Synthesis and characterization of two dodecacopper(I) extended metal atom chains (EMAC) assembled by two hexadentate bis(pyridylamido)amidinate-supported hexacopper(I) string complexes (monomers) via the ligand-unsupported cuprophilicity are described. In addition to short unsupported Cu-Cu contacts, two hexacopper fragments in these two dodecacopper EMACs show a bent conformation based on X-ray crystallography. Compared with their THF-bound hexacopper(I) monomers and protonated ligands, these ligand-unsupported cuprophilic interactions are shown to be weak by Raman spectroscopy. DFT calculations suggest the ligand-unsupported cuprophilicity originate from weak attractive orbital interactions, and the strength is estimated to be 2.4 kcal mol .

Three dimeric vanadium(I) β-diketiminates [V{μ-(η(6)-ArN)C(Me)CHC(Me)C(N-Ar)}](2) (Ar = 2,6-Me(2)C(6)H(3) (2), 2,6-Et(2)C(6)H(3) (3), 9-anthracenyl (4)) were prepared and isolated upon reduction of their corresponding dichloro precursors VCl(2)(Nacnac). Compounds 2-4 all show a structure with each vanadium atom being η(2) bonded to the β-diketiminate framework and η(6) bonded to a flanking ring of a β-diketiminato ligand, attached to the other vanadium centre within the dimer. No metal-metal bonding interactions are observed in these dimers due to long vanadium-vanadium separations. Compounds 2-4 display an antiferromagnetic exchange between the two vanadium centres. An imido azabutadienyl complex (η(2)-PhCC(H)C(Ph)NC(6)H(3)-2,6-(i)Pr(2))VN(C(6)H(3)-2,6-(i)Pr(2))(OEt(2)) (5) was isolated from the reduction of VCl(2)(HC(C(Ph)NC(6)H(3)-2,6-(i)Pr(2))(2)) by KC(8). Compounds 2-4 and the inverted-sandwich divanadium complex (μ-η(6):η(6)-C(6)H(5)Me)[V(HC(C(Me)NC(6)H(3)-2,6-(i)Pr(2))(2))](2) (1) reduce Ph(2)S(2) to give two vanadium dithiolates V(SPh)(2)[(HC(C(Me)NC(6)H(3)-2,6-R(2))(2))] (R = Et (6), (i)Pr (7)) through an oxidative addition. Most notably, 1 and 3 catalyze the cyclotrimerization of alkynes, giving tri-substituted benzenes in good yields and a 1,3,5-triphenylbenzene coordinated intermediate 8 was isolated and characterized.

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Although quadruple bonding in transition-metal chemistry has been considered a thoroughly studied area, [1a] the concept of multiple bonding [1b] was reinvigorated in 2005 by the seminal discovery of the first CrÀCr quintuple bond in the isolable dimeric chromium compound Ar'CrCrAr' (Ar' = 2,6-(2,6-iPr 2 C 6 H 3 -) 2 C 6 H 3 ) by Power and co-workers. [2] Since then, the structures of several Group 6 homobimetallic compounds with very short CrÀCr (1.73-1.75 ) and MoÀMo (2.02 ) quintuple bonds have been characterized. [3] All these remarkable quintuple-bonded bimetal units are supported by either C-or N-based bridging ligands. Based on their structures, these quintuple-bonded dinuclear compounds can be simply classified into two types as illustrated in Figure 1. The existence of the type I quintuple bond was recently corroborated by experiments, [4a] and the bonding paradigms of both types were realized by theoretical investigations. [4] Preliminary reactivity studies on the type I complexes show that they are reactive towards the activation of small molecules and display interesting complexation with olefins and alkynes. [5] Up to now, both type I and II compounds have been exclusively synthesized by a procedure analogous to the Wurtz reductive coupling reaction of the corresponding chloride coordinated precursors. [2, 3] The previously reported quintuple-bonded dichromium examples were obtained by alkali metal reduction of the mononuclear [LCrCl 2 -(THF) 2 ] [3c,e] or dimeric complexes [LCr(m-Cl)] 2[3] (L = monodentate or bidentate ligand). It should be noted that all these precursors lack Cr À Cr bonding. Besides, we have recently demonstrated that the metal-metal quintuple and quadruple bond can be constructed from the corresponding quadruple and triple bond, respectively. For example, the d bonds in the quintuple-bonded species [Mo 2 {m-h 2 -RC(N-2,6-iPr 2 C 6 H 3 ) 2 } 2 ] (R = H, Ph) [3h] and quadruple-bonded complex [Mo 2 {m-h 2 -Me 2 Si(N-2,6-iPr 2 C 6 H 3 ) 2 } 2 ] [6] are formed by alkali metal reduction of the corresponding chloride-coordinated quadrupleand triple-bonded species, respectively. However, the formation mechanism of the metalÀmetal quintuple bonds has not been investigated. To this end, continuing our exploration in the field of quintuple-bond chemistry, we herein report the construction of a complex with a Cr À Cr quintuple bond by two subsequent one-electron-reduction steps from a halidefree homo-divalent dichromium complex to a mixed-valent intermediate (Cr I , Cr II ), and then to the final quintuplebonded product. Structural characterization of these dichromium compounds is important to shed light on the formation mechanism of the metal-metal quintuple bonds. Moreover, the metal À metal quadruple bonds can be dramatically elongated by intramolecular axial coordination, but such an interaction in the quintuple-bonding system has not been investigated. We report herein that the CrÀCr quintuple bond can be readily cleaved by disproportionation induced by intramolecular axial coo...

Herein, we report the employment of the Mo-Mo quintuple bonded amidinate complex to stabilize Group 10 metal fragments {(Et3P)2M} (M=Pd, Pt) and give rise to the isolation of the unprecedented δ complexes. X-ray analysis unambiguously revealed short contacts between Pd or Pt and two Mo atoms and a slight elongation of the Mo-Mo quintuple bond in these two compounds. Computational studies show donation of the Mo-Mo quintuple-bond δ electrons to an empty σ orbital on Pd or Pt, and back-donation from a filled Pd or Pt dπ orbital into the Mo-Mo δ* level (LUMO), consistent with the Dewar-Chatt-Duncanson model.