Phosphine Substitution in Indenyl- and Cyclopentadienylruthenium Complexes. Effect of the eta5 Ligand in a Dissociative Pathway

The indenyl complex [RuCl(eta5-C9H7)(PPh3)2] (1) reacts with monodentate (L: PMePh2, PMe2Ph, PMe3) or bidentate [L-L: Ph2PCH2PPh2 (dppm), Ph2P(CH2)2PPh2 (dppe)] phosphines to give monosubstituted [RuCl(eta5-C9H7)(PPh3)(L)], bisubstituted [RuCl(eta5-C9H7)(L)2], or chelated complexes [RuCl(eta5-C9H7)(L-L)] in toluene or tetrahydrofuran. The corresponding cyclopentadienyl complex [RuCl(eta5-C5H5)(PPh3)2] (2) reacts similarly, at higher temperatures or longer reaction times. In refluxing toluene, PMe3 and dppm give ionic products [Ru(eta5-C9H7)(L)3]Cl. The kinetics of PPh3 substitution by PMePh2 and PMe2Ph 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 PPh3 or saturation behavior at high [PPh3] indicates that the reaction proceeds by a dissociative mechanism, in which extrusion of PPh3 is rate determining. Kinetics for the reaction with PMePh2 in the temperature range 12-40 °C for the indenyl and 20-50 °C for the cyclopentadienyl complex give the following activation parameters: ¢Hq ) 26 ( 1 kcal mol-1 and ¢Sq ) 11 ( 2 cal mol-1 K-1 for 1 and deltaH ) 29 ( 1 kcal mol-1 and deltaS ) 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(eta5-ligand)(PPh3) by the indenyl group. Cyclic voltammetry measurements for [RuCl(eta5-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