This review is intended to provide an overview of metal carbene insertion reactions into carbon-hydrogen bonds that encompasses both intra-and intermolecular transformations and is focused on reaction selectivity. Since there is convincing theoretical and experimental evidence for the involvement of metal carbenes in these reactions, we will use that terminology, rather than "metal carbenoid" (like a metal carbene), for this transformation. In addition, although popular in current reports, we will not use the terminology "C-H bond activation" to refer to C-H insertion so that clear differentiation can be made between the metal carbene insertion and those reactions in which the metal catalyst forms a complex with a C-H bond, 33,34 activating it for subsequent transformations (Scheme 2). Reaction MechanismA recent theoretical treatment by Nakamura and coworkers 35 confirmed the mechanistic proposal originally advanced by Doyle (Scheme 3) 36 that C-C and C-H bond formation with the carbene carbon occurs as the ligated metal dissociates at the same time but not necessarily to the same degree. 37 Prior to this density functional theory (DFT) calculation, alternate proposals included transfer of hydrogen from the C-H bond to the metal of the metal carbene, Michael P. Doyle was born in Minneapolis, MN. He received his B.S.

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A metal‐free, visible light‐induced [4+2] benzannulation of biaryldiazonium salts with alkynes was developed. With eosin Y as photoredox catalyst, a variety of 9‐substituted or 9,10‐disubstituted phenanthrenes were obtained via a cascade radical addition and cyclization sequence.

In this work, heterogeneous nanocomposite reactions of Al/CuO, Al/Fe2O3 and Al/ZnO systems were characterized using a recently developed T-Jump/time-of-flight mass spectrometer. Flash-heating experiments with time-resolved mass spectrometry were performed at heating rates in the range of ∼105 K/s. We find that molecular oxygen liberated during reaction is an active ingredient in the reaction. Experiments also conducted for neat Al, CuO, Fe2O3, and ZnO powders show that the oxygen are produced by decomposition of oxidizer particles. Mass spectrometric analysis indicates that metal oxide particles behave as an oxygen storage device in the thermite mixture and release oxygen very fast to initiate the reaction. A clear correlation is observed between the capability of oxygen release from oxidizing particles and the overall reactivity of the nanocomposite. The high reactivity of the Al/CuO mixture can be attributed to the strong oxygen release from CuO, while Fe2O3 liberates much less oxygen and leads to moderate reactivity, and ZnO’s poor oxygen release capability caused the Al/ZnO mixture to be completely not reacting, even though the reaction is overall exothermic. It is likely that the role of the oxygen species is not only as a strong oxidizer but also an energy propagation medium that carries heat to neighboring particles.

A Pd-catalyzed three-component reaction of N-tosylhydrazone, terminal alkyne, and aryl halide follows a mechanism involving a sequence of Pd carbene migratory insertion-transmetalation-reductive elimination, leading to the formation of one sp(2)-sp(3) C-C bond and one sp-sp(3) C-C bond.