Synthesis and solvent induced halide exchange of the electron rich, half sandwich complexes [FeI(dppe)Cp] and [MoX(dppe)(η7-C7H7)] (X = Br, Cl; dppe = Ph2PCH2CH2PPh2)

Improved synthetic routes to [FeI(dppe)Cp], and [MoX(dppe)(η7-C7H7)] (X = Br, Cl) are described. [FeI(CO)2Cp] reacts with dppe in refluxing toluene to give multi-gram quantities of [FeI(dppe)Cp], 3 without the need for photochemical activation. The direct thermal reaction of [MoX(CO)2(η7-C7H7)], 4 with dppe is complicated by competition between associative and dissociative substitution processes. Where X = Br, the associative pathway, which features [MoBr(CO)2(dppe)(η3-C7H7)], 5 as an intermediate, yields cationic [Mo(CO)(dppe)(η7-C7H7)]Br, 7 as the major product. However conditions which promote a dissociative mechanism give good yields of [MoX(dppe)(η7-C7H7)], 6 albeit contaminated with small quantities of [Mo(CO)4(dppe)], 8. The separation of 8 from 6 can be effected by chromatography on alumina but this procedure activates 6 to halide exchange with chlorinated solvents as demonstrated by 31P{1H} NMR investigations on [MoBr(dppe)(η7-C7H7)].