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Photoinduced Se−C Insertion Following Photolysis of (η5-C4H4Se)Cr(CO)3. A Picosecond and Nanosecond Time-Resolved Infrared, Matrix Isolation, and DFT Investigation

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journal contribution
posted on 2008-08-11, 00:00 authored by Peter Brennan, Michael W. George, Omar S. Jina, Conor Long, Jennifer McKenna, Mary T. Pryce, Xue-Zhong Sun, Khuong Q. Vuong
The photochemistry of (η5-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 (λexc= 406 nm) of (η5-C4H4Se)Cr(CO)3 in either an Ar or CH4 matrix at 20 K produced the selenophene ring-opened insertion product (C,Se-C4H4Se)Cr(CO)3. Further irradiation of this matrix produced the CO-loss species (C,Se-C4H4Se)Cr(CO)2. Pulsed irradiation at 400 nm produced the CO-loss species (η5-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 (η5-C4H4Se)Cr(CO)2(S) reacts with CO (k2 = 5.8 × 106 dm3 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 chromaselanabenzene structure, which is consistent with previously observed metal insertion into coordinated selenophene ligands.

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