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)((PPr3)-Pr-i)(2), 1, RuCl2(CO)((PPr3)-Pr-i)2, 2, and Ru(Ph)Cl(CO)((PBu2Me)-Bu-i)2, 12, are reported. All three of these complexes have square-based pyramid geometry with the strongest sigma-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 ct-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 = (PBu2Me)-Bu-i, Ar' = 3,5-C6H3(CF3)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(BR2)(CO)L-2]BAr'4. However, the reaction with Me3SiCCH undergoes a multistep transformation to give a PhCCSiMe3- and Me3SiCCH-coupled product, the mechanism of which is discussed. Reaction of RuCl2(CO)L-2 with 1 equiv MeLi affords RuMeCl(CO)L-2, 5, which further reacts with MeLi forming RuMe2(CO)L-2, 7. Variable-temperature C-13(H-1) NMR spectra reveal the two methyls in 7 are inequivalent and exchange by overcoming an energy barrier of 6.8 kcal/mol at -30 degrees C. The chloride of 5 can be removed to give [RuMe(CO)L-2]BAr'4.