Strong bis-cyclometalated iridium photoreductants, in combination with a single sacrificial reductant, enable visible-light-promoted reductive activation of a variety of challenging substrates under simple and general reaction conditions.

Net selective bromination and chlorination of activated C−H bonds can be effected in generally high yield via a simple perhalogenation/dehalogenation sequence. The photochemical reductions require no photocatalyst, relying instead on the formation of an electron donor−acceptor complex of the substrate and reductant, or alternatively autophotocatalysis. Some reactions proceed despite any apparent photon absorption, serving as a cautionary tale for other photochemical reactions involving amines. Mechanistic experiments provide an explanation for this observation.