Chemistry of di- and tri-metal complexes with bridging carbene or carbyne ligands. Part 39. Interconversion of ethylidyne, ethylidene, vinyl, and ethylene groups at a platinum–tungsten centre; X-ray crystal structure of [PtW(µ-CO)2(PEt3)2(η-C2H4)(η-C5H5)][BF4]

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Abstract
Treatment of the bridged ethylidyne complexes [PtW(µ-CMe)(CO)2(PR3)2(η-C5H5)](PR3= PMe3, PEt3, PMe2Ph, or PMePh2) with the reagent HBF4·Et2O affords the salts [PtW(µ-CO)2(PR3)2(η-C2H4)(η-C5H5)][BF4]. The product with PR3= PEt3 has been structurally characterised by an X-ray diffraction study. The tungsten atom is ligated by a cyclopentadienyl group, the ethylene molecule, and two carbonyl ligands. The latter semi-bridge an unusually short Pt–W bond [2.602(1)Å]. The two PEt3groups are co-ordinated to the platinum in a cis arrangement with the PtP2plane being at 90° to that defined by the two carbons of the µ-CO groups and the W atom. In contrast with protonation using HBF4·Et2O, addition of CF3CO2H to [PtW(µ-CMe)(CO)2(PMe3)2(η-C5H5)] affords the ethylidene-bridged complex [PtW(O2CCF3)(µ-CHMe)(CO)2(PMe3)2(η-C5H5)], while methylation gives the vinyl- and hydrido-bridged compound [PtW(µ-H){µ-C(Me)CH2}(CO)2(PMe3)2(η-C5H5)][CF3SO3]. Treatment of [PtW(µ-CO)2(PMe3)2(η-C2H4)(η-C5H5)][BF4] with NaBH4 yields [PtW(µ-H)(µ-CHMe)(CO)2(PMe3)2(η-C5H5)], while PMe3 deprotonates the salt to give [PtW(µ-CHCH2)(CO)2(PMe3)2(η-C5H5)]. The 1H, 13C-{1H}, 31P-{1H}, and 195Pt{1H} n.m.r. spectra of the new complexes are reported and discussed.

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