Nitrene-Transfer Chemistry to C–H and C═C Bonds Mediated by Triangular Coinage Metal Platforms Supported by Triply Bridging Pnictogen Elements Sb(III) and Bi(III)

Abstract

Tripodal ligands (TMG 3 trphen-E) that feature heavy pnictogen elements (E = Sb(III), Bi(III)) and tetramethylguanidinyl (TMG) arms have been explored in stabilizing Cu(I) and Ag(I) sites and facilitating nitrene-transfer chemistry. Compounds [(TMG 3 trphen-E)M 3 (μ-X) 3 ] (M = Cu(I), Ag(I); X = Cl, Br, I) have been generated upon extraction of M 3 (μ-X) 3 units from MX sources, exhibiting support of the crown-shaped M 3 (μ-X) 3 fragment by M−N TMG bonds and triply bridging E → M 3 interactions. Orbital interactions between Cu(I) sites and N TMG residues are more dominant than Sb/Bi → Cu 3 donor interactions between the Sb 5s or Bi 6s orbitals and admixed Cu 4s/3d orbitals, with larger interaction energies computed for Sb → Cu 3 . Nonhalogenated copper compounds [(TMG 3 trphen-E) 2 Cu 2 ] 2+ 2Y − (Y = PF 6 , B(C 6 F 5 ) 4 ) have been synthesized via dechlorination by TlPF 6 or by application of halide-free Cu(I) sources with TMG 3 trphen-E ligands. Nitrene-transfer to olefins mediated by [(TMG 3 trphen-E)Cu 3 (μ-Cl) 3 ] (E = Sb and Bi) affords aziridines in good yields, primarily for unencumbered styrenes and with the more robust Sb catalyst. Amination of C−H bonds is most effective with sec-benzylic substrates and requires a more electrophilic nitrene (NTces) to achieve practicable yields with halogenated or nonhalogenated copper precursors. Hammett plots indicate that the competitive amination of para-substituted ethylbenzenes enabled by [(TMG 3 trphen-Sb)Cu 3 (μ-Cl) 3 ] involves stepwise C−H functionalization.