Synthesis and structures of platinum A-frame complexes

Reactions of TPtCl2(cod)] with the appropriate Grignard reagents produce [P tR2(cod)] CR C6H5, C6H4CH3-4, C6H4CH3-2, CH2C6H5), which, on treatment with 1 mol equiv of HCl, yield the corresponding chloroplatinum complexes [PtCl R(cod)]. The 2-tolyl compounds exhibit hindered rotation about the Pt-C bon ds at ambient temperature, the barrier to rotation being greater in [PtCl(C 6H4CH3-2)(cod)] than in the ditolyl derivative. The chloroplatinum compound s react with 1 mol equiv of dppm to give [PtClR(dppm)], which are in equili brium with the A-frame complexes [Pt2R2(mu -Cl)(mu -dppm)(2)]Cl. The extent of dimerization depends on the nature of R, but in each case the A-frame c omplex could be obtained quantitatively by treatment of the solution with N H4PF6 or TIPF6. The structures of [Pt2R2(mu -Cl)(mu -dppm)(2)] PF6 (R = CH2 C6H5, C6H4CH3-4) were determined by X-ray crystallography. In the benzyl de rivative, one of the ortho hydrogens on each phenyl (benzyl) ring points to wards the centroid of a dppm phenyl ring, and this may account for the low- frequncy signal associated with the ortho hydrogens in solution. The chlori de-bridged A-frames could be converted to the corresponding hydride-bridged derivatives, [Pt2R2(mu -H)(mu -dppm)(2)]PF6 (R = C6H5, C6H4; CH3-4, CH2C6H 5), by treatment with NaBH4.