Diazocarbene precursors

In this chpter, we analyzed electronic factors affecting the mechanism of transition-metal-catalyzed C-H bond alkylation by diazocarbene precursors. We demonstrated that efficient transition-metal-catalyzed alkylation of C-H, C=C, and C=C bonds by diazocarbenes requires a fine balance ... 

On the basis of these analyses, we hypothesized the use of an earth-abundant transition-metal complex containing a non-redox-active metal center and redox-active (non-innocent) ligand as a catalyst. We demonstrated our prediction on [(PDl)Ca(THF)3], where PDI is a non-innocent pyridine-2,6-diimine ligand, and the catalyzed benzyhc (of the MeCH2Ph substrate) C-H bond alkylation by unsubstituted and diphenyl (termed the iio or-(io or)-substituted diazocarbene precursors, N2CH2 and N2CPh2. 

To date, bis(diazomethyl)silanes represent the only precursors to silylene-dicarbenes. It should be noted, however, that the extrusion of N2 from the two diazo functions can occur more or less simultaneously or successively. In the latter case, a diazocarbene is formed in the first place, which is supposed to undergo a fast carbene reaction before the generation of a carbene from the second diazo function occurs. This should be kept in mind for all transformations which are explained mechanistically with the participation of silylene-dicarbenes. There are even examples where only one of the two diazo groups enters carbene chemistry at all (see equations 35 and 36 below). 

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