Rearrangement of Iridabenzvalenes to Iridabenzenes and/or η5-Cyclopentadienyliridium(I) Complexes:  Experimental and Computational Analysis of the Influence of Silyl Ring Substituents and Phosphine Ligands

Lithium−halogen exchange of either (Z)-1-phenyl-2-trimethylsilyl- (5a) or (Z)-1,2-bis(trimethylsilyl)-3-(2-iodovinyl)cyclopropene (5b) and addition to either Vaska's or Vaska-type complexes generated iridabenzvalenes (9, 14, 17), iridabenzenes (10, 18), and/or cyclopentadienyl complexes (11, 15, 19), depending on both the substituents on the C5 framework and the phosphine ligands on Ir. Specifically, the reaction of 5a with Vaska's complex afforded a mixture of 9, 10, and 11. Heating this mixture to 75 °C converted 9 and 10 to 11. NMR studies at 75 °C showed that samples of 9 isomerize to 11 in high yield and generate regioisomeric iridabenzene 12 as an intermediate. The reaction of 5b with Vaska's complex produced benzvalene 14 as the sole product. Complex 14 transformed completely to cyclopentadienyliridium complex 15 at 75 °C with no benzene intermediate detectable by NMR spectroscopy. The reaction of cyclopropene 5a with Vaska-type complexes containing alkylphosphines of varying cone angles yielded only benzvalene complexes, which either rearranged or decomposed depending upon the extent of heating. A hybrid-DFT computational study was carried out to investigate reactivity differences between phenyl and trimethylsilyl iridabenzvalenes, regioselective rearrangement of 9, and the unexpected stability/instability of 14/16. These calculations rationalize the sometimes contradictory experimental results.