The photochemistry of cyclopentadienyl platinum carbonyl dimers: characterization of [Pt2(µ-CO)(η5-C5R5)2](R = H or Me) using matrix isolation and fast time-resolved infrared spectroscopy

Abstract

U.v. photolysis of [{Pt(CO)(η⁵-C₅H₅)}₂], (1a), or [{Pt(CO)(η⁵-C₅Me₅)}₂], (1b), isolated in Ar, N₂, or CO matrices at 20 K causes ejection of a CO group and formation of [Pt₂(µ-CO)(η⁵-C₅H₅)₂], (2a), and [Pt₂(µ-CO)(η⁵-C₅Me₅)₂], (2b), respectively. Isotopic enrichment with ¹³CO shows that these photoproducts contain only one bridging CO group. Photolysis using plane-polarised light demonstrates that this CO group occupies a position bridging the Pt–Pt bond symmetrically. Both (2a) and (2b) have strong absorptions in the visible region. Irradiation with light corresponding to these absorptions causes recombination with the photoejected CO to regenerate (1a) or (1b). The unsaturated species, (2a) and (2b), have also been identified at room temperature in solution, using time-resolved i.r. spectroscopy. They are found to have lifetimes in excess of 2 ms under these conditions, even in the presence of CO or CH₃CN. Prolonged u.v. photolysis also causes homolysis of the Pt–Pt bond of (1a) or (1b) in CO matrices, the resultant photoproduct being [Pt(CO)₄].