Synthesis, structure and reactivity of tri- and penta-hapto-bonded cycloheptadienyl complexes of molybdenum

Abstract

Protonation by HBF₄·Et₂O of the cycloheptatriene complexes [Mo(CO)₂L(η⁶-C₇H₈)] in the presence of CO has yielded the cycloheptadienyl products [Mo(CO)₃L(η⁵-C₇H₉)][BF₄](L = CO 1a, CNBu^t1b or PPh₃1c); subsequent treatment of 1a or 1b with acetonitrile afforded the trihapto-bonded complexes [Mo(CO)₂L(NCMe)₂(η³-C₇H₉)]⁺(L = NCMe 2a or CNBu^t2b). Reaction of 2a with sodium cyclopentadienide Na(cp) gives [Mo(CO)₂(η³-C₇H₉)(cp)]3 for which an X-ray structural characterisation confirmed the trihapto-bonding mode of the cycloheptadienyl ligand. The monodentate ligands PPh₃ and CNBu^t react in a 2 : 1 ratio with 2a to give [Mo(CO)₂L₂(η⁵-C₇H₉)]⁺(L = PPh₃4a or CNBu^t4b) and chelate ligands L–L react with 2a to give [Mo(CO)₂(L–L)(η⁵-C₇H₉)]⁺(L = Ph₂PCH₂PPh₂5, 2,2′-bipyridyl 6, cyclohexa-1,3-diene 7 or norborna-2,5-diene 8). The crystal structure of 5 reveals a highly asymmetric molecule in which the carbonyl carbon and phosphorus donor atoms exhibit significant deviation from a common basal plane.