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Four dinuclear Ir I complexes with macrocyclic diamine‐tetracarbene ligands were synthesized and characterized, two of which and a related mononuclear complex were found to be the first examples of Ir N‐heterocyclic carbene complexes exhibiting catalytic performance toward 1,4‐addition of arylboronic acids to cyclohex‐1‐en‐2‐one.

Four macrocyclic hybrid salts with different numbers of benzimidazolium and amine units, [H2L][PF6]2 (L = L1, L2, L3) and [H4L4][PF6]4, have been employed as the heterocyclic carbene (NHC) precursors toward new Ag(I)– and Au(I)–NHC complexes. Three trinuclear and one tetranuclear Ag(I) complexes 1–4 have been obtained from the reactions of the NHC precursors and Ag2O in acetonitrile. Four dinuclear Au(I)–NHC complexes 5–8 have been prepared by reacting the NHC precursors and AuCl(SMe2) in the presence of NaOAc in DMF. The molecular structures of all the complexes are established by single-crystal X-ray diffraction studies. The metal ions in the Ag(I) complexes 1–3 and the Au(I) complexes 5–7 are coordinated with two macrocyclic NHC ligands to form a sandwiched structure. In contrast, a trinuclear Ag3 core is located in the cavity of one macrocyclic ligand in [Ag3(L4)][PF6]3 (4). The photoluminescence properties of Au(I) complexes 5–8 have also been investigated.

A hexadentate macrocyclic N-heterocyclic carbene (NHC) ligand precursor (H4L)(PF6)4 containing four benzimidazolium and two secondary amine groups, has been synthesized and characterized. Coordination chemistry of this new macrocyclic diamine-tetracarbene ligand has been studied by the synthesis of its Ag(I), Au(I), Ni(II), and Pd(II) complexes. Reactions of (H4L)(PF6)4 with different equiv of Ag2O result in Ag(I) complexes [Ag(H2L)](PF6)3 (1) and [Ag2(H2L)](PF6)4 (2). A mononuclear Au(I) complex [Au(H2L)](PF6)3 (3) and a trinuclear Au(I) complex [Au3(H2L)(Cl)2](PF6) (4) are obtained by transmetalation of 1 and 2 with AuCl(SMe2), respectively. Reactions of (H4L)(PF6)4 with Ni(OAc)2 and Pd(OAc)2 in the presence of NaOAc yield [Ni(L)](PF6)2 (5) and [Pd(L)](PF6)2 (6), respectively, containing one Ni(II) and Pd(II) ion with distorted square-planar geometry. Using more NaOAc results in the formation of unusual dinuclear complexes [Ni2(L–2H)](PF6)2 (7) and [Pd2(L–2H)](PF6)2 (8) (L–2H = deprotonated ligand after...

The reaction of a pentadentate NHC ligand precursor with Ni(OAc)2·4H2O or Pd(OAc)2 in the presence of a base yields four-coordinate square-planar Ni(II) and Pd(II) complexes with an unusual ligand generated in situ. A series of experimental studies point to a ring-opening and ring-closing process via novel C–N bond cleavage and formation.