Bimetallic systems. Part 6. Chromium(0)–, molybdenum(0)–, or tungsten(0)–platinum(II) acetylide complexes containing bridging Ph2PCH2PPh2, including their efficient formation from platinum–silver complexes by transmetallation. Crystal structure of [(p-MeC6H4CC)-Pt(µ-CCC6H4Me-p)(µ-Ph2PCH2PPh2)2W(CO)3]

Abstract

Treatment of trans-[Pt(CCR)₂(dppm-P)₂](dppm = Ph₂PCH₂PPh₂) with [W(CO)₃(NCMe)₃] gave [(RCC)Pt(µ-CCR)(µ-dppm)₂W(CO)₃](R = Ph, p-tolyl, or Me) accompanied by [Pt₂(CCR)₄-(µ-dppm)₂] and other products. Treatment of trans-[Pt(CCPh)₂(dppm-P)₂] with [Mo(CO)₄-(1,5-cod)](1,5-cod = cyclo-octa-1,5-diene) or with [Mo(CO)₃(cht)](cht = cyclohepta-1,3,5-triene) gave [(PhCC)Pt(µ-CCPh)(µ-dppm)₂Mo(CO)₃], in 20—25% yield, but the corresponding chromium compound could not be made in this way. However, treatment of the readily available complexes [(RCC)₂Pt(µ-dppm)₂AgX](X = Cl or l) with [W(CO)₃(NCMe)₃] or [Mo(CO)₃(cht)] gave the above mentioned platinum–tungsten or –molybdenum complexes with displacement of silver halide (transmetallation), usually in good yield and without formation of the diplatinum complexes. Purple [(PhCC)Pt(µ-CCPh)(µ-dppm)₂Cr(CO)₃] was made similarly but not isolated. ¹H-{³¹P} N.m.r. studies at different temperatures showed the complexes to be fluxional, corresponding to rapid terminal–bridging CCR interchange with inversion of the Pt(µ-dppm)₂M boat-shaped eight-membered rings. The complexes [(RCC)Pt(µ-CCR)(µ-dppm)₂W(CO)₃](R = Me or Ph) were rapidly and reversibly protonated by CF₃CO₂H to give [(RCC)Pt(µ-CCHR)(µ-dppm)₂W(CO)₃]⁺, isolated as the PF₆^– salts; preliminary studies suggested that the molybdenum complexes could also be protonated. Phosphorus-31 and ¹H n.m.r. data are given and discussed. With the Pt(µ-Ph₂PCH₂PPh₂)₂M moieties, platinum-195 was observed to be quite strongly (magnetically) coupled to one of the methylene hydrogens, that which was pseudo-equatorial, but coupling to the pseudo-axial hydrogen was not observed. Crystals of the title compound are monoclinic, space group P2₁, with a= 11.847(3), b= 16.023(4), c= 18.351 (4)Å, β= 116.23(1)°, and Z= 2; final R factor 0.026 for 4 043 observed reflections. The structure shows that the two metal centres [Pt ⋯ W 3.037(1)Å] are asymmetrically bridged by one of the p-tolylacetylide groups such that the Pt–C and W ⋯ C distances are 2.094(9) and 2.398(9)Å, respectively, with the CC vector perpendicular to the PtP₄W plane.