Stereoelectronic Effects Characterizing Nucleophilic Carbene Ligands Bound to the Cp*RuCl (Cp* = η⁵-C₅Me₅) Moiety:  A Structural and Thermochemical Investigation

Abstract

The reaction of [Cp*RuCl] 4 ( 1 ) with carbene ligands affords unsaturated Cp*Ru(L)Cl [Cp* = η 5 -C 5 Me 5; L = 1,3-R 2 -imidazol-2-ylidene [R = cyclohexyl (ICy, 2 ); 4-methylphenyl (ITol, 3 ); 4-chlorophenyl (IpCl, 4 ); adamantyl (IAd, 5 )] and 4,5-dichloro-1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMesCl, 6 )] complexes 2 − 6 in high yield. Solution calorimetric investigations of this series provides a measure of the electron donor properties of all ligands, and comparisons are made with IMes [1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene] and the widely used PCy 3 . Structural information from single X-ray studies for complexes 2, 3, 5, 6, Cp*Ru(IMes)Cl ( 7 ), Cp*Ru(PCy 3 )Cl ( 8 ), and Cp*Ru(P i Pr 3 )Cl ( 9 ) permits a quantitative treatment of steric parameters associated with these ligands.