Reactions of acetylenes with noble-metal carbonyl halides. Part 6. Carbonyl insertion to give cyclic organo-carbene complexes of platinum(II): synthesis and X-ray structure of the complex cis-[Pt{CC(CO2Et)C(Ph)C(CO2Et)C(Ph)O}(PPh3)Cl2]

Abstract

The complex [Pt(CO)₂Cl₂] reacts with ethyl phenylpropiolate, PhCCCO₂Et, to give [Pt{[graphic omitted]}(CO)Cl][Pt(CO)Cl₃](1) which contains a six-membered carbenoid ring bonded to platinum. In acetonitrile, complex (1) gives cis-[Pt{[graphic omitted]}(CO)Cl₂](2). The interconversion of complexes (1) and (2) with KCl and [Pt(CO)₂Cl₂] respectively are reported and a mechanism for the formation of (1) is proposed. Reaction of complex (1) with PPh₃results in displacement of CO to give cis-[Pt{[graphic omitted]}(PPh₃)Cl₂](3). ¹³C N.m.r. studies of complexes (2) and (3) with specific isotopic labelling are reported. The crystal structure of complex (3) has been solved by Patterson and Fourier methods from counter data and refined by block-matrix least squares to a final conventional R of 0.048 for 5 842 independent observed reflections. Crystals of (3) are triclinic, space group P, with unit-cell dimensions a= 11.523(3), b= 11.994(4), c= 14.512(6)Å, α= 106.2(1), β= 88.8(1), γ= 73.7(2)°, and Z= 2. The crystals contain discrete molecules in which the co-ordination of the platinum atom is slightly distorted square planar. Selected bond lengths (Å) are Pt–P 2.244(2), Pt–C 1.933(8), Pt–Cl (trans to carbenoid carbon atom) 2.350(3), and Pt–Cl (trans to PPh₃) 2.347(2). On the basis of reactivities and spectroscopic data, an unambiguous relationship has been established between compound (3) and its precursors.