IPr<sup>#</sup> ComplexesHighly-Hindered,\nSterically-Bulky Cu(I) and Ag(I) N‑Heterocyclic Carbenes: Synthesis,\nCharacterization, and Reactivity

Metal–N-heterocyclic carbene (M–NHC) complexes\nare\nwell-known as an important class of organometallic compounds widely\nused in transition-metal catalysis. Taking into account that the steric\nhindrance around the metal center is one of the major effects in M–NHC\ncatalysis, the development of new, sterically hindered M–NHC\ncomplexes is an ongoing interest in this field of research. Herein,\nwe report the synthesis and characterization of exceedingly sterically\nhindered, well-defined, air- and moisture-stable Cu(I) and Ag(I) complexes,\n[Cu(NHC)Cl] and [Ag(NHC)Cl], in the recently discovered IPr<sup>#</sup> family of ligands that hinge upon modular peralkylation of anilines.\nThe complexes in both the BIAN and IPr families of ligands are reported.\nX-ray crystallographic analyses and computational studies were conducted\nto determine steric effects, Frontier molecular orbitals, and bond\norders. The complexes were evaluated in the model hydroboration of\nthe alkynes. We identified [Cu(BIAN–IPr<sup>#</sup>)Cl] and\n[Ag(BIAN–IPr<sup>#</sup>)Cl] as highly reactive catalysts with\nthe reactivity outperforming the classical IPr and IPr*. Considering\nthe attractive features of well-defined Cu(I)–NHC and Ag(I)–NHC\ncomplexes, this class of sterically bulky yet wingtip-flexible complexes\nwill be of interest for catalytic processes in various areas of organic\nsynthesis and catalysis.