Solution structures and dynamic behaviour of some iron chalcogen derivatives

13C-n.m.r. spectra of (μ-SR)2Fe2(CO)6, (μ-SR)2Fe2(CO)5P(n-Bu)3 and (μ-X)2Fe2(CO)6 (X=S or Se) show that the solid state structure is maintained in solution. N.m.r. evidence indicates that two isomeric species, not separable by means of the usual physicochemical methods, are present for (μ-SPh)2Fe2(CO)6 with an overwhelming predominance of theanti form. The phosphine substitutes a COtrans to the iron-iron bond. For any of the iron chalcogen derivatives examined, variable temperature13C-n.m.r. spectra show that carbonyl exchange occur in one step. The energy barrier for the exchange of carbon monoxide in the phosphine derivative is lower than that in the unsubstituted complex.