Photolytic Release of CS2 from Bis(trityl)trithiocarbonate Using Green Light

Reaction of Ph3CSH with 1 equiv of Na{N(SiMe3)2} in THF, followed by addition of excess CS2 and 1.2 equiv of 18-crown-6, results in formation of the mono(trityl) trithiocarbonate, [Na(18-crown-6)(THF)2][Ph3CSCS2] (1a), which was isolated in high yield after workup. Reaction of 1a with 1 equiv of Ph3CCl in pyridine results in formation of the bis(trityl) trithiocarbonate, Ph3CSC(S)SCPh3 (2). Compounds 1a and 2 were characterized by NMR spectroscopy and X-ray-crystallography, and their ultraviolet–visible (UV–vis) spectra were simulated with TD-DFT calculations. Photolysis of 2 using a green LED lightstrip for 6 h results in formation of CS2, Ph3CSSCPh3, Ph3CH, and 9-phenyl-fluorene as the major products. CS2 is formed in 85% yield in this reaction. For comparison, we also evaluated the CS2-releasing properties of bis(benzyl) trithiocarbonate, PhCH2SC(S)SCH2Ph (3). Photolysis of 3 in CD2Cl2 for 26 h, using a medium-pressure Hg lamp, results in formation of CS2 in 50% yield. Also formed in the reaction are toluene, bibenzyl, PhCH2SCH2Ph, PhCH2SSCH2Ph, PhCH2SH, and PhCH2SCH2SCH2Ph, along with a large number of unidentified products. The identities of the major products were confirmed by comparison of the reaction mixture spectra with the 1H and 13C{1H} NMR spectra of authentic materials. We attribute the lower CS2 yield of 3 vs 2 to the lower stability of the benzyl radical vs the trityl radical, highlighting the importance of stable radical formation in the photo-uncaging of molecular cargo.