Dinuclear vanadium complexes

Newer types of the dinuclear vanadium(IV) complex catalysts 84 have been developed. The abovementioned dinuclear vanadium complexes possess a VO V linkage whereas the ESR study on the catalyst 84 revealed no V—O—V linkage. The sense of enantioselection by the catalyst 84 of the (R,5,5)-structure is opposite to that of the binuclear complex 78a of the same (R,5,5)-structure. These results suggested two active sites attached to the binaphthyl skeleton in the catalyst 84 performed the dual activation of 2-naphthols in the oxidative couphng to achieve high enantioselectivity ... 

Table 3.5 EPR parameters for dinuclear vanadium complexes. A values in units of 10 em. ...

Dinuclear vanadium complexes with bridging diazenido(2—). The ligands are 2,6-bis(l-iminoethyl)pyridine (53)h h mesityl(l—) (54),h l 2-dimethylaminophenyl(l—) and pyridine (55),h l tolane, trimethylphosphine and dimethylamino-Cp(l—) (56),and benzamidinate(l —) (57).P 1 The complexes 54 and 55, containing (r-aUcyls, produce ammonia and hydrazine on protonation. 

Scheme 9.17 Enantioselective oxidative coupling of 2-anthracenol (39) and 9-phe-nanthrol (41) catalysed by a chiral dinuclear vanadium complex, reported by Sasai and Takizawa. ...

Kaliva, M., T. Giannadaki, A. Salifoglou, C.P. Raptopoulou, and A. Terzis. 2002. A new dinuclear vanadium(V)-citrate complex from aqueous solutions. Synthetic, structural, spectroscopic and pH-dependent studies in relevance to aqueous vanadium(V)-citrate speciation. Inorg. Chem. 41 3850-3858. 

Ahmed, M., P. Schwendt, J. Marek, and M. Sivak. 2004. Synthesis, solution and crystal structures of dinuclear vanadium(V) oxo monoperoxo complexes with man-delic acid (NR4)2[V202(02)2(mand)2]xH20 [R = H, Me, Et mand = mandelato(2-) = CSI fp,. Polyhedron 23 655-663. 

A further type of dinuclear VO2+ complex has terminal V=0 groups but a pendant alkoxy group from a coligand on each vanadium gives rise to a bis(/x-alkoxy) system, as in [ V02Ad 2] (Ad = adenosine). ... 

The dinuclear enolate complex (105) is then formed by treatment of (104) with carbon monoxide, which inserts into the vanadium-carbon bonds. 

A number of ternary complexes with simple dicarboxylic acid complexes supported by other ligands have been reported. These include the mixed valence Viv,v complex with 2,2 -bipyridine (bpy) as the supporting ligand134 and the dinuclear vanadium(V) oxalate-bridged complex.135 The structure-reactivity relationship in the redox series Vv,iv ni chelated to 2-ethyl-2-hydroxybutanate... 

The electrochemistry of dinuclear vanadium o-A-salicylideneamino-ethylphenyl complexes were investigated.372 Conversion of Viv—Viv dimers to Vv—Vv dimers was reported and serves as a representative model system for oxidation reactions.294 296 A related class of these dinuclear complexes form mixed valence vanadium(IV/V) complexes upon oxidation and exhibit an unusual electron delocalization over the V203 3+ core.310 A V111—Vlv mixed valent, dinuclear bis(salicy-lidene)ethylenediamine (salen) complex underwent multielectron oxidation with dioxygen to yield a Vv—Viv mixed valence complex.302... 

New complexes containing azo- and hydrazinato-derivatized Schiff base ligands298 375 continue to be used for the analytical determination of vanadium.376 The vanadium complex was characterized for the Schiff base derived from the condensation reaction of benzoyl acetone and Girard s reagent P.377 Azophenolates of mononuclear and mixed valence dinuclear species have been reported.378 Naphthanol- or quinolinol-derivatized ligands prefer to chelate iron over vanadium.379... 

A cyanohydridoborato vanadium(II) complex, tra s-[V(NCBH3)2(thf)4], has been synthesized and structurally characterized (212).858 Additional oligomeric complexes have been prepared complexes that have been characterized include trinuclear vanadium complexes,859-862 dinuclear V-Fe complexes,863 and the first tetranuclear V11 species [V4(/x3-Cl)2(M-Cl)2(M-CF3C02)2(thf)6].864 The addition of tris(pyrazolyl)borate ligand to the tetranuclear species results in the dissociation of the complex to form a neutral dimeric species [V(tpb)-(/x-Cl)(/x-CF3CO2)2V(th03] (213) in which one of the vanadium centers is facially coordinated by tpb.864... 

A theoretical evaluation of ligands that would stabilize a vanadium-vanadium triple bond was undertaken and concluded that O- and N-donors in amidates would yield the greatest stability.890 A lantern-type metal-metal bonded dinuclear V11 complex was synthesized by the reduction of [VCl3(thf)3] with NaHBEt3 followed by addition of the lithium salt of V,V -di-p-tolylformamidate (215). 65 The crystal structure shows the V V distance to be 1.98 A, which is consistent with a fairly strong metal-metal triple bond.865... 

Vanadium compounds with oligodentate ON and ONS ligands. Each of the vanadium complexes represents an example of a specific subgroup. 33, dioxo—V, square pyramidal (sqp) 34, monooxo-sqp 35, monooxo-V, trigonal bipyramidal 36, dioxo-V, octahedral (oct) 37, monooxo-V, oct 38, monooxo-V, oct/sqp 39, monooxo-V, sqp 40, monooxo-V, oct. In the mixed-valence dinuclear complexes 41 and 42, the two vanadium centres are indistinguishable (41) and isolated (42), respectively. 

Other dinitrogen vanadium complexes have been introduced in the last two decades, all of which are dinuclear and contain dinitrogen (originally stemming from aerial N2) in the... 

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