Organic matrix photochemical studies of rhenacarborane nitrosyl complexes. Evidence for linkage isomeric nitrosyl photointermediates

The photochemistry of the rhenacarborane nitrosyl compounds [1,2-R-2-3,3-(CO)(2)-3-NO-closo-3,1,2-ReC2B9H9], where R = H, I, and R = Me, II, has been studied in Nujol and methytetrahydrofuran (MeTHF) frozen glasses at ca. 90 K. Visible light photolysis gives rise to a new species that has been assigned to the isonitrosyl linkage isomer, while ultraviolet photolysis gives rise to a second species believed to be the eta(2)-NO linkage isomer. In MeTHF high-energy photolysis also gives rise to a CO-loss product. Photolysis of derivatives of I, [3-L-3-L'-3-NO-closo-3,1,2-ReC2B9H11], where L = CO, L'-= PMe3, III; L = CO, L'= CNC6H3Me2-2, 6, IV, and L = L' = CNC6H3Me2-2,6, V, all give rise to a photoproduct believed to be the eta(2)-NO Inkage isomer. There was no evidence of the isonitrosyl isomer in these cases. Complexes III and IV also undergo CO loss. Ultraviolet photolysis of [3,3,3-(CO)(3)-closo-3,1,2-RuC2B9H11], VI, in MeTHF results in CO loss and formation of the corresponding [3,3-(CO)(2)-3-MeTHF-closo-3,1,2-RuC2B9H11] derivative. In frozen Nujol, ultraviolet photolysis of VI gives rise to a CO-loss species. Upon visible light back-photolysis or annealing of the sample, this photoproduct gives rise to a second dicarbonyl species of unknown structure.