OXOVANADIUM(V) ALKOXO CHLORO COMPLEXES OF THE HYDRIDOTRIPYRAZOLYLBORATES AS MODELS FOR THE BINDING-SITE IN BROMOPEROXIDASE

Vanadium(III) and -(V) alkoxo complexes of the ligands hydridotripyrazolylborate, L, and hydridotris(3,5-dimethylpyrazolyl) borate, L*, have been prepared and characterized by X-ray diffraction, H-1, C-13, and V-51 NMR, electrochemistry, optical spectroscopy, and EXAFS. Two general classes of V(V) complexes have been synthesized with the general formulas LVO(OR)2 and LVO(OR)Cl. The latter complexes contain the shortest V-OR bonds yet reported (1.706-1.754 angstrom) and show that a vanadium-alkoxide bond could account for the short vanadium ''light atom'' interaction seen in the EXAFS of the enzyme, bromoperoxidase. The alkoxides undergo facile hydrolysis to yield a variety of oxo-bridged multinuclear species. One of these has been characterized by X-ray crystallography as the cyclic tetramer [LVO2]4. Crystallographic parameters for complexes prepared in this study: L*V(Cl)OMe(DMF).CH2Cl2, I (C20H34BCl3N7O2V), MW = 572.6, a = 17.189(2) angstrom, b = 10.039(2) angstrom, c = 16.618(3) angstrom, beta = 103.039(12)degrees, V = 2793.9(8) angstrom3, monoclinic (P2(1)/c), Z = 4; LVO(O-Pr(i)))Cl, V (C12H17BClN6O2V), MW = 374.5, a = 13.361(3) angstrom, b = 14.583(3) angstrom, c = 18.016(4) angstrom, V = 3510.2(13) angstrom3, orthorhombic (Pbca), Z = 8; LVO(O-Bu(t))Cl, VI (C13H19BClN6O2V), MW = 388.5, a = 12.783(3) angstrom, b = 15.312(3) angstrom, c = 18.843(4) angstrom, V = 3688.1(14) angstrom3, orthorhombic (Pbca), Z = 8; L*VO(O-Bu(t))Cl, X (C19H30BClN6O2V), MW = 471.7, a = 8.619(2) angstrom, b = 17.761(4) angstrom, c = 16.139(3) angstrom, beta = 104.58(3), V = 2389.9(9) angstrom3, monoclinic (P2(1)/n), Z = 4; [LVO2]4.2CH2-Cl2.2H2O, XI (C38H44B4Cl4N24O10V4), MW = 1385.8, a = 15.634(3) angstrom, b = 16.202(3) angstrom, c = 24.406(5) angstrom, V = 6182(2) angstrom3, orthorhombic (Pccn); Z = 4.