SYNTHESIS AND CHARACTERIZATION OF A SERIES OF VANADIUM TUNICHROME-B-1 ANALOGS - CRYSTAL-STRUCTURE OF A TRIS(CATECHOLAMIDE) COMPLEX OF VANADIUM

Two isomeric tris(pyrogallol) derivatives, 2,3,4-TRENPAM and 3,4,5-TRENPAM, have been synthesized with the use of β,β',β̋-triaminotriethylamine (TREN) as the molecular skeleton and the 2,3,4 or 3,4,5 isomers of trihydroxybenzoic acid ligand groups. Vanadium(IV) complexes of these ligands have been prepared in 25 and 66% yields, respectively. The water-soluble 2,3,4-TRENPAM complex of vanadium(IV) has been characterized by spectrophotometric and voltammetric methods; the (3,4,5-TRENPAM)VIV complex is an insoluble polymer. The reduction potential for the vanadium(IV/III) couple of [V(2,3,4-TRENPAM)2- is pH dependent, varying from -0.41 V (vs NHE in H2O, pH 7) to -0.67 V (vs NHE in H2O, pH 11.7). Complexes of the previously described macrocyclic tris(catecholate) ligand (TRENCAM) with vanadium(III) and vanadium(IV) are reported. The vanadium(III)-TRENCAM salt K3[V(TRENCAM)] crystallizes in cubic space group P213 with Z = 4. The vanadium ion is ligated by the six catechol oxygens in a distorted octahedral environment (crystallographic C3 symmetry) with V-0 distances of 1.985 (5) and 2.007 (5) Å and a trigonal twist angle of 40.8 (6)°. The reduction potential for the vanadium(IV/III) couple of [V(TRENCAM)] is -0.37 V (vs NHE in H2O, pH 11.7) and is essentially pH independent. The reduction potential of the vanadium(V/IV) couple is +0.53 V (vs NHE in dimethylformamide). The implications of these results for the in vivo stabilization of vanadium(III) by tunichrome B 1 are discussed. © 1993, IEEE. All rights reserved. © 1990, American Chemical Society. All rights reserved.