METHYL(HYDRIDO)PLATINUM(IV) COMPLEXES - X-RAY STRUCTURE OF THE FIRST (MU-HYDRIDO)DIPLATINUM(IV) COMPLEX

The complex fac-[PtMe(3)(SO3CF3)(bu(2)bpy)] (1) (bu(2)bpy = 4,4'-di-te rt-butyl-2,2'-bipyridine) reacts with NaBH4 to give [Pt-2(mu-H)Me(6)(b u(2)bpy)(2)]SO3CF3 (2), which is the first example of a (mu-hydrido)di platinum(IV) complex. Complex 2 was fully characterized on the basis o f microanalytical, H-1 and Pt-195 NMR spectroscopic, and X-ray crystal lographic data. The reaction of 1 with a large excess of NaBH4 results in the formation of an equilibrium mixture of 2 and fac-[PtHMe(3)(bu( 2)bpy)] (3). Complex 3 was characterized by H-1 NMR spectroscopy in so lution but could not be isolated in pure form due to the ease of rever sion to 2. Both complexes 2 and 3, which have no ligand that can easil y dissociate, are thermally stable to reductive elimination of methane (both in solution and, in the case of complex 2, in the solid state) and to isotopic exchange within Pt(D)CH3 groups, thus giving strong su pport to the theory that both reactions must occur from within a five- coordinate intermediate, Complex 2 reacts slowly with HX (HX = HCl, HO 2CCF3, HSC6H5, NH4+) to give either 2 equiv of fac-[PtClMe(3)(bu(2)bpy )] (4), fac- [PtMe(3)(O2CCF3)(bu(2)bpy)](5), and fac-[PtMe(3)(NH3)(bu( 2)bpy)]SO3CF3 (6) or 1 equiv of [Pt-2(mu-SC6H5)Me(6)(bu(2)bpy)(2)]SO3C F3 (7), respectively. Qualitatively, the relative rates of these react ions follow the order of acid strength, i.e. HCl approximate to HO2CCF 3 >> HSC6H5, indicating that the rate-determining step involves electr ophilic attack of H+ on 2, Complex 2 reacts very slowly with nucleophi les such as PPh(3) to give 1 equiv of fac-[PtMe(3)(PPh3)(bu(2)bpy)]SO3 CF3 (8) and 1 equiv of 3, The reaction of CC4 with 2 gives fac-[PtClMe (3)(bu(2)bpy)] (4), [PtCl(2)Me(2)(bu(2)bpy)] (11), and mer-[PtCl(3)Me( bu(2)bpy)] (12) in a 1.0:0.8:0.2 product ratio but without formation o f chloroform.