Cataloguing a renaissance in late transition metal PCcarbeneP pincer complexes

Abstract

The emergence of the PCP pincer ligand as a platform to enhance or allow challenging bond activations and catalysis is an important development in coordination chemistry. Within the sub-classes of PCP pincer ligands, PCcarbeneP pincer ligands (featuring a central carbene donor) have lagged in their development, with relatively few reports of such ligands in the 20th century, despite their discovery shortly after the seminal report of the first aryl based PCP pincer ligand. However, the last 10–15 years has seen renewed activity and multiple reports concerning PCcarbeneP pincer ligands. Practical solutions to problems concerning the kinetic stability of and synthetic access to PCcarbeneP ligands has allowed these ligands to be installed on metals from group 8, 9 and 10, and most importantly, on first row transition metals iron, cobalt and nickel. Further, the expansion of examples containing the PCcarbeneP ligand has allowed discovery of the many unique facets of reactivity this ligand platform offers to metal complexes. These result in the ability of the PCcarbeneP pincer complexes to activate E–H (E = H, C, Si, B, N, O), S–S, N-O, CC, CO, CN, CS, C≡N and C≡C bonds through 1,2-addition and [2+2] addition, stabilize a number of formal metal oxidation states, partake in frustrated Lewis pair chemistry and sequester ligands to generate vacant metal coordination sites. Part of the diversity of reactivity seen in PCcarbeneP pincer complexes can be attributed to the ambiphilic nature of the carbene position, allowing electrophilic, radical and nucleophilic character. This review aims to catalogue examples of PCcarbeneP pincer complexes (specifically) and the recent developments in this field.