14-Electron Four-Coordinate Ru(II) Carbyl Complexes and Their Five-Coordinate Precursors:  Synthesis, Double Agostic Interactions, and Reactivity

The structure of five-coordinate Ru(II) complexes RuHCl(CO)(P i Pr 3 ) 2, 1, RuCl 2 (CO)(P i Pr 3 ) 2, 2, and Ru(Ph)Cl(CO)(P t Bu 2 Me) 2, 12, are reported. All three of these complexes have square-based pyramid geometry with the strongest σ-donor ligand trans to the vacant site. These 16-electron complexes do not show bona fide agostic interactions. This is attributed to the strong trans influence ligand (H, CO, and Ph) and π-donation of the Cl, which is further supported by the fact that two agostic interactions are present in the Cl - removal product of 12, i.e., the four-coordinate [RuPh(CO)L 2 ]BAr‘ 4 (L = P t Bu 2 Me, Ar‘ = 3,5-C 6 H 3 (CF 3 ) 2 ), 16 . Structural comparison of 16 and 12 reveals that removal of Cl - does not change the remaining ligand arrangements but creates two low-lying LUMOs for agostic interactions, which persist in solution as evidenced by IR spectroscopy. Reactions of 16 with E−H (E = B, C(sp)) bonds cleave the Ru−Ph bond and form Ru−E/H bonds by different mechanisms. The reaction with catecholborane gives [RuH(CO)L 2 ]BAr‘ 4, which further reacts with catecholborane to give [Ru(BR 2 )(CO)L 2 ]BAr‘ 4 . However, the reaction with Me 3 SiCCH undergoes a multistep transformation to give a PhCCSiMe 3 - and Me 3 SiCCH-coupled product, the mechanism of which is discussed. Reaction of RuCl 2 (CO)L 2 with 1 equiv MeLi affords RuMeCl(CO)L 2, 5, which further reacts with MeLi forming RuMe 2 (CO)L 2, 7 . Variable-temperature 13 C{ 1 H} NMR spectra reveal the two methyls in 7 are inequivalent and exchange by overcoming an energy barrier of 6.8 kcal/mol at −30 °C. The chloride of 5 can be removed to give [RuMe(CO)L 2 ]BAr‘ 4 .