Silver(I) complexes of fluorinated scorpionates: Ligand effects in silver catalyzed carbene insertion into C–H bonds in alkanes

Activation of C–H bonds of hydrocarbons via intermolecular carbene insertion has been investigated using tris(pyrazolyl)boratosilver(I) catalysts [MeB(3-(CF3)Pz)3]Ag(C2H4), [MeB(3-(C2F5)Pz)3]Ag(C2H4) and [HB(3,5-(CF3)2Pz)3]Ag(C2H4). Cyclopentane, 2-methylbutane, and 2,3-dimethylbutane were used as substrates. Carbenes derived from ethyl and tert-butyl diazoacetates have effectively been inserted into tertiary, secondary, as well as primary C–H bonds of hydrocarbons at room temperature using these catalysts. Tertiary C–H bonds in these substrates get preferentially activated over secondary C–H followed by primary C–H bonds. However, it is possible to increase the amount of primary C–H bond activated product by utilizing catalysts with increasingly acidic silver sites and sterically bulky tris(pyrazolyl)borate ligands. The carbene insertion into primary C–H bonds increases in the order: [MeB(3-(CF3)Pz)3]Ag(C2H4) < [MeB(3-(C2F5)Pz)3]Ag(C2H4) < [HB(3,5-(CF3)2Pz)3]Ag(C2H4). The carbene derived from tert-butyl diazoacetate with these catalysts shows slightly lower selectivity for primary C–H bonds compared to the ethyl diazoacetate-based carbene.