Small Molecule Activation and Catalytic Reactivity of Rhodium andCobalt Complexes of Bulky PNP Ligands

摘要

Pincer ligands and their transition metal complex have been a focus of organometallicresearch for a long time.Pincer ligands are widely used in catalysis and in small moleculeactivation due to their ability to stabilize reactive species,or to induce new modes of reactivitythat lead to new catalytic reactivity.We have recently reported a new family of bulky,electronrichPNP pincer ligand (Me4PNP~R = 2,6-bis[(dialkylphosphino)propyl]pyridine,R = ~iPr,tBu)where CH2 arms of the pincer ligand are substituted with four Me group,which preventundesired arm deprotonation,increases steric hindrance and create more electron-richcoordination environment as compared to the parent unmethylated PNP ligands.Using theseligands,we have recently been able to stabilize unusual Ni(I) complexes featuring either squareplanar or see-saw geometry controlled by ligand sterics.Very recently,we have reported theuncommon reactivity of nickel methyl and hydride complexes in the presence of strongreductants which lead to either C-H or C-C bond formation at the para-position of the pyridinering.In both cases,no reactivity was observed on the pincer arm.Finally,we have also reportedthe observation of a highly reactive and short-lived Ni superoxo complex.[1]