Monoanionic Phosphorus-Supported Air Stable Cu(I)₈, Ag(I)₇, and Ag(I)₅ Nanoclusters Exhibiting TADF: A Novel Photocatalyst for Stereoselective Carbene Transfer Reactions

Applications of structurally well-defined coinage-metal nanoclusters (NCs) as optoelectronic materials and homogeneous catalysts have been restricted due to their inherent lower stability. Herein, the syntheses, structural characterizations, and photoluminescence properties of three novel air-stable coinage-metal(I) NCs-supported by carbene-anchored monoanionic phosphorus (cAAC=P-) with molecular formulae [(Cy-cAACP)(4)(Cu)(4)(CuCl)(4)] (4), [(Cy-cAACP)(4)(Ag)(4)(AgOTf)(3)] (5), and [(Cy-cAACP)(4)(Ag)(5)]NTf2 (6) (cAAC = cyclic alkyl(amino) carbene; Tf = CF3SO2) exhibiting thermally activated delayed fluorescence (TADF) are reported. Apart from attractive metallophilic interactions [M-M; M - Cu, Ag], the enhanced kinetic and thermodynamic stability of 4-6 can be attributed to the excellent.pi-accepting ability of cAAC=P- surrounding the metallic cores. cAAC=P- anion is generated either in situ by anion-induced cleavage of P-Sb/B bonds of corresponding stibanyl/boryl phosphaalkenes in the presence of coinage-metal(I)-Cl/OTf/NTf2 salts or by directly introducing alkali-metal phosphinidenide. The TADF properties of 4-6 are established by smaller energy gaps between the lowest singlet excited state and triplet excited state. In solid-state, the delayed fluorescence lifetimes of 4-6 are found to be in the microsecond range with absolute photoluminescence quantum yields up to 20%. The redox-active Cu(I) (8) NC 4 is successfully exploited as an efficient photo-catalyst for the selective carbene transfer reaction at ambient conditions, affording cyclopropanated indoles/styrenes with excellent yields and diastereoselectivity.