baAE COORDINATION COMPOUNDS OF RHENIUM. A Thesis submitted by COLIN JAMES LYNE LOCK, B.Sc., A.RX.S. for the Degree of Doctor of Philosophy of the University of London. July, 1963. Royal College of Science South Kensington, S.W.7. To Helen, Nicola and Allison who hindered rather than helped, but who made it worthwhile. It is more laborious to accumulate facts than to reason concerning them; but one good experiment is of more value than the ingenuity of a brain like Newton's. Sir Humphrey Davy. Refrain from illusions, insist on work and not on words. Patiently search divine and scientific truth. Mendeleev t s Mother. Acknowledgements. I mould like to thank Professor G. Wilkinson for his encouragement, criticism and advice during his supervision of this work. My thanks are also due to Dr. L. Pratt for advice on nuclear magnetic resonance techniques, Dr. J. Wood for advice on infra-red spectroscopy, and Dr. W. P. Griffith for general discussion and biscuits. I would like to thank my colleagues, especially N. P. Johnson, R. Gillard, Dr. A. Davison, and Dr. J. McCleverty for their advice and company. Finally I am indebted to my wife who typed this thesis and who has had to suffer Rhenium Chemistry for the past three years. CONTENTS. Chapter Title Page Abstract 1. Introduction 1 2. Phosphina complexes 15 3. Analysis of cyanide in. cyanide complexes 30 4. Cyanide comp la xo 38 5. Dioxo-complexes of rhenium 52 6. 2:4-propanedione complexes 60 7. Oxides of rhenium 65 8. Experimental 73 9. Appendix 104 10. References 105 Abstract. Two compounds previously described as trichloro- bis(triphenylphosphine)rhenium(III) have been shown to be trichlorobis(triphenylphosphine oxide)rhenium(III) and oxotrichlorobis(triphenylphosphine)rhenium(V). Other phosphine complexes of Re(III) and Re(II) prepared in a similar manner to the latter have been shown to be com- pounds of Re(V). A new arsine complex of Re(V) and other arsine and arsine oxide complexes of rhenium(III) have been prepared. A triphenylphosphine complex of Re(II) has been prepared. Previously reported cyanide complexes of Re(VI) and Re(V) have been confirmed, although the purification procedure described for the latter causes hydrolysis of the compound. The supposed purple hydroxocyanide complex of Re(VII) has been shown to be the oxohydroxocyanide complex of_Re(V),- as have previously reported purple salts of the dioxotetracyanorhenate(V) have also been shown to be salts of this anion. The first transition metal- nitridocyanide complex has been prepared. A new method of preparing potassium dioxotetracyanorhenate(V) is described. It has been shown that the diagnostic region for M=0 infra-red stretching frequencies must be extended -1 from 900 cm. down to at least 780 cm.-1 where a linear 04\1=0 group exists in an octahedral complex. Stable phases Re205 and Re308 have been prepared by the oxidation of rhenium dioxide hydrate. The former is a mixture of Re0 3 and an unidentified oxide. The latter does not contain any Re03. Mixed phosphine 2:4-propanedione complexes of rhenium(V) and rhenium(III) have been prepared. 1. 1. INTRODUCTION. Rhenium has been anelemont of chemical con- troversy since its discovery was first claimed by Noddack2 Tacke2 and Berg in 1925 (1). Th3 validity of this claim has been challenged, particularly by Druce (2) and Prandtl (3). The work of Noddack appears doubtful be- cause he claimed to have isolated both technetium and rhenium in macro-quantities from certain platinum ores and columbite. Since that time all attempts to isolate naturally occurring technetium (all isotopes of which are radioactive) in macro-quantities have been unsuccess- ful (4). Prandtl (3) was also unable to isolate any rhenium from the columbite ore and Russian workers could not find rhenium in the platinum ores (52 6). Later, and independently, Loring and Druce (728) isolated the element from pyrolusite and molybdenum glance, and this was later confirmed by other workers (2). Probably Druce and Loring should be credited with the actual discovery of rhenium. The Noddacks (92 10)2 however, were certainly the first workers to isolate the element in any quantity and to prepare a number of chemical com- pounds2 and their name for the element has been retained. The chemistry of rhenium is complicated for a number of reasons. Compounds have been prepared in all the formal valency states from Re(-1) through Re(7)2 and 2. coordination numbers of , 4 through 8 have been character- ised, arid even a coordination number of 9 has been claimed. Examples of these compounds are given in Table 1. Rhenium also shows a remarkable ability to bond strongly to groups such as -H, =02 -OH, ;1\12 and -OMe, which, because many of the compounds of rhenium are stabilised by organic ligands with high molecular weight, have not been detected analytically. It is only with the advent of modern techniques such as infra-red and nuclear magnetic resonance spectroscopy that these groups have been detected. One other difficulty that has boon en- countered is that the presence of impurities apparently affects the course of reaction of rhenium metal. It was shown by Colton (11) that very pure rhenium metal gave hexachlororhenium(VI) on chlorination whereas the com- mercial metal gave pentachlororhenium(V). This has also been observed by us and in fact the formation of ReC1 is 6 a good indication of the purity of the metal. In the initial stages of this work the rhenium metal available contained z,,,/1,5% potassium salts and gave onlyReC1,) (<1% ReC16) on chlorination. The latest batch of com- mercial metal made by the hydrogen reduction of ammonium perrhenate and claimed to be 99.9% pure gavei\-/10 RoC16 on chlorination. A result of these effects is that many papers 3 Table 1 The different valen0 states and coordination numbers of rhenium in its compounds. Formal valency Compound Coordi- Compound of rhenium nation Number -1 NaRe(00) (12) 4 ReC14 (26) 5 (Ph3P) 2RoI + 2 Roo(c0)10 (13) (Ph3 P2 Fo(Co) 4 (14) 5 (Ph3P0) 2ReC13 + (Ph3P) 211eNC12 (27) 0 K Re(CN) (15) 5 6 6 (Ph3P),Re0C1-4 + (Ph,P),JleI (Repy402)C1 '+(28) 2 2 L-)Reel22 (16) 3 Re2C16, (17) 7 (Ph:AP)4ReHR (29) +(18) <ReL2C12)07(C104k (Ph3 P Re01.)3 2 4 K2Req6 (19a,b). 8 K Re(CN)8 (31) CN)14(20) A 3Re(CN)7NO (31) 5 (Phg) 2ReO.C1:1 +(21) 3(Re02(CN)47 +(20) 9 K3Re(CN)80H (31 6 Rep- .(22) ReF (23) 7 Re,Oij (24) (25) L is the chelating ligand o-phenylenebis(dimethyl- arsine)i + This work. 4. on the chemistry of rhenium are at least partly inaccurate. Before any new experiments could be started it ti as usually necessary to investigate the starting product, and in some cases to reformulate the reactions and compounds. The chemistry of rhenium has been reviewed exten- sively recently (309 329 339 349 35)9 but little attention has been paid to the coordination chemistry of rhenium apart from in Nyholm's reviem.(30) A general review of the coordination complexes of rhenium will be made hare, except for some phosphine complexes and the cyanides which will be treated more fully in the chapters on the new work on these complexes. Rhenium(-11 The only complex of rhenium mith a formal valency of (-I) which has been substantiated is NaRe(C0)5. (12) Polarogrephic reduction of the perrhenate ion (36) suggested that the rhenide ion Re(-I)- existed, and salts supposed to be rhenides mere isolated (37). Colton et al. (38) have also shown that polarographic reduction of a number of rhenium compounds gave products which, from the number of electrons in the reduction, are com- pounds of Re(-I). Homover, it mas shown by nuclear mag- netic resonance studies of the reduced solutions that Re-H bonds were present and subsequently it has been suggested that the so-called rhenides are hydrides of 5. the type KRo 111114.2H20 (39) or Dc.2Rovill82 (40). From the disagreement that still exists this matter is probably not yet finally settled. Rho nium(0) Rhenium(0) occurs in the dimcric carbonyl Ro2(CO) (13) mhich contains a metal - metal bond (41). 10 By analogy with carbon in ethane this might be regarded as a compound of Ra(I). True Ro(0), however, occurs in the monomeric complex (Ph3P)2Re(C0)4 (14). Rhcnium(I) This formal state exists in a number of com- pounds. There are many types of carbonyl complex such as the hydride HRe(C0)5 (12), cyanide Do(C0)4(CN)a (43),halides, both monomeric Ro(C0)5X (X = Cl, Br, I) (44), and dimerictlie(C0)1X2(45) with halide bridges. A number of substituted carbonyls of the typo L2Ro(C0)3X (L = py9 Ph3P, 2(o-phon), aniline) (43,45) have boon prepared, as has the bridged hydroxocarbonyl compound K[SCO)4R0 e(C0)4y and a similar thio-compound (C0)4Re Re(C0)4 (46). Other carbonyl complexes are of the type Die(C0)4L21C1 (L = CN.C61-14.CH3, NH3, and PPh3) (43,47). Other salts containing Re(I) in the cation have been prepared recently. They are isocyanides of the type Pie(CH3C6H4NC)d+ (48), the carbonyl [!to(C0)61A1C14 (49) and the diethylcnc carbonyl ble(C0)4(C2H4)21+ (50) and the arena sandwich complexes 6. of the typo [RciAr 1+ (Ar = benzene or mesitylene) (51). 2 Diamagnetic compounds of Re(I) have been prepared by the reaction of halide complexes of Re (ITT) and acetylenes (52)5 for example; RoCl(Ph.C.;CH)5 ReLa(HOGH(CH3)CH2C=0H2), and ReC1.(Ph P)(HOCH(CH )CH T=ICH) 3 3 2 2' Rhenium(II) This must be considered as one of the rarest valency states of rhenium.