The structure of [Co2(CO)5(μ2,η4-CPhCHCHCPh)] a cobalt analogue of the ‘ferroles’

Synthesis of Dicarbonyl(η4-tricarbonylcobaltacyclopentadiene)cobalt Complexes from Co2(CO)8. A General Route to Intermediates in Cobalt Carbonyl Mediated Alkyne Trimerization

“…By analogy with the long-known Fe 2 (CO) 6 analogue 18 and the predominant formation of 1,2,4-triphenylbenzene in most cyclotrimerization reactions of ethynylbenzene, complex 2d was expected to have its phenyl substituents in the 2-and 5-positions of the cobaltacyclopentadiene ring. This was confirmed when the report of its independent synthesis and crystal structure analysis 7 became available. It is also consistent with the position of the phenyl group in complex 2n (see above).…”

“…By this approach, we have indeed obtained all the cobaltacyclopentadienes, 2 , listed in Table . Of these, complex 2d has previously been reported . The yields, which we have not attempted to optimize, are low to modest, and in many cases (listed in the Experimental Section) the expected cobaltacyclopentadienes were detected either in only trace amounts or not at all.…”

“…Of these, complex 2d has previously been reported. 7 The yields, which we have not attempted to optimize, are low to modest, and in many cases (listed in the Experimental Section) the expected cobaltacyclopentadienes were detected either in only trace amounts or not at all. Our concern, however, in the present study was to show that the straightforward route does yield such complexes in "nonexceptional" cases and that they do react further to yield flyover complexes (3) and behave as catalysts of alkyne cyclotrimerization to arenes.…”

“…X-ray Crystal Structure of 2n. As the known structures relate to symmetrical compounds, − we selected the unsymmetrical complex 2n for X-ray crystallographic study. Selected bond lengths and angles are shown in Table , and the structure of 2n is shown in Figure .…”

“…Three further complexes of a similar type have been reported, but all result from other reaction paths: Yamazaki and co-workers obtained the triphenylphosphine-substituted analogue 6 as a product of the reaction of octacarbonyldicobalt with the mononuclear cobaltacyclopentadiene 5a , a process which must involve complex ligand transfers and which did not occur with analogues including the symmetrical isomer 5b . Moldes and co-workers have obtained the simple diphenyl-substituted complex 2d (10% yield) from a mixture of ethynylbenzene, Fe 2 (CO) 9 , [Co(CO) 4 ] - , and trifluoroacetic acid, apparently by a process involving the anionic iron complex 7 as a source of at least one of the “alkyne” units and hence a metal exchange. These authors conclude “This shows that the formation of [ 2 ] is possible only in unusual circumstances (reaction conditions or particular alkynes).” Very recently Giordano et al reported a cobaltacyclopentadiene complex of this type, derived from two molecules of HC 2 CMe 2 OH, as having been formed from the corresponding flyover by a novel decomposition, apparently promoted by the silica of a TLC plate.…”