OXIDATIVELY INDUCED REDUCTIVE ELIMINATION FROM RU(C(2)PH)(2)(CO)(P(T)BU(2)ME)(2) AND RU(CHCHPH)(C(2)PH)(CO)(P(T)BU(2)ME)(2)

In acetonitrile, the 16-electron species Ru(C(2)Ph)(2)(CO)(P(t)Bu(2)Me)(2) (1) and Ru(CHCHPh)-(C(2)Ph)(CO)(P(t)Bu(2)Me)(2) (2) exist as the corresponding 18-electron acetonitrile adducts. A single-crystal X-ray structure determination showed 1 to be square pyramidal with apical CO and the two acetylide ligands to be trans to each other. Crystal data (-90 degrees C): a = 9.765(6) Angstrom, b = 15.786(10) Angstrom, c = 11.239(6) Angstrom, beta = 99.87(3)degrees with Z = 2 in space group P2(1). The complexes undergo overall two-electron oxidation at 0.28 and 0.10 V vs Cp(2)Fe/Cp(2)Fe(+), respectively. In dichloromethane 1 and 2 underwent 2-electron oxidations at 0.20 and 0.15 V. The lower oxidation potential of 2 compared to 1 is interpreted as an effect of the more electron-donating vinyl ligand. The electrochemical and chemical oxidations result in the intramolecular elimination of [PhC(2)](2) from 1 and PhC(2)CHCHPh from 2. In acetonitrile, [Ru(CO)(NCMe)(3)(P(t)Bu(2)Me)(2)](BF4)(2) (3(BF4)(2)) is formed as the main Ru-containing product. The main organometallic product in dichloromethane appears to exist as a Ru(CO)(L)2(n+) (n = 1, 2) fragment, possibly stabilized by interaction with solvent and/or counterion BF4-. A mechanistic and kinetic investigation of the elimination reactions by derivative cyclic voltammetry (DCV) showed the reductive eliminations from 1 and 2 to be first-order in 1(+) and 2(+). The DVC analysis provided kinetic parameters for the reaction of 1(+) in acetonitrile and dichloromethane and for the reaction of 2(+) in MeCN. Oxidation of 1 in acetonitrile gave k(O degrees C) = 0.74 s(-1), Delta H double dagger = 74.1(1.7) kJ/mol, and Delta S double dagger = 5.9(5.4) J/(K mol) for the elimination from 1(+), whereas the analysis in dichloromethane gave k(0 degrees C) = 0.93 s(-1), Delta H double dagger = 76.1(3.3) kJ/mol, and Delta S double dagger = 8.1(11.7) J/(K mol). For 2 in acetonitrile, k(O degrees C) = 0.89 s(-1), Delta H double dagger = 61.9(5.4) kJ/mol, and Delta S double dagger = -6.4(20.1) J/(K mol).