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Tri- and Tetravalent and Mixed-Valence Niobium Complexes Supported by a Tripodal Tripyrrolylmethane Trianion

The reaction of Nb2Cl6(TMEDA)2 with the potassium salt of tripyrrolylmethane in a 1:1 ratio afforded two products which have been isolated and characterized. The first compound is the dinuclear {[HC(C4H3N)3]Nb(THF)}2·2THF (1), with two trivalent and diamagnetic metal centers bridged by two tripyrrolyl trianions. Each of the two ligands adopted a rather unusual bridging mode, with two rings each σ-bonding one of the two metal centers and the third both π-bonded to one of the two niobium atoms and σ-bonded to the other. The second product of the reaction is {([H(C4H3N)3]2NbK)2}{Nb4Cl11[K(THF)2]2}·2THF (2), which displays some unusual features. The complex is ionic, with the cationic {Nb4Cl11[K(THF)2]2}2+ unit containing the metal in a mixed-valence state. The two positive charges of the cationic moiety are balanced by two identical anionic {([HC(C4H3N)3]2NbK)2}- units, each containing Nb in the tetravalent state. Each anion is connected to an identical one by the bridging potassium atom, thus assembling a l...