85221-50-7Relevant academic research and scientific papers
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.
Photochemistry of >. Formation of Alkyne-Carbene Complexes and Studies of Their Decomposition Reactions
Foley, Henry C.,Strubinger, Leslie M.,Targos, Tom S.,Geoffroy, Gregory L.
, p. 3064 - 3073 (2007/10/02)
The photochemistry of > has been examined and been shown to involve CO loss as the only detectable photoreaction.Irradiation in acetonitrile solution leads smoothly to the formation of > in quantitative yield.The 366 and 313-nm quantum yields for disappearance of > in CH3CN solution are 0.009 and 0.011, respectively, but the quantum yield drops to -4 at 436 nm, even though the complex absorbs strongly at the latter wavelength.The lowest intense absorption band (λmax 402 nm) (εmax 10560 L mol-1 cm-1) has been assigned as a W -> carbene(?*) charge-transfer transition with ligand field bands lying at higher energy.The low-lying W -> carbene charge-transfer state is inactive with respect to CO loss, with the latter occuring from ligand field excited states.Low-temperature photolysis in the presence of PhC=*CPh, MeC=*CPh, MeC=*CMe, PhC=*CH, and n-BuC=*CH leads to spectroscopically observable alkyne-carbene adducts, with the diphenylacetylene complex > isolated as a crystalline solid.None of the alkyne adducts are stable at 25 deg C in solution, and they decompose to give products that depend markedly upon the nature of the alkyne.With terminal alkynes, only polyacetylenes form, whereas the PhC=*CPh and PhC=*CMe adducts decay exclusively to form 1-methoxy-2,3-diphenylindene and 1-methoxy-2-methyl-3-phenylindene, respectively.The MeC=*CMe adduct leads to both poly-2-butyne and 1-methoxy-2,3-dimethylindene.
