Controlled electronic tuning of PCP pincer complexes is an area of increasing interest, and several literature examples underpin how the nature and hybridization of the coordinating carbon atom can alter the reactivity and catalytic activity.   We have previously reported on the coordination behaviour of cyclohexyl based pincer ligands. Here we report that the reactivity of iridium pincer complexes with cyclohexane backbone also significantly differs from that of their benzene-based counterparts. The PC(sp3)P environment of the ligand stabilizes the Ir(V) oxidation state, and because of the presence of a hydrogen atom in the a-position the pincer ligand often demonstrates non-innocent behaviour. While this limits the thermal stability of the dihydride species, which results in lower activity in catalytic dehydrogenaton compared to benzene-based compounds, it is also responsible for some unique C-H activations. At elevated temperatures PCyP ligand undergoes aromatization, initiated by formation of an iridium carbene complex. Interestingly though, the iridium carbene complex also undergoes further C�H activation resulting in the first example of an intramolecular coupling reaction where two aliphatic carbons are coupled to give an olefin while extruding two molecules of dihydrogen.   As opposed to palladium and platinum, nickel undergoes cyclometallation with a cyclohexyl phosphinite ligand forming the POCsp3OPNi-Cl complex. This complex can be converted to the corresponding methyl, hydoxide and hydride complexes, which are unusally stable and reactive towards a number of small molecules.

Iridium and nickel pincer complexes with saturated frameworks: Dehydrogenation and C�C bond formation

248th National Meeting (2014)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.