Vanadium complexes bonds

These dimeric complexes involve, in their neutral state, two metal atoms in the (III) oxidation state. In the vanadium complexes such as [CpV(bdt)]2 and [CpV(tft)]2, the V—V bond length, 2.54 A in [CpV(bdt)]2, are shorter than observed in model complexes with a single V—V bond, indicating a partial double-bond character, also confirmed by a measured magnetic moment of 0.6 fiB in [CpV(tfd)]2, lower than expected if the two remaining unpaired electrons contribute to the magnetic susceptibility [20, 49]. This class of complexes most probably deserves deeper attention in order to understand their exact electronic structure. 

Since the oxidative polymerization of diphenyl disulfide catalyzed by VO(acac)2 results in selective formation of thioether bonds without any oxygenated compounds such as sulfoxides and/or sulfones, it should be noted that H20 should be produced predominantly by the reduction of 02 catalyzed by the vanadium complex without the formation of partially reduced side products such as H202. 

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

Labeling studies have clearly shown that the active catalyst is not a peroxo compound but an alkyl peroxide in which the alkyl peroxide group is probably 0,0-triangularly bonded to the metal,as illustrated by the X-ray crystal structure of the vanadium complex (22). The well-characterized d" metal 0,N-bonded N,JV-dialkylhydroxylamino complexes (79), (80) and (81) might be reminiscent of the alkyl peroxide complexes of Mo " , V " and Ti ", which are difiBcult to isolate and involved as reactive intermediates in reactions (64) or (65). 

This reaction occurs in benzene in 40% yield. The structures of the isostructural series V2(CO)s(PMe2)2, Cr2(CO)s(PMe2)2 and Mn2(CO)s(PMe)2 show, as expected by electron counting, that the vanadium complex contains a V=V bond, the chromium complex contains a Cr-Cr bond, and the manganese complex does not contain a metal-metal bond. 

Peroxo examples formed by the direct reaction with molecular dioxygen in the first row of the transition metals are few. One of the first examples of a peroxo vanadium complex formed by the direct reaction with dioxygen is a Tp Pr-bound seven-coordinate pentagonal-bipyramidal Vv complex Tp PrV0(f72-02)(pz PrH), with a relatively short O—O distance of 1.379(6) A and relatively high O—O stretching frequency of 960 cm-1, relative to typical peroxo species.14 First-row transition metalloproteins which bond molecular dioxygen are discussed, with their models, in Volume 8. 

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... 

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