Bis-N-heterocyclic Carbene Aminopincer Ligands Enable High Activity in Ru-Catalyzed Ester Hydrogenation.

Bis-N-heterocyclic carbene (NHC) aminopincer ligands were successfully applied for the first time in the catalytic hydrogenation of esters. We have isolated and characterized a well-defined catalyst precursor as a dimeric [Ru2(L)2Cl3]PF6 complex and studied its reactivity and catalytic performance. Remarkable initial activities up to 283,000 h(-1) were achieved in the hydrogenation of ethyl hexanoate at only 12.

Mechanistic insights into C-H amination via dicopper nitrenes.

We examine important reactivity pathways relevant to stoichiometric and catalytic C-H amination via isolable β-diketiminato dicopper alkylnitrene intermediates {[Cl2NN]Cu}2(μ-NR). Kinetic studies involving the stoichiometric amination of ethylbenzene by {[Cl2NN]Cu}2(μ-N(t)Bu) (3) demonstrate that the terminal nitrene [Cl2NN]Cu═N(t)Bu is the active intermediate in C-H amination. Initial rates exhibit saturation behavior at high ethylbenzene loadings and an inverse dependence on the copper species [Cl2NN]Cu, both consistent with dissociation of a [Cl2NN]Cu fragment from 3 prior to C-H amination.

Reaction of Cu(I) with dialkyl peroxides: Cu(II)-alkoxides, alkoxy radicals, and catalytic C-H etherification.

Kinetic analysis of the reaction of the copper(I) β-diketiminate [Cl(2)NN]Cu ([Cu(I)]) with (t)BuOO(t)Bu to give [Cu(II)]-O(t)Bu (1) reveals first-order behavior in each component implicating the formation of free (t)BuO(•) radicals. Added pyridine mildly inhibits this reaction indicating competition between (t)BuOO(t)Bu and py for coordination at [Cu(I)] prior to peroxide activation. Reaction of [Cu(I)] with dicumyl peroxide leads to [Cu(II)]-OCMe(2)Ph (3) and acetophenone suggesting the intermediacy of the PhMe(2)CO(•) radical.

Catalytic C-H amination with aromatic amines.

Aniline joins the club: A β-diketiminato copper(I) catalyst enables C-H amination of anilines employing low catalyst loadings to preclude oxidation to the diazene ArN=NAr. Electron-poor anilines are particularly resistant towards diazene formation and participate in the amination of strong and unactivated C-H bonds. N-alkyl anilines also take part in C-H amination.