-E-bridged trinuclear triple-decker complexes (E = P, As) containing a triply-bonded Mo unit and their isomerisation.

The reaction of the low-coordinate quadruply-bonded dimolybdenum complex Mo[μ,κ-PhB(-2,6-PrCH)] (1) with Cp*Fe(η-E) (E = P, As) gives two trinuclear species Cp*Fe(μ,η-E)Mo[μ,κ-PhB(-2,6-PrCH)] (E = P (4) and As (5)). 4 undergoes facile isomerisation upon heating to give Cp*FeMo[κ-PhB(-2,6-PrCH)](μ,κ:κ:η-P)[μ,κ:κ:ηκ-PPhB(-2,6-PrCH)] (6), where the FeMoP core motif displays a cubane-like structure.

Cuprophilic Interactions in and between Molecular Entities.

Despite being weak attractive forces, closed-shell metallophilic interactions play important roles in the Group 11 metal complexes on their diverse structural and physical features. A plethora of experimental and computational studies has thus been dedicated to such weak attractive d -d interactions, particularly aurophilic and argentophilic interactions. Although d -d Cu -Cu forces had been recognized for four decades, cuprophilic interactions are less explored and they are best evidenced by single-crystal X-ray crystallographic analysis on Cu complexes and aggregates thereof, by which precise information about the Cu⋅⋅⋅Cu contacts, shorter than the sum of two van der Waals radii (3.

Ligand-Unsupported Cuprophilicity in the Preparation of Dodecacopper(I) Complexes and Raman Studies.

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.

Reversible Cleavage/Formation of the Chromium-Chromium Quintuple Bond in the Highly Regioselective Alkyne Cyclotrimerization.

Herein we report the employment of the quintuply bonded dichromium amidinates [Cr{κ -HC(N-2,6- Pr C H )(N-2,6-R C H )}] (R=iPr (1), Me (7)) as catalysts to mediate the [2+2+2] cyclotrimerization of terminal alkynes giving 1,3,5-trisubstituted benzenes. During the catalysis, the ultrashort Cr-Cr quintuple bond underwent reversible cleavage/formation, corroborated by the characterization of two inverted arene sandwich dichromium complexes (μ-η :η -1,3,5-(Me Si) C H )[Cr{κ -HC(N-2,6- Pr C H )(N-2,6-R C H )}] (R= Pr (5), Me (8)). In the presence of σ donors, such as THF and 2,4,6-Me C H CN, the bridging arene 1,3,5-(Me Si) C H in 5 and 8 was extruded and 1 and 7 were regenerated.

Synthesis and Characterization of an Eclipsed Digermylene as a Building Block to Construct a Cyclic Octagermylene.

The preparation of an unprecedented Ge -Ge bonded digermylene [K {Ge (μ-κ :η :η -2,6-(2,6- Pr C H -N) -4-CH C H N) }] in an eclipsed conformation stabilized by two bridging diamidopyridyl ligands is presented. Although it exhibits an eclipsed conformation, the Ge-Ge bond length is 2.5168(6) Å, which is shorter than those in the trans-bent and gauche digermylenes.

A Family of Multiply Bonded Dimolybdenum Boraamidinates with the Formal Mo-Mo Bond Orders of 3, 4, 4.5, and 5.

A boraamidinato ligand [PhB(N-2,6-(i) Pr2 C6 H3 )2 ](2-) was employed to stabilize a new family of multiply bonded dimolybdenum complexes [MoCl(μ-κ(2) -PhB(N-2,6-(i) Pr2 C6 H3 )2 )]2 (4) and [Mo(μ-κ(2) -PhB(N-2,6-(i) Pr2 C6 H3 )2 )]2 (n-) (n=0 (5), 1 (6), 2 (7)), with the respective formal Mo-Mo bond orders of 3, 4, 4.5, and 5. Each metal center in 5-7 is two-coordinate with respect to the ligands.

The Mo-Mo Quintuple Bond as a Ligand to Stabilize Transition-Metal Complexes.

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.

Theory, synthesis and reactivity of quintuple bonded complexes.

This perspective reviews recent advances in the newly discovered metal-to-metal quintuple bonded complexes. The idea of the structures of the metal-metal quintuple bonded complexes was initiated by theoreticians in 1979 and 2001 based on two types of model compounds, the D3h M2L6 and trans-bent M2H2, respectively. This theoretical hypothesis was put into practice in 2005 with the preparation of the first isolable quintuple bonded chromium terphenyl dimer Cr2Ar'2 (Ar' = 2,6-(2,6-i-Pr2C6H3)2C6H3).

Discovering complexes containing a metal-metal quintuple bond: from theory to practice.

Although the field of metal-to-metal multiple bonding has been considered as mature, it was recently reinvigorated by the discovery of quintuple bonded dinuclear complexes. Initiated by theoretical studies, quintuple bonding was promoted by the recognition of the first isolable quintuple bonded chromium phenyl dimer Ar'CrCrAr' (Ar' = 2,6-(2,6-(i)Pr2C6H3)2C6H3) by Power and co-workers in 2005. Soon afterwards, many dinuclear group VI metal-to-metal quintuple bonded complexes stabilized by sterically hindered N-based bidentate ligands were subsequently characterized.

Divergent reactivity of nitric oxide with metal-metal quintuple bonds.

Reactions of NO with the quintuple bonded chromium and molybdenum amidinate dimers, respectively, gave dichromium nitrosyl nitrito amidinato complexes, and the quadruple bonded dimolybdenum nitrito amidinato species with a paddlewheel configuration.

An electron-rich molybdenum-molybdenum quintuple bond spanned by one lithium atom.

Take five: A unique quintuply bonded dimolybdenum complex [Mo(2)(μ-Li){μ-HC(N-2,6-Et(2)C(6)H(3))(2)}(3)] (see picture) was synthesized and characterized. The Mo-Mo interaction includes an unexpected bridging Li(+) ion. Calculations indicate the bridging Li(+) ion does not perturb the Mo-Mo bond length (2.

Bond characterization on a Cr-Cr quintuple bond: a combined experimental and theoretical study.

A combined experimental and theoretical charge density study on a quintuply bonded dichromium complex, Cr(2)(dipp)(2) (dipp = (Ar)NC(H)N(Ar) and Ar = 2,6-i-Pr(2)-C(6)H(3)), is performed. Two dipp ligands are bridged between two Cr ions; each Cr atom is coordinated to two N atoms of the ligands in a linear fashion. The Cr atom is in a low oxidation state, Cr(I), and in low coordination number condition, which stabilizes a metal-metal multiple bond, in this case, a quintuple bond.

Ligand-controlled synthesis of vanadium(I) β-diketiminates and their catalysis in cyclotrimerization of alkynes.

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.

Coordination-mode control of bound nitrile radical complex reactivity: intercepting end-on nitrile-Mo(III) radicals at low temperature.

Variable temperature equilibrium studies were used to derive thermodynamic data for formation of eta(1) nitrile complexes with Mo(N[(t)Bu]Ar)(3), 1. (1-AdamantylCN = AdCN: DeltaH(degrees) = -6 +/- 2 kcal mol(-1), DeltaS(degrees) = -20 +/- 7 cal mol(-1) K(-1). C(6)H(5)CN = PhCN: DeltaH(degrees) = -14.

Journey from Mo-Mo quadruple bonds to quintuple bonds.

Heating K(4)Mo(2)Cl(8) and 2 equiv of Li[RC(NDipp)(2)] (R = H, Ph; Dipp = 2,6-i-Pr(2)C(6)H(3)) in tetrahydrofuran (THF) at 60 degrees C gives two paddlewheel type quadruply bonded dimolybdenum complexes, Mo(2)(mu-Cl)[Cl(2)Li(OEt(2))][mu-eta(2)-RC(N-2,6-i-Pr(2)C(6)H(3))(2)](2) (R = H (1), Ph (2)). The Mo-Mo bond lengths of 1 and 2 are 2.0875(4) and 2.

Thermodynamic and kinetic studies of H atom transfer from HMo(CO)3(eta(5)-C5H5) to Mo(N[t-Bu]Ar)3 and (PhCN)Mo(N[t-Bu]Ar)3: direct insertion of benzonitrile into the Mo-H bond of HMo(N[t-Bu]Ar)3 forming (Ph(H)C=N)Mo(N[t-Bu]Ar)3.

Synthetic studies are reported that show that the reaction of either H2SnR2 (R = Ph, n-Bu) or HMo(CO)3(Cp) (1-H, Cp = eta(5)-C5H5) with Mo(N[t-Bu]Ar)3 (2, Ar = 3,5-C6H3Me2) produce HMo(N[t-Bu]Ar)3 (2-H). The benzonitrile adduct (PhCN)Mo(N[t-Bu]Ar)3 (2-NCPh) reacts rapidly with H2SnR2 or 1-H to produce the ketimide complex (Ph(H)C=N)Mo(N[t-Bu]Ar)3 (2-NC(H)Ph). The X-ray crystal structures of both 2-H and 2-NC(H)Ph are reported.

Synthesis and reactions of beta-diketiminato divanadium(I) inverted-sandwich complexes.

Reduction of VCl(2)(Nacnac) (Nacnac = HC(C(Me)NC(6)H(3)-iPr(2))(2)) with KC(8) in toluene leads to the formation of a toluene-bridged inverted-sandwich divanadium(I) complex, (mu-eta(6):eta(6)-C(7)H(8))[V(Nacnac)](2), which behaves as a source of V(Nacnac) and a multi-electron reductant in the two reactions studied in this report.

Structural transformations in dinuclear zinc complexes involving Zn-Zn bonds.

Reduction of Zn(2)(mu-eta(2)-Me(2)Si(NDipp)(2))(2) with 4 equiv. of KC(8) resulted in a dramatic structural transformation into [(eta(2)-Me(2)Si(NDipp)(2))ZnZn(eta(2)-Me(2)Si(NDipp)(2))](2-) featuring a Zn-Zn bond instead of [Zn(2)(micro-eta(2)-Me(2)Si(NDipp)(2))(2)](2-); the mechanism of the observed structural transformations arising from the Zn-Zn bond formation involving the intermediate of [Zn(2)(mu-eta(2)-Me(2)Si(NDipp)(2))(2)](-) was elucidated by elaborate computations.