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.