Development of [CpRu(η 6 -benzylcarbamate)]X salts as two-stage photobase generators

Abstract In order to develop a new class of transition-metal-based, two-stage photobase generators (PBGs), the synthesis, structural characterization, spectroscopic properties and base-generation ability of a series of [CpRu(η 6 -benzylcarbamate)]X salts (X = [PF 6 ] − , [O 3 SCF 3 ] − ) are reported. Treatment of [CpRu(NCMe) 3 ]PF 6 with the N , N -dialkylcarbamate PBGs 2-nitrophenylmethyl N , N -dicyclohexylcarbamate (2NC), 4-nitrophenylmethyl N , N -dicyclohexylcarbamate (4NC) and 3,5-dimethoxyphenylmethyl N , N -dicyclohexylcarbamate (DMC) results in η 6 -complexation of the arene fragment and formation of the corresponding [CpRu(η 6 -benzylcarbamate)]PF 6 salt. The [PF 6 ] − salt, [CpRu(η 6 -DMC)]PF 6 , is converted to the triflate salt (triflate = [O 3 SCF 3 ] −  = [OTf] − ) by treatment with Me 3 SiOTf. The molecular structures of the [CpRu(η 6 -benzylcarbamate)]X salts were determined by X-ray diffraction and varied by the orientation of the carbmamate unit relative to the η 5 -Cp ligand. Experimental UV–Vis data and Time-Dependent DFT calculations suggest that the [CpRu(η 6 -benzylcarbamate)] + cations possess high-energy excitations that potentially render these salts as useful two-stage PBGs. The photobase generation ability of the [CpRu(η 6 -benzylcarbamate)]X salts at 254 nm irradiation is assessed in both acetonitrile solution and polymethacrylate thin films. The irradiation studies demonstrate that η 6 -coordination of a benzylcarbamate PBG does not deactivate photolytic base generation.