Preparation, fluxionality and some reactions of ring-linked A-B-C5H4>(CO)4-n(CNMe)n> complexes

Article abstract of DOI:10.1016/0022-328X(94)05067-L

A-B-C5H4>(CO)2(μ-CO)2> reacts with CNMe in refluxing xylene when A-B = R,S-CH(NMe2)CH(NMe2) or CH2C(O) to give A-B-C5H4>(CO)4-n(CNMe)n> (n = 1 or 2).This thermal reaction does not take place when A-B = R,R/S,S-CH(NMe2)CH(NMe2), CH2CH(NMe2), CHC(NMe2), CH2CH(OH) or CH2CH2, but photolysis allows the preparation of A-B-C5H4>(CO)4-n(CNMe)n> (n = 1-3), and (CO)3(CNMe)> may be prepared by the LiAlH4-reduction of (CO)3(CNMe)>.All the complexes react with MeI, EtI or MeOSO2CF3 to give derivatives containing one or two μ-CNMe2⁺ ligands. 1H NMR studies show that all the neutral complexes are fluxional, with processes taking place within the C5H4-A-B-C5H4 ligands comparable to those observed in the tetracarbonyl precursors as well as CO/CNMe site exchange.This last is more restricted than in the counterparts, so that two non-interconverting A-B-C5H4>(CO)2(CNMe)2> species are possible, and have been separated in most instances; one has the structure A-B-C5H4>(CO)(CNMe)(μ-CO)(μ-CNMe)> and the other is A-B-C5H4>(CO)2(μ-CNMe)2>, which is in equilibrium with A-B-C5H4>(CNMe)2(μ-CO)2> in solution.Their formation provides unequivocal evidence for the validity of the Cotton-Adams rules on fluxionality in derivatives.The structure of R,S-(CO)2(μ-CNMe)2> has been determined by an X-ray diffraction study. Keywords: Iron; Carbonyl; Cyclopentadienyl; Fluxionality; Isocyanide