sp3 C-H and sp2 C-H agostic ruthenium complexes:: a combined experimental and theoretical study

Halide abstraction from the 18 electron Ru(II) complex RuCl(CO)(2)[2,6-(CH2P'Bu-2)(2)C6H3] (2) with AgPF6 results in the exclusive formation of the cationic complex {Ru(CO)(2)[2,6-(CH2P'Bu)(2)C6H3]}+PF6-(3). The molecular structures of 2 and 3 were determined by complete single-crystal diffraction studies. X-ray crystallographic analysis of 3 reveals that the "open" coordination site is occupied by an agostic interaction between the metal center and an sp(3) C-H bond of a tert-butyl substituent. DFT gas phase calculations (B97-1/SDD) show the necessity of two sterically demanding tert-butyl substituents on one P donor atom for the agostic interaction to occur. The reaction of 3 with H-2 results in the quantitative conversion to {Ru(H)(CO)(2)[2,6-((CH2PBu2)-Bu-t)(2)C6H4]}+PF6- (4) where the aromatic C-ipso-H bond is eta(2)-coordinated to the metal center. Treatment of the agostic complex 4 with Et3N results in the formation of the neutral complex Ru(H)(CO)(2)[2,6-((CH2PBu2)-Bu-t)(2)C6H3] (5). The mechanistic details of 3 + H-2 --> 4 were investigated by DFT calculations at the B97-1/SDB-cc-pVDZ//B97-1/SDD level of theory. (C) 2003 Elsevier B.V. All rights reserved.