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

The reaction of ( Me 2 L)CuCl with either NaS 2 CX [X = OEt, NEt 2 or carbazolate (Cz)] or with 1,3-diarylguanidine, 1,3-diarylformamidine or thioacetaniline in the presence of KO t Bu affords the corresponding S- or N-bound copper complexes ( Me 2 L)Cu(S^S) 1-3 , ( Me 2 L)Cu(N^N) 4 / 5 and ( Me 2 L)Cu(N^S) 6 (aryl = 2,6-diisopropylphenyl; Me 2 L = 2,6-bis(isopropyl)phenyl-3,3,5,5-tetramethyl-2-pyrrolidinylidene). The crystal structure of ( Me 2 L)Cu(S 2 CCz) ( 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 CS 2 and forms ( Me 2 L)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%. Copper( i ) complexes of cyclic (alkyl)(amino)carbenes coordinated to monodentate or hemilabile guanidinato and formamidinato complexes show intense photoluminescence including white emissions.