STEPWISE CLUSTER ASSEMBLY USING VO2(ACAC) AS A PRECURSOR - CIS-[VO(OCH(CH3)(2))(ACAC)(2)], [V2O2(MU-OCH3)(2)(ACAC)(2)(OCH3)(2)], [V3O3(MU,MU-(OCH2)(3)CCH3)(2)(ACAC)(2)(OC2H5)], AND (3)-OCH3)(2)(ACAC)(2)(OCH3)(2)]CENTER-DOT-2CH(3)CN

The studies of an underexplored synthetic reagent, VO2(acac) (Hacac = acetylacetone) and semirational strategies for the formation of a comp lete series of simple vanadiunm(V) alkoxide clusters in alcohol-contai ning solvents. The neutral mono-, di-, tri-, and tetranuclear oxovanad ium(V) complexes [V2O2(mu-OCH3)(2)(acac)(2)(OCH3)(2)] (1), (2)(mu-OCH3 )(2)(mu(3)-OCH3)(2)(acac)(2)(OCH3)(2)]. 2CH(3)CN (2), u-O)2(mu-OCH3)2( mu(3)-OCH3)(2)(acac)(2)-(OCH3)(2)] (3), [V3O3{mu,mu-(OCH2)(3)CCH3}(2)( acac)(2)(OR)] (R = CH3 (4), C2H5 (5)), and cis-[VO(OCH(CH3)(2))(acac)( 2)] (6) with alkoxide and acac(-) ligands were obtained by reaction of VO2(acac) with a monoalcohol and/or a tridentate alcohol. The structu res of complexes 1-3, 5, and 6 were determined by X-ray diffraction me thods. Complex 1 crystallized in the monoclinic system, P2(1)/n, with a = 7.8668(5) Angstrom, b = 15.1037(9) Angstrom, c = 8.5879(5) Angstro m, beta = 106.150(1)degrees, V = 980.1(1) Angstrom(3), Z = 2, and R (w R2) = 0.040 (0.121). Complex 2 crystallized in the monoclinic system, P2(1)/n, with a = 8.531(2) Angstrom, b = 14.703(3) Angstrom, c = 12.57 4(2) Angstrom, beta = 95.95(2)degrees, V = 1568.7(5) Angstrom(3), Z = 2, and R (wR2) = 0.052 (0.127). Complex 3 crystallized in the triclini c system, P (1) over bar, with a 8.5100(8) Angstrom, b = 8.9714(8) Ang strom, c = 10.3708(10) Angstrom, alpha = 110.761(1)degrees, beta = 103 .104(1)degrees, gamma = 100.155(1)degrees, V = 691.85(11) Angstrom(3), Z = 1, and R (wR2) = 0.040 (0.105). Complex 5 crystallized in the mon oclinic system, P2(1)/n, with a = 14.019(2) Angstrom, b = 11.171(2) An gstrom, c = 19.447(3) Angstrom, beta = 109.18(1)degrees, V = 2876.5(8) Angstrom(3), Z = 4, and R (wR2) = 0.062 (0.157). Complex 6 crystalliz ed in the monoclinic system, P2(1)/n, with a = 15.0023(8) Angstrom, b = 8.1368(1) Angstrom, c = 26.5598-(2) Angstrom, beta = 95.744(1)degree s, V = 3225.89(8) Angstrom(3), Z = 8, and R (wR2) = 0.060 (0.154). Com plex 1 is a discrete, centrosymmetric dimer in which two vanadium atom s are bridged by two methoxide ligands. Compound 2 contains a V4O4 eig ht-membered ring with both mu-oxo and mu-alkoxo bridging ligands; the ring is capped above and below by two triply bridging methoxo ligands. Compound 3 has the same structure as 2. The three vanadium atoms in c omplex 5 are linked by four bridging oxygen atoms from two tridentate thme(3-) ligands to form a V3O4 chain in which V-O bonds alternate in length. The V-O(isopropoxo) bond in 6 is cis to V=O, and the V-O(acac) bond trans to the oxo group is relatively long. The V2O2 rings of com plex 1 and the mononuclear 1:2 complex can be considered to be the bas ic building block of the trinuclear complexes 4 and 5 and the tetranuc lear complex 2, acting to extend the vanadium-oxide framework. V-51 an d H-1 NMR spectroscopic studies of the solution state of complexes 1-6 revealed dramatic differences in structural and hydrolytic stability of these complexes. Compounds 1 and 3 only remained intact at low temp erature in CDCl3 solution, whereas the mononuclear compound 6 could re main at ambient temperature for similar to 10 h. Compound 4 only maint ained its solid-state structure at low temperature in CDCl3 solution, whereas compound 5 was significantly more stable. The structural integ rity of oligomeric vanadium-oxygen frameworks increased significantly when the coordinating alkoxide group showed more resistance to exchang e reactions than the methoxide group. The solid state and solution pro perties of this new group of complexes not only testify to the versati lity of VO2(acac) as a vanadium(V) precursor but also raise questions relating to solution structure and properties of related vanadium comp lexes with insulin-mimetic properties and catalytic properties.