Published: 1996
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This thesis describes studies on the synthesis and reactivity of a variety ofmolybdenum thiolate hydride complexes; tungsten complexes were also prepared forcomparison. The original purpose of this research was to examine the behaviour of sulphurligatedmolybdenum complexes as models for the molybdenum site in nitrogenase, but thiswork has demonstrated that the 5-coordinated complexes [MoH(SC6H2R3-2,4,6)3(PR1Ph2)] (R= Me or Pr'; R1 = Me or Et) are very reactive versatile starting materials for thepreparation of a wide range of derivatives, some of which model aspects of the chemistry ofother molybdenum enzymes such as xanthine oxidase.It is known that the reaction of thiols HSC6H2R3-2,4,6 with [MoH4(PR'Ph2)4] or trans-[Mo(N2)2(PMePh2)4] produces unsaturated thiolato-hydride complexes of molybdenum(IV)[MoH(tipt)3(PMePh2)] (A) (tipt = SC6H2PrV-2,4,6). Here we report an extension of thesestudies in which we have prepared the oxygen-sensitive, five- and six-coordinated complexes[MoH(SC6H4F)3(PMePh2)] (2.3) and [MoH(SC6HF4-2,3,5,6)3(PMePh2)2] (2.1) and[MoH(SC6F5)3(PMePh2)2] (2.4).Some reactions of (2.3), (2.1) and (2.4) have been investigated, including the reactionof (2.4) with carbon monoxide which yields [Mo(SC6F5)2(CO)2(PMePh2)2] (6.7). Thereaction of (2.1) with pyridine gives [MoH(SC6HF4-2,3,5,6)3(C5H5N)(PMePh2)] (6.1).The reaction of the electron-deficient hydride thiolate complex [MoH(tipt)3(PMe2Ph)2](B) with phenylacetylene gives the novel square pyramidal, diamagnetic phosphoniumalkylidenecomplex[MoO{=C(Ph)CH=C(Ph)CH2PMe2Ph)(SC6H2Pri3-2,4,6)3](3E), whereasthe reaction of /Molylacetylene with (A) yields the novel phosphonium ylide complex[MoO(SC6H2Pri3)2(HC=CC6H4Me-4){(C6H4Me-4) (C=CHPMePh2)}](3D),thathas relevanceto the species derived from xanthine oxidase when it is inhibited by aldehydes. These twocomplexes have been characterised by X-ray structure determination. [WH(tipt)3(PMe2Ph)2j(C) with phenylacetylene and p-tolylacetylene gives products resulting from oligomerisationreactions.In the reaction o f [MoH(tipt)3(PMePh2)] (A) with hydrazines, both binding of hydrazineto Mo and disproportionation/reduction have been observed. The bright green andtemperature- and oxygen-sensitive complex [MoH(tipt)3(NH3)(PMePh2)J (4.1) has beenobtained from the reaction of NH2NH2 with (A). Its X-ray structure determination at -10°Cshows that it is a hydride ammonia complex with trigonal bipyramidal geometry. Thereaction of phenylhydrazine with (A) gives dark green single crystals that have been thesubject of an X-ray crystallographic analysis. This compound crystallised in a much-distortedtrigonal bipyramidal geometry and is formulated as [MoH(tipt)3(NH2NHPh)(PMePh2)] (4.4).Isocyanides are substrates or inhibitors of nitrogenase. The interaction of isocyanides withthe five- and six-coordinate hydride complexes has been investigated. The reaction of[MoH(tipt)3(PMePh2)] (A) with MeNC and t-BuNC and also the reaction of[WH(tipt)3(PMe2Ph)2] (C) with MeNC, produce [MoH(tipt)2(MeNC)4] (5.1), [MoH(tipt)2('-BuNC)4] (5.3) and [WH(tipt)2(MeNC)4] (5.2) respectively. The structures of these complexeshave been confirmed by X-ray structure determination.The reaction of molybdenum hydride complexes with carboxylic acids give productswhich show carboxylate groups in their IR and NMR spectra.