Oxidatively Induced Reductive Eliminations. A Mechanistic Study of the Oxidation Chemistry of CnRhMe(3) (Cn = 1,4,7-Trimethyl-1,4,7-triazacyclononane).

The trimethylrhodium(III) complex CnRhMe(3) (1, Cn = 1,4,7-trimethyl-1,4,7-triazacyclononane) undergoes a nearly reversible one-electron oxidation at E degrees = -0.15 V vs Cp(2)Fe/Cp(2)Fe(+) (cyclic voltammetry, 1.0 V/s) in acetonitrile/0.1 M Bu(4)NPF(6). Preparative electrolysis as well as homogeneous oxidations with substituted ferricinium salts gives a mixture of CnRhMe(2)(NCMe)(+) (2) and CnRhMe(NCMe)(2)(2+) (3), the 2:3 ratio being independent of the nature of the oxidant. In addition, the reactions yielded ethane, mostly by intramolecular elimination. An investigation of the kinetics of the reaction of 1(*)(+) by derivative cyclic voltammetry revealed a unimolecular reaction (DeltaH() = 57.0 +/- 0.9 kJ/mol, DeltaS() = -35.4 +/- 3.0 J/(K.mol), k(20 degrees C) = 5.9 s(-)(1)) with negligible solvent effects (MeCN vs CH(2)Cl(2)). It is proposed that 1(*)(+) eliminates ethane to generate the formally 15-electron CnRhMe(*)(+) in the rate-determining step. The final Rh-containing products are likely formed from this species and 1(*)(+).