Synthesis, structure, and spectroscopic properties of vanadium(III) and -(IV) complexes containing hydridotris(pyrazolyl)borate ligands. 3

Tale of Three Molecular Nitrides: Mononuclear Vanadium (V) and (IV) Nitrides As Well As a Mixed-Valence Trivanadium Nitride Having a V3N4 Double-Diamond Core

Transmetallation of [VCl₃(THF)₃] and [TlTp^tBu,Me] afforded [(Tp^tBu,Me)VCl₂] (1, Tp^tBu,Me = hydro-tris(3-tert-butyl-5-methylpyrazol-1-yl)borate), which was reduced with KC₈ to form a C_3v symmetric V^II complex, [(Tp^tBu,Me)VCl] (2). Complex 1 has a high-spin (S = 1) ground state and displays rhombic high-frequency and -field electron paramagnetic resonance (HFEPR) spectra, while complex 2 has an S = 3/2 ⁴A₂ ground state observable by conventional EPR spectroscopy. Complex 1 reacts with NaN₃ to form the V^V nitride-azide complex [(Tp^tBu,Me)V≡N(N₃)] (3). A likely V^III azide intermediate en route to 3, [(Tp^tBu,Me)VCl(N₃)] (4), was isolated by reacting 1 with N₃SiMe₃. Complex 4 is thermally stable but reacts with NaN₃ to form 3, implying a bis-azide intermediate, [(Tp^tBu,Me)V(N₃)₂] (A), leading to 3. Reduction of 3 with KC₈ furnishes a trinuclear and mixed-valent nitride, [{(Tp^tBu,Me)V}₂(μ₄-VN₄)] (5), conforming to a Robin-Day class I description. Complex 5 features a central vanadium ion supported only by bridging nitride ligands. Contrary to 1, complex 2 reacts with NaN₃ to produce an azide-bridged dimer, [{(Tp^tBu,Me)V}₂(1,3-μ₂-N₃)₂] (6), with two antiferromagnetically coupled high-spin V^II ions. Complex 5 could be independently produced along with [(κ₂-Tp^tBu,Me)₂V] upon photolysis of 6 in arene solvents. The putative {V^IV≡N} intermediate, [(Tp^tBu,Me)V≡N] (B), was intercepted by photolyzing 6 in a coordinating solvent, such as tetrahydrofuran (THF), yielding [(Tp^tBu,Me)V≡N(THF)] (B-THF). In arene solvents, B-THF expels THF to afford 5 and [(κ₂-Tp^tBu,Me)₂V]. A more stable adduct (B-OPPh₃) was prepared by reacting B-THF with OPPh₃. These adducts of B are the first neutral and mononuclear V^IV nitride complexes to be isolated.

Preparation and Spectroscopic Characterisation of a Series of Heterobimetallic N-phenyldiethanolaminate-alkoxide Derivatives of Oxovanadium(V)

Reaction of VO(OPri)3 with two equivalents of N-phenyldiethanolamine (PhDEAH2) yields a homometallic complex [VO(PhDEA)(PhDEAH)] 1, which reacts with a number of metal alkoxides to afford heterobimetallic oxovanadium(V) complexes of the types [VO(PhDEA)2{M(OR)n-1}] [where PhDEA = C6H5N(CH2CH2O–)2], [M =: Al (n = 3, R = Pri) 2; Al (n = 3, R = But) 3; Ti (n = 4, R = Pri) 4; Zr (n = 4, R = Pri) 5; Nb (n = 5, R = Pri) 6; Ta (n = 5, R = Pri) 7. The derivative [VO(PhDEA)(OSiPh3)] 8 has been prepared by the equimolar interaction of [VO(PhDEA)(OPri)] with Ph3SiOH. All of these complexes have been characterised by spectroscopic (IR; 1H, 13C, 27Al and 51V NMR) studies, elemental analyses, and molecular weight measurements. The derivative 2 has also been characterised by FAB mass spectral studies, which supports for its monomeric nature.

Synthesis, structures and properties of the catalytic bromination reaction of a series of novel scorperate oxidovanadium complexes with the potential detection of hydrogen peroxide in water

A series of scorpionate oxovanadium (IV) complexes: [VO(Tp(4I))(pz)(SCN)]·1/2CH2Cl2 (1), [VO(Tp)(pzTp)]·2H2O (2), [VO(Bp)(Tp(4I))] (3) and [VO(C5H7O2)(Tp(4I))]·CH3OH (4) (Bp: [H2B(pz)(2-)], Tp: [HB(pz)(3-)], Tp(4I): [HB(4I-pz)(3-)], pzTp: [B(pz)(4-)]) have been synthesized and characterized by elemental analysis, IR spectra, UV-Vis spectroscopy, powder X-ray diffraction, single-crystal X-ray diffraction and thermal gravimetric analysis (TG). Structural analysis shows that the coordination environment of vanadium atom is N5O, to form a distorted octahedron geometry. In addition, the catalytic activities of the bromination reactions for complexes 1 and 2 in phosphate buffer with phenol red as a trap were evaluated primary by UV/Vis spectroscopy, and a practical application of H2O2 detection was firstly observed in the catalytic reaction system.

Synthesis and structure of a new scorpionate-dithio carboxyl oxovanadium complex and an organic dithio carboxyl compound

A new complex of oxovanadium(IV), V(2)O(2)[(HB(pz)(3))(2)(pyrro)(2) (1) and a dimer-dithio carboxyl compound (C(5)H(8)NS(2))(2) (2) have been synthesized by the reaction of VOSO(4).nH(2)O with NaHB(pz)(3) and pyrrolidine dithio carboxylic acid ammonium salt. They were characterized by element analysis, IR spectra, UV-vis spectra and X-ray diffraction. Structural analyses of 1 and 2 gave the following parameters: 1, triclinic, P-1, a=7.732(4)A, b=14.285(8)A, c=17.802(9)A, alpha=101.314(8) degrees , beta=92.682(9) degrees , gamma=92.228(9) degrees , V=1923.6(18)A(3), and Z=4; 2, monoclinic, C2/c, a=13.857(2)A, b=10.4213(18)A, c=9.436(2)A, beta=97.099(2), V=1352.1(4)A(3), and Z=4. In complex 1, vanadium atom adopts a distorted tetragonal bipyramid structure, which is typical for oxovanadium(IV) complexes. Compound 2 is a dimer-dithio carboxyl compound with S-S bond. In addition, thermal analysis was performed for analyzing the stabilization of the complexes.

Biphenyl derived oxovanadium(IV) and copper(II) salen-type complexes – structure and redox tuning

A series of vanadyl(IV) salen (N,N'-bis(salicylidene)ethylenediaminato)-type complexes (1-4) bearing phenyl or 2-hydroxyphenyl moieties have been prepared and characterized by means of mass spectrometry, infra-red, electron paramagnetic resonance (EPR), UV/Vis spectroscopy, cyclovoltammetry and X-ray crystallography. Their structures have been compared to their copper(II) analogs 5-8. Hydrogen intralinkages have been observed in the crystal structure of 5. The pendant hydroxy groups fine-tune the redox properties of the complexes. The catalytic activity in the oxygenation of ethyl phenyl sulfide to the corresponding sulfoxide was investigated. Results indicate that complex 1 bearing hydroxyphenyl subunits and a phenylene bridge is the most selective under these reaction conditions, with the smallest amount of the over-oxidized product, sulfone.

Carbohydrate Binding to VO(3+). Sugar Vanadate Esters Incorporating L-Amino Acid Schiff Bases as Coligands

The glycosides methyl-2,6-dimethoxy-beta-D-galactopyranoside (beta-D-H(2)Me(3)GP), methyl-4,6-dimethoxy-alpha-D-mannopyranoside (alpha-D-H(2)Me(3)MP), and methyl-5-methoxy-beta-D-ribofuranoside (beta-D-H(2)Me(2)RF) have been synthesized, and their reaction with VO(L-Asal)(OMe)(OHMe) in dichloromethane has afforded esters of the type VO(beta-D-HMe(3)GP)(L-Asal), VO(alpha-D-HMe(3)MP)(L-Asal), and VO(beta-D-HMe(2)RF)(L-Asal) as dark-colored solids (red in solution). Here, L-Asal(2)(-) is the deprotonated salicylaldimine of L-alanine (A = a), L-valine (A = v), and L-phenylalanine (A = p). The X-ray structures of VO(beta-D-HMe(3)GP)(L-vsal).H(2)O and VO(alpha-D-HMe(3)MP)(L-psal).H(2)O have revealed five-membered (O,O)-chelation by monoionized carbohydrates, the undissociated hydroxyl group lying trans to the oxo oxygen atom. In the carbohydrate frame, the alkoxidic oxygen atom is axial in the former ester and equatorial in the latter. The V-O(alkoxidic) and V-O(alcoholic) distances are, respectively, approximately 1.80 and approximately 2.30 Å. The ONO coordinating tridentate salicylaldimine ligand is folded (by approximately 35 degrees ) along a C-N bond. The chiral configuration of the metal site corresponds exclusively to the endo disposition of the V=O and the amino acid C-R (R = Me, CHMe(2), CH(2)Ph) bonds. In VO(beta-D-HMe(3)GP)(L-vsal).H(2)O two ester molecules constitute the asymmetric unit and these along with the two water molecules form a macrocyclic supramolecule (diameter, approximately 6.1 Å) held by hydrogen bonds involving alcohol and an OMe function as well as water (O.O distance, 2.59-2.86 Å). On the other hand, in VO(alpha-D-HMe(3)MP)(L-psal).H(2)O the water molecule bridges two symmetry-related ester molecules via alkoxide.water and alcohol.water hydrogen bonds forming an infinite chain structure (O.O lengths, 2.65 and 2.85 Å). The molecular structures observed in the solid state are preserved in solution ((1)H and (51)V NMR). No isomerization is detectable either at the metal site or at the anomeric carbon atom, and the V-O(alkoxidic) and V-O(alcoholic) sites and the metal-carbohydrate binding remain in tact. The VO(beta-D-HMe(2)RF)(L-Asal) species did not afford single crystals but NMR results are consistent with (O,O)-chelation by the ribose fragment, the alkoxidic carbon being C3. Crystal data are as follows. VO(beta-D-HMe(3)GP)(L-vsal).H(2)O: chemical formula, C(21)H(32)NO(11)V; crystal system, orthorhombic; space group, P2(1)2(1)2(1); a = 13.146(7) Å, b = 15.142(5) Å, c = 25.631(9) Å; Z = 8. VO(alpha-D-HMe(3)MP)(L-psal).H(2)O: chemical formula, C(25)H(32)NO(11)V; crystal system, monoclinic; space group, P2(1); a = 13.645(4) Å, b = 7.022(2) Å, c = 15.500(4) Å; beta = 113.98(2) degrees; Z = 2.

Structural and functional characterization of seven spermicidal vanadium(IV) complexes: potentiation of activity by methyl substitution on the cyclopentadienyl rings

In a systematic effort to identify and develop effective vanadocene(IV) complexes as a new class of contraceptive agents, the effect of methyl substitution in the cyclopentadienyl rings of Cpx2VCl2 on their spermicidal activity has been examined. The spermicidal activities of compounds Cpx2VCl2 [Cpx = Me5Cp (Cp*) (1), Cp (3), MeCp (Cp') (5)], as well as two of their corresponding vanadium(V) oxidation products Cp*V(O)Cl2 (2) and CpV(O)Cl2 (4), were examined by computer-assisted sperm analysis (CASA). These analyses have established that penta-substitution of the Cp ring by electron-donating methyl groups augments the spermicidal activity 10-fold. The corresponding V(V) oxo compounds, Cp*V(O)Cl2 (2) and CpV(O)Cl2 (4), tested under identical conditions did not show as effective spermicidal activity even though these complexes have a pseudo-tetrahedral geometry similar to the active vanadocene(IV) dichlorides. Two pseudo-octahedral V(IV) complexes with tris-pyrazolyl borate as ligand, (HBpz3)V(O)Cl.DMF (6) and (HB(3,5-Me2pz)3)V(O)Cl.DMF (7), were also found to exhibit potent spermicidal activity. Although some vanadium(IV) complexes may immobilize sperm due to the generation of .OH radicals, the lack of spermicidal activity of VOSO4 which generates .OH radicals, and the potent spermicidal activity of [Cp2V(acac)][O3SCF3] (8), and [Cp2V(DeDtc)][O3SCF3] (9) which do not generate .OH radicals, indicate that .OH radical mediated reactions may not be essential for the spermicidal activity of vanadium(IV) complexes.

A Heterobimetallic Vanadium-Manganese Complex as a Model for the Structural Dynamics in Oxo-Bridged Metal Dimers

The heterobimetallic complex 1, [LV(&mgr;-O)(&mgr;-OAc)(2)MnL] (where L = hydridotris(pyrazolyl)borate), has been synthesized and characterized. X-ray crystal structural analysis of 1 gave the following parameters: C(24)H(29)B(2)N(13)O(5)VMn, Cmc2(1), a = 13.364(2) Å, b = 17.383(3) Å, c = 14.132(3) Å, Z = 4, V = 3289.9(16) Å(3). An analysis of the structure, optical and resonance Raman spectroscopies, and magnetic measurements indicates that a V(IV)=O.Mn(II) valence formulation is the best description of the oxo-bridged core in 1, although other resonance forms must also contribute.

Vanadium Hydrotris(pyrazolyl)borate Complexes of Diphenyl Phosphate. Heterometallic Complexes of the [LV{(PhO)(2)PO(2)}(3)](-) Fragment

The synthesis and characterization of nine trinuclear, mixed metal complexes of the type [LV{&mgr;-(PhO)(2)PO(2)}(3)](2)M, where the vanadium is in the 3+ oxidation state, L = hydrotris(pyrazolyl)borate, and M = Ba(II) (1), Ca(II) (2), Mg(II) (3), Mn(II) (4), Co(II) (5), Ni(II) (6), Fe(II) (7), 2 Na(I) (8), Al(III) (9), and La(III) (10), are described. X-ray crystal structural analysis of 1, 3, and 4 gave the following parameters: 1, C(92)H(84)B(2)N(12)O(24)P(6)Cl(4)BaV(2), C2/c, a = 26.730(5) Å, b = 15.521(3) Å, c = 27.648(6) Å, beta = 100.53(3) degrees, Z = 4; 3, C(94)H(80)B(2)N(14)O(24)P(6)MgV(2), P&onemacr;, a = 13.410(3) Å, b = 14.179(3) Å, c = 15.694(3) Å, alpha = 112.22(3) degrees, beta = 101.31(3) degrees, gamma = 106.15(3) degrees, Z = 1; 4, C(111)H(80)B(2)N(12)O(28)P(6)MnV(2), R&thremacr;c, a = 18.670(3) Å, b = 18.671(3) Å, c = 61.114(12) Å, Z = 6. Magnetic measurements indicate that compounds containing an integral spin central ion display moderate antiferromagnetic coupling while those with half-integral spins give more complex behavior.