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, CNBut1b 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 CNBut2b). 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 CNBut react in a 2 : 1 ratio with 2a to give [Mo(CO)2L2(η5-C7H9)]+(L = PPh34a or CNBut4b) 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.