Photoinduced Se-C insertion following photolysis of (η5-C4H4Se)Cr(CO)3.: A picosecond and nanosecond time-resolved infrared, matrix isolation, and DFT investigation

The photochemistry of (eta(5)-C4H4Se)Cr(CO)(3) was investigated by matrix isolation, time-resolved infrared spectroscopy, and steady-state photochemical methods. Density functional theory (DFT) was used to assist in the identification of the photoproducts. Irradiation (lambda(exc) = 406 nm) of (eta(5)-C4H4Se)Cr(CO)(3) in either an Ar or CH4 matrix at 20 K produced the selenophene ring-opened insertion product (C,SeC4H4Se)Cr(CO)(3). Further irradiation of this matrix produced the CO-loss species (C,Se-C4H4Se)Cr(CO)(2). Pulsed irradiation at 400 urn produced the CO-loss species (eta(5)-C4H4Se)Cr(CO)(2)(S) in n-heptane (S) along with the insertion products (C,Se-C4H4Se)Cr(CO)(3) and (C,Se-C4H4Se)Cr(CO)(2), both of which may have triplet character. Time-resolved measurements on the microsecond time scale confirmed that the CO-loss species (eta(5)-C4H4Se)Cr(CO)(2)(S) reacts with CO (k(2) = 5.8 x 10(6) dm(3) mol(-1) s(-1) at 298 K), while (C,Se-C4H4Se)Cr(CO)(3) and (C,Se-C4H4Se)Cr(CO)(2) do not react on this time scale. DFT calculations provide an explanation of the stability of the triplet (C,Se-C4H4Se)Cr(CO)(3) species in terms of a chromaselana-benzene structure, which is consistent with previously observed metal insertion into coordinated selenophene ligands.