PHOSPHINE SUBSTITUTION IN INDENYLDIENYLRUTHENIUM AND CYCLOPENTADIENYLRUTHENIUM COMPLEXES - EFFECT OF THE ETA(5) LIGAND IN A DISSOCIATIVE PATHWAY

The indenyl complex [RuCl(eta(5)-C9H7)(PPh(3))(2)] (1) reacts with mon odentate (L: PMePh(2), PMe(2)Ph, PMe(3)) or bidentate [L-L: Ph(2)PCH(2 )PPh(2) (dppm), Ph(2)(CH2)(2)PPh(2) (dppe)] phosphines to give monosub stituted [RuCl(eta(5)-C9H7(PPh(3))(L)], bisubstituted [RuCl(eta(5)-C9H 7)(L)(2)], or chelated complexes [RuCl(eta(5)-C9H7)(L-L)] in toluene o r tetrahydrofuran. The corresponding cyclopentadienyl complex [RuCl(et a(5)-C5H5)(PPh(3))(2)] (2) reacts similarly, at higher temperatures or longer reaction times. In refluxing toluene, PMe(3) and dppm give ion ic products [Ru(eta(5)-C9H7)(L)(3)]Cl. The kinetics of PPh(3) substitu tion by PMePh(2) and PMe(2)Ph in tetrahydrofuran yield first-order rat e constants that are independent of the concentration or the nature of phosphine. Rate decrease in the presence of added PPh(3) or saturatio n behavior at high [PPh(3)] indicates that the reaction proceeds by a dissociative mechanism, in which extrusion of PPh(3) is rate determini ng. Kinetics for the reaction with PMePh(2) in the temperature range 1 2-40 degrees C for the indenyl and 20-50 degrees C for the cyclopentad ienyl complex give the following activation parameters: Delta H double dagger = 26 +/- 1 kcal mol(-1) and Delta S double dagger = 11 +/- 2 c al mol(-1) K-1 for 1 and Delta H double dagger = 29 +/- 1 kcal mol(-1) and Delta S double dagger = 17 +/- 2 cal mol(-1) K-1 for 2. Complex 1 is 1 order of magnitude more reactive than 2, indicating more efficie nt stabilization of 16-electron intermediates RuCl(eta(5)-ligand)(PPh( 3)) by the indenyl group. Cyclic voltammetry measurements for [RuCl(et a(5)-ligand)(L)(2)] in dichloromethane indicate that indenyl or pentam ethylcyclopentadienyl complexes are oxidized at lower potentials than cyclopentadienyl complexes. Kinetics and electrochemistry suggest that indenyl is electron donating toward the metal fragment, with respect to cyclopentadienyl.