The reaction of alkynes with triangulo-clusters [Pt3(μ-CO)3(PR3)3]

Abstract

The reaction of the cluster complexes [Pt₃(μ-CO)₃(PR₃)₃] (PR₃ = PPh₃  1, PPh₂Bz  2, PCy₃  3 and PⁱPr₃  4) with dialkyl acetylenedicarboxylate, R′O₂CCCCO₂R′ (R′ = CH₃ or ^tBu) have been examined under various conditions. At low temperature the alkyne reacts quantitatively giving the unstable adducts [Pt₃(CO)₃(PR₃)₃(μ₃-alkyne)]. The stereochemistry of the intermediate [Pt₃(CO)₃(PPh₃)₃(μ₃-^tBuO₂CCCCO₂^tBu)] 5 has been deduced from low temperature ¹⁹⁵Pt-{¹H}, ³¹P-{¹H} and ¹³C-{¹H} NMR spectra. At higher temperature a fluxional process renders two of the three platinum atoms equivalent on the NMR timescale. At room temperature the alkynes convert the starting clusters 1–4 to the stable dinuclear complexes [Pt₂(CO)₂(PR₃)₂(μ-R′O₂CCCCO₂R′)] (R′ = CH₃, PR₃ = PPh₃  6; R = ^tBu, PR₃ = PPh₃  7; PPh₂Bz  8; PCy₃  9 and PⁱPr₃  10) in which the alkyne coordination has the C–C bond collinear with the Pt–Pt bond (6 and 7) or perpendicular to the Pt–Pt axis (9 and 10). The stereochemistry of these two types of dinuclear complexes has been established by NMR and IR studies and confirmed by X-ray diffraction analyses of 8 and 9.