Ruthenium(II)-Catalysed Functionalisation of C-H Bonds with Alkenes: Alkenylation versus Alkylation

This chapter describes the recent achievements since 2011 of ruthenium(II)-catalysed transformations of sp(2)C-H bonds of a variety of functional arenes, heterocycles, alkenes and ferrocene derivatives on their reaction with alkenes, either via oxidative dehydrogenation to produce functional alkenes or via formal insertion of alkene into C-H bonds to afford alkylated products. The regioselectivity of ortho C-H bond alkenylation or alkylation is shown to be directed by both strongly and weakly coordinating functional groups from N-heterocycles and bidentate groups to carbonyl-containing groups such as ketone, ester, amide, carbamate and sulfonic acid derivatives. The ruthenium(II) catalysts often based on [RuCl2(p-cymene)](2) or RuCl2(PPh3)(3) derivatives sometimes require the presence of a halide abstractor and an oxidant. The alkenylation of heterocycles will be shown to occur in the presence of base and their alkylation in the presence of proton source to give branched or linear alkylated isomers. Discussion of catalytic mechanism will involve the initial formation of a cyclometallate via C-H bond deprotonation and that of an intermediate resulting from alkene insertion into the Ru-C bond before its evolution to alkenylation or alkylation.