The reactions of tetrahydridotetrakis(methyldiphenylphosphine)-molybdenum(IV) and -tungsten(IV) with acids

Abstract

Neutral and cationic hydrido-complexes of molybdenum and tungsten have been prepared by interaction of the compounds MH₄(PMePh₂)₄(M = Mo and W) with acids HX (X = CF₃CO₂, p-MeC₆H₄SO₃, BF₄, and PF₆). The reactions of MoH₄(PMePh₂)₄ are accompanied by hydrogen evolution and yield different Mo^IV products that depend on the nature of the anion, namely neutral species MoH₂X₂(PMePh₂)₃(X = CF₃CO₂ and p-MeC₆H₄SO₃) and cationic species [MoH₃(PMePh₂)₃]X (X = BF₄ and PF₆). By contrast WH₄(PMePh₂)₄ is readily protonated to give the cationic pentahydrido-species [WH₅(PMePh₂)₄]⁺. The corresponding trifluoroacetate isolated as [WH₅(PMePh₂)₄][H(O₂CCF₃)₂]·toluene loses hydrogen on melting to yield the neutral compound WH₂(CF₃CO₂)₂(PMePh₂)₃.

With hydrochloric acid MoH₄(PMePh₂)₄ gives a green compound Mo₂Cl₄(PMePh₂)₄ which readily transforms into a blue isomer, while WH₄(PMePh₂)₄, gives again the WH₅(PMePh₂)₄⁺ ion. The compounds are characterised by i.r. and ¹H and ³¹P n.m.r.spectroscopy.