Coordination, Agostic Stabilization, and C-H Bond Activation of N-Alkyl Heterocyclic Carbenes by Coordinatively Unsaturated Ruthenium Hydride Chloride Complexes

摘要

The products formed upon reaction of Ru(PPh3)(3)HCl and [Ru((PPr3)-Pr-i)(2)HCl](2) with the N-heterocyclic carbenes 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene ((IPr2Me2)-Pr-i, 1) and 1,3-diethyl-4,5-dimethylimidazol-2-ylidene (IEt2Me2, 2) proved to be dependent on the phosphine and the N-substituent of the carbene. Thus, Ru(PPh3)(3)HCl reacts with both 1 and 2 at room temperature in CH2Cl2 to give a mixture of products consisting of cis-/trans-PPh3 isomers of the agostic complexes Ru(NHC)(PPh3)(2)HCl (NHC = (IPr2Me2)-Pr-i, 3a/3b; IEt2Me2, 8a/8b), the anagostic species Ru(NHC)(PPh3)(2)HCl (NHC = IiPr(2)Me(2), 4; IEt2Me2, 9) and in the case of (IPr2Me2)-Pr-i the C-H activated complex Ru((IPr2Me2)-Pr-i)(PPh3)(2)Cl (5). Addition of 1 atm of C2H4 to the mixture of 3a/3b, 4, and 5 leads to complete conversion to 5. [Ru((PPr3)-Pr-i)(2)HCl](2) reacts with both 1 and 2 to yield only the anagostic complexes Ru(NHC)(PiPr(3))(2)HCl (NHC = (IPr2Me2)-Pr-i), 6; IEtMe2, 10), which on the basis of NMR evidence react with C2H4 to give the doubly C-H activated alkenyl-NHC complexes Ru{eta(2)-C((NPr)-Pr-i)CMeCMeN(CMe=CH)}((PPr3)-Pr-i)(2)Cl (7) and Ru{eta(2)-C(NEt)CMeCMeN(CH=CH)}-((PPr3)-Pr-i)(2)Cl (11). Addition of 1 to Ru((PPr3)-Pr-i)(2)(CO)HCl affords the agostic stabilized monocarbene complex Ru((IPr2Me2)-Pr-i)((PPr3)-Pr-i)(CO)HCl (12) and the tris-carbene species Ru((IPr2Me2)-Pr-i)(3)(CO)HCl (13). Complexes 3a, 4, 5, 6, 8a, 10, 12, and 13 have been structurally characterized.