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-R-2-imidazol-2-ylidene (R = (R)-1-cyclohexylethy1 ((-)ICMe), (1S,2S,3S,5R)-isopinocamphenyl ((+)-I(i)PCamp), (R)-alpha -methylbenzyl ((+)IBMe)) affords the unsaturated chiral Cp*Ru(L)Cl(Cp* = eta (5)-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.