Recent Developments on N-Heterocyclic Carbene Supported Zinc Complexes: Synthesis and Use in Catalysis

The present contribution reviews the synthesis, reactivity, and use in catalysis of NHC–Zn complexes reported since 2013. NHC-stabilized Zn(II) species typically display enhanced stability relative to common organozinc species (such as Zn dialkyls), a feature of interest for the mediation of various chemical processes and the stabilization of reactive Zn-based species. Their use in catalysis is essentially dominated by reduction reactions of various unsaturated small molecules (including CO2), thus primarily involving Zn–H and Zn–alkyl derivatives as catalysts. Simple NHC adducts of Zn(II) dihalides also appear as effective catalysts for the reduction amination of CO2 and borylation of alkyl/aryl halides. Stable and well-defined Zn alkoxides have also been prepared and behave as effective catalysts in the polymerization of cyclic esters/carbonates for the production of well-defined biodegradable materials. Overall, the attractive features of NHC-based Zn(II) species include ready access, a reasonable stability/reactivity balance, and steric/electronic tunability (through the NHC source), which should promote their further development. 1 Introduction 2 NHC-Supported Zinc Alkyl/Aryl Species 2.1 Synthesis 2.2 Reactivity and Use in Catalysis 3 NHC-Supported Zinc Hydride Species 3.1 Synthesis 3.2 Reactivity and Use in Catalysis 4 NHC-Supported Zinc Amido/Alkoxide Species 4.1 Synthesis 4.2 Use in Catalysis 5 NHC-Supported Zinc Dihalide Species 5.1 Synthesis 5.2 Use in Catalysis 6 Other NHC-Stabilized Zn Species 7 Conclusion