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-tert-butyl-2,2'-bipyridine) reacts with NaBH4 to give [Pt-2(mu-H)Me(6)(bu(2)bpy)(2)]SO3CF3 (2), which is the first example of a (mu-hydrido)diplatinum(IV) complex. Complex 2 was fully characterized on the basis of microanalytical, H-1 and Pt-195 NMR spectroscopic, and X-ray crystallographic 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 solution but could not be isolated in pure form due to the ease of reversion to 2. Both complexes 2 and 3, which have no ligand that can easily 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 support to the theory that both reactions must occur from within a five-coordinate intermediate, Complex 2 reacts slowly with HX (HX = HCl, HO2CCF3, 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)]SO3CF3 (7), respectively. Qualitatively, the relative rates of these reactions follow the order of acid strength, i.e. HCl approximate to HO2CCF3 >> HSC6H5, indicating that the rate-determining step involves electrophilic attack of H+ on 2, Complex 2 reacts very slowly with nucleophiles such as PPh(3) to give 1 equiv of fac-[PtMe(3)(PPh3)(bu(2)bpy)]SO3CF3 (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 of chloroform.