RAPID REVERSIBLE OXIDATIVE ADDITION OF GROUP-14 HALIDE BONDS TO PLATINUM(II) - RATES, EQUILIBRIA, AND BOND-ENERGIES

The reversible oxidative addition reactions of methyl(halogeno)tin and methyl(halogeno)germanium compounds to electron-rich platinum(II) com plexes of the type [PtMe2(diimine)] have been studied. Complete kineti c and thermodynamic parameters have been obtained by VT H-1 NMR for th e reversible oxidative addition of Me3EX (E = Sn, X = Cl, Br, I) to [P tMe2(bpy-(t)bu(2))] (bpy-(t)bu(2) = 4,4'-di-tert-butyl-2,2'-bipyridyl) and related compounds, while partial data have been obtained for the reductive elimination of Me2SnCl2 from [PtClMe2(Me2SnCl)-(bpy-(t)bu(2) )] and for the oxidative addition of Me3GeCl to [PtMe2(bpy-(t)bu(2))]. W-visible spectroscopic studies have also yielded equilibrium constan ts and Delta G degrees for the reversible oxidative addition reactions of Me3SnX (X = Cl, Br, I) to [PtMe2(diimine)]. Thermodynamic studies quantitatively establish the halogen effect on the oxidative addition reactions studied according to the favorability series I > Br > Cl. Ki netic studies clearly point to an S(N)2 mechanism for the reactions st udied, and this is further supported by the observation of the cationi c complex [PtMe2(Me3Sn)-(bpy-(t)bu(2)){OC(CD3)(2)}](+) at low temperat ure in acetone-d(6). Extremely large second-order rate constants are o bserved for the oxidative addition of Sn-X bonds to dimethylplatinum(I I) complexes, some being greater than 10(8) M-1 s(-1), and it is estab lished that rates follow the series Sn > Ge > Si > C and I > Pr > Cl. Estimates have been made of the Pt-MMe3 bond dissociation energies for [PtXMe2(MMe3)(bpy-(t)bu(2))], X = halide, and these are 233, 182, and 172 kJ mol(-1) for M = Si, Ge, and Sn, respectively; the values are u seful in rationalizing the chemistry of the Pt-M bonds.