Synthesis of copper(i) cyclic (alkyl)(amino)carbene complexes with potentially bidentate N^N, N^S and S^S ligands for efficient white photoluminescence

Abstract

The reaction of (^Me₂L)CuCl with either NaS₂CX [X = OEt, NEt₂ or carbazolate (Cz)] or with 1,3-diarylguanidine, 1,3-diarylformamidine or thioacetaniline in the presence of KO^tBu affords the corresponding S- or N-bound copper complexes (^Me₂L)Cu(S^S) 1–3, (^Me₂L)Cu(N^N) 4/5 and (^Me₂L)Cu(N^S) 6 (aryl = 2,6-diisopropylphenyl; ^Me₂L = 2,6-bis(isopropyl)phenyl-3,3,5,5-tetramethyl-2-pyrrolidinylidene). The crystal structure of (^Me₂L)Cu(S₂CCz) (3) confirmed the three-coordinate geometry with S^S chelation and perpendicular orientation of the carbene and S^S ligands. On heating 3 cleanly eliminates CS₂ and forms (^Me₂L)CuCz. The N-bound complexes show strongly distorted T-shaped (4) or undistorted linear (5) geometries. On excitation with UV light the S-bound complexes proved non-emissive, while the guanidinato and formamidinato complexes are strongly phosphorescent, with excited state lifetimes in the range of 11–24 μs in the solid state. The conformationally flexible formamidinato complex 5 shows intense green-white phosphorescence with a solid-state quantum yield of >96%.