85221-50-7Relevant articles and documents
Time-Resolved Resonance Raman Spectroscopy and Solution Kinetics of Photogenerated Transients in the Metal-Carbene Complex (OC)5W=C(OMe)Ph
Bell, Steven E. J.,Gordon, Keith C.,McGarvey, John J.
, p. 3107 - 3112 (2007/10/02)
Laser flash photolysis and time-resolved resonance Raman (RR) spectroscopy of the metal carbene complex (CO)5W=C(OMe)Ph (1) in several solvents are reported.Irradiation within the ligand-field (LF) absorption region of 1 with a Q-switched laser pulse (Nd/YAG, 354.7 nm) results in prompt formation of a transient species with a solvent-dependent lifetime in the microsecond range, measured by rapid response spectrophotometric monitoring.The lifetimes measured in Ar-purged or CO-saturated solutions are the same, within the experimental uncertainties.In acetonitrile solution, fast formation of the substitution product cis-(CH3CN)(CO)4W=C(OMe)Ph (2) occurs in addition to the transient species; in the other solvents investigated (CH2Cl2, n-hexane, benzene), formation and decay of the transient are the only observable processes.A CW laser (Ar+, 363.8 and 488 nm) is used to obtain the ground electronic state RR spectra of 1 and pulsed excitation,both single- and two-laser pump and probe, to investigate scattering by photogenerated transients.Several features in the pulsed-laser-excited RR spectra occur with the same relative intensities as corresponding bands in the CW-excited ground-state spectra, suggesting that the enhanced scattering arises through resonance with the same type of electronic transition, W->carbene charge transfer (CT), in both ground-state and transient species.The transient RR spectrum also shows a band at 1105 cm-1, with no ground-state counterpart.A similar feature is observed in the transient spectrum of deuteriated 1, (CO)5W=C(OCD3)Ph, but a higher frequency, 1156 cm-1.By contrast, all other features in this spectrum are shifted by -1 compared to those of the undeuteriated transient.Two-laser studies, in which RR spectra are recorded at several delays (150 ns to 20 μs) between the pump (351 nm, excimer) and probe (405 nm, dye) laser pulses, confirm that scattering is due to the same transient as that monitored in the laser flash photolysis experiments.It is proposed that the transient is the result of rapid intramolecular rearrangement, within the laser pulse duration, in the primary CO-dissociated fragment, , created by LF excitation.The rearrangement is suggested to involve a two-electron, three-center interaction between the W center and the C-H bonds of the OMe group; this impedes access to the vacant coordination site at the metal but allows the carbene ligand skeleton to retain its essential identity, in line with the resonance Raman spectroscopic evidence.A possible scheme for the -independent decay of the transient is presented.The fact brought out by the RR evidence, that the transient can be formed by laser excitation throughout the wavelength range (350-405 nm), suggests the existence of two LF transitions in this wavelength interval.
