Site selectivity in carbon monoxide insertion into a PtC σ-bond of the binuclear complex [(CH3)ClPt(μ-Cl) (μ-Ph2PPy) Pt(CH3)(DMSO)]DMSO. Structural characterization of the derivatives [(CH3CO)ClPt(μ-Cl)(μ-Ph2 PPy)Pt(CH3)(DMSO)] and [(CH3)ClPt(μ-Ph2PPy)2Pt(COCH3)]+

Title full: Site selectivity in carbon monoxide insertion into a PtC σ-bond of the binuclear complex [(CH3)ClPt(μ-Cl) (μ-Ph2PPy) Pt(CH3)(DMSO)]DMSO. Structural characterization of the derivatives [(CH3CO)ClPt(μ-Cl)(μ-Ph2 PPy)Pt(CH3)(DMSO)] and [(CH3)ClPt(μ-Ph2PPy)2Pt(COCH 3)]+. Carbon monoxide reacts with [(CH3)ClPt(μ-Cl)(μ-Ph2PPy)Pt(CH3) (DMSO)]DMSO, 1, to give [(CH3CO)ClPt(μ-Cl)(μ-Ph2 PPy)Pt(CH3)(DMSO)] 2. The insertion of CO into a platinum-carbon σ-bond of 1 shows a site selectivity, occurring at the Pt CH3 bond involving the metal atom connected to the P atom of the 2-(diphenylphosphino)pyridine (Ph2PPy). Under a carbon monoxide atmosphere for about 30 h, 1 forms the ionic compound [(CH3)ClPt(μ-Ph2PPy)2Pt(COCH3 )][Pt(CO)(COCH3)Cl2], 3. Complex 2 changes slowly into 3. It was not possible to obtain crystals of 2 or 3 suitable for X-ray investigations. A crystal species was isolated containing both 2 and 3 in a 1 : 1 ratio. The crystals are triclinic, space group P1 (no. 2), with a = 10.326(4) Å, b = 16.648(4) Å, c = 22.203(4) Å, α = 90.95(2)°, β = 96.50(2)°, γ = 95.44(2)°. The refinements, based on 3255 significant reflections, gave a final R value of 0.0621. The molecular structure of the neutral species 2 is similar to that of the parent compound 1, with a CH3CO group in place of a methyl. The structure of the anion of 3 was incompletely characterized because of disorder. The [(CH3)ClPt(μ-Ph2PPy)2Pt(COCH3 )]+ cation has a direct PtPt bond of 2.728(3) Å bridged by the two Ph2PPy ligands in a head-to-tail fashion. One of the Pt atoms completes its coordination with an acetyl group and is four-coordinate, whereas the second containing both a chlorine atom and a methyl group, is five-coordinate. Semi-empirical MO calculations for the cation have been performed, and show the dative nature of the PtII → PtII bond.