Regioselective Formation of β-Alkyl-α-phenyliridabenzenes via Unsymmetrical 3-Vinylcyclopropenes: Probing Steric and Electronic Influences by Varying the Alkyl Ring Substituent

The synthesis of unsymmetrical (Z)‐1‐alkyl‐3‐(2‐iodovinyl)‐2‐phenyl‐1‐cyclopropenes (R=Me (8 a), Et (8 b), iPr (8 c), and tBu (8 d)) and their reactions with Vaska's complex [Ir(CO)Cl(PPh3)2] and its trimethylphosphine analogue [Ir(CO)Cl(PMe3)2] were investigated. Iridabenzvalene (13/20), iridabenzene (14/21), and/or η5‐cyclopentadienyliridium complexes (15/22) were obtained in modest yields and were fully characterized by spectroscopic means. X‐ray structural data was secured for iridabenzvalene 13 d and iridabenzenes 14 a,b,d. Whereas iridabenzenes 14 a–c were stable at 75 °C for 48 h, 14 d, which possesses a bulky tBu group, rearranged cleanly to cyclopentadienyliridium 15 d at 50 °C over 15 h and displayed first‐order kinetics. The influence of the alkyl substituent on the mechanisms of iridacycle generation, isomerization, and iridabenzene regioselectivity is discussed. More complicated than originally thought, the reactions of unsymmetrical (Z)‐1‐alkyl‐3‐(2‐iodovinyl)‐2‐phenyl‐1‐cyclopropenes with Vaska's complex and its trimethylphosphine analogue led to the formation of iridabenzvalenes, iridabenzenes, and/or η5‐cyclopentadienyliridium complexes. In the case of the iridabenzvalenes, their valence isomerization to the corresponding iridabenzenes proceeds in a highly regioselective manner.