PREPARATION AND X-RAY STRUCTURE OF A PLATINUM(II) HYDROXYCARBONYL, PT(CO2H)(C6H3(CH2PPH2)2-2,6), CONTAINING A TRANS-SPANNING, TRIDENTATE P,C,P-LIGAND

The ligand 1,3-{bis(diphenylphosphino)methyl}benzene, 1,3-C6H4(CH2PPh2)2 (3a) undergoes cyclometallation on heating in 2-methoxyethanol either with PtCl(CH3)(COD) or, in the presence of 2-methylaminoethanol, with PtCl2(COD) to give PtCl{C6H3(CH2PPh2)2-2,6} (6). In this complex, the tridentate anionic ligand C6H3(CH2PPh2)2-2,6 (2a) is attached to platinum via a sigma-bonded carbon atom and mutually trans-phosphorus atoms. Successive treatment of 6 with AgBF4 and KOH gives the hydroxo-complex Pt(OH)(2a) (11), which reacts with CO to give the corresponding hydroxycarbonyl Pt(CO2H)(2a) (12). The structure of 12.1.5C6H6 was determined by X-Tay diffraction methods and shown to consist of a dimer in which two planar trans-Pt(CO2H)(2a) units are joined by hydrogen-bonded carboxylate groups. The hydrogen-bonded O ... O distance [2.750(4)angstrom] is significantly larger than that in trans-Pt(CO2H)(C6H5)(PEt3)2 (1) [2.695(8)angstrom], which may be related to the greater tendency of 2a to form a monomer in dichloromethane.