Phosphine substitution in indenyl- 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 monodentate (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 monosubstituted [RuCl(eta(5)-C9H7(PPh(3))(L)], bisubstituted [RuCl(eta(5)-C9H7)(L)(2)], or chelated complexes [RuCl(eta(5)-C9H7)(L-L)] in toluene or tetrahydrofuran. The corresponding cyclopentadienyl complex [RuCl(eta(5)-C5H5)(PPh(3))(2)] (2) reacts similarly, at higher temperatures or longer reaction times. In refluxing toluene, PMe(3) and dppm give ionic products [Ru(eta(5)-C9H7)(L)(3)]Cl. The kinetics of PPh(3) substitution by PMePh(2) and PMe(2)Ph in tetrahydrofuran yield first-order rate constants that are independent of the concentration or the nature of phosphine. Rate decrease in the presence of added PPh(3) or saturation behavior at high [PPh(3)] indicates that the reaction proceeds by a dissociative mechanism, in which extrusion of PPh(3) is rate determining. Kinetics for the reaction with PMePh(2) in the temperature range 12-40 degrees C for the indenyl and 20-50 degrees C for the cyclopentadienyl complex give the following activation parameters: Delta H double dagger = 26 +/- 1 kcal mol(-1) and Delta S double dagger = 11 +/- 2 cal 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 efficient stabilization of 16-electron intermediates RuCl(eta(5)-ligand)(PPh(3)) by the indenyl group. Cyclic voltammetry measurements for [RuCl(eta(5)-ligand)(L)(2)] in dichloromethane indicate that indenyl or pentamethylcyclopentadienyl 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.