American Chemical Society
om050600c_si_003.cif (21.58 kB)

Ruthenium Hydride Complexes of 1,2-Dicyclohexylimidazol-2-ylidene

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posted on 2005-11-21, 00:00 authored by Suzanne Burling, Gabriele Kociok-Köhn, Mary F. Mahon, Michael K. Whittlesey, Jonathan M. J. Williams
The mono and bis N-heterocyclic carbene (NHC) complexes Ru(ICy)(PPh3)2(CO)H2 (1) and Ru(ICy)2(PPh3)(CO)H2 (2) (ICy = 1,2-dicyclohexylimidazol-2-ylidene) were isolated from the reaction of Ru(PPh3)3(CO)H2 with ICy at elevated temperature. X-ray crystallography revealed that 1 contains a trans arrangement of the PPh3 ligands with the ICy trans to hydride; in complex 2, the two ICy ligands are cis to one another. Both 1 and 2 undergo H/D exchange with D2, as well as reacting rapidly with CO to give Ru(ICy)(PPh3)(CO)3 (3) and Ru(ICy)2(CO)3 (4). Addition of CO2 to solutions of 2 resulted in insertion into one of the Ru−H bonds to afford both the κ1- and κ2-formate complexes Ru(ICy)2(PPh3)(CO)(κ1-OCHO)H (5) and Ru(ICy)2(CO)(κ2-OCHO)H (6). Addition of CO2 to 1 gave solely Ru(ICy)(PPh3)(CO)(κ2-OCHO)H (7). The product from reaction of ICy with Ru(PPh3)3HCl proves to be solvent dependent, generating two isomers of the mono-NHC complex Ru(ICy)(PPh3)2HCl (8a,b) in dichloromethane but the bis-NHC species Ru(ICy)2(PPh3)HCl (10) in THF. An agostic interaction between Ru and a β-CH2 hydrogen of the ICy ligand is apparent both in the X-ray crystal structure of 8a and also in solution. This interaction is broken upon addition of CO, which yields Ru(ICy)(PPh3)2(CO)HCl (9). The molecular structure of the coordinatively unsaturated species 10 is devoid of any agostic bonding.