ISSN:
0947-6539
Keywords:
homolytic cleavage
;
organometallic compounds
;
photochemistry
;
rhenium complexes
;
time-resolved spectroscopy
;
Chemistry
;
General Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
MLCT excitation of the complexes [Re(R)(CO)3(α-diimine)] (R = Me, Et, benzyl (Bz); α-diimine = iPr-PyCa, R′-DAB) results in the homolysis of the Re-R bond leading to the formation of radicals R. and [Re(CO)3(α-diimine)]. as primary photoproducts. The quantum yield of this photoprocess is dependent on the alkyl group used. For R = Me, the quantum yield is low (10-2) and depends on the temperature and excitation wave-length, whereas for R = Et and Bz the quantum yield is near unity and independent of T and λexc. The reaction is shown to proceed via a σ(Re-R)π* excited state that is rapidly (〈 20 ps) populated by a nonradiative transition from the optically excited MLCT state. Time-resolved IR and UV/Vis absorption spectra studied in the ns-μs and ps-μs time domains, respectively, show that the σπ* excited state is rather long-lived (τ ≈ 250 ns) in noncoordinating solvents; the dissociation of the Re-R bond from this state is strongly accelerated by polar or coordinating solvents (τσπ*〈 20 ps). The σπ* excited state is spectroscopically characterized by a (presumably σπ* → MLCT) transition at approximately 500 nm and by CO stretching frequencies closely resembling their ground-state values. The relative energies of the MLCT and reactive σπ* states, controlled by the nature of the alkyl lig-and, determine the photoreactivity of the complexes.
Additional Material:
8 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/chem.19960020216
