The CO-substitution reactions of analogues of in which the two cyclopentadienyl ligands are linked by a two-carbon chain

Article abstract of DOI:10.1016/0022-328X(94)88072-7

The CO ligands in various complexes A-B-C5H4>(CO)2(μ-CO)2> have been substituted by PR3 (1 CO ligand replaced), P(OR)3 (1 CO ligand replaced), and Ph2P(CH2)nPPh2 where n=1, 2, or 3 (1 or 2 CO ligands replaced).When A-B=R,S-CH(NMe2)CH(NMe2) or CH2C(O) the substitution may be brought about thermally in refluxing di-n-butyl ether, but when A-B=R,R/S,S-CH(NMe2)CH(NMe2) this fails, and UV photolysis is required.The thermal reaction between R,S-(CO)2(μ-CO)2> and Ph2P(CH2)nPPh2 gives two products, R,S-(Ph2P(CH2)nPPh2>(μ-CO)2> and (μ-CO)2>.The latter species were isolated as (μ-CO)2>, and their proportion found to increase with increasing n.The IR spectra of the A-B-C5H4>(CO)(L)(μ-CO)2> complexes where L=PMePh2 show a doubling of the absorption band of the terminal CO (t-CO) which is attributed to isomerism arising from restricted rotation about the Fe-P bond, whilst comparison of the ν(CO) frequencies where L=P(OR)3 and L=PR3 suggests that the variation of electron density on one Fe atom is largely experienced by the remaining t-CO ligand coordinated to the other Fe atom and not by the two shared μ-CO ligands.Dynamic NMR studies show that when A-B=R,S-CH(NMe2)CH(NMe2) there is a slowable restricted rotation about the ring-linking C-C bond but not for other A-B, and that for the various diphosphine complexes, it is possible to slow conformational changes within the Ph2P(CH2)nPPh2 ligand when n=2 or 3, as it is in their (μ-CO)2> counterparts.Key words: Iron; Cyclopentadienyl; Phosphine; Substitution; Fluxionality