Structural and Thermochemical Studies of Chiral Nucleophilic Carbenes in the Cp*RuCl(L*) (Cp* = η⁵-C₅Me₅; L* = Chiral Nucleophilic Carbene) System

The reaction of [Cp*RuCl]₄ (1) with chiral nucleophilic carbene ligands L = 1,3-R₂-imidazol-2-ylidene (R = (R)-1-cyclohexylethyl ((−)ICMe), (1S,2S,3S,5R)-isopinocamphenyl ((+)IⁱPCamp), (R)-α-methylbenzyl ((+)IBMe)) affords the unsaturated chiral Cp*Ru(L)Cl (Cp* = η⁵-C₅Me₅) complexes 2−4 in high yields. A solution calorimetric investigation in this series clarifies the electron donor properties of these chiral ligands, and comparisons are made with other recently reported nucleophilic carbene complexes and with the widely used PCy₃. Structural information from single-crystal X-ray studies for complexes 2, 3, Cp*Ru(IMes)Cl (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene; 5), Cp*Ru(ICy)Cl (ICy = 1,3-dicyclohexylimidazol-2-ylidene; 6), and Cp*Ru(IAd)Cl (IAd = 1,3-diadamantylimidazol-2-ylidene; 7) allows for an initial quantitative treatment of steric parameters associated with these ligands.