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 (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 (λ_exc= 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.