Unexpected Synthesis of an Unsymmetrical μ-Oxido Divanadium(V) Compound through a Reductive Cleavage of a N−O Bond and Cleavage-Hydrolysis of a C−N Bond of an N,N-Disubstituted Bis-(hydroxylamino) Ligand

Abstract

Reaction of the N,N-disubstituted bis-(hydroxylamino) ligand 2,6-bis[hydroxy(methyl)amino]-4-morpholino-1,3,5-triazine, H(2)bihyat, with V(IV)OSO(4).5H(2)O in water for 6 h followed by the addition of methyl alcohol resulted in the isolation of the unsymmetrical mu-oxido divanadium(V) compound [V(V)(2)O(2)(mu(2)-O)(bihyat)(hyta)(hyto)].3H(2)O (1.3H(2)O) and of the methylhydroxylamido derivative [V(V)O(bihyat)(CH(3)NHO)].H(2)O (2.H(2)O). The N,N-disubstituted mono(hydroxylamino) ligands Hhyta, Hhyto, and CH(3)NHOH were formed by the decomposition of the ligand H(2)bihyat in the presence of vanadium. The structures of compounds 1.3H(2)O and 2.H(2)O were determined by X-ray crystallography. The structure of 1.3H(2)O consists of one five-coordinate vanadium(V) atom and one six-coordinate vanadium(V) atom bridged by an oxido group and ligated to a tridentate bihyat(2-) and two bidentate hyta(-) and hyto(-) ligands, respectively. The two terminal oxido groups in 1.3H(2)O are syn-directed, lying on the same side of the V-O-V plane. The coordination environment of the vanadium atom in 2.H(2)O approximates to a highly distorted pentagonal pyramid with the oxido ligand occupying the apical position. Compounds 1.3H(2)O and 2.H(2)O were studied by multinuclear NMR ((1)H, (13)C, and (51)V) to elucidate their solution structures. The (51)V NMR of 1.3H(2)O in anhydrous CD(2)Cl(2) gave two signals at -199 and -508 ppm, which were assigned to the five- and six-coordinate vanadium(V) atoms, respectively. The resonance of the five-coordinate vanadium nucleus, in a field much lower than that expected from Rehder's [Inorg. Chem., 1988, 27, 584-587] referencing scale, was attributed to the low-energy ligand-to-metal charge transfer transition at 605 nm [epsilon(M) = 5050 M(-1) cm(-1)] of 1.3H(2)O according to Pecoraro et al. [J. Am. Chem. Soc., 1992, 114, 9925-9933]. Electrospray ionization-mass spectrometry studies were used to follow the decomposition products of H(2)bihyat in the presence of vanadium.