Syntheses, X-ray Structures, and Solution Properties of [V(4)O(4){(OCH(2))(3)CCH(3)}(3)(OC(2)H(5))(3)] and [V(4)O(4){(OCH(2))(3)CCH(3)}(2)(OCH(3))(6)]: Examples of New Ligand Coordination Modes.
Tetranuclear vanadium complexes with alkoxy ligands, [V(4)O(4){&mgr;,&mgr;,&mgr;(3)-(OCH(2))(3)CCH(3)}(2)(OCH(3))(6)] (1) and [V(4)O(4){&mgr;-(OCH(2))(3)CCH(3)}{&mgr;,&mgr;(3)-(OCH(2))(3)CCH(3)}{&mgr;,&mgr;,&mgr;(3)-(OCH(2))(3)CCH(3)}(OR)(3)] (R = C(2)H(5) (2), R = CH(CH(3))(2) (3), R = CH(3) (4)), were synthesized by reacting VO(OR)(3) and H(3)thme (H(3)thme = 1,1,1-tris(hydroxymethyl)ethane) in alcohol. Complex 1 crystallized in the monoclinic space group P2(1)/n with a = 9.646(4) Å, b = 11.502(3) Å, c = 11.960(3) Å, beta = 90.20(3) degrees, V = 1326.9 (7) Å(3), Z = 2 and R (wR(2)) = 0.045 (0.143). Complex 2 also crystallized in the monoclinic space group P2(1)/n with a = 8.290(8) Å, b = 12.237(2) Å, c = 29.118(4) Å, beta = 89.455(9) degrees, V = 2954(3) Å(3), Z = 4, and R(wR(2)) = 0.049 (0.126). Both 1 and 2 are neutral, discrete complexes possessing a common [V(4)O(16)](12)(-) core, which consists of four vanadium(V) atoms chelated by two (1) or three (2) tridentate thme(3)(-) ligands and by six (1) or three (2) RO(-) groups. Compound 1 exhibits a crystallographically required inversion center; in contrast, complex 2 exhibits no crystallographically imposed symmetry, and its three trialkoxy ligands each coordinate differently (one thme(3)(-) is coordinated in a new coordination mode with the oxygens in a terminal, doubly-bridging and triply-bridging mode). Both compounds 1 and 2 maintain their structures in solution, although compound 1 also forms a second minor species upon dissolution. Sequential exchanges of the RO(-) groups in complexes 2 and 3 were investigated by (51)V and (1)H NMR spectroscopy. For example, [V(4)O(4)(thme)(3)(OC(2)H(5))(3)] will react with CH(3)OH to generate [V(4)O(4)(thme)(3)(OCH(3))(3)] (4). These reactions were found to be reversible. The time scale of the alcohol exchange reactions were found to vary depending on the vanadium center that is undergoing the exchange.
Crans
Debbie C.
DC
Department of Chemistry, Colorado State University, Fort Collins, Colorado 80523-1872.
Jiang
Feilong
F
Chen
John
J
Anderson
Oren P.
OP
Miller
Mary M.
MM