Add time:09/28/2019         Source:sciencedirect.com

The control of the presence of OH−/CN− nucleophiles in an aqueous-ethanolic solution of [Mo(CN)4O(pcn)]2− anions (pcn = 2-pyrazinecarbonitrile) allows for selective transformation of the organonitrile ligand. The nucleophilic addition of CN− to the triple bond of the pendant nitrile group in pcn results in reduction of the nitrile group to an imine which is subsequently deprotonated and coordinated to the molybdenum(IV) atom in a bidentate mode to afford the complex anion [Mo(CN)3O(pnccn)]2− (Hpnccn = pyrazinecyanoimine), as revealed by its X-ray crystal structure. Such a synthetic and crystallographic demonstration of the reduction of an organonitrile with the capture of a metal-bound imine intermediate is uncommon. Elemental analysis verified the formulation [PPh4]2[Mo(CN)3O(pnccn)]·2.5H2O (1) and the physicochemical behaviour of [Mo(CN)3O(pnccn)]2− was investigated using spectroscopy (IR, UV–Vis and NMR) and cyclic voltammetry. The compound is the first known example with coordinated primary imine group among cyanocomplexes of Mo. The structural and spectroscopic properties of 1 are compared with those of the compounds resulting from the competitive metal-assisted ligand hydrolysis. The equilibrium constant for the protonation of the cyanoimine ligand, pK = 5.54 ± 0.03, has been determined by the spectrophotometric titrations at room temperature.

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