Achieving (quasi)-monocoordination in metal complexes with an exceptionally bulky carbene ligand

Bulky N-heterocyclic carbenes (NHCs) are powerful tools for controlling the coordination environment and reactivity at inorganic elements. Herein, we report an exceptionally bulky NHC, ^BnITr (^BnITr = [(C₆H₄){NCPh₃}₂C:]), which features a percent buried volume (%V _bur) that exceeds 60%. The steric and electronic properties of ^BnITr were elucidated through a combined experimental and computational study focused on selected silver, gold, and rhodium complexes. The structural impact of the benzylated backbone in ^BnITr leads to the positioning of phenyl rings within the flanking N-trityl (CPh₃, Tr) groups in close proximity to the carbene donor center, enabling the isolation/stabilization of hitherto elusive examples of (quasi)-monocoordinated lithium and gallium(i) cations. Attempts to generate the one-coordinate Pd(0) complex, [^BnITr-Pd], led to an unusual redox-triggered ligand activation/-CPh₃ group migration to palladium.