SITE SELECTIVITY IN CARBON-MONOXIDE INSERTION INTO A PT-C SIGMA-BOND OF THE BINUCLEAR COMPLEX [(CH3)CLPT(MU-CL)(MU-PH(2)PPY)PT(CH3)(DMSO)]DMSO - STRUCTURAL CHARACTERIZATION OF THE DERIVATIVES [(CH3CO)CLPT(MU-CL)(MU-PH(2)PPY)PT(CH3)(DMSO)] AND [(CH3)CLPT(MU-PH(2)PPY)(2)PT(COCH3)](+)

Carbon monoxide reacts with [(CH3)ClPt(mu-Cl)(mu-Ph(2)PPy)Pt(CH3)(DMSO)]DMSO, 1, to give [(CH3CO)ClPt(mu-Cl)(mu-Ph(2) PPy)Pt(CH3)(DMSO)] 2. The insertion of CO into a platinum-carbon sigma-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 (Ph(2)PPy). Under a carbon monoxide atmosphere for about 30 h, 1 forms the ionic compound [(CH3)ClPt(mu-Ph(2)PPy)(2)Pt(COCH3)][Pt(CO)(COCH3)Cl-2], 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 P (1) over bar (no. 2), with a = 10.326(4) Angstrom, b = 16.648(4) Angstrom, c = 22.203(4) Angstrom, alpha = 90.95(2)degrees, beta = 96.50(2)degrees, gamma = 95.44(2)degrees. 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(mu-Ph(2)PPy)(2)Pt(COCH3)](+) cation has a direct Pt-Pt bond of 2.728(3) Angstrom bridged by the two Ph(2)PPy 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 Pt-II --> Pt-II bond.