Catalytic C-H amination of alkanes with sulfonimidamides: silver(I)-scorpionates vs. dirhodium(II) carboxylates

The silver complex [Tp∗,BrAg]2 (Tp∗,Br: hydrotris(4-bromo-3,5-dimethyl)pyrazolyl borate) and the rhodium complex Rh2(S-nta)4 (nta: N-(1,8-naphthoyl)-alanine) are competent catalysts for C-H bond functionalization by nitrene insertion. Both complexes display similar catalytic activity for the functionalization of benzylic C-H bonds, although the silver derivative does not provide the very high diastereoselection induced by the rhodium complex. On the other hand, when starting from 5 equiv of alkanes, such as pentane and other C6-C8 branched non-activated hydrocarbons, it is the silver catalyst that promotes the amination of the C-H bonds with yields of up to 70%, higher than those provided by the rhodium counterpart. When available, the tertiary C-H bonds of the substrate are preferentially derivatized, as a consequence of a stepwise mechanism in which carbon-centered radicals are involved.