Mechanism of Metal-to-Ligand Charge Transfer Sensitization of Olefin Trans-to-Cis Isomerization in the fac-[ReI(phen)(CO)3(1,2-bpe)]+ Cation

Near-UV, largely Re I → phen, bpe metal-to-ligand charge transfer (MLCT) excitation of fac -[Re I (phen)(CO) 3 ( trans -bpe)] + [where phen is 1,10-phenanthroline and bpe is 1,2-bis(4-pyridyl)ethylene] in CH 3 CN results in isomerization at the bpe ligand and formation of fac -[Re I (phen)(CO) 3 ( cis -bpe)] + . Time-resolved absorption and infrared (TRIR) measurements reveal the existence of an intermediate with a lifetime of ∼28 ns ( k = 3.6 × 10 7 s -1 ). According to the results of the transient IR measurements, the intermediate is ligand-based, presumably the olefin-localized twisted triplet 3 p. TRIR measurements in the ν(C C) region point to a significant twisting around the C C bond in 3 p.