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)

Tripodal ligands (TMG₃trphen-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 [(TMG₃trphen-E)M₃(μ-X)₃] (M = Cu(I), Ag(I); X = Cl, Br, I) have been generated upon extraction of M₃(μ-X)₃ units from MX sources, exhibiting support of the crown-shaped M₃(μ-X)₃ fragment by M-N_TMG bonds and triply bridging E → M₃ interactions. Orbital interactions between Cu(I) sites and N_TMG residues are more dominant than Sb/Bi → Cu₃ donor interactions between the Sb 5s or Bi 6s orbitals and admixed Cu 4s/3d orbitals, with larger interaction energies computed for Sb → Cu₃. Nonhalogenated copper compounds [(TMG₃trphen-E)₂Cu₂]²⁺2Y^- (Y = PF₆, B(C₆F₅)₄) have been synthesized via dechlorination by TlPF₆ or by application of halide-free Cu(I) sources with TMG₃trphen-E ligands. Nitrene-transfer to olefins mediated by [(TMG₃trphen-E)Cu₃(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 [(TMG₃trphen-Sb)Cu₃(μ-Cl)₃] involves stepwise C-H functionalization.