The (Calix[4]arene)chloromolybdate(IV) anion [MoCl(Calix)](-): a convenient entry into molybdenum Calix[4]arene chemistry

The complex (HNEt(3))MoCl(NCMe)(Calix)] (1), prepared from the reaction of MoCl(4)(NCMe)(2)] with p-tert-butylcalix4]arene, H(4)Calix, in the presence of triethylamine, has been used as a source of the d(2)-Mo(NCMe)(Calix)] fragment. Complex 1 is readily oxidized with PhICl(2) to afford the molybdenum(VI) dichloro complex MoCl(2)(Calix)] (2). Both complexes are a convenient entry point into molybdenum(VI) and molybdenum(IV) calixarene chemistry. The reaction of 1 with trimethylphosphine and pyridine in the presence of catalytic amounts Ag(OTf)] led to the formation of neutral d(2) complexes Mo(PMe(3))(NCMe)(Calix)] (3) and Mo(NC(5)H(5))(NCMe)(Calix)] (4). The role of the silver salt in the reaction mixture is presumably the oxidation of the chloromolybdate anion of 1 to give a reactive molybdenum(V) species. The same reactions can also be initiated with ferrocenium cations such as Cp(2)Fe](BF(4)). Without the presence of coordinating ligands, the dimeric complex Mo(NCMe)(Calix)](2)] (5) was isolated. The reaction of 1 with Ph(2)CN(2) led to the formation of a metallahydrazone complex Mo(N(2)CPh(2))(NCMe)(Calix)] (6), in which the diphenyldiazomethane has been formally reduced by two electrons. Molybdenum(VI) complexes were also obtained from reaction of 1 with azobenzene and sodium azide in the presence of catalytic amounts of silver salt. The reaction with azobenzene led under cleavage of the nitrogen nitrogen bond to an imido complex Mo(NPh)(NCMe)(Calix)] (7), whereas the reaction with sodium azide afforded the mononuclear molybdenum(VI) nitrido complex (HNEt(3))MoN(Calix)] (8).