Tricarbonyl(carbaborane) complexes of the Group 6 metals as reagents for preparing heteronuclear dimetal compounds involving platinum

Abstract

The reagents Tl₂[M(CO)₃(η⁵-C₂B₉H₉Me₂)](M = Cr, Mo or W), generated in situ from Tl[TlC₂B₉H₉Me₂] and [M(CO)₃(NCMe)₃], react in thf (tetrahydrofuran) with the compounds [PtCl₂L₂](L = PPh₃ or PEt₃) to give the dimetal complexes [MPt(CO)₃L₂(η⁵-C₂B₉H₉Me₂)]. NMR studies revealed that the tungsten–platinum species were produced as a mixture of two isomers of formulation [WPt(CO)₃L₂(η⁵-C₂B₉H₉Me₂)] and [WPt(µ-H)(µ-σ:η⁵-C₂B₉H₈Me₂)(CO)₃L₂]. The complexes [MPt(CO)₃L₂(η⁶-C₂B₁₀H₁₀Me₂)] have been prepared from reactions between [PtCl₂L₂] and Na₂[M(CO)₃(η⁶-C₂B₁₀H₁₀Me₂)](M = Mo or W), with the latter generated in situ from Na₂[C₂B₁₀H₁₀Me₂] and [M(CO)₃(NCMe)₃]. Similar reactions using [PtCl₂(cod)](cod = cycloocta-1,5-diene), followed by addition of PPh₃ to the reaction mixture, afforded the salts [PtH(PPh₃)₃][MPt(µ-σ:η⁶-C₂B₁₀H₉Me₂)(CO)₄(PPh₃)]. Protonation (HBF₄·Et₂O) of the latter yields the complexes [MPt(CO)₄(PPh₃)(η⁶-C₂B₁₀H₁₀Me₂)]. An X-ray crystallographic study of the molybdenum–platinum compound revealed that the molecule contained a Mo–Pt bond [2.814(1)Å] spanned by the nido-C₂B₁₀H₁₀Me₂ cage such that the latter is η⁶-co-ordinated to the molybdenum and linked to the platinum via a three-centre two-electron B–H⇀Pt bond. This bond involves the hydrogen atom attached to the boron atom which is β to the carbons is the CBCBBB face of the cage ligating the molybdenum atom. The NMR data (¹H, ¹³C-{¹H}, ³¹P-{¹H} and ¹¹B-{¹H}) for the new compounds are discussed in relation to the structures proposed.