Aromatic C–H Activation in the Triplet Excited State of Cyclometalated Platinum(II) Complexes Using Visible Light

The visible-light driven cyclometalation of arene substrates containing an N-donor heteroaromatic moiety as directing group by monocyclometalated Pt(II) complexes is reported. Precursors of the type [PtMe(C^N)(N^CH)], where N^CH is 2-phenylpyridine (ppyH) or related compunds with diverse electronic properties and C^N is the corresponding cyclometalated ligand, afford homoleptic cis-[Pt(C^N)2] complexes upon irradiation with blue LEDs at room temperature with evolution of methane. Heteroleptic derivatives cis-[Pt(ppy)(C′^N′)] are obtained analogously from [PtMe(ppy)(N′^C′H)], where N′^C′H represents an extended set of heteroaromatic compounds. Experimental and computational studies demonstrate an unprecedented C–H oxidative addition, which is initiated by a triplet excited state of metal-to-ligand charge-transfer (MLCT) character and leads to a detectable Pt(IV) methyl hydride intermediate.