Ruthenated acetonitrile: Unusual Bronsted acidity of a polar Aprotic solvent

Addition of acetonitrile to the complex [Ru(eta(5)-indenyl)(PR2)(PPh3)] (1) gives the unusual metalation product [Ru(eta(5)-indenyl)(CH2CN)(HPR2)(PPh3)] (2), which has been structurally characterized. This reaction clearly demonstrates high Bronsted basicity at the terminal phosphido ligand in 1. P-31{H-1} NMR studies show that less acidic N-donor solvents simply disrupt the Ru-P pi-bond in 1 to give adducts [Ru(eta(5)-indenyl)(L)(HPR2)(PPh3)] (L = benzonitrile (6) or pyridine (7)), which are in equilibrium with I and free L. The analogous acetonitrile adduct (4) was observed by NMR at 240 K during the formation of 2, but is,quickly replaced by 2 at higher temperatures. NMR studies of an alternate route to the metalated complex 2, starting from the cationic N-bound acetonitrile adduct [Ru(eta(5)-indenyl)(NCCH3)(HPCY2)(PPh3)][PF6] (3a), along with the demonstrated lability of the benzonitrile and pyridine adducts, suggest that the metalation of acetonitrile by I proceeds via an intermolecular C-H addition across the Ru=P double bond, rather than the intramolecular C-H activation of N-bound acetonitrile. This is confirmed by the observation, by P-31{H-1} NMR, of multiple product isotopomers in the reaction of I with a 1:1 mixture of d(3)- and d(0)-acetonitrile. O-Donor solvents also deprotonated by 1 include water, alcohols, and acetone, which give the complexes [Ru(eta(5)-indenyl)(X)(HPCy2)(PPh3)], where X = OR (8), CH2(=O)CH3 (10).