Interplay of Weak Interactions: An Iridium(III) System with an Agostic tert -Butyl but a Nonagostic Isopropyl Group

The solid state structure and NMR data of 2-substituted benzoquinoline Ir(III) complexes show that the pendant group G does not necessarily become agostic despite the presence of an available nearby coordination site at the Ir center. Thus for G = t -Bu the agostic structure is observed, but for G = i -Pr, the potentially agostic i -Pr methyl groups point away from the metal. ONIOM(B3PW91/UFF) calculations reproduce the experimental observations and suggest that several ligand−ligand interactions (parallel aromatic stacking and C−H···H−Ir interactions) successfully compete in energy with the agostic interaction. Fluorobenzene (PhF) was found to be a much better noncoordinating polar solvent for synthesis of the t -Bu complex than dichloromethane.