Cobalt complexes, molecular structures

Herrmann, W.A., Schweizer, 1., Creswick, M. and Bernal, I. (1979) The preparation and unusual rearrangement of triply bridged p-heteromefhylenecobalt complexes. Molecular structure of p-ethoxycarbonylmethylenebis [carbonyl- (r) cyclopentadienyl)cobalt] (Co(Co). Journal of OrganometaUic Chemistry, 165, C17-C20. 

Examples of the pendant-type polymer-metal complexes represented by Schemes 4 and 5 are shown in Table 2. They are obtained by the reaction in Scheme 8 a polymer ligand is made to coordinate to a vacant site of a previously prepared, stable, low-molecular-weight metal complex. The structure and hence the functions of the metal complex are hardly changed by attachment to the polymer ligand. The metal complexes attached to the polymer ligands 1 to 8 are the classic cobaltic... 

The molecular structure of the manganese dimer clearly reveals that there is an Mn—Mn bond (Fig. I5.la. b). In the cobalt structure, two of the CO ligands are bridging, i.e.. they are simultaneously bound to both Co atoms (Fig. IS.Ic, d). This does not affect the electron count, however, because CO and other neutral ligands donate two electrons to a complex whether they are terminal or bridging (Table IS. I) ... 

Finally, phosphole sulfides can behave as 77 4-electron or Tj -CjTj -Y-b-electron donors toward transition metals. For example, derivative 106 reacts with CpCo(CO)2 to afford the [7] -(phosphole sulphide)]cobalt(I) complex 107 (Scheme 31), which was characterized by X-ray diffraction <2006HAC344>. The chromium complex 109 was obtained in high yield from thioxophosphole 108 and its molecular structure determined crystallographically (Scheme 31). 

The molecular structures obtained by X-ray crystallography for the cobalt sandwich complex with two B-Me- or B-OMe-containing rings show that both molecules have planar and parallel rings arranged centro-symmetrically (74CB3786). Similar structures were found for metallic complexes with M — Fe or Mn, and R = Me or Ph (72CB3484). 

The chemistry of non-peroxo polynuclear cobalt(III) ammines is reviewed with particular emphasis on Werner s major contributions. Modern work in this area has shown that Werner s conclusions regarding the structures of these compounds are substantially correct in spite of the relatively primitive techniques he had available. There is much current interest in polynuclear cobalt(III) complexes because of their relationship to oxygen carriers and intermediates in electron transfer reactions. Modern techniques such as spectroscopy and x-ray diffraction have been used to determine the electronic and molecular structures of these compounds. 

Co is available as an isomorphous replacement for Fe in haems (cobaltmyoglobin, for example, still binds oxygen) and structural information has been obtained about cobalt porphyrin molecular complexes with steroids [89] and caffeine [90] in solution. 

The lacunar cyclidene ligands are the first family of totally synthetic ligands to form both iron(II) and cobalt(II) Oj carriers. The molecular structure of the lacunar cyclidene complexes is most simply represented by the flat projection (la), while the stereochemistry is shown in Ib. Cyclidene refers to the parent macrocycle encircling the metal ion and the lacuna is the permanent void created by bridging the cleft arising from the saddle shape of the cyclidene macrocycle. 

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