MOLYBDENUM(VI) DIOXO COMPLEXES WITH MACROCYCLIC AMINE LIGANDS

Reaction of MoO2Cl2 with the tetradentate amine ligand 1,4,8,12-tetraa zacyclopentadecane ([15]aneN4) yields the molybdenum(VI) dioxo complex [MoO2 ([15]aneN4-H)]Cl (I), a rare example of a cationic complex cont aining the MoO22+ unit The oxo ligands are cis and the macrocyclic ami ne coordinates in a non-planar fashion, as revealed by X-ray crystal s tructure and NMR data. One of the nitrogen donors cis to the oxo group s has been deprotonated to give an amide ligand (NR2-). In contrast, r eaction of MoO2Cl2 with tetramethylcyclam ,11-tetramethyl-1,4,8,11-tet raazacyclotetradecane, TMC) yields the neutral adduct MoO2Cl2(eta2-TMC ) (III), in which only two of the amine nitrogens are coordinated. An X-ray structure of III shows it to have an all-cis octahedral geometry , very unusual for MoO2X2L, complexes, with one oxo ligand trans to an amine and the other trans to a chloride. Compounds [MoO2([15]aneN4-H) ]BPh4 II and III are not very stable in solution; II is not reduced el ectrochemically or by PPh3.