The reactions of some diynes with (C5H5)Co(CO)2 and Fe(CO)5: Inter- or Intra-molecular cyclizations?

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Abstract
The reactions of several diynes MeC≡C(CH2)nC≡CMe, n = 2-4, with (η- C5H5)Co(CO)2 and Fe(CO)5 have been compared. A p-benzoquinone complex, (η-C5H5)Co[(C8H10)2(CO)2], and three isomers of the cyclopentadienone complex, (η-C5H5)Co[(C8H10)2CO], are formed in the reaction of (η- C5H5)Co(CO)2 with octa-2,6-diyne. In each complex, the ligand is formed by intermolecular cyclization of two diynes with inclusion of CO. The corresponding reactions with nona-2,7-diyne and deca-2,8-diyne give complexes (η-C5H5)Co[(C9H12)CO] and (C5H5)Co[(C10H14)CO] in which a bicyclic cyclopentadienone has been formed by intramolecular condensation of the diyne. Intramolecular cyclization is also achieved when all three diynes are treated with Fe(CO)5. The reactions with octa- 2,6-diyne and deca-2,8-diyne give metallodiene complexes, Fe2(CO)6(diyne), in which the ferracyclopentadiene ring is fused to either a 4- or 6-membered ring. With nona-2,7-diyne, a cyclopentadienone complex of formula Fe(CO)3[(C10H14)CO] is isolated. In the reactions with Fe(CO)5,organic products of the type (diyne)2, (diyne)3 and [(diyne)CO]2 are also isolated.

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