An on/off photocatalytic switch: from a carbon monoxide surrogate to controlled carbonylations

Carbon monoxide surrogates have become valuable tools in carbonylation chemistry, enabling safer and more practical access to carbonylated products while avoiding the direct handling of toxic CO gas. We report a visible-light-controlled ex situ system for carbon monoxide generation using triphenylacetyl chloride as a structurally simple CO surrogate. Under photocatalytic conditions, the precursor undergoes rapid decarbonylation, enabling CO release to be switched on and off by irradiation. The generated CO was delivered in a two-chamber setup and applied to several transition-metal-catalyzed carbonylations, including oxidative carbonylative cyclizations, aminocarbonylations, alkoxycarbonylations, and carbonylative Suzuki couplings. CO formation was monitored using deoxyhemoglobin trapping and 13C NMR analysis, while Stern–Volmer experiments and DFT calculations support a mechanism involving initial reduction of the acyl chloride followed by rapid decarbonylation of the resulting acyl radical. This PhotoCOgen platform provides a practical and controllable approach for laboratory-scale carbonylation chemistry without direct handling of gaseous CO.