Cyclopentadienyl Ru(II) Complexes as Highly Efficient Catalysts for the N-Methylation of Alkylamines by Methanol

The ruthenium(II) half-sandwich complex [RuCl(eta(5)-C5H5)(PPh3)(2)] (1) catalyses the reaction between methanol and alkylamines RNH2 or (RRNH)-R-1-N-2 to afford RN(CH3)(2) and (RRNCH3)-R-1-N-2 products, respectively. The reaction is quantitative and generally fast, at the methanol reflux temperature, for a wide spectrum of substrates. Starting from primary amines, the stepwise formation of RN=CH2, RNHCH3, and RN(CH3)(2) has been observed. Both PPh3 and Cl- dissociation from 1 are key-steps in forming the effective catalytic species. The catalytic activity of several half-sandwich neutral or cationic complexes (2-15) related to 1 is also discussed.