Cyclic (alkyl)(amino)carbene (CAAC) ligands: Electronic structure and application as chemically- and redox-non-innocent ligands and chromophores

The chemistry of cyclic (alkyl)(amino) carbene (CAAC) ligands is presented. Their electronic structure is discussed and put into the context of conventional N-heterocyclic carbene (NHC) ligands. Then, we present their ligand-centered reactivity as well as redox- and photochemistry in detail. This includes the coordination chemistry of low-valent transition metal- and main group complexes. Accordingly, an overview regarding the photochemistry with CAAC complexes as well as organic CAAC-scaffolds is given. Further, their chemical non-innocence or rather “ligand cooperativity” is summarized focusing on their capability to reversibly bind hydrides. For selected compounds, specific applications in catalysis and as chromophores (luminophores, respectively) are highlighted.