Sterically Demanding Ag<sup>I</sup> and Cu<sup>I</sup> N‐Heterocyclic Carbene Complexes: Synthesis, Structures, Steric Parameters, and Catalytic Activity
Alejandro Cervantes‐Reyes, Frank Röminger, A. Stephen K. Hashmi
Abstract
Abstract The synthesis and full characterization of new air‐stable Ag I and Cu I complexes bearing structurally bulky expanded‐ring N‐heterocyclic carbene (erNHC) ligands is presented. The condensation of protonated NHC salts with Ag 2 O afforded a collection of Ag I complexes, and their first use as ligand transfer reagents led to novel isostructural Cu I or Au I complexes. In situ deprotonation of the NHC salts in the presence of a copper(I) source, provides a library of new Cu I complexes. The solid‐state structures feature large N ‐C NHC ‐N angles (118–128°) and almost identical angles between the aryl groups on the nitrogen atoms and the plane of the N ‐C‐N unit of the carbene (i.e. torsion angles close to 0°). Among the steric parameters, the percent buried volume (% V bur ) values span easily in the 50–57 % range, and that one of (9‐Dipp)CuBr complex (% V bur =57.5) overcomes to other known erNHC–metal complexes reported to date. Preliminary catalytic experiments in the copper‐catalyzed coupling between N ‐tosylhydrazone and phenylacetylene, afforded 76–93 % product at the 0.5–2.5 mol % catalyst loading, proving the stability of Cu I erNHC complexes at elevated temperatures (100 °C).