Time-Resolved IR Characterization of cis- and trans- in n-Heptane Solution: The Solvent as a Token Ligand in Short-Lived Reaction Intermediates

Article abstract of DOI:10.1021/ja00248a015

Time-resolved IR spectroscopy is used to identify the cis (6) and trans (5) isomers of (L = PPh3, P(O-i-Pr)3 and P(OEt)3, (s) = solvent) as the major primary photoproducts of the photolysis of LW(CO)5 (2) and cis-(pip)LW(CO)4 (3) (pip = piperidine) in n-heptane solution at room temperature.Matrix isolation experiments in solid Ar at 20 K with (PPh3)W(CO)5 help with the interpretation of these time-resolved spectra.In heptane solution, for each L, the cis isomer (6) is shorter lived than the trans (5), and there is no evidence for thermal interconversion of the two isomers, which react with CO at different rates.Intermediates with bulky ligands react with CO faster than those with sterically less demanding ligands.For all L, both isomers react with CO faster than does (4), the intermediate generated by flash photolysis of W(CO)6 under similar conditions.All of these formally unsaturated species appear to be solvated even in n-heptane solution, to give pseudooctahedral quasicoordination compounds .The term Token Ligand is proposed to signify this specific interaction of a solvent molecule with an otherwise vacant coordination site in reaction intermediates.