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91P4D148-1-31 T ORGANOMETALLIC COMPOUNDS of BORON and SOME TRANSITION METALS a Thesis Submitted for the Degree of Doctor Of

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91P4D148-1-31 T ORGANOMETALLIC COMPOUNDS of BORON and SOME TRANSITION METALS a Thesis Submitted for the Degree of Doctor Of 91P4D148-1-31T ORGANOMETALLIC COMPOUNDS OF BORON AND SOME TRANSITION METALS A Thesis submitted for the Degree of Doctor of Philosphy in the University of London by APAR SINGH Imperial College of Science and Technology, London, SOV.7. December, 1959. DEDICAT7D TO MY PROF7,SSOR. ABSTRACT. Part I describes the preparation and properties of tristr:Lalkyl- silyl esters of boron. The most convenient method was, howeve:7, by the silanolysis of trisdiethylamino boron. Bistriethylsilyl phenyl boronate [(2t3Si0)2BPh)] and triethylsilyldiphenyl borinate [(Tqt3Si0BPh21 have been prepared. These compounds undergo slow hydrolysis and rapid dealkylation with halogen acids, and are thermally very stable. The trisalkylsilyl metaborates have been formed :from bori oxide and the corresponding orthoborates. They are trimeric (cryoscopic measurement) and possess cyclic boroxole structure, which is supported by the presence of a doublet at 720 and 735 cm. in the infrared structure recently assigned to the out-of-plane vibration of boroxole skeleton. Part II describes a number of substituted binuclear cyclopentadienyl carbonyls of molybdenum, tungsten and iron, which have been made by the direct interaction of the metal carbonyls with fulvones. The corres- ponding mononuclear iodides and some alkyl derivatives have been obtained. n-Cyclopentadianyl molybdenum 7-cyclopentadienyl tungsten hexacarbonyl, 7t-05115Mo(C0)6W.n-05H5, is the first reported complex compound with a metal-metal bond between different transition metal atoms. Abstract (continued). Triphenylphosphonium cyclopentadienylide metal complexes of molybdenum, tungsten, chromium and iron have been prepared by the direct interaction of the metal carbonyl with triphenylphosphonium cyclopenta- dienylide in which the five-membered carbocyclic ring (cyclopentadienyl ring) has a sextet of electrons and acts as a six-electron donor ligand comparable to aromatic hydrocarbons. N.M.R. studies have shown beyond doubt that the -M(C0)3 residue is attached to the cyclopentadienyl ring and not to one of the phenyl groups, since there is no change in the resonances of the phenyl group protons whereas the line due to the protons on the cyclopentadienyl ring shifts to higher fields in the metal complexes compared to the original ligands. Molybdenum(II) dibenzoate, a novel type of oxygen chelatate complex, where, in addition, the arene nucleus is bound to the metal atom by a sandwich-type bond, as in arene-metal carbonyls, is described. From physical and chemical data, the structures of molybdenum(II) dibenzoate and related compounds have been assigned. C ONTENT S. Chapter PART I Page, Historical I The Esters of Boron 1 II The Trialkyl/aryl Siloxy Inorganic Compounds 4 Discussion III Preparation of Trialkylsilyl Esters of Boron 10 IV Properties of Trialkylsilyl Esters of Boron (Chemical and Physical) 14 Experimental V Preparation and Techniques 16 Preparation of Trialkylsilyl Esters 17 Hydrolysis of Trialkylsilyl Esters 18 Dealkylation of Trialkylsilyl Esters 21 Formation of Silylmetaborates 22 References 23 Contents (continued) Chapter PART II Page I Introduction (a) Fulvenes and related compounds, their preparation, reactions and theoretical importance 27 (b) n-Cyclopentadienyl metal carbonyls and their special characteristic features 31 II Discussion (a) 7c-Substituted cyclopentadienyl carbonyls of molybdenum, tungsten, chromium and iron 36 (b) Triphenylphosphonium cyclopentadienylide metal complexes 42 (c) Molybdenum(II) dibenzoate and related compounds 44 III Experimental Preparations and Reactions: 48 Preparation of substituted di-cyclopentadienyl metal carbonyls of iron, tungsten and molybdenum 50 Preparation of substituted I-cyclopentadienyl molybdenum tricarbonyl iodides 53 Preparation of metal alkyl derivatives of certain substituted cyclopentadienyl molybdenum tricarbonyls 54 Preparation of 7t-cyclopentadienyl molybdenum 7-cyclopentadienyl tungsten hexacarbonyl 54 Preparation of triphenylphosphonium cyclopentadienylide metal complexes of molybdenum, tungsten, chromium and iron 55 Contents, Part II (continued) Chapter III. Page Infrared Spectra 57 Ultraviolet Spectra Preparation of Molybdenum(II) Dibenzoate and Related Compounds 60 References 62 PART I TIE TR 'ALKYL SILYL E ST.ER S OF BORON HISTORICAL 1. CHAPTER I. The Esters of Boron. (1) The Orthoborates. In the present study we are mainly concerned with the organic derivatives of boric acid. The best known and most stable of these compounds are the trialkyl and triaryl orthoborates. These have now been prepared by a large variety of methods. The first mention of orthoborates was made by Ebelman and Bouquet (1), who utilised the reaction between boron trichloride and the respective alcohols to prepare trimethyl, triethyl and triamyl borates. 3ROH BC13---+ B(003 3HC1 This method has now been found to be of very wide application (2,3,4,5,6,7). It was found, however, that in the cases where the alcohol had a powerfully electron-releasing group (e.g. tort-butyl and 1-phenylethyl alcohols). the products were mainly the alkyl halides and boric acid. This has been interpreted as being due to the rapid SN1 dealkylation of the borate by the hydrogen halide (8,9) also formed, this rapid SN1 reaction being characteristic of powerful electron-releasing groups. Quantitative yields of these borates have been obtained, however, by the reaction of the alcohol and boron trihalides in the presence of pyridine (8,10). BC13 + 3ROH + 5C5H5N B(OR)3 + 3C5H5N.HC1 Um.mmoire sie 4iet-errr-tri-i-err-44te—peepara..t.i.a41--- -er+itebrrvItes 2. The use of boron trioxide in the preparation of orthoborates was introduced by Schiff (11), who prepared a number of borates from the oxide, and alcohols in an autoclave. Though boric oxide is now widely used for the preparation of borates, there has been no report of the fission of dialkyl or diaryl ethers by boron trioxide to produce borates. The preparation of tristrimethylsilyl borate in this way by the fission of hexamethyldisiloxane has, however, been reported (12). B203 + 3(CH3 )3SiOSi(CH3 )3.,.4 2[(CH3)3Si0]3B Boric acid has recently become widely used (13,14,15,16,17) for the preparation of the orthoborates. B(OH)3 + 3ROH --+B(OR)3 + 3H20 Although the method was first utilised by Cohn (18), who carried out the reaction in the presence of concentrated sulphuric acid to remove the water formed, later workers removed the water as it was formed — as a binary azeotrope of the alcohol being used (17); a further modification (19) now incorporates an inert solvent like benzene or toluene, and the water is removed as a ternary azeotrope. Easily obtained borates have been used as starting materials for the preparation of those less readily obtained, by an alcoholysis reaction. B(OR)3 + 3R'OH -4 B(OR' 3 3ROH This method has now been shown to have a wide application to the esters of boron (20). 3. (2) The Metaborates. Until recently the existence of alkyl metaborates has been in some doubt (20). Goubeau and Keller (21) obtained methyl metaborate by heating the orthoborate and boron trioxide in a sealed tube in equi- molecular quantities. They found the product to be trimeric. B203 (CH30)3B (CH30B0)3 The Raman spectrum of this compound (22) was evidence for a ring formulation (I) of the trimer. CH3 Lappert (23) has recently prepared an extensive 0 series of these compounds by the interaction of 1 boric oxide and the corresponding orthoborate, and 0 0 also by the decomposition of the corresponding B B aialkylchloroborinate. Neither of these methods / / 0 0 0\ worked for the preparation of tert-butyl metaborate, CH3 CH3 however, and to date this compound has not been (I) reported. (3) The Phonylboronates and Diphenylborinates. These compounds are respectively the esters of phenylboronic and diphenylborinic acids. The alkyl and aryl esters have been prepared and extensively studied (24,25,26,27) and shown to have parallel preparative methods to those of the orthoborates, and further to be similar in many of their reactions. 4. CHAPTER II The Trialkyl/aryl Siloxy Inorganic Compounds. Here we are mainly concerned with the methods used for the preparation of trialkyl/aryl siloxy compounds, and at the end of this chapter a complete list of these compounds known to date, along with their physical properties, is given in Table I. A glance at the periodic table will give one an impression as to the very little progress made in these compounds (especially the siloxy compounds of transition metals) as com— pared to the corresponding known metalalkoxides, because the two elements in question show considerable differences in their chemical properties. Moreover the siloxy compounds undergo very easily curious side reactions such as polymerisation, dehydration, etc. The trialkyl/aryl siloxy compounds can chiefly be prepared by the following methods: (1) By the interaction of the alkali metals or their hydroxides with trialkyl silanols (1,2,3). 2R3SiOH + 2Na 2R3SiONa + H2 R3SiOH NaOH R3SiONa + H20 (2) By the interaction of silyl ethers with sodium hydroxide in the presence of methanol (4,5). (R3S020 + 2NaOH > 2R3 SiONa + H20 5. (3) By the interaction of alkali metal silanolates with various metal halides (1,6). 2R3SiONa + [R3Si0]2 Eg + 2NaC1 4R3SiONa + 4 [R3SiO]4Ti + 4NaC1 (4) By the fission of silyl ethers with acidic oxides (7,8,9,10,11). 3R3SiO—Si—R3 + P205 —4 2[R3Si]3PO4 2[R3SiO]3B (5) By the interaction of silanol with metal halides in the presence of ammonia or an amine (12,13). (CH3 )3SiOH + TiC14 + 4NH3 4NH4C1 C(CH3 )3Si0L.Ti However, Bradley
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