for 2 months. Large white clusters of phenylphosphonic anhydride (0.59 g) crystals separated over this period - i.r. 2600, 2150, 1670 (/P\qt|)»

1240, 1115 and 950 cm- (P-O-P), identical to authentic material.

The filtrate was exposed to dry air for one week; t.l.c. on the solution after this time showed no tetraphenyldiphosphine dioxide. - 93 -

(b) The Dienone

Phenylphosphinic acid (l.O g) was treated with DCC (0.725 g,

0.5 mole) in ethyl acetate (20 ml). The solution was filtered under vacuum to remove the dicyclohexylurea, and added (over a period of 40 minutes) to a boiling solution of the dienone (2.7 g,

1 mole) in ethyl acetate (50 ml) under nitrogen; reflux was continued for 1 hour. T.l.c. showed the presence of ^5 products in addition to the dienone and v. polar material. The cooled solution was extracted with sodium bicarbonate solution and water, and then chromatographed on silica gel. A series of red, green, and yellow bands was observed and 8 fractions were obtained, but only in milligram quantities; the reaction was not studied further.

(c) Toluene

Toluene was purified by stirring with concentrated sulphuric acid, washing with water, followed by bicarbonate solution and then more water; it was dried over potassium carbonate and distilled. Phenylphosphinic anhydride 2 g) prepared in toluene

(25 ml) was slowly run into boiling toluene (50 ml) over a period of 0.5 hour. The solution was refluxed for a further 1 hour and then analysed by g.l.c. Only a trace of dibenzyl (<0.1 ft) was observed - a hardly discernible blip for the concentrated solution; phenylphosphine was present. The toluene was removed by passing nitrogen over the hot, stirred solution and (PhP)j- precipitated by addition of ethanol (45 mg, 3$). It is most likely that some

(PhP)^ was oxidised during the removal of toluene by the above - 94 -

technique, thus accounting for the low yield.

(d) t-Butyl Alcohol

When phenylphosphinic anhydride was treated with dry,

refluxing t-butyl alcohol, the only product obtained was phenyl

phosphinic acid (85$).

(e) Azobenzene

Phenylphosphinic anhydride (2 g) prepared in ethyl acetate

(20 ml) was added to a boiling solution of azobenzene (5*2 g,

2 mole) in ethyl acetate (15 nil) under nitrogen over a period of

6-7 minutes. The solution was refluxed for 0.75 hour. G.l.c.

showed the presence of phenylphosphine (~10$). The solution was

filtered to remove the oily solid formed. The oily solid was

treated with THF to give a fawny coloured precipitate (0.25 g)

insoluble in most solvents but soluble in trifluoroacetic acid,

hot DMSO and DMF, m.p. > 300°, although decomposition occurred at

~'240°.

Found; C, 56.5; H, 4.9; 4.7; P, 13.9 - corresponds to

C^H^N^P^O^ or PhyN^P^HgO^ . This material appeared identical

(i.r.) to material obtained from the reaction of (PhP)j- with azobenzene. Concentration of the ethyl acetate solution and

treatment with chloroform gave another amorphous precipitate, m.p. >260°. The compound was insoluble in 17M acetic acid but

soluble in aqueous acetic acid. This reaction was not further

investigated, as it was found that (PhP)^ reacts with azobenzene.

Azobenzene did not react with phenylphosphinic acid when - 95 -

refluxed in ethyl acetate for 1 hour. Addition of morpholine and further reflux for 3 hours had no noticeable effect.

Phenylphosphine did not react with azobenzene in refluxing (3 hours) ethyl acetate solution.

Reaction of (PhP),- with Azobenzene

(PhP)j- (0.47 g), azobenzene (0.4 g, 12.5 moles) and aceto nitrile (5 ml) were heated under reflux, under nitrogen, for 3 hours. The ivory coloured precipitate formed was removed by filtration (0.34 g) m.p. 255-265°.

Found: C, 62.4; H, 5*0; N, 3.3; P, 19.3 - corresponds to

C42H41N2P5°5- i-*3- (Ph)7N2P505Hg?

The orange filtrate was concentrated and chloroform added to give another white polymer (0.075 g) m.p. 225-230°.

Found: C, 57.6; H, 5.7; N, 5.8; P* 7.4 - corresponds to

C80H94H7024P4’

Preparation of Pentaphenylcyclopentaphosphine, (PhP)^.

Phenylphosphonous dichloride (80 g) in THF (50 ml) was added with stirring to magnesium turnings (10.8 g, 1 mole) in THF

(200 ml) with cooling (ice/water) over 1.5 hours. Stirring was continued for several hours, then oxygen-free ethanol (200 ml) and water (250 ml) were added slowly. The solution was stirred overnight, the product removed by filtration, and recrystallised - 9 6 -

from carbon disulphide/ethanol. Total yield 36 g (75$), m.p.

(S.T.) 151-153°, lit.20 154-156°. A small amount (1.6 g) of

insoluble material, m.p. 200-210°, which smelt of phenylphosphine,

was also isolated.

Note: In several preparations, the (PhP),_ was spontaneously

inflammable upon exposure to air. This was attributed to traces

of phenylphosphine and small particle size. Other recrystallis

ation solvents that were found to be satisfactory were THF/ethanol,

benzene/ethanol, and chloroform/ethanol.

Phenylphosphine was prepared in 73$ yield by pyrolysing phenyl-

phosphinic acid (over a low bunsen flame); b.p.1 60°, i.r.

2300 cm"1 (P-H).

'H n.m.r. Doublet 62.20, 5.52 (1JpH 199.5Hz) (2H) - - P-H

Multiplet 67 - 7.3 (5H) - - - - Ar-H

Diphenylphosphine. Diphenylphosphinous chloride (41 ml) was added slowly over 1.5 hours to a stirred suspension of lithium (3.08 g,

2 mole) in THF (70 ml) under nitrogen, at room temperature.

Stirring was continued for 24 hours, then water (150 ml) and petrol

(200 ml) were added. The aqueous phase was extracted with petrol, then ether, and the combined extracts dried over sodium sulphate and evaporated under a stream of nitrogen. The residue was distilled (b.p. 162-167°) under a water-pump vacuum to yield diphenylphosphine (29.7 g, 72^) as a clear, mobile, foul smelling

A liquid; i.r. 2280 cm" (P-H); ’ H n.m.r, showed only one half of - 97 -

the P-H doublet at 63.4, the other half being obscured by the 99 o aromatic protons. Lit.'"' b.p. 280 .

2,3,5,7,8-Pentaphenyl-1,4,6,9-tetraoxa-5-phospha-spiro[4,4]- nonadiene (25)

The title compound was prepared according to the method of 1 3 Schmidt et al. by treating phenylphosphonous dichloride with the magnesium-benzil enolate (i.e. stilbene diolate) complex.

Recrystallisation from benzene/ethanol gave material of m.p.

212-215 . P n.m.r. in pyridine gave an absorption at +16.68 p.p.m. (b IT^PO^ = 0). Lit.^, m.p. 216-218°. The solid material appeared to be fairly stable but solutions of the phosphorane in chloroform decomposed on standing in air for several hours.

Tetra-nhenyldirhosphine dioxide

Tetraphenyldiphosphine dioxide was prepared according to the 52 method of Quin and Anderson by adding diphenylphosphinous chloride (5.0 g) in ether (25 ml) over 0.75 hour to a chilled (-10°) solution of lT,IT-diethylaniline (3.39 g, 1 mole) and water (0.245 g,

0,6 mole) in ether (30 ml). The solution was stirred in air for

1 hour, overnight under a drying tube, and for a further 1.5 hours in air before filtering. The white solid was washed with ether, then water and dried (3«3 g). As the product contained diphenylphosphinic acid, it was washed with aqueous bicarbonate solution, then water, and recrystallised from dry acetone, then dry - 98 -

methylethylketone, m.p. 165-170°, lit.'* 167-169°.

Reaction of phenylphosphinic acid with pentaphenylcyclopentaphosphine

Phenylphosphinic acid (3.0 g) was mixed with (PhP),- (1.14 g,

0.1 mole) in a 25 ml flask. The flask was flushed with nitrogen, evacuated to 0.1 mm and heated in a water bath at 85-90° for 2.5 hours. The magnetically stirred mixture slowly but steadily evolved a gas (PhPH^) which soon built up sufficient pressure to condense and reflux up the sides of the flask. The viscous liquid at the bottom of the flask consisted of a yellow oil floating on top of a clear, colourless oil. The vessel was then reconnected to the vacuum pump and evacuated for 2 hours.

Phenylphosphine, PhPH^, (1 *5 g> 0.65 mole) was obtained from the cold trap (-80°) and identified by g.l.c. comparison with an authentic sample. The evacuated mass (the yellow material appeared to be identical to the colourless oil by i.r.) was refluxed with ethyl acetate (20-25 ml) for several hours, cooled and filtered to yield white crystals of phenylphosphonic anhydride, m.p. 115-118° (2.33 g» 0.37 mole) which were identified by the following procedures:

(a) Titration with sodium hydroxide gave an equivalent weight

of ~153 (theoretical value, 149)•

(b) Conversion to the bis-morpholinium salt of phenylphosphonic

anhydride in high yield: the acid (0,2 g) was treated with

excess morpholine (0.5 ml) in ethyl acetate to give bis-salt - 99 -

10 (0.298 g, 94$) identical with authentic material by i.r.

and mixed m.p. 203-206° (ethanol). The crude material melted

at 180-190°.

(c) Refluxing the acid-anhydride in methanol gave a mixture of

phenylphosphonic acid and methyl phenylphosphonate, identified

by ’H n.m.r. (methyl doublet 53.58, J = 11.2 Hz).

(d) The compound analysed for a dihydrate.

Found:(M7909) C, 43.1; H, 5.2; P, 18.5

C1?H120j-P2#2H20 requires: C, 43.1} H, 4.8; P, 18.5

(e) Refluxing the acid-anhydride in v/et ethyl acetate gave

phenylphosphonic acid, m.p. and mixed m.p. 151-154°.

(f) The i.r. spectrum showed absorption at 2600, 2150, 1670

('P?0H)*» 1240 'P=0)’ 950 (p-°-p) cm"1.

This reaction was repeated under a variety of conditions using various molar ratios of reagents. When carried out in a solvent such as acetonitrile or ethyl acetate under reflux, the reaction was considerably slower and the estimation of product yields less efficient. Reaction took place in chloroform solution at room temperature, but was only 40$ complete after standing for

10 days. Table 2 shows the results obtained, using the melt- procedure just outlined, for various molar ratios of reagents.

* These absorptions were also found in diphenylphosphinic acid and phenylphosphinic acid. 100

TABLE 2

Wt. of Wt. (PhP)5 Yield Yield * $ PhPH(0)0H, PhPH2 [PhP(o)(0H)]20 Recovery (Rel.No.Moles) (Rel. Ho. moles P) of P

3.0 g (2.0) 1.14 g (1.0) 1.35 g (1.17) 0.74 mole 89

1.0 g (2.0) 0.76 g (2.0) 0.43 g (1.13) - -

1.0 g (2.0) O.254 g (0.667) 0.41 g (1.07) 1.26 g 96 (0.755 mole)

1.0 g (2.0) 0.228 g(0.60) 0.39 g (1.025) 1 .25 97 (0.75 mole)

1.0 g (2.0 0.304 g(0.80) 0.40 g (1.05) 1.31 94 (0.79 mole)

Estimated as the bis-morpholinitun salt.

Phenylphosphinic acid h- (PhP),- in the presence of base

Phenylphosphinic acid (2.0 g) was mixed with (PhP)^ (0.76 g,

0.1 mole) and morpholine (0.625 g» 0.51 mole) in a small flask which was then evacuated and sealed. The mixture was heated to

100° for 4 hours with no apparent reaction. On cooling, addition

of ethanol gave a crystalline precipitate of (PhP)^ (0.702 g, 92$ recovery), m.p. and mixed m.p. 149-150°. Similar results were

obtained when ethyl acetate was used as a solvent, and also using

triethylamine (0.5 mole) as base. However, the presence of a trace

of triethylamine (0.1 mole) did not noticeably inhibit the reaction. 101

Blank on Phenylphosphinio acid

By determining the m.p. before and after heating, phenyl-

phosphinic acid was found to be quite stable, in the absence of

(PhP)^, under the melt-conditions employed above.

Preparation of Tolylphosphinio acid

Phosphorous trichloride (412 g) was added slowly to powdered, anhydrous aluminium chloride (133 g, 0.33 mole) and toluene (92 g,

0.33 mole) under nitrogen. The mixture was stirred and heated at

80-90° for 3 hours, stirred overnight at room temperature, and then refluxed for a further 2 hours. Pyridine (81 g, 0.34 mole) was added slowly to the cooled solution which was then diluted with benzene, filtered through celite and distilled. Tolyl- phosphonous dichloride was not isolated; the distillate being converted directly into the phosphinic acid by pouring into excess

80io ethanol/water. Recrystallisation of the product from benzene gave p-tolylphosphinic acid (16 g, 10^), m.p. 104-106°, lit.88

104-105°.

«H n.m.r. (CDCl^s Doublet 612.28, 2.85 (1H) JpR = 567Hz H-P

Singlet 52.36 (3H) CH^-Ar

Singlet 613.38 (1H, exchanged D^O) " '

ABX aromatic region: Doublet of doublets 6H^ 7.65 (2H), Jp^ 13.8 Hz nA Doublet of doublets, 6Hg 7.23 (2K), JPTT 3.7 Hz;

JAB 8,1 Hz 102

p-Tolylphosphinic acid + (PhP)^

p-Tolylphosphinic acid (1.2 g) was melted and stirred under vacuum in a stoppered flask with (PhP)^ (0.25 g, 0.06 mole) at

100-105° for 3 hours. The melt was then evacuated for 3 hours to give a mixture of phenylphosphine and p-tolylphosphine (0.46 g,

52:48 mixture of phenylstolyl - corresponds to 0.27 mole phenylphos phine and 0.25 mole p-tolylphosphine). The white crystalline residue was treated with excess morpholine in ethyl acetate to give the bis-morpholinium salt of p-tolylphosphonio anhydride (1.376 g,

0,36 mole) recrystallised from ethanol, m.p. 213-217°.

Found (M2759): C, 53.5; H, 6.3; N, 5.4; P, 12.6

C^IL^N^OyP^ requires: C, 53.0; H, 6.8; N, 5.6; P, 12.4

* H n.m.r. (l>20) Singlet 62.31 (6H) - Ar-CH3

Multiplets 63.17, 3.85 (16H) - - morpholinium-H

Multiplet 67-7.6 (8H) - - Ar-H

TH n.m.r, (phenylphosphine/tolylphosphine sample)

Singlet 62.12 (3.6 units) - - Ar-CH^

Doublet 65.51, 2.20 (5.05 units),

JpH 199.5 Hz - - P-H

Multiplet 67.1 (10,8 units) - - Ar-H

io recovery of phosphorus, 967b.

Phenylphosphinic acid-d^, PhP(0)D(0D)

Freshly distilled phenylphosphonous dichloride (10 g) in THF

(30 ml) was added dropwise over a period of 2.5 hours to a refluxing 103

solution of D,p0 ( 5 ml) £m THP («90 ml). The solution was; refluxed fo>r a further 1 hour, evaiporated to dryness;, and hot "benzene addled to> .yield crystalline phemylnhosphinic acid-d^ (5*78 g, 73$)* m»p>.

84—87°; i.r. 1750 (P-~D) and 1900-2000 cm”^ (P-OD.). The product; was shown to he JO$ i soto>pical.ly pure by rK n.im. r. (CDC1) whichi indicated about 8$ F’-H amd 10°fo P-O'H. 11 P n.m.r.: triplet 6-1 9^8 p. p.m. , 95 Hz? doublet 6-19«8t

Jprr '560 Hz.

The rate of P-D exchange was quite fast in methanol. Addition of

H^O to a chloroform solution of the acid brought about immediate exchange of P-O-D but left; P-D unchanged. Evaporation of the sample to dryness however, resulted in at least 80$ exchange of both P-D and P-OD ( by rH n.m. r.). A solidl sample left exposed to the atmosphere for 1 day showred no exchange.

Phenylphosphinio acid-d^ , PhP(o)D)(

Phenylphosphini-c acicd-d^ (lOO mg) was dissolved in ethanol-free chloroform (1 ml) * 10 dLrcnps of water were added, and the mixture shaken for a few minutes. Anhydrous sodium sulphate was then added and the solution allowed -to stand, for 0.75 hour. It was then filtered* evaporated at; rcooim temperature, and dried under vacuum

(0.1 non.) for 2 hours. ’ H n.m.r. show'sd 83$ P-D, P-OH compound. The dry sample was then heat ecd at 85-9^° for 1 hour; ’ H n.m.r. showed that 3 9$ P-D compound renmained, i.e. complete exchange upon heating. - 104 -

Phenylphosphine-cL, PhPD^

Phenylphosphinic acid-d^ (0.3 g) was melted under vacuum with

(PhP),- (O.O91 g) in a sealed flask at 85-90° for 1.5 hours. The

resulting PhPD^ was pumped into a cold trap. ’ H n.m.r. showed the

compound to be 8 5$ PhPlU. P-H occurred as two sets of doublets,

65.63, 2.67 and 65.58, 2.22 p.p.m. (Jp^ 202 Hz); ratio of Ar-H:P-H =

18:1 .05.

Methyl/phenylphosphinate was prepared according to the method of

Kosolapoff^ by adding phenylphosphonous dichloride (61 ml) slowly

(2-3 hours) to an excess of methanol [230 ml, distilled from Mg(0Me)g] under nitrogen. The mixture was stirred for several hours, concen trated, and allowed to stand overnight in a desiccator containing

KOH. The product was distilled (b.p. 106-108°/2.3 mm, lit."'^ 91 -93°/lmm) to give a clear mobile oil (41 g, 58$); i.r. 2340 cnT"1 (P-H).

*H n.m.r. Doublet 512.26,2.83 (1H), 566 Hz P-H

Doublet 63.75 (3H), 3JpH 12.2 Hz - - - P-0CH3

Multiplet 67.4-8.0 (5H) - - Ar-H

Dimethylphenylphosphonate was prepared from phenylphosphonic acid by esterification with diazomethane in methanol.

1H n.m.r. (CDC^) Doublet 63.73 (6H), 3JpH 11.2 Hz P-0CH.

Multiplet 67.3-8.0 (5H) Ar-H - 105 -

Reaction of (PhP),- with Methanol j (PhP)^ (0.807 g) was refluxed in dry methanol (10 ml) in dry

air (silica gel drying tube) for 4.5 days. All the (PhP)^ had

dissolved after this time and the solution smelt strongly of phenyl-

phosphine. Evaporation (0.2 mm, 0.5 hour) gave a clear mobile oil

(0.89 g» 76$), i.r. identical to authentic methylphenylphosphinate.

There was very little reaction when (PhP)^ was refluxed in either

methanol or aqueous methanol in the absence of oxygen for periods of

up to 70 hours, 70-80$ of the (PhP)^ being recovered unchanged.

(PhP)^ did not react with methyljphenylphosphinate at 85-90° (5.5

hours), and irradiation (u.v.) of an ether solution of these reagents

gave no apparent reaction. Neither (PhP),- nor methylphenylphosphinate

appeared to undergo any change upon irradiation of dilute (0.5$)

solutions of these compounds in ether.

Reaction of (PhP),- with Water

(PhP)^, (0.5 g) was refluxed in DME/water (5 ml, 50$) in the

presence of p-toluenesulphonic acid (0.2 g) under nitrogen for 10

hours [the (PhP)j- had all dissolved after 6-7 hours reflux). The

solvent and phenylphosphine were pumped off (0.212 g phenylphosphine,

42$), the residue treated with water and extracted with benzene to

give phenylphosphinic acid (0.21 g, 32$). Phenylphosphinic acid was found to catalyse the reaction in the same way as p-toluene

sulphonic acid. It was recovered unchanged at the end of the

reaction. - 106 -

Reaction of Phosphorous Acid with (PhP)r ------—------

(a) Phosphorous acid (1.056 g) was melted with (PhP)^ (1.39 g*

0.2 mole) under a nitrogen/water atmosphere, the evolved gas being collected over water (downward displacement). The stirred mixture was maintained at 85-90° for 17 hours, although gas evolution ceased after 5 hours. The phosphine liberated (145 ini at 17.5° and

76.2 cm Hg, 0.226 g, 51. 5$) was run into a TeCl^ solution (in methanol) to give 1.039 g Te, equivalent to 0.14 g PH^ or 32$

(relative to phosphorous acid). The residual mixture was evacuated to give phenylphosphine (0.175 g» 12.5$). Treatment of the residual oil with ethanol gave a yellow powder (0.212 g) which appeared to be impure (PhP),- by i.r. and reaction with TeCl^ solution [see (b)].

The filtrate was treated with barium acetate solution to give a white powder (1.856 g, 49$) which was shown to be barium phenylphosphonate containing a little barium salt of phenylphosphonic anhydride by its i.r. spectrum and by electrophoresis.

In another experiment (carried out for 4.5 hours) the yield of phenylphosphine was 15.4$, recovered (PhP)^ 10$, phenylphosphonic anhydride (as Ba salt) 16.3$ and phenylphosphonic acid (as Ba salt)

55$.*

(b) Phosphorous acid (1.07 g) was melted and stirred with (PhP)^

(1.41 g, 0.2 mole) in an evacuated flask at 85-90° for 0.75 hour.

The mixture was 'pumped down' (2.5-3 hours) to give phenylphosphine

* These values are estimates based on a (quantitative)estimation of Ba in the precipitated barium salts, followed by isolation of the phenylphosphonic acid. - 107 -

(0,46 g, 33?6 - but may have contained a little phosphine). The residue, upon treatment with ethanol, gave a canary-yellow powder

[0.34 g, 22$, assuming 90/6 pure (PhP)^] which was still yellow and amorphous looking after "recrystallisation” from chloroform/acetone, m.p. 145-150°, The determination of the mass spectrum of this yellow material resulted in "low molecular weight material which flashed off first" (PH^, PhPH^ ?) then above 220°, the spectrum was similar to that of (PhP)^ except that the former had major peaks at

448 [(PhP)^O ?] and 510 [(PhPj^PgO ?]. There were metastable peaks corresponding to the transitions 51° 448 (i.e. loss of P^) and

448 -> 324 or 293 -f 262, [i.e. (PhP^O -> (PhP)3 + PhPO or

Ph^Pg —> Ph^P] - see Appendix. Estimation of the yellow material

(30 mg) as Te (54 mg) corresponds to the compound (PhPj^P^O containing

456 PH^ impurity.

The filtrate, after removal of the yellow material, was treated with barium acetate to give barium phenylphosphonate (1.54 g, 40^6) and barium phosphonate (0.175 g> 696).

(c) The reaction between phosphorous acid and (PhP),- was repeated using various molar ratios of reagents (Table 3) and also under other conditions. In all cases a complex range of products was obtained.

Apart from the starting materials, products identified were phosphine, phenylphosphine, phenylphosphonic acid, phenylphosphonic anhydride, pyrophosphate and probably phosphate. Phosphorous acid itself was quite stable when heated for 4 hours under vacuum at 80°. When equimolar amounts of the reagents were refluxed in ethyl acetate

(~ 2096 solution) for 7.5 hours, phosphine was formed in 26.4/6 yield 108 -

and phenylphosphine in 18$ yield. When DME was used as solvent,

only some of the phosphine formed was evolved from the refluxing

mixture; much of it distilled over into the cold trap along with

the DME and phenylphosphine, making (quantitative)estimations rather

difficult.

TABLE 3

0 Wt. H3P03 Wt.(PhP)5 Yield PH3 PhPH, Pyro- $ Recovery P 2 PhP(0H)o po4 io (Rel.mole) (Rel.mole P) ml, * $ * 2 * * p(oh)3 (php),

1.02 g (1) 1.075 (0.8) 146, 50 5 43 - 50 48

1.07 g (1) 0.845 (0.6) 150, 50 3.6 61 23.5 74 65

0.842 g (1) 0.498 (0.45) 85, 36 9.4 89 45 80 98

Reaction of Hypophosphorous Acid with (PhP),-

Hypophosphorous acid (0.959 g) was mixed with (PhP)^ (0.945 g»

0.12 mole) and the reagents warmed (70°). As a homogeneous melt did

not result, ethyl acetate (5 ml) was added and the solution kept at

70° for 0,5 hour. The reaction vessel was sealed from the atmosphere

by a downward displacement-of-water set-up to allow collection of

evolved gas. After stirring for 0.5 hour all the (PhP)j- had

dissolved; the temperature was then raised and the solution refluxed - 109 -

overnight. Much phosphine (^100 ml) was evolved after only 15 minutes of reflux; gas evolution had almost ceased after 2 hours.

Volume of PH^ collected = 142 ml at 20° and 76.93 cm Eg (44$). T^e residue was connected to a vacuum pump, and the volatiles, collected in a cold trap, were treated with TeCl^ in methanol to give black elemental Te (0.323 g) equivalent to 0.193 g, 20$ PhPH^.

The residue, on treatment with barium acetate, gave a white precipitate (1.341 g); i.r. and electrophoresis showed the presence of phenylphosphonic acid together with pyrophosphate and two other acids, one possibly HP0^“; the other had an R^ ~half way between pyrophosphate and phenylphosphonic acid.

Decreasing the molar ratio of (PhP)^rhypophosphorous acid to

0.08 gave PH^ (34$) and PhPH^ (19$)« A molar ratio of 0.16 gave yields of 47$ and 16$, respectively. Rypophosphorous acid decom posed only slightly (~ 5$) in refluxing ethyl acetate after 20 hours.

Dimethylphosphonate + (PhP)r-

Equimolar amounts of these reagents did not react when heated at 100° for 4-5 hours under nitrogen. Addition of ethanol gave

(PhP),- (95$); the residual oil showed P-H and P=0 absorptions in the i.r., consistent with (unchanged) dimethylphosphonate.

Formic acid + (PhP)!-

(PhP)^ (0.5 g) was refluxed in benzene (0.5 ml) with formic acid (0.21 g, 5 mole) for 2 hours. Only a trace of phenylphosphine 110

was formed ('-'4 mg). (PhP)^ could not be recovered from the

residual oil by addition of ethanol. (Note: Although a slight

effervescence was observed upon the addition of formic acid, no

CO^ could be detected.) Phenylphosphine did not react with formic acid under these conditions.

Diphenylphosphine oxide + (PhP)^

(PhP)t- (0.27 g) and diphenylphosphine oxide (1 g, 10 mole) were refluxed in acetonitrile (8 ml) under nitrogen for 2 hours.

G.l.c. showed the formation of an insignificant amount (1-2$) of phenylphosphine. The cooled reaction mixture deposited crystals of (PhPjj- (0.2 g, 7 5$), m.p. 148-150°. Evaporation of the filtrate and addition of ether gave diphenylphosphine oxide (0.6 g, 60$) and some diphenylphosphinic acid.

Reaction of Phenylphosphinic acid with 2,21-azobis-isobutyronitrile

Phenylphosphinic acid (1.0 g) and the azobis-nitrile (2.36 g,

2 mole) were refluxed in benzene (7.5 nil) under nitrogen for 5 hours; HCN was detected in the effluent gas. Addition of morpholine and a further period of reflux (1.25 hours) gave a white precipitate of the bis-morpholinium salt of phenylphosphonic anhydride (0.134 g,

8$), m.p. 206-210°. Addition of methanol/acetonitrile gave (PhP),-

(0.078 g, 11$). Evaporation and addition of ethyl acetate gave white crystals of the morpholinium salt of phenylphosphonic morpholinamide, (32), (0.88 g, 40$), m.p. 149-152°; i.r. 2650-2240

(NH2), 1200, 1160 (P=0), 950 (P-N-C)cm' 111

Found: C, 52.4; H, 7.1; N, 8.3; P, 10.1

C14H23N204P requires: C, 53.4; H, 7.4; N, 8.9; P, 9.8

Further crystallisation [after removing (32)] gave a total

of 0.310 g (18.6$) of the anhydride salt. Tetramethylsuccino-

nitrile, TMSN, (0.6 g) was isolated from the residues, i.r.

identical to authentic material. The morpholinamide (32) was

converted to the bis-morpholinium salt of phenylphosphonic

anhydride when boiled for a few minutes in ethyl acetate contain

ing a trace of water.

When the reaction was carried out in the presence of an

excess of morpholine, a 64$ yield of anhydride salt was obtained.

Using equimolar amounts of acid and azobis-nitrile in benzene under reflux for 18 hours, resulted in a 61$ yield of anhydride

salt and a 10$ yield of (PhP)^. When ethyl acetate was used as

solvent, and the reagents refluxed for 7 hours, only a 22$ yield

of anhydride salt was obtained. No reaction was observed with methanol or ethanol as solvent. Reducing the molar ratio to

0.5 mole azobis-nitrile (refluxed in benzene 5 hours) did not affect the yield of anhydride salt (63$)» but reduced the yield of (PhP)c- to 5$. A 3$ yield of phenylphosphine was obtained.

Reducing the molar ratio still further to 0.1 mole azobis-nitrile, gave a 7.5$ yield of anhydride salt.

Reaction of Phenylphosphine with 2,2 *-azobis-isobutyronitrile

Phenylphosphine (1 ml) and azobis-nitrile (1.5 g> 1 mole) 112

were refluxed in benzene (10 ml) under oxygen-free nitrogen for

9 hours. The mixture was ’freeze-dried’, and methanol added,

to give a white solid (0.7 g, 70$), m.p. 142-150°, i.r. identical

to (PhP),-. The only other product identified was TMSN.

The conversion of phenylphosphine to (PhP)^ was also achieved by refluxing the phosphine (0.76 g) in carbon tetra

chloride (10 ml) and lT,N-diethylaniline (2.6 ml) under nitrogen

for 1 hour. The carbon tetrachloride was extracted with water and methanol added to give (PhP)^ (0.37 g, 49$).

Diphenylphosphine Oxide

Diphenylphosphinous chloride (30 g) in carbon tetrachloride

(150 ml) was treated with water (2.5 ml, added dropwise over 1.5 hours) under nitrogen. The mixture was stirred at room temperature for a further 6 hours and allowed to stand overnight. The white, precipitated solid was removed by filtration and dissolved in chloroform. The solution was extracted with bicarbonate solution, washed with water, dried, and evaporated at 30-35°. A small aliquot was dissolved in benzene and ’freeze-dried’. The resulting white powder brought about immediate solidification of the remaining oil. The crude product (22.5 g» 82$, m.p. 47-50°) was recrystallised from ether, m.p. 53-56°; lit.’ " 53-56°. 113

Estimation of Phenylphosphine using Tellurium Tetrachloride

Phenylphosphine (0.210 g) was treated with excess tellurium

tetrachloride (1.3 g) in oxygen-free methanol (10-15 ml) under

nitrogen. The mixture was allowed to stand at room temperature

for 5 minutes. The black precipitate of elemental tellurium was removed by filtration, washed with methanol, acetone and

chloroform, and dried under vacuum. Weight = 0.353 g or 9?.2$

of theory.

Other P(lll) compounds: Pentaphenylcyclopentaphosphine (97.8$), triphenylphosphine (98$), tris(dimethylamino)phosphine (97.7$), trimethylphosphite (80$), phosphorous trichloride (22$).

Refluxing phenylphosphinic acid with tellurium tetrachloride in ethanol for 0.5 hour gave a 99°/° yield of tellurium.

Tellurium Complexes

Elemental tellurium dissolved in a mixture of bromine and pyridine in methanol to give a red complex, m.p. 310° (dec), soluble in DMSO and hot nitromethane. The red complex could be reduced to elemental tellurium by phenylphosphine or by (PhP)^.

Estimation by this method gave Te, 16.5$.

Found (13778): C, 15.7; H, 1.6; IT, 3.7

TeBr^G^H^ 21T9 requires: C, 15.7; H, 1.6; IT, 3.7; Te, 16.5-

One further complex was obtained when tellurium tetrachloride was treated with morpholine hydrochloride in methanol/acetonitrile. - 114 -

Bright yellow crystals, m.p. 199-200°(dec) were isolated, which analysed for 16.5$ Te.

Found (M0790): C, 25.3; H, 5.3; N, 7.3

TeClgC^ requires: C, 25.2; H, 5.3; N, 7.3; Te, 16• 7.

Reaction of Tris(dimethylamino)phosphine with Tetraphenylcyclo- pentadienone

Tris(dimethylamino)phosphine (0.42 g) was stirred with the dienone (0.5 g> 0.5 mole) in benzene (3 ml) at room temperature for 3 days under a blanket of nitrogen. After this time the solution had lost its red colour completely and a white precipi tate had formed (0.45 g). The filtrate was concentrated and ethanol added to give a further 0.23 g white precipitate. This was a 1:1 adduct of the tris-aminophosphine and the dienone; total yield 0.68 g, 97$, m.p. 164-168°(dec).

Found (14207, M3676): 0, 76.6; H, 7.3; N, 7.9; P, 5.6

Ck _ELoN-0P requires: C, 76.8; H, 7.0; N, 7.7; P, 5.7 jo j fH n.m.r. (CDC1 ) Multiplet 66.8-7.4 (20H) - Ar-H

Doublet 62.62, J 9.5 Hz (3H) - - P-H-CH3

Doublet 62.12, J 9.8 Hz (15H) - - P-N-CH3

cf. (Me2N)3PO 62.6 (J 9-5) (CC14)

(Me2H)3P 62.5 (J 9.0) (CDC13)

* H n.m.r. (C^D^) Doublet 61.71, J 9*9 Hz (18H)

^P n.m.r. (pyridine) 6-31.8 p.p.m. - 115 -

I.r. showed no carbonyl or phosphoryl absorption, but strong -1 -1 absorption at 1000 cm" and weaker absorptions at 1060, 973 cm”

(P-0-C, P-IT-C ?). u.v. (cyclohexane) \ax 376 (4.15)» 352 (4.24), 323 (4.28),

235 (5.01).

The solid material was very air sensitive and rapidly turned red on exposure to air. Larger crystals were colourless or straw-coloured and more air stable. (They could be kept for several weeks in a sealed tube under nitrogen without any apparent change.) The adduct appeared to undergo some decomposition when dissolved in chloroform as a red solution was obtained. A chloroform solution of the dienone and the tris-aminophosphine did not decolourise after stirring for several days at room temperature, possibly because of a reaction between the aminophosphine and CHC1^.^°^

In the absence of oxygen and moisture the adduct is quite stable and is more conveniently prepared by refluxing the reagents in benzene (*-20fo solution) for 1-2 hours. This reflux period increases rapidly with increasing dilution of the solution. The adduct is readily prepared in the absence of solvent by heating the reagents together under vacuum or under nitrogen. It does not appear to decompose until near the m.p. and is quite stable at

120°. The adduct gave no e.s.r. signal. - 116 -

Reactions of the 1:1 adduct

(a) Oxidation. Dry air was passed through a suspension of the

1:1 adduct (100 mg) in methanol to yield purple crystals of the dienone (31 mg, 44$) - by t.l.c. and i.r. Oxidation of the adduct (200 mg) with 30$ hydrogen peroxide (1 ml) in acetone also gave the dienone (67 mg, 48$).

(b) Acid treatment. The dienone (0.5 g) was refluxed in benzene

(1.5 ml) with the tris-arainophosphine (0.5 ml, 2 mole) under nitrogen for 0.5 hour. The clear solution was cooled, more benzene

(8 ml) added, followed by hydrogen bromide in acetic acid (0,5 ml,

45$) with stirring for 1 hour. The solution was filtered, evaporated at 40°, and dry acetonitrile added to give bright yellow crystals of 5-bromo-1,2,3,4-tetraphenylcyclopentadiene together with some 1 ,2,3,4-tetraphenylcyclopentadiene (0.307 g). Concen tration of the filtrate and addition of ethanol gave a further batch of yellow/brown crystals (0.186 g) identical to the former by t.l.c. and i.r. By n.m.r., estimated yield of bromodiene =

0.37 g (64$) and of diene 0.12 g (25$). Recrystallisation from o 102 benzene/acetonitrile gave material of m.p. 198-200 , lit.

190-1910.

The tetraphenylcyclopentadiene almost certainly arises as a result of the excess tris(dimethylam.ino)phosphine present; when the 1:1 adduct was obtained free of tris-aminophosphine, treatment with HBr in acetic acid gave only the bromodiene. - 117

»II n.rn.r. (CDC1 ) Singlet 65.89 (1H) - ^CKBr

Multiplet 66.9-7.4 (20H) - - ArH

The 1:1 adduct was quite stable in an alkaline medium, being unaffected by boiling with 20$ potassium hydroxide solution (in

50$ DME/water) for 1 hour.

Treatment of the 1:1 adduct (0.66 g) with 2M sulphuric acid

gave a white crystalline salt, tris(dimethylamino)-2,3,4,5-tetra-

phenylcyclopenta-2,4-dienyloxyphosphonium hydrogen sulphate,

(0,6 g, 77$), m.p. 176-177°(dec), (from acetonitrile/benzene); i.r.

showed no carbonyl absorption.

Found (M5679): C, 65.5; H, 6.9; N, 6.2; P, 4.8

C^H^qN^OcjPS requires: C, 65.1; H, 6.2; N, 6.5; P, 4.8

H n.rn.r. (acetonitrile)

Doublet 62.3, J 10.3 Hz (18H) - - P-N-CH3

Doublet 65.47,J 6.2 Hz (1H) - - P-O-CH

Two peaks 67.45, 7.05 (20H) - - - Ar-H

Treatment of this salt with aqueous potassium hydroxide solution

regenerated the 1:1 adduct (73$).

(c) Alkylation with methyl iodide. The dienone (1.0 g) was

refluxed in benzene (2 ml) with the tris-aminophosphine (0.5 g,

1.2 mole) under nitrogen for 1.5 hours. The solution was cooled and excess methyl iodide (2 ml) added. Chromatography on silica

gel (30 g) and elution with benzene/petrol gave fiery, orange-

red crystals (0.23 g, 23$) of 1,2,3,4-tetraphenylfulvene, m.p.

212-213° (chloroform/acetonitrile), lit.^ ' 211-212°. 118

’H n.m.r. (CDC1 ) Multiplet 66.7-7.3 (20H) ArH

Singlet 65.99 (2H) - - - =GH2

The only other products identified from the chromatography v/ere dienone and free iodine, considerable amounts of which eluted v/ith benzene. No increase in the yield of tetraphenyl-

fulvene was obtained when the addition of methyl iodide was carried out in the presence of a base, NaH (added to remove any HI formed).

(d) Phenylphosphine reaction. The 1:1 adduct (0.5 g) was heated and stirred in phenylphosphine (1 ml, 10 mole) at 160° for 0.5 hour.

The phenylphosphine was pumped off (0.1 mm) and the residue dissolved in chloroform and treated with ethanol to give white crystals of 1,2,3,4-tetraphenylcyclopentadiene (0.295 g, 87$), m.p. 176-177° (cyclohexane), lit.10^ 179-180°.

*H n.m,r. (CDCl^) Multiplet 67.1 , 7.17 (20H) - ArH

Singlet 64.0 (2Il) - - 'CH2

Lit.1'"^’ value, 64.01 (CDCl^). u.v.(cyclohexane) >. 343 (4.10), 268 (4.29), 245 (4.37). ■"" max In another experiment using only 5 moles PhPH2, the yield of diene dropped to 55$, but 1,1 *-dihydro-octaphenylfulvalene (10$) and the ’dimer’, (43), (5$) were also isolated, together with

(PhP)j. (80$). The latter 7/as isolated by virtue of its insolu bility in hot ethanol; the former compounds were obtained by chromatography on silica gel and elution with benzene/petrol.

(e) Diphenylphosphine reaction. The dienone (2.0 g) was stirred under nitrogen with the tris-aminophosphine (5 ml, 5 mole) at - 119 -

100-120° for 10 minutes. The solidified mass was treated with

diglyme (5 ml) and diphenylphosphine (1 ml, 1 mole) and stirring

continued for 1 hour at 130°. The temperature was then raised

to 160-170° for 0.5 hour. Addition of cyclohexane to the cooled

solution gave an ivory white precipitate (0.977 g). Extraction

with boiling methanol gave 1,11-dihydro-octaphenylfulvalene

(0.22 g). The methanol extract was treated with ethyl acetate

to give tetraphenyldiphosphine dioxide, m.p. and mixed m.p.

180-184°, identified by i.r. (0.75 g, 70$).

The residues from the reaction were chromatographed on

silica gel (60 g); elution with benzene/petrol gave tetraphenyl-

cyclopentadiene (0.18 g, 10$), dimer (43), (0.18 g, 10$) and

1,11-dihydro-octaphenylfulvalene (0.86 g total, each

identified by i.r. and mixed m.p.: diene 176-177°, dimer 310-314°,

dihydrofulvalene 183-195° (cyclohexane). One sample of dihydro-

fulvalene had m.p. 195-198° (chloroform/acetonitrile). The diene,

dimer, and dihydrofulvalene had different R^'s on t.l.c. and also,

each had a slightly different coloured fluorescence under u.v. light. On silica gel with a solvent system of 10-20$ ether/petrol,

the diene had R^ 0.6 and was bright blue under u.v., the dimer had R^ 0.5 and was a purplish-blue, the dihydrofulvalene had

Rf 0.45 and was a similar blue to the diene, but slightly deeper.

When the 1:1 adduct and diphenylphosphine were allowed to stand in benzene at room temperature for one week, t.l.c. showed the presence of some diene. Refluxing in benzene for 3 hours 120

gave diene and tetraphenyldiphosphine dioxide (work-up in air).

(f) Methyl/phenyl phosphinate reaction. The dienone (1.0 g) was heated and stirred with the aminophosphine (1.5 ml, 3 mole) at

100-120° under nitrogen for 1 hour. A little benzene was added

to increase homogeneity, and after refluxing for a further 0.5 hour, the mixture was evacuated (0,5 hour, 0.2 mm). Methyljphenyl-

phosphinate (2 ml, 5.7 mole) was added and the mixture heated at

100-120° for 1 hour, and for a further 1 hour under vacuum (0.2 mm).

Addition of ethanol gave tetraphenylcyclopentadiene (0,312 g, 31$)i m.p. 176-178°, identified by i.r. The filtrate was chromato graphed on silica gel (20 g); elution with benzene/petrol gave dihydrofulvalene (0.09 g, 10$), m.p. and mixed m.p. 193-195°

(chloroform/ethanol), trans-2,3»4,5-tetraphenylcyclopent-2-enone

(0.18 g, 18$) identified by i.r., and dimer (0.025 g, 2.6$), m.p.

310-314°. A more polar fraction was obtained (0.146 g), i.r.

1180 cm ; it appeared to be a mixture by n.m.r.

*H n.m.r. (CDCl^) Multiplet 56.3-7.6 (25H) Ar-H

Singlets 55.72 (O.36H), 5.59 (0.3H),

5.3 (0.15H), 3.29 (0.3H)

Doublet 53.31, J 11 .5 Hz (1H) - - - P-0CH

The 1:1 adduct did not react with methyljphenylphosphinate when refluxed in benzene for 0.5 hour.

(g) Reaction with ethanol. A solution of the 1:1 adduct in benzene was treated with ethanol and allowed to stand 1 month. Yellow 121

crystals of 5-(N,N-dimethylamino)-1,2,3.4-tetraphen.ylcyclopenta-

1 ,3-diene formed slowly over this time, m.p. 152-155° (acetonitrile/ ethanol).

Pound: (15749) C, 89.3; H, 6.6; N, 3.2

0^HoyN requires: C, 89.9; H, 6.6; N, 3.4

'H n.m.r. (CLCl.^) Multiplet 66.7-7.5 (20H) - - - - ArH

Singlet 64.80 (1H) - - - - Me2N-CH

Singlet 62.57 (6H) - - - NMe2

The same product was formed by allowing dimethylamine to react with the adduct in ethanol, but no reaction occurred in benzene.

The dimethylamine in the above reaction presumably arises by way of 105 reaction between residual tris-aminophosphine and ethanol.

(h) Pyrolysis. The dienone (4.0 g) was heated and stirred under nitrogen with the tris-aminophosphine (4 ml, 2 mole) at 120°.

After a few minutes, the mixture thickened at the periphery, then gradually towards the centre until the stirrer stopped. The colour at this stage was still a dark, black-red. Then, over the next few minutes the colour lightened to a berry-red, and from the centre outwards, all traces of red disappeared, leaving a solid, straw-coloured mass which appeared crystalline at the periphery.

The temperature was then raised to 160-180° for 1.5 hours. As the temperature rose, the colour changed to a burnt red-brown, and after a few minutes, the mixture was fluid and began refluxing.

The reaction vessel was then connected to a vacuum pump (0.2 mm,

0.5 hour) to remove excess aminophosphine. The mixture was cooled, dissolved in chloroform and ethanol added to give a white 122

crystalline precipitate of deoxy-dienone-dimer (’dimer’) (3.09 g,

80$), m.p. 310-313°. (The crude dimer usually melted at 302-305°;

a single recrystallisation from chloroform/ethanol gave material

of m.p. 310-313° with very little loss; further purification by

chromatography on silica gel and recrystallisation from chloroform/

acetonitrile gave material of m.p. 334-338°. The low m.p. is

attributed to traces of oxide impurities - the mass spectrum

showed small peaks at M+16 andM+32.) The structure assigned, (43),

may be named 1,2,3,4,5,6,6a-heptaphenyl-10bH-benz[e]-as-indacene.

’H n.m.r., 100 Me (CDCl^) Singlet 65.232 (1H) - dienyl H

Multiplet 66.2-6.4 (3-5H) ArH

Multiplet 66.6-7.7 (34-36H) ArH

Found: (14305) C, 93.7; H, 5.5; M.W. 736.3144 - .0014 a.m.u.

C-qH^q requires: C, 94.5; H, 5.5; M.W. 736.31298 a.m.u. u.v.(cyclohexane) X 362 (4.13), 310 (4.39), 258 (sh, 4.58), niciix. 235 (4.7)

(chloroform) X 366 (4.11), 314 (4.34), 255 (4.57). nicijl

X-ray Analysis Direct Cell Dimensions o a = 10.294 A a = 78°44' o b = 18.695 A 3 = 88°7'

c = 11.937 A Y = 77°9i

Reciprocal Cell Dimensions * 9-1 a O.O9995 A a* = 102°

b f3* = 94°35»

* 0-1 c 0.08569 A Y = 103° 30’ 123 -

_ o Volume of unit cell = 2195*47 cuA

No. of molecules/unit cell = 2

Space Group P1 or PI.

The residues from the reaction yielded approximately 12

products after chromatography on silica gel, hut none were obtained

in a pure crystalline state. The volatile material from the

pyrolysis was identified as hexamethylphosphoric triamide by its high b.p. (it could not be pumped off at 0.2 mm/l60°, but merely refluxed inside the flask) and by its i.r. spectrum which was

identical to authentic material.

Decomposition of the 1:1 adduct in Diglyme

Dienone (1.0 g) was refluxed in diglyme (7.0 ml) with the aminophosphine (1 ml, 2 mole) under nitrogen for 1.5 hours. The solution was cooled and ethanol added to give dimer (0.59 g» 62$), m.p. and mixed m.p. 303-306°. Concentration of the filtrate gave a precipitate (0.23 g) consisting of at least four other products

(by t.l.c.). A similar decomposition in mesitylene (7.5 nil) gave dimer (0.47 g, 50$), m.p. and mixed m.p. 300-303°.

Decomposition of the 1:1 adduct in tributylphosphine

The adduct (0.5 g) was heated at 160-170° in tributylphosphine

(3 ml) under nitrogen for 2 hours. Ethanol was added to the cooled solution to give dimer (0.11 g, 33$)» m.p. and mixed m.p. 304-307°.

No other pure crystalline material could be isolated from the filtrate.

A similar decomposition of the adduct in the presence of -124-

triphenylphosphine (2 mole) gave the dimer as the major product («#).

Decomposition of the 1:1 adduct in Diethyl maleate

The dienone (1.5 g) was heated and stirred with the amino-

phosphine (0.7 g, 1.1 mole) and diglyme (7 ml) at 100-120° for

1-2 hours under nitrogen. The solution was then added slowly to

stirred, hot (170-185°) diethyl maleate (8 ml, 16 mole) under

nitrogen over a period of 10-15 minutes. The mixture was refluxed for 1 hour, cooled, and ethanol added to give the dimer (0.604 g,

42$), m.p. and mixed m.p. 302-305°. The filtrate was reduced in volume and chromatographed on silica gel (60 g). Eluting with benzene/petrol gave the dihydrofulvalene (40 mg, 3$) identified by

its mass spectrum, and a small quantity (0.15 g) of an aromatic, carbonyl containing material, m.p. 193-195°(dec) (benzene/ cyclohexane). i.r. 1790, 1720 cm"1 ; u.v. (ethanol) \ 270 m/i (4.1 ).

Found: (M6231) C, 80.0; H, 6.0; M.W. 556

C ?H 0 requires: C, 79.9; H, 5.8; M.W. 556.

'H n.m.r., 100 MHz (CDC1 )

Triplet 50.80, Jj.3 Hz (3H) -CH2-CH3

Triplet 51.32, J 7.2 Hz (3H) - - -CHo-0H3

Doublet 53.84, J 5.0 Hz (1H) CH

Quartet 53.84, J 7.3 Hz (1H) ) diatereotopic ) methylene Quartet 53.88, J 7.3 Hz (1H) ) hydrogens of OEt group - 125 -

Quartet 64.28, J 7.2 Hz (2H) - - O-CH Me

Doublet 64.33, J 5.0 Hz (1H) - - CH

Multiplet 66.4-7.6 (20H) ArH

The same compound was obtained when the dienone (0.1 g) and

diethyljmaleate (1 ml) were heated and stirred together at 180° for

1 hour. Evaporation of the mixture (0.2 mm/l00°) and addition of

acetonitrile gave white crystals (98 mg, 70$), m. p. and mixed m.p.

193-195° with gas evolution. It appears to be a 1:1 adduct of the

dienone and diethyl maleate but the n.m.r. excludes the expected

cis-addition product.

(i) U.v. irradiation of the 1:1 adduct. The dienone (1.0 g) was

refluxed in benzene (5 ml) with tris(dimethylamino)phosphine (1 ml,

2 mole) for 1.5 hours under nitrogen. The solution was diluted with benzene (45 nl) and irradiated over a small u.v. lamp (under

reflux) for 1 hour. The mixture was concentrated and chromato

graphed on silica gel (30 g); elution with benzene/petrol gave

1 ,2,3,4,5-pentaphenylcyclopentadiene (0.314 g, 27$) as the major

product, m.p. 247-249° (chloroform/ethanol), 260-263° (benzene);

lit.”* 2 52-2 54°. It had an slightly greater than the dimer but less than the diene.

*H n.m.r. (CDClJ Singlet 65.07 (1H) )CHPh

Multiplet 66.8-7.3 (25H) ArH

(C6D6) Singlet 65.02

(cyclohexane) X 340 (4.07), 267 (4.36), 246 (4.43) u.v* r . nicix Found: M.W., 446. requires 446. -12 6 -

A small amount (0,07 g) of an isomeric material was eluted

from the column just prior to the pentaphenyldiene. It had m.p.

196-1980 and a similar mass spectrum to that for 1,2,3>4,5-penta-

phenylcyclopentadiene.

u.v. (cyclohexane) \__ , 254 (4.62). 1 * nicix

Reactions of the deoxy-dienone-dimer (43)

The dimer was a very stable compound. It did not decompose when heated to 350-360° for 20 minutes and was unaffected by

refluxing in trifluoroacetic acid for 4 hours. After refluxing with aqueous potassium permanganate/sodium periodate for 3-4 hours,

81 $ of the dimer was recovered. Attempted hydrogenation of the

dimer (200 mg) over PtO^ (20 mg) in acetic acid (50 ml) at 4 atmospheres, with shaking, for 3 hours gave a 92$ (184 mg) recovery of dimer. Similarly, hydrogenation over 10$ palladium on charcoal

in acetic acid/benzene at 1 atmosphere for 20 hours, and over

Raney nickel in 50$ benzene/ethanol for 24 hours gave no noticeable reaction. The following reactions were also tried; all gave an

80-90$ recovery of dimer:

(1) Benzoyl peroxide in carbon tetrachloride at room

temperature, 48 hours.

(2) Heating with palladium on charcoal at 300-340° for

1.5 hours.

(3) Refluxing in benzene with silver oxide overnight.

(4) Refluxing with morpholine and iodine in benzene for

2 hours. -127-

(5) Stirring with potassium mercuri-iodide in benzene/water

for 24 hours.

(6) Melting with tetracyanoethylene at 200° under nitrogen

for 2 hours, then refluxing in diglyme for 2 hours.

(7) Treatment with hydrogen peroxide/hypochlorous acid in

methanol/t-butanol for 3 hours.

(8) Treatment with alkaline hydrogen peroxide in refluxing

acetone.

(9) Irradiation with u.v. light in refluxing benzene under

nitrogen for 2.5 hours.

(10) Fusion with maleic anhydride at 110°, then refluxing

for 2 hours in acetonitrile.

Ozonolysis in chloroform at 0° decomposed the dimer but no pure crystalline material could be isolated by chromatography.

Stirring the dimer (1.5 g) with powdered sodium (0.1 g, 2 mole) in

DME (10 ml) at room temperature for 2 days gave a deep red-black solution. Addition of methanol (10 ml) discharged the colour and gave dimer (0.8 g, 53$) and a dirty yellow coloured powder (0.53 g), m.p. 175-185°♦ The mass spectrum of this substance indicated a mixture of dimer and dihydrodimer(s) (peaks at 736 and 738). N.m.r.

(CDCl.^) showed peaks at 64.5* 5«2 and 5.5»together with numerous smaller peaks. The substance was not further investigated as it appeared to be a complex mixture of dihydrodimer isomers.

Although oxidations under neutral and alkaline conditions were unsuccessful, oxidation was achieved under acidic conditions. 128

The dimer (250 mg) was refluxed with potassium permanganate in acetic acid (0.5 g/10 ml) for 2-3 hours. Dilute sulphurous acid was added to the cooled mixture to give a pale yellow powder

(230 mg), i.r. 1775» 1670, and 1205 cm" . Chromatography on silica gel gave about six products, none of which could be obtained in a pure crystalline state. Chromium trioxide in acetic acid appeared to give a similar product in addition to a low yield (7$) of benzoic acid.

Oxidation with Chromium trioxide in Trifluoroacetic acid

The dimer (250 mg) was refluxed in trifluoroacetic acid (4 ml) with CrO^ (1.5 g) for 4 hours. A little water was added and the mixture extracted with chloroform and with ether. The combined extracts were treated with sodium hydroxide solution which was then acidified and re-extracted. The organic phase was treated with excess diazomethane and analysed by g.l.c. Peak enhancement was observed with methyl benzoate, phthalic anhydride and the methyl ester of o-benzoyl benzoic acid. Another product formed in substantial amount, but unidentified, had a retention slightly less than dimethyl phthalate (this could have been a trifluoroacetate of an oxidation product). The mixture was evaporated to dryness and heated on the steam bath with a few drops of oleum for 3 hours. Addition of ice, and recrystallisation of the resulting precipitate from acetic acid gave anthraquinone

(2.3 mg, 3.3$)» m.p. and mixed m.p. 275-277°. Anthraquinone was -129-

also isolated in low yield by oleum treatment of the acidic material obtained from an oxidation of the dimer with CrO^ in acetic acid; it was not obtained from a CrO^/pyridine oxidation.

Photo-oxidation in Benzene

The mass spectrum of the dimer usually showed small peaks at m/e M+16 and M+32, suggesting aerial oxidation. Though unaffected by dry air in a variety of solvents, the dimer readily absorbed oxygen when irradiated.

The dimer (1.5 g) in dry benzene (600 ml) containing a little eosin (20 mg) (reaction appeared to be very slow in the absence of eosin) was irradiated with u.v. light from a medium pressure lamp

(emitting predominantly 254* 265, 297, 313, 366 m/i - Hanovia IL reactor) while a slow stream of dry air was bubbled through the solution. The progress of the oxidation was followed by t.l.c.

Irradiation was continued for 1.5 hours. The solution was concen trated and chromatographed on silica gel (50 g); elution with benzene/petrol gave two minor fractions. Both were dimer-dioxides.

Fraction 1, pale yellow crystals (0,18 g, 11.5$), m.p. 242-244°

(chloroform/acetonitrile), i.r. 1665 cm" (C=0).

Found: (M5301) C, 90.2; H, 5.4; M.W. 768

C53H400o requires: C, 90,5; H, 5.3; M.W. 768

»H n.m.r. (CDC1 ) Singlet 55.72 (1H) - - - - C-H

Multiplet 56.3-8.0 (39*0 [outer arms,

57.7-8.0, and 56.3-6.6] Ar-H - 130 -

u« v. (cyclohexane) 7\ 348 ( . ), 282 (4.53), 245 (4.59) 1 max 4 05

Fraction 2, white-very pale yellow crystals (0,47 g, 30$), m.p.

286-288° (chloroform/acetonitrile/ethanol) , i.r. 1?00 cm"^ (0=0).

Found: (M2444) C, 90.1; H, 5.4; M.W. 768

C^gH^O^ requires: C, 90,5; H, 5.3; M.W. 768

*H n.m.r. (CDC13) Singlet 54.58 (1H) - - - C-H

Multiplet 66.7-7.5 (39H) - - ArH u.v. (cyclohexane) 312 (4.49), 300 (4,47), 260 (sh, 4.47)

243 (4.61).

Photo-oxidation in benzene/ethanol

The dimer (2.0 g) in benzene/ethanol (750 ml, 2:1) containing a little eosin (20 mg) was irradiated with u.v. light for 1.5 hours while a slow stream of dry air was bubbled through the solution.

The solution was concentrated and chromatographed on silica gel

(60 g). A fairly high yield (0.89 g» 44$) of the dimer dioxide with i.r. 1665 cm" (i.e. Fraction 1 from previous photo-oxidation) was obtained. Only a small amount (80 mg, 4$) of the second dimer dioxide was obtained.

No other pure crystalline materials were isolated from the dozen or so fractions eluted subsequent to the two dioxides.

Reduction of Dimer Dioxides

Fraction 1 (100 mg) was refluxed with sodium borohydride

(150 mg) in water/DME (10 ml, 10$) for 3-4 hours. The mixture - 131

was concentrated and water/chloroform added. The chloroform layer was removed, evaporated, and ethanol added to give white crystals of dihydroder1vative (A), (73 mg, 73$) which had a softening point 160-180° (rec. chloroform/ethanol). I.r. showed no carbonyl absorption.

Found: (M5299) C, 89.6; H, 5.5; M.W. 770.3191 - .0015

C£-QH^20o requires: C, 9°.4; H, 5.5; M.W. 770.3185 a.m.u. yH n.m.r. (CDCl-J Singlet (broad) 62.1 (1H, exchanged DO) OH

Singlets 66.33, 5.90 (1H each)

Multiplet 66.15, 6.04 ('•'OH) ArH

Multi pi et 66.5-7.7 (~37h) ArH b. v. (cyclohexane) 355 (3.59)» 275 (sh, 4.22), 255 (4.45)

Fraction 2 was not reduced by sodium borohydride in boiling methanol or in DMF at 100°. However, it was reduced by lithium aluminium hydride: The dioxide (200 mg) was stirred in ether (7 ml) with LiAlH^ (100 mg, 10 mole) for 20 hours. A little ethyl acetate was added to remove excess hydride, followed by dilute hydrochloric acid. The acidified solution was extracted with chloroform.

Evaporation of the chloroform and addition of ethanol gave white crystals of dihydroderivative (B) (l40 mg, 70$) which had a softening point of 210-215° (chloroform/ethanol) but appeared to

i 1 remelt1 fairly sharply at 265'. I.r. showed 350° cm” (v. weak),

1120 cm but no carbonyl.

Found: (M2681 ) C, 89.2; H, 5.5; M.W. 770.3184 - .001 a.m.u.

C58H42°2 recluires: c> 9°.4; H, 5.5; M.W. 770.3185 a.m.u. - 132

*H n.m.r. (CDCl.) Doublet 60.73 (1H, J 4.5 Hz, exchanged 5 DO) - - - - OH

Singlet 64.71 (1H)

Doublet ^ "50 (1TJ -T A e; TT^ ^nllct^o^

Multiplet 66.4-8.0

Doublet u.v. (cyclohexane) 322 (sh, 4.20), 305 (sh, 4.36), 292 (4.4l), 1 max 253 (4.50)

Bromination of Dimer

The dimer (0.5 g) was refluxed in carbon tetrachloride (5 ml) with N-bromosuccinimide (0.16 g, 1.3 mole) for 5 hours. The solution was filtered to remove succinimide, concentrated, and acetonitrile added to give canary-yellow crystals of bromodimer

(66; X = Br) (0.51 g, 92$)* m.p. 295-298° (benzene/acetonitrile).

Found: (M2841) C, 85.6; H, 4.9; Br, 10.1

Cj-gH^Br requires: C, 85.3; H, 4.8; Br, 9.8

1H n.m,r. (CDCl^) showed only aromatic hydrogens. u.v. (cyclohexane) 7smax 39° (3.79), 365 (3.87), 310 (4.15),

270 (4.47), 235 (4.71).

The bromodimer could be slowly sublimed (300°/0.1 ram) without much decomposition. A small amount of dimer was apparent by t.l.c.

(initial treatment with methanol was necessary as the bromodimer had the same R^ as the dimer; the resulting methoxydimer had an appreciably different R^, to the dimer.) 133 -

Reactions of Broraodimer

1. Methanol. The bromodimer (0.355 g) was refluxed in methanol/

benzene (10 ml, 50$) for 10 minutes. A white crystalline precipi

tate of a methyl ether was obtained (0.33 g, 99$)» m.p. 267-270°

(benzene/acetonitrile).

Found; (M3787) C, 91.4; H, 5.6; M.W. 766.3246 t .0015

C^H^O requires; C, 92.3; H, 5.5; M.W. 766.3235 a.m.u.

1H n.m.r. (CDClJ Singlet 63-1 (3H) - - - - 0-CH3

Multipiet 66.3-8.2 (39H) •- ArH

(C^Hg) Singlet 63.1 u.v. (cyclohexane) Xmax 315 (4.45), 255 (4.6l); log e at 360 m/i, 3.65

380 m/jLt 3.51

345 m/i, 4.0

Pyrolysis of the methyl ether (45 mg) at 350° under nitrogen for 1 hour resulted in gas evolution at 280° and formation of the original dimer (30 mg, 70$) identical by i.r. and u.v.

2. Tris(dimethylamino)phosphine. Bromodimer (0.25 g) was stirred with the aminophosphine (1 ml) under nitrogen for 2 hours. A dark copper-brown solution was obtained. Addition of benzene gave a chocolate-brown precipitate. Addition of ethanol to the suspension gave the dimer (43) (0.18 g, 80$) identical by i.r. and t.l.c.

Addition of methyl iodide to the brown suspension did not appear to give a simple methyl-dimer. A crystalline product was -134-

isolated with = dimer by t.l.c. (although the blue fluorescence

turned pinkish after several minutes under u.v. light. The n.m.r.

spectrum (CDCl^) of this product showed two singlets 65.32, 5.25

(total 1H) and a complex aromatic multiplet 66.1-7.9 (39H).

3. Water. The bromodimer (0.14 g) was refluxed in THF with a little water for 2-3 hours. Evaporation and addition of ethanol gave a white precipitate (0.03 g) of apparently, hydroxydimer: n.m.r.(CLCl^) singlet 62.5 (1H, exchanged ); multiplet 66.3-8.1

(39H).

Most of the bromodimer was recovered after refluxing in aqueous acetone for 3.5 hours.

4. Sodium borohydride. The bromodimer (100 mg) was stirred at

60-70° in DME/benzene (6 ml, 50^) with NaBH^ (10 mg, 2 mole) for

5-6 hours. Filtration, evaporation, and addition of boiling ethanol gave a small amount of dimer, identical by i.r. and t.l.c. to authentic material.

5. Lithium aluminium hydride. The bromodimer (200 mg) was stirred with excess LiAlH^ (20 mg) in benzene/ether for 2 hours.

Ethyl acetate was added and the mixture extracted with water.

Evaporation, and chromatography on silica gel (15 g) by elution with benzene/petrol gave dimer (70 mg) (identified by n.m.r.) and a small amount (~ 20 mg) of an isomeric material (44), m.p. 240-242°. - 135 -

H.m.r. (CDCl^)s singlet 65*30

u.v. (cyclohexane) 347 (sh, 3*91)» 312 (4.47), 253 (4.61 ).

The isomeric material had an identical mass spectrum to that of

the dimer (43) and appeared to be identical (i.r., n.m.r.) to

the material obtained by treating the broraodimer with the tris-

aminophosphine followed by methyl iodide.

The chlorodimer (66 s X = Cl) was obtained by refluxing the

dimer (200 mg) with N-chlorosuccinimide (73 mg, 2 mole) in tetra-

chloroethylene (4-5 ml) for 2 hours. Concentration and addition

of acetonitrile gave the chlorodimer (111 rag, 53^) as yellow

crystals, m.p. 313-316° (benzene/acetonitrile or acetone).

_I._r. 868 cm“^ (C-Cl).

Found; (M5812) C, 89.9; H, 5*3; Cl, 4.5; M.W. 770, 772

C^H Cl requires; C, 90.3; H, 5.1; Cl, 4.6; M.W. 770, 772

u.v.(cyclohexane) X 395 (sh, 3.66), 365 (3*93), 353 (sh, 3.90), TTlcLX 308 (4.13), 265 (4.56).

Oxidation of Dimer with Selenium Dioxide

The dimer (0.5 g) was refluxed in DME/ethanol (10 ml, QOfo)

with SeO^ (0.5 g, 6.6 mole) for 24 hours. T.l.c. still showed

mostly dimer. The mixture was evaporated to dryness, toluene

added and reflux continued overnight. The toluene was evaporated

and ethanol added to give a white precipitate (0.35 g) which was

chromatographed on silica gel; elution with benzene/petrol gave

crystalline hydroyydimer (66; X = OH), m.p. 295-299° (acetone/ethanol), - 136 -

i.r. 3500 cm"

Found: (15737) C, 92.6; H, 5.5; M.W. 752

requires: C, 92.5; H, 5.4; M.W. 752

!H n.m.r. (CDCl^) Singlet 62.4 (1H, exchanged D?0) - - C-OH

Multiplet 66.0-7.7 (39H) - ArH u,v. (cyclohexane) \ 365 (4.01), 310 (4.23), 298 (sh, 4.16), max 260 (4.55)

1,1*-Dihydro 2,3,4,5,2*,3*,4*,5*-octaphenylfulvalene was prepared 77 in 30$ yield by the method of Pauson and Williams by refluxing

5-bromo-1,2,3,4-tetraphenylcyclopenta-1,3-diene with zinc powder in benzene for 15 hours, m.p. 183-185° (lit.'7 180-182°).

*H n.m.r., 100 MHz (CDC1 )

Singlet 64.999 (2H) - dienyl H

Multiplet 66.8-7.2 with two

symmetrical wings 66.65,7.50 (40H) - - ArH u.v. (CHC13) >^ax 352 (4.33), 250 (4.53)

Lit.7^ values 350 (4.33), 250 (4.54).

The 5-bromodiene was prepared in 82$ yield by the method of 102 Kainer, ~ by refluxing tetraphenylcyclopentadiene with NBS (1.03 mole) in carbon tetrachloride for 3 hours. Recrystallisation from cyclohexane/benzene gave canary yellow crystals, m.p, 195-197°

(lit.^°^ 190-1910). The bromodiene could be sublimed (210°/0.1 mm) without decomposition (no parent diene formed by t.l.c.) and was recovered unchanged after refluxing in 50$ benzene/methanol for 3 hours. - 137 -

Dehydrogenation of 1,11-dihydro-octaphenylfulvalene

The dihydrofulvalene (50 nig) was heated with 10$ palladium/ charcoal (20 mg) at 300° under nitrogen for 2 hours. A small amount of 1,2,3,4-tetraphenylcyclopentadiene sublimed out of the reaction vessel (identified by t.l.c. and i.r.). The cooled melt was treated with chloroform, filtered, and ethanol added to give deoxy-dienone-dimer (16 mg, 32$) identical by t.l.c., i.r. and mixed m.p. (326-329°) to the product (43) obtained from pyrolysis of the aminophosphine-dienone adduct. A few milligrams of another polyaromatic material were obtained from the filtrate; 7^

(cyclohexane) 260 (4.17 for M.W. 736).

Refluxing the dihydrofulvalene in benzene with azobis-isobutyronitrile or with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone did not effect this conversion. Benzoyl peroxide gave a material with the same R^ as the dimer but with an orange fluorescence under u.v. light.

Bromo 1,2,3*4,5-pentaphenylcyclopentadiene and methanolysis

1,2,3>4,5-Pentaphenylcyclopentadiene (50 mg) was refluxed in carbon tetrachloride with N-bromosuccinimide (20 mg) for 5 hours.

Filtration, evaporation and addition of acetonitrile gave red-orange crystals of the mono bromocompound (45 mg), m.p. 196-199° (dec). u.v. (cyclohexane) 368 (3.45)» 268 (4.38), 250 (4.44).

The bromocompound (20 mg) was refluxed in 50$ benzene/methanol for

1 hour; evaporation and addition of acetonitrile gave 8.4 mg red 138 -

crystals, m.p. 195-198° (starting material) and 8,3 mg pale yellow crystals of methoxy 1,2,3,4,5-pentaphenylcyclopentadiene, m.p.

183-187° (lit.109 192-195°). u.v. (ethanol) \iav 360 (3.85), 269 (4.32), 250 (4.45)

Tetraphenyldiazocyclopentadiene

The dienone (2.0 g) and toluene-jD-sulphonylhydrazide (1.0 g,

2.06 mole) were refluxed in DME (15 ml) containing concentrated sulphuric acid (1.5 ml) for 3.5 hours under nitrogen. The mixture was reduced in volume and ethanol added to give a pale copper- coloured powder (2.18 g) which still contained some dienone (i.r.).

The copper-coloured powder (2.1 g) was added to methanol containing a little sodium methoxide (~3$) and the mixture refluxed for 1 hour; a brown powder (1.15 g) was obtained on cooling. The pure diazo compound was obtained by chromatography on silica gel (40 g)

(elution with 30$ benzene/petrol) as red-brown crystals (0.26 g), m.p. 132° (dec); i.r. 2070 cm""* (=N2) (lit.8^ 142° (dec).

Photolysis of Tetraphenyldiazocyclopentadiene in Benzene

The diazodiene (120 mg) was dissolved in dry benzene (40 ml) and irradiated for 2 hours under nitrogen with a small u.v. lamp.

The solution was concentrated and chromatographed on silica gel

(7 g). Elution with petrol/benzene gave pentaphenylcyclopentadiene

(11 mg, 8$) identical to authentic material by i.r., t.l.c. and mixed m.p. -139-

Pyrolysis of Tetraphenyldiazocyclopentadiene

A. The diazodiene (80 mg) was heated under vacuum at 170° for

0.5 hour. Rapid evolution of gas occurred and the colour changed

from red-brown to black. The melt was cooled and chloroform added.

T. l.c. showed no dimer (43).

B. The diazodiene (50 mg) was stirred with HMPT (4.5 ml) at 160° under nitrogen for 1.5 hours. T.l.c. showed the same as for A.

A and B were combined and chromatographed on silica gel (12 g).

Elution with petrol/benzene gave tetraphenylfulvene (19 mg) as

orange crystals, m.p. 212-213° (chloroform/acetonitrile) (lit.^

211-212°). Treatment with morpholine converted the fulvene into 107 tetraphenylcyclopentadiene - a test for this substance, ' and some black-brown crystals (17.5 mg) of apparently azo-tetraphenylcyclo pentadiene, m.p. 282-285°.

Found: M.W, 764; requires 764.

U. V» (cyclohexane) 520 (sh, 3.01 ), 410 (sh, 4.21 ), 357 (4.41),

265 (sh, 4.58), 255 (4.59).

Reaction of Tris(dimeth,ylamino)phosphine with 1,2,3,4-Tetraphenyl- fulvene

The tris-aminophosphine was added dropwise to a stirred solution of the fulvene (50 mg) in benzene (2 ml) at room temperature under nitrogen. There was immediate decolourisation and large white crystals of a 1 :1 adduct (37) formed (54 mg, 76/&), m.p. 115-120° (dec) - 140 -

Found: (15934, M5811) C, 78.8; H, 7.1; N, 8.0; P, 5.7

C^H^N^P requires: C, 79.2; H, 7.4; N, 7.7; P, 5.7

’H n.m.r. (CDC1^) Doublet 62.10, J 9 Hz (18H) P-N-CH.

Doublet 63.86, J 12 Hz (2H) -ch2-p

Multiplet 66.7-7.4 (20H) - ArH u.v. (2io Et-jF/ethanol) X 325 (3.93)

The mass spectrum did not show a parent ion but showed strong peaks at m/e 382 (fulvene) and 163 P(FMe2)^ and a metastable peak at m/e 48.7 corresponding to loss of P(FMe^)-^ from the parent ion.

Reaction of Trimethylphosphite with Tetraphenylcyclopentadienone

The dienone (1.0 g) and trimethylphosphite (2 ml, 6 mole) were shaken together in a stoppered flask for 2 days. Addition of cyclo hexane (10 ml) gave (after 1 month) large white crystals of dimethyl-5-methyl-2,3,4,5-tetraphenylcyclopenta-1,3-dien-1-ol phosphate

(68) (0.617 g, 47$), m.p. 139-140° (cyclohexane).

A i,r. 1280 (P=0), 1035 cm” (P-0-C), no carbonyl absorption.

Found: (M5250) C, 75.8; H, 5.7; P, 5.7; M.W. 508

C32H2904P requires: C, 75.5; H, 5.7; P, 6.1; M.W. 508

*H n.m.r. (CDC1 ) Singlet 61.46 (3H) c-ch3

Doublet 63.1, J 11.7 Hz (6h) P-OCH.

Multiplet 66.5-7.6 (20H) - ArH

(cci4) Singlet 61.45, doublet 62.99

u,v. (ethanol) >. 316 (4.0), 244 (4.2). r msx The filtrate was evaporated to dryness (0.6 g), dissolved in

benzene and chromatographed on silica gel (35 g). Elution with

petrol/benzene and benzene/chloroform gave an oil consisting of two

enol phosphate isomers, Rp*s 0.7 (above isomer) and 0.69 by t.l.c.

(silica gel/ether). Both isomers exhibited a blue fluorescence

under u.v. light. The isomer of lower was dimethyl-5-methyl-

1>3»4»5-tetraphenylcyclopenta-1,3-dien-2-ol phosphate (6 g); 'H n.m.r.

analysis of the oil showed a ratio of 2-ol:1-ol = 5*2:1; in the

original reaction mixture, the ratio was 2-ol:1-ol = 35*47.

The i.r. spectrum of the oil (i.e. mainly 2-ol) was very

similar to that of the 1-ol isomer.

u.v. (ethanol) (5.2:1 mixture) 7\ 312 (3.77), 240 (4.38) ~x insx !H n.m.r. (CCl^) 2-ol isomer Singlet 61.73 (3H) - C-CH3

Pair of doublets (J 11.5 Hz)

63.19* 6*3.10 (6H) - - - P-0CH3

Multiplet 66.5-7.5 (20H) - - ArH

The pair (6,6') of doublets did not coalesce with increasing

temperature:

6-6' Solvent Temp. P0CH3 6 C-CH3 0 0 3.2 Hz 1.94 C6H6 60° 1.94 C6H6 3.9 " 0 0 CO 4.2 - 1.94 C6H6

DMS0 160° 5.7 - 1.79 -142-

In another reaction, in which the dienone and trimethylphosphite were heated together at 100-120° for 15 minutes, a low yield (0.8$) of 1,2,3,4-tetraphenylfulvene was isolated by chromatography on silica gel.

Hydrolysis of the enolphosphates

The 1-ol isomer was quite stable to refluxing potassium hydroxide solution (20$) and to concentrated hydrochloric acid/ methanol. Both isomers were hydrolysed by 75$ sulphuric acid.

The 1-ol phosphate (1.46 g) was refluxed with 75$ HpSO^ ^or 2hours.

Extraction with chloroform gave 5-methyl-2,3*4,5-tetraphenylcyclo~oent-

2-enone (1.11 g, 95$)» m.p. 149-153° (ethanol). As two crystal forms were present, separation of the two diastereoisomers was possible by fractional crystallisation. Trans isomer (72), m.p. 164-165°» i.r. 1695 cm”1 (C=0)

Found: (M14466) C, 89.9; H, 6.2; M.W. 400

C^H^O requires: C, 90• 0; PI, 6.0; M.W. 400

Cis isomer (7l), m.p. 188-190° i.r. 1695 cm-1 (0=0)

Found: (M14488) C, 90.4; H, 6.1; M.W. 400

The cis and trans isomers had identical mass spectra; *H n.m.r, analysis showed a ratio of trans:cis = 1.36:1 in the mixture obtained by hydrolysis.

The remaining oil (2-ol phosphate) was refluxed with 70$ sulphuric acid (5 ml) for 2-3 hours. Extraction with chloroform - 143 -

and evaporation gave a glassy mass (0.14 g) 'which could not be induced to crystallise. The i.r. spectrum of this glass was very similar to that of the mixture obtained by hydrolysis of the 1-ol isomer, v 1700 cm” (C=0). ’ H n.m.r. showed that it consisted of a mixture of two new ketones (70$) together with some of the previous diastereoisomeric ketones.

Acid hydrolysis of a reaction mixture obtained by heating tr.imethylphosphite and the dienone (1.0 g) at 80-90° for 0,5 hour, followed by careful chromatography on aluminium oxide (Woelm, activity 1 ) and elution with petrol/benzene, then benzene/chloroform, afforded a clean first fraction of trans-4-methyl-2,3,4,5-tetraphenylcyclopent-2-enone (74) as a glass (225 mg, 22$) i.r. 1700 cm"1 (C=0).

Found: (15935) 0, 89.1; H, 6.0; M.W. 400

Ck^H^O requires: C, 90.0; H, 6.0; M.W. 400

'H n.m.r. (CCl^) Singlet 61.07 (3H) C-CH.

Singlet 64.72 (1h) - PhCH

Multiplet 67-7.4 (20H) ArH

The mass spectrum of this material was very similar to that of the diastereoisomeric 5-methyl ketones (see Appendix).

Further elution gave a small amount of the cis-4-methyl isomer together with the two previously isolated 5-methyl ketones (the trans 5-methyl compound being followed by the cis 5-methyl isomer) and a little (8$) 2,3,4,5-tetraphenylcyclopent-2-enone. The cis

4-methyl isomer was not isolated in pure form; the yield (34 mg, 3$) - 144 -

was estimated by n.m.r, The mixture of diastereomeric 5-methyl ketones accounted for 0.468 g, 45$.

Trimethylphosphite appeared to react with the dienone at a somewhat slower rate than did tris(dimethylamino)phosphine. Reaction was complete after 18 hours at 30° using the trimethylphosphite

(6 mole) as solvent; the dienone (0.5 g)* (MeO)^P (0,33 ml* 2 mole) and benzene (5 ml) required 10 hours under reflux before decolourisation of the dienone was effected. Cf. the aminophosphine - a 4$ w/v solution of the dienone in benzene required 3 hours refluxing with the aminophosphine (2.6 mole) for decolourisation. Reaction between the dienone and (MeO)^P was very much faster in methanol, however.

The dienone (0.5 g), trimethylphosphite (1 ml) and methanol

(1 ml) were refluxed under nitrogen for 10 minutes; decolourisation was effected in 4-5 minutes. Evacuation (0.1 mm/80°) and addition of ethanol gave trans-2,3,4,5-tetraphenylcyclopent-2-enone (7)

(0.3 g* 60$), m.p. 162-164°, i.r. identical to authentic material.

Concentration of the filtrate gave dimethyl 1,3,4,5-tetraphenylcyclopent-1,3-dien-2-ol phosphate (75) (65 mg* 10$), i.r, identical to authentic material, and a little (45 mg, 9$) methyl 5-(1,2,3,4- tetraphenylcyolonenta-1,3-dienyl)ether, m.p. 163-165°. fH n.m.r. (CDCl^) Singlet 63.42 (3H) — - — OCH^

Singlet 64.96 (1H) - — - dienyl H

Multiplet 66.9-7.7 (20H) - - - ArH - 145 -

Reaction of the dienone with other P(lll) Compounds

Tributylphosphine. Dienone (100 mg) and excess Bu^P (210 mg) were refluxed in benzene (1 ml) and methanol (2.5 ml) under nitrogen for 2 hours, after which time the solution had decolourised.

Evaporation of the solution and addition of ethanol gave trans-

2,3>4,5-tetraphenylcyclopent-2-enone (94 mg, 94$), i.r. identical to authentic material.

Neither triphenylphosphine nor triphenylphosohite reduced the dienone when refluxed in methanol/benzene for 3 days. In the absence of a solvent, the dienone did not react with Ph^P (melt,

160° for 3 hours) or with (PhO)^P (200°/l hour) but it did react with rhenylphosphine: The dienone (1.6 g) was refluxed in phenylphosphine (1 ml, 2 mole) under nitrogen for 0.5 hour. Addition of ethanol to the cooled mixture gave trans-2,3,4,5-tetraphenylcyclopent-2-enone (1.48 g, 92$) identified by i.r. and mixed m.p. 160-162°.

A small amount (0.1 g, 20$) of (PhP)j- was isolated from the filtrate; most of the (PhP)^ was presumably lost by aerial oxidation.

Reaction of tris(dimethylamino)phosphine with 2,5-dimethyl-3,4- diphenylcyclopentadienone

The dimethyldienone (2.0 g) was stirred v/ith P(Nlle2)^ (2.2 ml,

1.6 mole) at 110-120° for 0.5 hour under nitrogen. The temperature was then raised to 160-170° for 0.5 hour. The mixture was cooled and ethanol added to give a brown powder (1.06 g). Concentration of the filtrate and addition of water gave a second batch of powder

(0.48 g). Chromatography on silica gel of both of these products - 146 -

gave a large number of fractions (>12) with colours ranging from yellow ochre to a very dark rusty brown. None were homogeneous or crystalline. The mass spectra of three of the major fractions gave strong peaks with m/e ~ 1000, 752, 748, 732, 730, 504, 5°2, 490*

488, 288, 244, indicating a mixture of products arising from the polymerisation (n = 2-4) of the expected carbene intermediate, m/e 244.

Trimethylphosphite did not appear to react with the dimethyldienone at temperatures below 100°. At 160°, the ketone was consumed, but owing to the complex mixture of products formed, the reaction was not further investigated.

Tris(dimethylamino)phosphine with Benzophenone

Benzophenone (2.0 g) was stirred with the aminophosphine (2 ml,

2 mole) and diglyme (5 ml) overnight at 110-120° under nitrogen; there was no apparent reaction. The mixture was then refluxed for

1-2 hours. T.l.c. showed the formation of a small quantity of tetraphenylethylene. Reflux was continued for 40 hours and the solution analysed by g.l.c. An(approximate quantitative)estimation gave hexamethylphosphoramide (~1 mole^ tetraphenylethylene (0.07 mole,

7$) and sym-tetraphenylethane (0.21 mole, 21$). Fractional crystal lisation (ethanol) gave both these latter products; tetraphenylethylene (0.135 g, 7$), m.p. 231-233° (lit.108 223-224°), i.r. identical to authentic material, and sym-tetraphenylethane (0.39 g>

21$), m.p. 217-218° (benzene/ethanol) (lit.11 u 211°). - 147 -

»H n.m.r. (CDC13) Singlet 64.76 (2H) - CHPh2

Singlet 67.1 (20H) - - - ArH

A reaction between benzophenone (2.0 g) and tris-aminophosphine

(5 ml, 5 mole) at 170-180° for 46 hours under nitrogen (in the

absence of diglyme) gave tetraphenylethylene (0,21 g, 11.5$), sym-

tetraphenylethane (0,25 g» 13.5$) and (recovered) benzophenone

(0.56 g, 26$).

Acetylation of 2,3,4,5-tetraphenylcyclopent-2-enone.

Attempted acetylation of the mono-enone with acetic anhydride

and concentrated sulphuric acid catalyst (at room temperature for

20 hours) gave tetraphenylcyclopentadienone in 20$ yield.

Acetylation was accomplished by prolonged refluxing with isopropenyl

acetate and an acid catalyst.

The mono-enone (0,5 g) was refluxed in isopropenyl acetate

(5 ml) with a little p-toluenesulphonic acid (0,1 g) for 18 hours.

The mixture was cooled and triethylamine (0.5 ml) added. After

extraction with water, the ester mixture was concentrated and

ethanol added to give 1,3,4,5-tetraphenylcyclopenta-1,3-dien-2-ol

acetate (0.465 g, 84$); three colourless crystalline (polymorphic)

forms were obtained on recrystallisation from chloroform/ethanol, all interconvertible by recrystallisation and all identical by t.l.c. and n.m.r., but each had distinct m.p's and different i.r, 1 o absorptions in the region 680-1000 cm" ; m.p, (l) 172-174 , m.p.

(2) 187-189°, m.p. (3) 186-188°; a mixture of (1) and (2) melted - 148 -

at 186-188°. i.r. 1765 (C=0), 1200 cm"1 (O-O)

Found: (M5405) C, 86.6; H, 5.6; M.W. 428

requires: C, 86.8; H, 5.6; M.W. 428

*H n.a.r, (CDCl^) Singlet 61.98 (3H) coch3

Singlet 65.13 (1H) dienyl H

Multiplet 66.9-7.5 (20H) ArH u,v. (ethanol) \ax 335 248 (4-2^)

Acetylation of 5-meth,yl-2,3.4,5-tetraphenylcyclopent-2-enone

The 5-methyl ketone (150 mg) was refluxed in isopropenyl acetate (5 ml) with p-toluenesulphonic acid (40 mg) for 30 hours.

Evaporation and addition of ethanol gave pale straw cubes (84 mg), m.p. 126-128 i.r. 1760 cm"1 (C=0)

'H n.m.r. (CDC1.,) Singlet 61.57 (3H) CH,

Singlet 61.97 (3H) COCH.

Multiplet 66. 5-7.6 (20H) ArH u»v. (ethanol) > 320 (4.06), 250 (4.31 ) " max The 4-methyl ketone was not acetylated under the conditions used above. Partial acetylation was effected using concentrated sulphuric acid/isopropenyl acetate; refluxing acetic anhydride/ boron trifluoride etherate (6 hours) gave a very dark solution. - 149-

The Reaction of Methyl/phenylphosphinate with Tetraphenylcyclo-

oentadienone and Dimethylamine

The dienone (1.0 g) and methyl/phenylphosphinate (0.75 ml,

2 mole) were mixed in benzene (10 ml) under nitrogen. Gaseous

dimethylamine, passed over the solution for 2 minutes, resulted in

a rapid colour change from red to yellow. Further stirring for 5

minutes gave a canary-yellow precipitate which was removed by

filtration after 1 hour (1.4 g, 92$), m.p. 124-127° (dec).

i.r. showed 2700, 2400 (NHg), 1240, 1200 (m, P=0), 1030 cm“1

(vs, P-O-C) but no carbonyl absorption.

Found: (M4559) C, 76.0; H, 6.6; IT, 2.2; P, 5.3

C^gH^gNO^P requires: C, 77.8; H, 6.2; N, 2.4; P, 5.3

1H n.m.r. (CDCl^ - deep green solution)

Singlet 52.33 (6H) - NMe2

Multiplet 63.3-4.1 (5H) - made up of

two doublets (j 11 Hz)--P-0CIL

63.8, 3.72 (3H) + broad (2H)

Multiplet 57.6-6.7 (25H) - ArH

Addition of DO gave Doublet 65.82, J 14 Hz (1H) ) > cf. (84) Doublet 63.75, J 11 Hz (3H) )

Singlet 64.6 (1H)

Broad peaks 62.57, 2,4 (5H) u.v. (ether) ^max ^4° (sh» 3.23), 260 (4.22)

Refluxing the canary-yellow compound (0.57 g) in benzene under nitrogen for 3 hours gave methyl cis-2,3,4,5-tetraphenylcyclopent- - 150

2-enon-4-ylphenylphosphinate (84) (0.46 g, 87$) identical by i.r. and n.m.r. to authentic material.

Methyl/phenylphosphinate + Morpholine + Tetraphenylcyclopentadienone

A. Room Temperature. The dienone (0,6 g), morpholine (0.27 g,

2 mole) and methyl/phenylphosphinate (O.365 g» 1.5 mole) were stirred together in ethyl acetate (5 ml) under nitrogen. Over about 5 minutes, the solution changed gradually from red to canary-yellow.

The mixture was stirred for a further 20 minutes, then filtered to give a canary-yellow powder (0.710 g, 73$)» m.p. 110-113° (dec); + i.r. showed 2700, 2400 (NH0), 1210 (m, P=0), 1100 (C-O-C) and 1040 cm” (P-O-C) but no carbonyl absorption. The substance dissolved in chloroform to give a green solution which on standing turned red-brown. Addition of ethyl acetate gave the yellow powder again

[m.p. 119-120° (dec), i.r. unchanged] but in a deep red solution.

Found: (M3503) C, 73.9; H, 6.2; N, 1.9; P, 5.1

C40H3QN04P requires: C, 76.7; H, 6.1; N, 2.2; P, 4.9

*H n.m.r. (CDCl^) - v. broad signals

'doublet' 63.46, J 11-12 Hz (3H) - - - P-0CH3

63.67 (4H), 2.9 (4H)-- morpholine H + 65.55 (2H) - - - - HH2

66.5-8.0 (25H) - ArH

31P n.m.r. (CHC13) 6-40.03 (&H3P04 = 0)

The yellow material was not stable to air; it turned a dirty yellow-green on standing in a desiccator for several hours. The - 151

yellow substance, dissolved in chloroform, gave a very strong e.s.r.

signal with an overall doublet appearance (^ 12 gauss splitting);

the spectrum showed hyperfine splitting 0.8 gauss) and 32 lines were counted in this instance (cf. Fig. 1).

When dissolved in ethanol and dry air passed through the

solution, tetraphenylcyclopentadienone (30$) was isolated. Pyrolysis

of the substance (300 mg) at 180-200° under vacuum for 15 minutes gave a 20$ mixture of the dienone with trans-2,3»4,5-tetraphenylcyclopent-2-enone (0.126 g, 69$) (estimated by n.m.r.). Acetylation of the yellow complex with acetic anhydride, followed by chromato graphy on silica gel gave a greenish-red oil; i.r. showed 1750,

1700, 1640 cm” ; this material was not further investigated.

2,3*4,5-Tetraphenylcyclopent-2-enone did not react with methyl- phe^'lphosphinate in the presence of morpholine in refluxing ethyl acetate.

B. 80°. The dienone (2 g), methyl/phenylphosphinate (0.895 g, l. 1 mole) and morpholine (0,453 g» 1 mole) were refluxed in benzene

(8 ml) under nitrogen for 2 hours. Evaporation and addition of ethanol afforded morpholinium cis-2,3*4,5-tetraphenylc,yclopent-2- enon-4-ylphenylphosphinate (92, HNR^ = morpholine) (0.8 g, 25$), m. p. 187-189° (ethanol). + 1 i.r. 26-2700, 2400 (NH ), 1680 (C=0), 1190 (P=0), 1040 cm”1

Found: (M3677) C, 74.8; H, 6.0; N, 2.0; P, 5.1

C^H^NO^P requires: C, 76.4; H, 5.9; N, 2.3; P, 5.1 - 152 -

1H n.m.r. (CDCl^ Multiplet 66.8-7.8 (25H) - ArH

Doublet 65.49, J 13 Hz (1H) - - - PhCH

Multiplet 63.62 (4H) morpholinium protons Multiplet 62.60 (4H)

(CF COOH) Multiplet 66.8-8.0 (25H)

Doublet 65.75, J 14 Hz (1H)

Multiplet 64.08 (4H)

Multiplet 63.48 (4H) u,v. (ethanol) V 2^.5 (4.08)

Concentration of the filtrate gave methyl cis-2,3.4,5-tetraphenylcyclopent-2-enon-4-ylphenylphosphinate (84) (0.99 g, 35$), m.p. 180-183° (ethanol). i.r. 1690 (C=0), 1225 (H=0), 1020 cm“1 (P-O-C).

Found: (M3754) 0, 79.8; H, 6.3; P, 6.2; M.W. 540.1856 - .001

(M5302) C, 78.6; H, 5.5; P, 5.7

C36H2903P requires: 0, 80.0; H, 5.4; P, 5.7; M.W. 540.1854

* H n.m.r. (CDC1 ) Multiplet 66.8-7.5 (25H) - - ArH

Doublet 65.82, J 14 Hz (1H) - - - PhCH

Doublet 63.7, J 11 Hz (3H) - - - P-OCH 3 u.v. (ethanol) % 298 (4.07). max y v ' The filtrate from the reaction was poured into water to give a white powder (1.04 g). N.m.r. showed that this was a mixture of the two previously isolated phosphino-ketones, (84) and (92), together with the diastereo isomeric ketones (84a) and (94). The ketone (94), methyl trans-2,3,4,5-tetraphenylcyclopent-2-enon-4- - 153 -

ylphegylphosphinate, was the predominant isomer in this mixture. i.r. 1695 cm”1 (C=0)

♦H n.m.r. (of mixture in CDCl^)

Multiplet 66.7-7.8 (-25H) ArH

Doublet 55.26, J 1.6 Hz Hh) - - PhCH

Doublet 63.0, J 11.2 Hz (~3H) - P-0CH. u.v. (ethanol) \&x 299 (4.07), 245 (sh, 4.13)

Reactions of methyl cis-2,3.4,5-tetraphenylcyclopent-2-enon-4- ylphenylphosphinate (84)

1. The ester (84) was partially isomerised when shaken with 70$ sulphuric acid for 1 hour. Extraction with benzene gave a material whose n.m.r. spectrum showed approximately equal amounts of (84) and the corresponding traps isomer. (94).

2. The ester (84) (100 mg) was refluxed in 30$ sodium hydroxide for 1 hour. Addition of dilute sulphuric acid and extraction with chloroform gave trans-2,3,4,5-tetraphenylcyclopent-2-enone (56 mg,

80$), i.r. identical to authentic material.

3. The ester (20 mg) was heated with morpholine (few drops) at

100° for 0.5 hour. Water (1 drop) was added and heating continued for 10 minutes. Addition of ethanol afforded morpholinium cis-

2,3,4,5-tetraphenylcyclopent-2-enon-4-ylphenylphosphinate (16.6 mg,

73$), m.p. and mixed m.p. 187-190°.

4. Recrystallisation of the ester from methanol gave a material of m.p. 110-112°, containing approximately 0.3 mole methanol (n.m.r.).

Heating to 150° under vacuum regenerated the methyl ester (84), - 154 -

m.p. 180-183°.

Reactions of morpholinium 2,3*4*5-tetraphenylcyclopent-2-enon-

4-ylphenylphosphinate (92, HNR2 = morpholine)

1. The morpholinium salt was treated with acetic acid and water to give the free phosphinic acid. The free acid (0.11 g) was treated with diazomethane in ethanol to give a methyl ester (84a)

(60 mg, 53$), m.p. 222-223° (ethanol).

1. r. 1690 cm“^ (C=0), 1210 cm~^ (P=0)

n.m.r. (CDC13) Multiplet 66.8-8.0 (25H) - - - - ArH

Doublet 65.52, J 14.5 Hz (1H) - - PhCH

Doublet 63.45, J 11 Hz (3H) - - P-0CH3 u.v. (ethanol) \ 301 (4.0)

2. Pyrolysis. The morpholinium salt (0.2 g) was pyrolysed under vacuum at 200° for 1.5 hours. Addition of ethanol gave trans-

2,3,4,5-tetraphenylcyclopent-2-enone (0.12 g, 95$), i.r. identical to authentic material. Concentration of the filtrate and addition of ethyl acetate afforded the bis-morpholinium salt of phenylphosphonic anhydride (30 mg, 40$), i.r. identical to authentic material.

3. Pyrolysis in D^O. The morpholinium salt (100 mg) was refluxed in D20 (1 ml) for 0.5 hour. The DgO was evaporated and the process + 1 + repeated; i.r. showed a shift of NH2 to 1900-2000 cm (ND2).

The deuterated salt was placed in a sealed tube with D^O (1 ml) and - 155 -

heated at 200° for 0.5 hour. The cooled mixture was extracted

with chloroform; evaporation of the chloroform and addition of

methanol gave 4-deuterio 2,3«4,5-tetraphenylc.yclopent-2-enone

(38 mg, 60$), m.p. 162-164° (ethanol); i.r. identical to non-

deuterated material.

Found: M.W. 387; C^^^^DO requires M.W. 387.

»H n.m.r. (CDC13) Multiplet 67.1-7.4 (20H) - - - ArH

Singlet 64.55 (-1H) - - PhCHCO-

Pyrolysis of the deuterated morpholinium salt by itself at

200-210° under vacuum for 1 hour afforded a mixture of the deuterio-

enone and the non-deuterated mono-enone.

2,3»4,5-Tetraphenylcyclopent-2-enone did not exchange the

protons a or P to the carbonyl group when treated with NaOD/D^O in

refluxing CDCl^. When refluxed in EtOD with NaOEt, an orange

solution resulted, and both a- and 0-protons exchanged (80$ by n.m.r.).

Methylphenylphosphinate + Sodium Hydride + Dienone

The dienone (0.5 g) was added as a solid to a mixture of methylphenylphosphinate (0,5 ml) and NaH (0.2 g) in benzene (10 ml).

The colour change from red to yellow was immediate; the mixture

gave only a very weak e.s.r. signal. Addition of acetic anhydride

(2 ml) gave a colourless solution. The solution was stirred for

5 minutes, extracted with water, evaporated, and chromatographed on

silica gel (40 g). Elution with benzene/petrol afforded ~ 5 impure

fractions. The major fractions were re-chromatographed to give a - 156 -

small amount of semi-crystalline material (from cyclohexane containing 5$ carbon tetrachloride), softening point 75-85°.

I.r. 1775 (C=0), 1230 (P=0), 1170, 1120, 1030 cm’1 (P-0 and C-0)

'H n.m.r. (CDC13) Multiplet 66.5-8.1 (25H) - - - - ArH

Doublet of doublets 63.34,

J 11.3 Hz, J» 1 Hz (3H) - - - - P-0CH3

Two doublets 61.76, 1.72 (3H) - COCH^

Singlet 61.9 (0.5H) - - - - - ? u.v. (ethanol) 7^ 335 (3.98), 260 (4.26)

Hydrolysis of this material with 70$ HgSO^ at 100° gave a little trans-2,3»4,5-tetraphenylcyclopent-2-enone, and a mixture of

A unidentified phosphonated ketones; i.r. 1685 (0=0) and 1240 cm” (P=0).

Dimethylphosphonate + Morpholine + Dienone

The dienone (2.49 g)> dimethylphosphonate (1.1 g, 1.5 mole) and morpholine (0.85 g» 1.5 mole) were stirred in ethyl acetate (20 ml) under nitrogen for 22 hours. Over this time, the red dienone colour slowly faded to a pale yellow. Addition of ether/petrol gave a white crystalline precipitate of morpholinium methyl-1,35-tetraphenylcyclopenta-1t3-dien-2-ol phosphate (97), m,p. 191-193° + * (ethanol); i.r. showed 2650, 2400 (NH^), 1220 (P=0), 1090, 1050 cm”

(P-O-C), but no carbonyl absorption.

Found: (M3502) C, 70.6; H, 6.4; H, 2.3; P, 5.3

C34H34N05P requires: C, 71.8; H, 6.0; N, 2.5; P, 5#5* - 157 -

*H n.m.r. (CDC1 ) Multiplet 66.8-7.8 (20H) - - - - ArH

Multiplet 63.52 (4H) ) > - - - morpholinium H Multiplet 62.45 (4H) )

Doublet 64.97, J 4.5 Hz (1H) - - - - PhCH

Doublet 62.97, J 11.5 Hz (3H) - - - P-OCH,

Broad singlet 69.52 (2H, , + exchanged I^O) -----

Concentration of the filtrate and addition of ethanol afforded

white crystals of dimethyl-1>3*4#5-tetraphenylcyclopenta-1,3-dien-

2-ol phosphate (75) (0.606 g, 19$)> m.p. 175-176° (ethanol).

i.r. 1270 (P=0), 1180, 1060, 1030 cm“1 (P-O-C) hut no carbonyl

absorption.

Found? (4971, M3755) C, 75.6; H, 5.8; P, 6.2; M.W. 494.1647 ± .001

C^H^O^P requires? C, 75.3; H, 5.5; P, 6.3; M.W. 494.1647

*H n.m.r. (CDCl^) Multiplet 67-7.5 (20H) - - - - - ArH

Doublet 65.09 (1H), J 5 Hz -

collapsed to a singlet on

irradiation of P - PhCH

Pair of doublets 63.13* 3.16 (6H),

J = J* = 11.6 Hz - - - - P(0CH3)2

(°6H6) Doublet 65.0, J 4.8 Hz Pair of doublets 63.06, 3.03»

J = J* * 11.7 Hz u.v. (ethanol) \ax 330 (4-13)’ 244 (4-25) Concentration of the filtrate and addition of ethanol and water - 158 -

gave trans 2,3,4,5-tetraphenylcyclopent-2-enone (0.326 g, 13$)* identical by i.r. to authentic material.

In a separate experiment, methyl 2,3,4,5-tetraphenylcyclopent-

2-enon-4-ylphosphonate was isolated: The dienone (1.0 g), dimethylphosphonate (0.5 ml, 2 mole) and morpholine (0.5 ml, 1.7 mole) were refluxed in benzene (2.5 ml) under nitrogen for 5 minutes; decolourisation was effected after 2-3 minutes. The mixture, which was treated with ethanol and allowed to stand over night, afforded white crystals of the morpholinium salt (97)

(0.26 g, 18$), i.r. identical to authentic material. The filtrate was evaporated, extracted between benzene and dilute hydrochloric acid, and the benzene layer washed with water and dried (Na^SO^).

Trimethylorthoformate (1 ml) was added and the solution heated (80°) for 5 minutes. Evaporation gave an oil (1.1 g), the n.m.r. of which was quite complex with 16 peaks in the P-OCH^ region. The oil was chromatographed on silica gel (25 g); elution with benzene/ether gave the major fraction as an oil (0.54 g). Crystal lisation occurred in carbon tetrachloride solution (150 mg/0.3 ml) in a spinning n.m.r. tube at 40°. Stalagmitic crystal growth occurred in the vortex of the spinning, viscous solution; no crystallisation occurred in an aliquot of the same solution left standing in a flask at room temperature. Recrystallisation from chloroform/ethanol gave white crystals of methyl cis-2,3,4,5- tetraphenylcyclopent-2-enon-4-ylphosphonate (0.39 g, 31$), m.p.

202-205° (DMSO/acetonitrile). - 159 -

i.r. 1700 (C=0), 1180 (P-0) and 1050 cm”1 (P-O-C)

Found: (16164, M7433) C, 74.7; H, 5.5; P, 6.3; M.W. 480

C^qH^^O^P requires: C, 75.0; H, 5.3; P, 6.5; M.W. 480

1H n.m.r. (d6-DMS0) Multiplet 66.6-7.6 (20H) ----- ArH

Doublet 65.48, J 15.5 Hz (1H) - - - PhCH

Doublet 63.48, J 11 Hz (3H) - - - - P-0CH3

The filtrate appeared to contain the trans-isomer (see dimethylphosphonate/sodium hydride reaction) together with some unidentified

P-OCH^ material (by n.m.r.). The n.m.r. of the original oil (prior to chromatography) indicated slightly more of the trans-compound than the cis (estimated yield of trans ~ 35$)•

Treatment of the above cis-monomethylphosphonate with excess diazomethane in benzene/ether afforded dimethyl cis-2,3f4.5-tetraphenylcyclopent-2-enon-4-ylphosphonate (95) as an oil.

*H n.m.r. (CCl^) Multiplet 66.7-7.6 (20H) ----- ArH

Doublet 65.34, J 16 Hz (1H) - - - - PhCH

Two doublets 63.68, 3.35 (6H),

J = J* =11 Hz — — — — - P-OCH^

Reactions of morpholinium methyl-1,3.4,5-tetraphenylcyclopenta-

1,3-dien-2-ol phosphate

1. Hydrolysis. The morpholinium enol phosphate (0.3 g) was refluxed in 50$ sulphuric acid (5 ml) for 5 hours under nitrogen.

Filtration of the cooled mixture afforded trans-2,3>4,5-tetraphenylcyclopent-2-enone (0.186 g, 95$)» i.r. identical to authentic material. - 160 -

B. Methylation. The morpholinium enol phosphate (0.1 g) was acidified with acetic acid, and the free enol phosphate precipitated with water, dried and treated with excess diazomethane in methanol to give dimethyl 1,3,4,5-tetraphenylcyclopenta-1,3-dien-2-ol phosphate (52 mg, 60$) identical to authentic material by i.r. and by t.l.c.

C. Pyrolysis. The morpholinium enol phosphate (0.142 g) was pyrolysed under vacuum at 200° for 2 hours. Addition of ethanol gave trans 2,3,4,5-tetraphenylcyclopent-2-enone (71 mg, 74$) together with a trace (2 mg) of tetraphenylcyclopentadienone. There was no reaction when the morpholinium salt was refluxed in benzene with a little morpholine for several hours.

Dimethylphosphonate + Sodium Hydride + Dienone

Dimethylphosphonate (0.6 g) was treated with sodium hydride

(0.14 g, 1.1 mole) in benzene (15 ml). Solid dienone (1 g, 0.5 mole) was added under nitrogen. There was an immediate colour change from red to yellow. On standing 1-2 hours, the yellow turned to orange; n.m.r. of this solution:

broad doublet 64.2, J 11.2 Hz

sharp doublet 53.6, J 11.2 Hz

broad singlets 63*58, 3.47, 3.27

The orange solution was unchanged after refluxing for 15 minutes.

The mixture was cooled and treated with acetic acid (1 ml); the resulting colourless solution was concentrated and ethanol added to give 2,3,4,5-tetraphenylcyclopent-2-enone (0.293 g, 29$). - 161

Treatment of the filtrate with water gave a white powder (0.604 g),

i.r. 1700 (C=0), 1240 (P=0), 1050, 1030 cm"1 (P-O-C), which was chromatographed on silica gel (30 g). Elution with petrol/benzene/ ether afforded the major fraction as a glass; l.r. 1700 (0=0), 1245 (P=0), 1055, 1035 on*1 (P-O-C)

*5 n.m.r. (CCl^) Multiplet 66.7-7.8 (20H) ----- ArH

Doublet 65*4, J 16 Hz (4/7 H) - dienyl H

Doublet 64.97, J 4.7 Hz (3/7 H) - dienyl H

Doublet of doublets 63.65,3.32, J=Jf=11 Hz ) > (6H) - - POCH Doublet of doublets 63.27,2.95, J=J*=11.5 Hz) *

The doublets 65.4, 3.65, 3.32 correspond to dimethyl cis-2,3,4,5- tetraphenylcyclopent-2-enon-4-yiphosphonate (95). The remaining set of doublets is attributed to the corresponding trans-isomer (96)

The dienone did not react with dimethylphosphonate by itself when refluxed in ethyl acetate for 19 hours; the addition of methanol caused no change (refluxed 8 hours). There was no reaction in the presence of p-toluenesulphonic acid at 120° in HMPT as solvent, nor when the dienone, dimethylphosphonate (2 mole) and azobis-isobutyronitrile (1 mole) were refluxed in benzene for several hours.

When 2,3,4,6,7,8,9,10-octahydropyrimido-[l,2-a]azepine (1 mole) was used as base, the same instantaneous colour change to yellow, as was obtained in the sodium hydride reaction, was observed. The sample gave a similar e.s.r. spectrum to that obtained with methyl- - 162 -

phenylphosphinate, morpholine and the dienone. A four-molar excess of morpholine did not bring about this spectacular colour change, nor did a 4-molar excess of morpholine containing ~0.2 mole of the azepine base. Dimethylamine, dimethyljphosphonate and the dienone gave the immediate colour change to yellow:

♦H n.m.r. (C^Hg) Doublets 63.47 (5 units), 63*25 (4 units),

63.0 (4 units) - all had J = 11 Hz

Singlets 62.18 (55 units), 62.03 (6 units)

Broad absorptions 65*9 (9 units) and 62.7 (9 units)

Addition of water to this sample (which contained excess dimethylamine,

62.18) showed no apparent change in the spectrum.

When the dienone, dimethylphosphonate and morpholine were refluxed in methanol/benzene (60$), decolourisation was effected after 4-5 hours. (No apparent reaction occurred when these reagents were stirred overnight at room temperature.) Concentration of the solution gave the morpholinium enol phosphate (97) (22$); the filtrate contained a mixture of the phosphonated ketones (95) and

(96), (n.m.r.).

Diphenylphosphine Oxide + Dimethylamine + Dienone

The dienone (0.7 g) and diphenylphosphine oxide (0.46 g, 1.2 mole) were mixed in benzene (10 ml) under nitrogen. Dimethylamine was passed over the stirred solution for 2 minutes, after which time the colour had changed from red to brown. The solution was refluxed for 20 minutes, whereupon it regained its dienone colour, - 163 -

but it lost it again on cooling (pale greenish-yelloYf). Addition

of cyclohexane to the concentrated solution afforded white crystals

(which had a pale pinkish tinge after drying at 80° under vacuum)

of 2,3.4,5-tetraphen.ylcyclopent-3-enon-5-.vldiphenylphosphine oxide

(101) (0.71 g, 66$), m.p. (dec) 190-193° (ethanol).

l.r. 1730 (C=0), 1200 cm"1 (P=0)

Found; (M4848) C, 83.1; H, 5.3s P, 5.2s M.W. 586

C^H^OgP requires: C, 83.9; H, 5-3; P, 5.3; M.W. 586

fH n.m.r. (CDCl^) Multiplet 66.4-8.2 (30H) ----- ArH

Singlet (broad) 63.2 (1H) - - - - PhCH

u.v. (ethanol) 263 (4.23), 267 (4.25), 273 (4.22)

Miscellaneous Reactions

2-Phenyl-1,3.2-dioxaphospholan.

Phenylphosphonous dichloride (60 g) in ether (50 ml), and

ethylene glycol (20.8 g, 1 mole) in triethylamine (70 ml), were added through isolated separating funnels to a stirred, cooled

(7-8°) solution of triethylamine (30 ml) in ether (1400 ml) over a

period of 1.5-2 hours. The solution was stirred for a further 1 hour at room temperature and allowed to stand for 2 days before filtering under nitrogen. The ether was distilled off in a nitrogen stream, and the product distilled under reduced pressure, b.p.

71-79° (1 mm) (32 g). Since this product still contained a little ethylene glycol, it was treated with more phenylphosphonous dichloride (3 g) and triethylamine (10 ml) in ether, and worked up - 164 -

as before, b.p. 69-71° (0.6 mm), n^2 = 1.5690; lit.^^ values

b.p. 81-82° (1.8 mm), n25 = 1.5849.

1H n.m.r. (neat) Multiplet 67.1-7.6 (5H) - - - — ArH

Multiplet 63.5-4.0 (4H) - - 0-CH2

The residue from the first distillation, on standing for 11 months

gave large crystals of (PhP),- (0.53 g), m,p. and mixed m.p. 149-

150°. A sealed ampoule of the cyclic ester became very viscous

after standing for 2 years. This phenomenon has recently been 111 shown to be due to a slow polymerisation at room temperature

(the process is reversed on distillation at 125°). Several phenyl phospholans undergo this polymerisation, but rather strangely, the corresponding dimethylamino- and methoxy-phospholans do not.

The irradiation of 2-phenyl-1,3,2-dioxaphospholan

The cyclic ester (5 ml) in dry, peroxide-free ether (550 ml) was irradiated at room temperature, under nitrogen, for 6 hours using a Hanovia IL medium pressure u.v. lamp. After 1 hour, a small amount of white precipitate had formed. After 2 hours, a slimy pale yellow oil was present; no further change was noted.

Evaporation of the ether and distillation (bath temp. 170°) of the residue gave starting material (3.9 g> 78$), b.p. 88-94° (2.5 mm), i.r. identical to the phenyl dioxaphospholan; this recovered material turned very viscous on standing for 7 months.

Irradiation of Triallylphosphite

Commercial triallylphosphite was distilled under reduced - 165 -

pressure at 37-38°. The ester (5.0 g) in ether (200 ml, distilled

from LiAlH^) was irradiated for 7 hours in a pyrex vessel using a

small u.v. lamp. Samples were withdrawn after 1.5> 3> and 4.5 hours but t.l.c. and i.r. showed only triallylphosphite. After 7 hours, i.r. showed the presence of a small amount of phosphoryl containing material. The only product isolated apart from starting material was a small quantity (0.5 g) of white polymer, m.p. >280° (turned black), insoluble in all solvents tried including DMS0, trifluoroacetic acid, thionyl chloride and concentrated sulphuric acid.

Found: C, 49*0; H, 6.9; P* 15.4

C9H15°3P re(luires; c> 53.5; H, 7.5; P, 15.4

The presence of benzophenone had no noticeable effect on the irradiation.

Irradiation of Diallyl allylphosphonate

The phosphonate was prepared in 80$ yield by a standard

Arbuzov reaction between triallylphosphite and allyl bromide, b.p.

66-68° (0.3 mm). U.v. irradiation of this material (0.5 g) in ether (200 ml) for 3.5 hours resulted in a small amount (11 mg) of off-white polymer. Addition of a few drops of triallylphosphite and irradiation for a further 3 hours gave more white polymer (46 mg).

Attempted preparation of Benzyldiphenylphosphinite

Diphenylphosphinous chloride (20 g) in ether (30 ml) was added with cooling (ice-water) over a period of 1 hour to a mixture of - 166 -

benzyl alcohol (9.8 g» 1 mole) and triethylamine (6,45 g> 1 mole) in ether (120 ml). The solution was allowed to reach room temperature (1 hour), filtered, and washed with dry ether (30 ml).

The filtrate was evaporated below 40°. Petrol (30 ml) was added and the mixture allowed to crystallise overnight. The precipitate was removed by filtration and recrystallised from ethyl acetate

(2.74 g), m.p. 170-178°. Pour recrystallisations from methanol/ ethyl acetate (5*1) gave material of m.p. 195-196.5°; t.l.c.

(10$ MeOH/CHCl^/SiO^) on this material gave two spots (R^s 0.65»

0.75).

Found: C, 71.0; H, 5.3

C24H20°2P2 recluires: c* 71.7; H, 5.0 *H n.m.r, (CDCl^) Multiplet 67.4 (1.55H) - ArH

Multiplet 68.0 (1H) - - - ArH

This material did not depress the m.p. of authentic tetraphenyldiphosphine dioxide and had an identical i.r. spectrum. Oxidation with hydrogen peroxide in acetone gave diphenylphosphinic acid (97$).

Other compounds isolated from this reaction were diphenylphos phinic acid (m.p. 188-189°) and a-hydroxybenzyldiphenylphosphine oxide, m.p. and mixed m.p. 171-173°.

Found: C, 74.1; H, 5.7; P, 10.1

^19^17^2^ re(lu*res: c* 74.0; H, 5.6; P, 10.1

*H n.m.r. (CDC13) Multiplet 67-8 (15H) - - - ArH

Doublet 56.0, 2 Jpg 2.5 Hz (1H) — - PhCH - 167 -

No benzyldiphenylphosphinite was detected, but some benzyldiphenyl- phosphine oxide was isolated, m.p. 188-189°, lit.^^ 192-193°*

Found: (M778) C, 77.9; H, 6.0; P, 10.8

C^H^OP requires: C, 78.1; H, 5.9; P, 10.6

'H n.m.r. (CDCl^) Multiplet 67.3-7.9 (10H) - - - ArH

Singlet 67.15 (5H) - benzyl ArH

Doublet 63.63, 2JpH 14 Hz (2H) - - - PhCH2> and some benzyldiphenylphosphinate, m.p. 75-76°, lit.^ 78-78.5°, i.r. 1215 (P=0) and 1020 cm‘1 (P-0-C).

♦H n.m.r. (CDC13) Doublet 65.07, 3JpH 7 Hz 6S Lit. value, doublet 65.05, J 7 Hz. -168-

Appendix - Mass Spectral Data

Mono- 4-Deuterio a-Me (3-Me Enol- f3-Phospho enone enone ketones ketone acetate ketone (7) (93) (71 X72) (74) (90) (84)

386(100) 387(100) 400(100) 400(100) 428(20) 540(41)

358 (22) 386 (9) 399(0.6) 399(2.5) 427 (0) 539(0.3)

309 (16) 359 (2) 398(0.4) 398(0.8) 386(100) 386(100)

281 (6) 358 (2) 385 (92) 385 (40) 348* 384 (22)

279 (5) 310 (16) 372 (1 ) 372 (1) 309 (3) 370 (8) „ * 267 (13) 282 (6) 371* 371 308 (3) 357 (4)

265 (5) 267 (15) 357 (1) 357 (3) 307 (3) 356 (4) . * 252 (3) 249 323 (15) 323 (21) 291 (2) 309 (15)

247* 204 (4) 282 (10) 309 (2) 279 (8) 291 (4)

203 (4) 192 (5) 279 (5) 295 (10) 278 (4) 279 (10)

202 (3) 178 (9) 267 (5) 280 (6) 265 (4) 267 (16)

191 (5) 168 (5) 265 (5) 279 (6) 246 252 (4)

179 (8) 167 (5) 252 (2) 267 (12) 203 (3) 202 (6)

178 (9) 105 (6) 203 (4) 265 (5) 202 (3) 191 (7)

167 (6) 77 (2) 202 (4) 252 (3) 178 (10) 178 (20)

165 (5) 178 (8) 217 (4) 167 (2) 167 (12)

152 (6) 105 (15) 205 (8) 165 (3) 165 (9)

149 (7) 178 (10) 105 (3) 155 (11)

105 (5) 118 (11) 267 (2) 149 (7)

105 (25) 265 (8) - 169 -

a-Phospho Enol Enol Dienone Yellow ketone Phosphate Phosphate Maleate (Php)5 Powder (101) Adduct P. 107 (75) (68)

586 (4) 494(100) 508 (26) 556(1.4) 540 (18) 602 (1)

58 5<:.05) 493(0.4) 383 (36) 542 (4) 432 (7) 540 (6)

384(100) 386 (1) 382(100) 528 (50) 370 (7) 510 (47)

356 (28) 385 (1) 305 (12) 511 (2) 355 (14) 448 (69)

330. 6* 384 (2) 303 (12) 497 (1) 324 (61) 393. 7* (• 307 (5) 370 (3) 291 (11) 482 (1) 317" 372 (12)

279 (7) 368 (3) 289 (10) 468 (1) 293 (5) 355 (12) 278 (7) 367 (5) 278 (5) 455 (25) 262(100) 324 (29) E- 276 (6) 365 (2) 276 (4) 440* 216 (12) 293 (10) E- 267 (5) 291 (10) 265 (3) 409(100) 212 278 (10)

265 (3) 289 (8) 215 (6) 384 (12) 185 (40) 262 (68)

201 (29) 279 (5) 204 (4) 382 (11) 183 (74) 247 (8)

192 (2) 278 (3) 191 (4) 370 (62) 152 (8) 234. 6* 178 (66) 276 (3) 178 (13) 302 (9) 110 (50) 216 (20) 108 (10) 265 (2) 165 (5) 291 (8) 108 (62) 185 (67) 208 (2) 152 (3) 289 (10) 77 (21) 183 (75)

191 (2) 109 (13) 215 (5) 139 (39)

178 (6) 84 (12) 178 (12) 124 (14) 109 (3) 77 (4) 165 (3) 110 (48)

267 (3) 127 (15) 108(100) 267 (2)

265 (3) - 170 -

Fulvene Pulvene Diene Bromo Penta-Ph Isomeric Adduct Diene Diene (36) (37) (52) (40) (40)

382(100) 382 (16) 370(100) 738 (6) 446(100) 446(100)

381 (10) 305 (2) 369(1.8) 450 (8) 445 (1) 445 (5)

365 (5) 303 (2) 368(0.9) 449 (3) 444(0.75) 444 (1)

305 (18) 302 (2) 291 (8) 448 (8) 370 (3) 432 (6)

303 (19) 291 (2) 289 (5) 370(100) 367 (3) 370 (9)

302 (18) 289 (1) 278 (4) 369 (30) 355 (2) 369 (24)

291 (15) 179 (9) 265 (2) 368 (2) 339 (2) 367 (8)

289 (13) 163 (88) 215 (6) 291 (13) 291 (9) 354 (8)

276 (5) 135 (15) 191 (3) 289 (10) 267 (4) 353 (9)

267 (5) 119 (39) 165 (3) 215 (8) 265 (4) 352 (8)

265 (5) 105 (10) 149 (4) 191 (7) 252 (2) 339 (6)

243- 7* 78(100) 267 (1) 149 (6) 191 (2) 326 (4) * 222. 3 76 (49) 128 (6) 165 (7) 313 (3)

204 (7) 60 (37) 289 (6) 291 (12)

203 (7) 48. 6* 289 (9)

202 (6) 279 (4)

191 (6) 276 (5)

165 (5) 265 (4)

152 (8) 252 (3)

151 (8)

* - 171

Dihydro Dimer Hydroxy Bromo Chloro Pulvalene Dimer Dimer Dimer (41) (43, 44) (66)

738(100) 736(100) 437* 752(100) 815 (0) 772(1.3)

737(1.8) 735(1.4) 426 (3) 751 (0) 736 (74) 771(1.5) , * 736 (1) 734(0.8) 425 737 (4) 735 (10) 770(2.2)

370 (20) 659 (6) 400 (2) 736 (4) 440 (14) 736(100)

369 (28) 645 (1 ) 391 (2) 411 (15) 368(0.1) 735 (23) * 291 (24) 590 368.5 (4) 368 (25) 278 (48) 734 (18)

289 (6) 582 (3) 368 (7) 279 (27) 232 (71) 659 (6)

267 (5) 581 (3) 290 ( 3) 256 (31 ) 207 (45) 658 (6)

265 (5) 567 (7) 251 (9) 243 (37) 197 (61) 657 (5) . * 252 (7) 565 212 (3) 239 (37) 149(100) 581 (5) .* 213 (7) 514 178 (2) 149(180) 111 (87) 580 (5) „ * 191 (16) 502 167 (3) 111(140) 97(135) 567 (5)

167 (14) 504 (3) 83 (2) 97(200) 95(140) 504 (3)

165 (7) 491 (3) 77 (1) 95(190) 85(135) 503 (3)

105 (28) 469 (6) 289 (1) 83(260) 81 (170) 502 ( 3)

77 (20) 267 (2) 78(380) 78(240) 481 (3)

265 (1) 469 (4)

165 (2) 368 (4)

291 (1) 290 (3)

252 (6)

251 (6)

167 (3) - 172 -

Methoxy Dimer Dimer Dimer Dimer Dimer

Dioxide . Dioxide Dioxide . Dioxide (67) 1665 cm” Reduced 1700 cm” Reduced

766(100) 580 (3) 768(100) 770(100) 768 (57) 770 (12)

765 (0) 567 (3) 767 (2) 769(2.6) 767 (2) 769(1.4)

751 (4) 557 (2) 766 (1) 768(2.7) 766 (2) 768(1*6)

736 (10) 504 (2) 752 (9) 752 (36) 750 ( 4) 752 (79)

735 (8) 503 (2) 736 (11) 736 (10) 691 (28) 675 (2)

723 (1) 502 (2) 691 (26) 696 (2) 663 (2) 585 (5)

705.4* 491 (3) 663 (8) 679 (9) 586 (2) 507 (4) E VO IfA —

689 (1) 478 (2) 601 (9) (10) 509 (2) 425 (22)

673 (1) 426 (2) 546 (9) 651 (43) 423 (57) 407 (14)

662 (3) 413 (3) 423 07) 575 (4) 407 (6) 396(100)

659 (3) 383 (11) 397 (24) 398 (11) 396(100) 374 (55)

658 (4) 367 (3) 396 (66) 373 (31) 384.5(3) 167 (15)

657 (3) 344 (2) 372 (47) 344 (8) 384 (5) 165 (6)

646 (1) 289 (4) 344 (27) 312 (8) 372 (69) 105 (24)

645 (1) 250 (5) 267 (14) 307 (8) 344 (46) 267 (7)

585 (2) 179 (3) 167 (9) 291 (6) 291 (7) 265 (5)

534 (4) 167 (4) 105 (43) 289 (6) 289 (14) 291 (6)

581 (3) 265 (2) 267 (10) 267 (23) 289 (6)

265 (8) 265 (16)

179 (10) 167 (5)

178 (8) 165 (12)

167 (27) I - 173 -

Part G

The mass-spectral data in the appendix is for the most part a listing of the 15-20 most intense peaks in the mass spectrum, measured at an ionising energy of 70 e.v. with direct insertion of sample into the ionisation chamber. Intensities (in brackets) are relative to the base peak, taken as 100$, of the spectrum except in two cases (the hydroxy dimer and bromo dimer; 66, X = OH and Br, respectively) where the low m/e region of the spectrum was very intense and a more convenient reference peak was chosen.

Several features in the mass spectra of the dimer and of the cyclopentadiene-type compounds (e.g. 40, 41 and 52) are rather striking. The first is the very low intensity (< 2$) of the M-1 peak in the spectrum. A possible explanation is that loss of the dienyl hydrogen atom from such structures would result in the formation of an "anti-aromatic" * J system (104) containing 4n electrons; such systems are destabilised by conjugation, i.e. allylic

(104) - 174 -

declocalisation of the positive charge in (104) raises the energy- 114 of the system. Although evidence for the existence of cyclopentadienyl cations in solution has been obtained,10^ these (anti- 88 aromatic) cations are unstable and very readily rearrange.

The very weak M-1 peaks found in these cyclopentadiene systems contrast with the relatively intense (80$ of M) M-1 peak observed^ for fluorene; the same relative intensity (M-1/ta = 80$) was 115 obtained for diphenylmethane. It is suggested that perhaps the strong M-1 peak of fluorene is not due to the fluorenyl cation (105), but to a tropylium-type cation (106) formed by ring expansion of one of the benzene rings in (10 5). Such a rearrangement is not possible

(10 5) (106)

for the cation (104). Cation (106) is aromatic, whereas (105) contains an anti-aromatic cyclopentadienyl cation system. It would be interesting in this connection to study the negative ion mass spectra of cyclopentadiene systems, as cyclopentadienyl anions are aromatic, containing (4n + 2) it -electrons.

A second feature in the mass spectra of the cyclopentadiene-type - 175 -

compounds is the anomalous behaviour of halogen derivatives. Thus, the bromodiene, bromodimer, and chlorodimer each give little or no parent ion, a relatively weak ion corresponding to loss of halogen and, most surprisingly, very strong peaks corresponding to the parent hydrocarbons. In addition, the bromodiene shows a peak corresponding to dimerisation with loss of two bromine atoms, i.e. formation of the dihydrofulvalene (41). These results could be due to a metal catalysed decomposition in the source of the spectrometer, but since the mass spectra of hydrocarbon and halogen derivative show distinct differences, hydrogen abstraction and dimerisation probably occur after ionisation. A somewhat similar dimerisation has been 116 reported for triphenylcyclopropenyl bromide; formation of 116 hexaphenylbenzene was thought to arise by ‘’resonance dissociative capture of an electron by the covalent halogenocyclopropene followed by coupling of two triphenylcyclopropenyl radicals to give bis(triphenylcyclopropenyl), followed by rearrangement to Ph^C^.”

Such a process might also account for the above formation of dihydro fulvalene, while hydrogen abstraction by the respective cyclopentadiene radicals would give rise to the parent hydrocarbons.

A peak common to all the tetraphenylcyclopentadiene structures studied, but very weak in the dimer and most of its derivatives, occurs at m/e 291. This peak corresponds to Ph^C^, i.e. loss of

C^-Hy from the diene (52), or of CyHy from 1,2,3»4-tetraphenylfulvene.

A possible structure for this ion (107) and mode of formation from the fulvene (36) and the diene (52) are shown in Scheme IX. - 17 6 -

Ph\____ .^Ph Ph ^Ph

ch2 H H m/e 382 m/e370

Phv._____-Ph Ph .^Ph

'..V P H-

-H n

Scheme IX - 177 -

The stability of a structure such as (107) derives from the aromatic 112 nature of the cyclopropenyl cation, which itself is further

stabilised by the attached phenyl and phenylacetylene groups.

Furthermore, the peak of m/e 291 is usually accompanied by a peak of

slightly lower intensity at m/e 289; this is readily explained by a

loss of hydrogen from (107) to give the aromatic cyclopropa- 116 phenanthrene ion (108). Such a process is not without analogy,

and most of the cyclopentadiene compounds studied show strong peaks

at m/e 267 and m/e 265* corresponding to loss of hydrogen from the

triphenylcyclopropenyl cation (m/e 267) to give a cyclopropa- 116 phenanthrene ion (109).

m/e 267

The mass spectral fragmentation pattern of the dimer bears little resemblance to that of the tetraphenylcyclopentadiene struc tures reported; it shows mainly loss of CgH^. > CgHg an<^ ^7^7 fragments as evidenced by metastable peaks:

1 . 736 659* m* 590

2. 736 —645* hi 565 - 178 -

-77 * 3 659 -LL> 582, m 514

4. 582 ^2+ 504, m* 436

5. 567 491, m* 425

This type of (minor) fragmentation may be indicative of a highly

congested molecule, so sterically crowded that loss of phenyl or

benzyl groups is the only favourable process for the parent ion.

The following metastable transitions are also assigned: -77. 1. Mono-enone (7) 309, m 247 -77 * 2. Deutero-enone (93) 387 310, m" 248.5 ~CE* * 3. Me-ketones (71-74) 400 --- 385, m 370.5 -CH CO - * 4. Enol-acetate (9°) 428 --- =—> 386 ■ • -■308, m 348 and 246,8

5. a-Diphenylphosphinoxy ketone (101) 384 ——> 356, m 330 -C0,C H ? . 6. Dienone-diethylmaleate adduct 528 ----- 482, m 439.9

7. (PhP)r 432 --- » 370, m 317

i.e. (PhP)4 --- * Ph2P-PPh2 + P2 and

324 * 262, m 212

i.e. (PhP)3 Ph3P + P2

8. Yellow powder P.1Q7. 510 448, m 393.6

i.e. (PhP)4P20 * (PhP)40 + p2

448 324, m 234.3 (or 293 262)

i.e. (PhP)40 ■> (PhP)3 + PhPO

9. 1 >2,3«4-Tetraphen.vlfulvene (36) 382 305» m* 243.7, -C7H7 * 382 ■ ■■■■*> 291, m 222.3

10. Pulvene - P(NMe2K adduct (37) 545 > -j63, m* 48.7 -CILO * 11. Methoxy dimer (67) 766 -- ^-* 735> m 705.3 - 179 -

In conclusion, an attempt has been made to rationalise a few

of the features of the mass spectra of several polyphenyl compounds.

The literature contains few reports of the detailed fragmentation 117 patterns of such systems. A recent report is of interest however,

as it has been demonstrated that the ions formed by loss of CO from

tetra-arylcyclopentadienones pass through a tetrahedral transition

state or intermediate (110) before they fragment.

Ar\____/Ph I I -CO ■>

(110)

Much more work will of course be necessary before fragmentation pathways in related systems are known with any degree of certainty. 180

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INDEX OF COMPOUNDS fisss Bromo-1,2,3,4,5-pentaphenylcyclopentadiene 137

5-Bromo-1,2,3»4-tetraphenylcyclopenta-1,3-diene 116,136

4- Deuterio 2,3>4,5-tetraphenylcyclopent-2-enone 155

5- Diazo 1,2,3,4-tetraphenylcyclopenta-1,3-diene 138

1,1*-Dihydro 2,3,4,5,2*,3*,4*,5,-octaphenylfulvalene 136

5-(N,N-Dimethylamino)l,2,3,4-tetraphenylcyclopenta-1,3-diene 121

Dimethyl phenylphosphonate 104

Dimethyl 1,3,4,5-tetraphenylcyclopenta-1,3-dien-2-ol phosphate 157

Dimethyl 2,3,4,5-tetraphenylcyclopent-2-enon-4-ylphosphonate 159

Diphenylphosphine 96

Diphenylphosphine oxide 112

1,2,3,4,5>6,6a-Heptaphenyl-lObH-benz[e]-as-indacene 122

1,2,3,4,5,6,6a-Heptaphenyl-3aH-benz[e]-as-indacene 134

Methyl phenylphosphinate 104

Methyl phenylphosphonate 99

5-Methyl-1,2,3,4-tetraphenylcyclopenta-1,3-dien-1-ol acetate 148

5-Methyl-2,3,4,5-tetraphenylcyclopenta-1,3-dien-1-ol phosphate 140

5-Methyl-1,3*4,5-tetraphenylcyclopenta-1,3-dien-2-ol phosphate 141

Methyl-5-(l,2,3,4-tetraphenylcyclopenta-1,3-dienyl)ether 144

5-Methyl-2,3,4,5-tetraphenylcyclopent-2-enones 142

4-Methyl-2,3,4,5-tetraphenylcyclopent-2-enones 143

Methyl 2,3,4,5-tetraphenylcyclopent-2-enon-4-ylphenyl-

phosphinate 149,152 - 191

Page

Morpholinium phenylphosphonicmorpholinamide 110

1,2,3,4,5-Pentaphenylcyclopentadiene 125

Pentaphenylcyclopentaphosphine 95

2,3,5>7,8-Pentaphenyl-1,4,6,9-tetraoxa-5-phospha-spiro[4,4]-

nonadiene 9?

Phenylphosphine 9 6

Phenylphosphine-d2 104

Phenylphosphinic acid-d^ 103

Phenylphosphinic acid-d2 102

1.2.3.4- Tetraphenylcyclopenta-1,3-diene 118

1>3,4,5-Tetraphenylcyclopenta-1,3-dien-2-ol acetate 147

2,3>4,5-Tetraphenylcyclopent-3-enon-5-yldiphenylphosphine oxide 163

Tetraphenyldiphosphine dioxide 97,166

1.2.3.4- Tetraphenylfulvene 117,139

p-Tolyphosphinic acid 101 p-Tolyphosphonic anhydride 102 - 192 -

ACKNOWLEDGEMENTS

The author is grateful to Professors S.J. Angyal and G.W.K.

Cavill for permission to carry out this work.

Appreciation is expressed to Dr. A.P. Russell for the electrophoresis determinations, to Dr. E. Challen and Mr. J.

Sussman for the microanalyses, to Mr. A. Oei and Mr. K. Davis for the e.s.r. measurements, to Mr. I. McCay for the gift of a sample of 2,5-dimethyl-3,4-diphenylcyclopentadienone, to Mr. J.P.

Beale and Mr. E.T. Pallister for the preliminary X-ray analysis, and to many people in the Chemistry Department for helpful dis cussions and comments.

The award of a Commonwealth Scientific and Industrial Research

Organisation post-graduate scholarship is gratefully acknowledged.

Finally, the author would like to express sincere gratitude to his supervisor, Dr. M.J. Gallagher, whose continued interest, valuable advice and active support is gratefully acknowledged.