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-(CH2PtBu2)2C6H3] (2) with AgPF6 results in the exclusive formation of the cationic complex {Ru(CO)2[2,6-(CH2PtBu2)2C6H3]}+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 sp3 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 H2 results in the quantitative conversion to {Ru(H)(CO)2[2,6-(CH2PtBu2)2C6H4]}+PF6− (4) where the aromatic Cipso–H bond is η2-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-(CH2PtBu2)2C6H3] (5). The mechanistic details of 3 + H2 → 4 were investigated by DFT calculations at the B97-1/SDB-cc-pVDZ//B97-1/SDD level of theory.