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-NTMG bonds and triply bridging E → M3 interactions. Orbital interactions between Cu(I) sites and NTMG 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.