Cobaltocene Co

Cobaltocene, [Co ()7 -C5H5)2], is a dark-purple air-sensitive material, prepared by the reactions of sodium cyclopentadiene and anhydrous C0CI2... 

The organocobalt catalysed synthesis of substituted pyridines from alk-l-enes and nitriles (Equation 22) has been extended further by the discovery that the leaction is catalysed by cobaltocene, Co(i7 -05145)2, a more easily obtained complex than earlier catalysts.Acetylene reacts with substituted nitriles to give 2-sub-stituted pyridines in up to 60% yield, whereas mono-substituted acetylenes react to give mixtures of 2,4,6- and 2,3,6-trisubstituted pyridines in moderate yield. 

Fischer and coworkers showed that [VO(bdc)] (MIL-47(V)) reacts with cobaltocene, [Co(> -C5H5)2], to form [Co( 7 -C5H5)2][VO(bdc)]2. In this process, cobaltocene is oxidized to cobaltocenium, and the framework contains a 1 1 mixture of vanadium(III) and vanadium(IV). Clet and coworkers demonstrated that MIL-47(V) can be formed with different proportions of vanadium(III) and vanadium(IV), depending on the activation protocol. They showed that the MOF containing only vanadium(III) is isostructural with the MIL-53 series and has a flexible structure, whereas MIL-47, which contains only vanadium(IV), has a rigid structure. " ... 

Cobaltocene is partially oxidized and in part undergoes insertion of a borylene group, RB. The borinato ligands derive from the unknown borabenzene ( 6.5.3.4). Some porphyrinatoindium and thallium complexes ( 6.5.2.2) can also be synthesized via oxidative addition reactions (TPP)InCl is added oxidatively to Co2(CO)g and Mn2(CO) to give (TPP)In—Co(CO)4 and (TPP)ln — Mn(CO)j, respectively, and (oep)InCl is added to CojfCOg to yield (oep)ln— 0(00)4. 

Further work on nickelocene and cobaltocene was done by Ross , who synthesized the respective compounds using Ni, Ni and " Co, which decay be E.C., jS and a fully converted isomeric transition, respectively, all producing radioactive cobalt isotopes. The results showed retentions, after sublimation, of 84%, 83% and 80%, respectively. The composition of the unsublimable residue was largely CoCp2, except for the highly converted "Co, where only 30% CoCpj could be detected. This was interpreted as showing that by internal conversion the molecules are totally destroyed, by the same sort of argument as was used by Riedel and Merz . 

In 1970, the synthesis of the orange-red sandwich cation 1 from cobaltocene and PhBCl2 (1) marked a further starting point in the chemistry of boron metal compounds. The presence of a planar benzenoid C5H5B ligand moiety in 1 was deduced from XH and UB NMR data (1). This was made ironclad by two X-ray structure determinations which revealed typical centrosymmetric sandwich structures for the 19-e complexes Co(C5H5BOMe)2 (6) (21,22) and Co(C5H5BMe)2 (7) (22) as shown in Fig. 1. 

Bora-2,5-cyclohexadienes have a much greater synthetic potential than is apparent from the examples given so far. This may be exemplified by two recent reactions. Reductive complex formation in the system Co(acac)3/COD/25/Mg/THF affords complex 51 via the organotin route (77) while an earlier synthesis used the cobaltocene route (60). Ni(COD)2 very cleanly forms the (Tj3-l,4,5-cyclooctenyl)nickel complex 52 (29). 

Borabenzene metal complexes, like their cyclopentadienyl counterparts, are not readily amenable to breaking of the metal-ligand bond. Such bond breaking will occur more easily in complexes with antibonding electrons. By fortuitous chance the cobaltocene route to borabenzene chemistry (Section V,A) provided 19-e complexes with the useful property of inherently weakened metal-ligand bonds. Thus most of this section centers on the reactivity of Co(C5H5BMe)2 (7) and Co(CsH5BPh)2 (13). 

The observation of radical anions has been confirmed by ESR measurements as illustrated by [Ir4(CO)12], (g = 2.002) 208). Similarly, a toluene solution of Co4(CO)i2 reacts with cobaltocene precipitating a brown compound which is extremely reactive and contains a cobaltocenium cation for each four cobalt atoms of the anion55. With excess cobaltocene (or alkali metals) in THF the reaction proceeds further as shown in Eq. (20),... 

The variation of D (M-Cp) with AHf (M, g) is shown in Fig. 4. The deviation of Co and Ni from the linear plot is to be expected in terms of the valence m.o. electron configuration of cobaltocene and nickelocene, both of which have electrons in the anti-... 

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