Interaction of VO2+ ion and some insulin-enhancing compounds with immunoglobulin G

Complexation of VO(2+) ion with the most abundant class of human immunoglobulins, immunoglobulin G (IgG), was studied using EPR spectroscopy. Differently from the data in the literature which report no interaction of IgG with vanadium, in the binary system VO(2+)/IgG at least three sites with comparable strength were revealed. These sites, named 1, 2, and 3, seem to be not specific, and the most probable candidates for metal ion coordination are histidine-N, aspartate-O or glutamate-O, and serinate-O or threoninate-O. The mean value for the association constant of (VO)(x)IgG, with x = 3-4, is log β = 10.3 ± 1.0. Examination of the ternary systems formed by VO(2+) with IgG and human serum transferrin (hTf) and human serum albumin (HSA) allows one to find that the order of complexing strength is hTf ? HSA ≈ IgG. The behavior of the ternary systems with IgG and one insulin-enhancing agent, like [VO(6-mepic)(2)], cis-[VO(pic)(2)(H(2)O)], [VO(acac)(2)], and [VO(dhp)(2)], where 6-mepic, pic, acac, and dhp indicate the deprotonated forms of 6-methylpicolinic and picolinic acids, acetylacetone, and 1,2-dimethyl-3-hydroxy-4(1H)-pyridinone, is very similar to the corresponding systems with albumin. In particular, at the physiological pH value, VO(6-mepic)(IgG)(OH), cis-VO(pic)(2)(IgG), and cis-VO(dhp)(2)(IgG) are formed. In such species, IgG coordinates nonspecifically VO(2+) through an imidazole-N belonging to a histidine residue exposed on the protein surface. For cis-VO(dhp)(2)(IgG), log β is 25.6 ± 0.6, comparable with that of the analogous species cis-VO(dhp)(2)(HSA) and cis-VO(dhp)(2)(hTf). Finally, with these new values of log β, the predicted percent distribution of an insulin-enhancing VO(2+) agent between the high molecular mass (hTf, HSA, and IgG) and low molecular mass (lactate) components of the blood serum at physiological conditions is calculated.     

A new family of insulin-mimetic vanadium complexes derived from 5-carboalkoxypicolinates

The reaction of 5-carboalkoxypicolinic acid (5 ROpicH, R=Me, Et, iPr, sBu; 1 a-d) with vanadyl sulfate yielded the complexes [VO(H(2)O)(5 ROpic)(2)], 2 a-d, with H(2)O and one of the picolinato ligands in the equatorial positions, and the second picolinate occupying equatorial (N) and axial (O) positions. Reaction of 1 a with [NH(4)][VO(3)] yielded [NH(4)][VO(2)(5 MeOpic)(2)], [NH(4)]-3, in which the N functions of the picolinates are trans to the doubly bonded, cis-positioned oxo groups. Complexes 1 a.H(2)O, 1 b, 1 c, 2 a.3.5 H(2)O and [NH(4)]-3.4 H(2)O have been structurally characterised. A detailed pH-potentiometric solution speciation analysis of the system VO(2+)-1 a revealed a dominance of VO(5 OMepic)(2) between pH 2 and 6, with the same coordination pattern, evidenced by EPR spectroscopy, as in the crystalline solid state. In ternary systems containing physiological concentrations of the low molecular mass biogenic binders (B) lactate, oxalate, citrate or phosphate, ternary species of general composition VO(5 MeOpic)B dominate at physiological pH, with citrate being the most effective competitor for picolinate. All of the complexes trigger glucose uptake and degradation by simian virus modified mice fibroblasts at non-toxic concentrations (<100 microM), with 2 a, [VO(2)(pic)(2)](-) and [VO(2)(dipic)](-) being at least as effective as insulin. Vanadium uptake by the cells is most effective in the case of 2 a. 2 a also effectively inhibits free fatty acid release by rat adipocytes treated with epinephrine, thus mimicking the inhibition of lipolysis by insulin.     

Oxovanadium(IV) and -(V) complexes of dithiocarbazate-based tridentate Schiff base ligands: syntheses,structure, and photochemical reactivity of compounds involving imidazole derivatives as coligands

The tridentate dithiocarbazate-based Schiff base ligands H(2)L (S-methyl-3-((5-R-2-hydroxyphenyl)methyl)dithiocarbazate, R = NO(2), L = L(2); R = Br, L = L(3)) react with [VO(acac)(2)] in the presence of imidazole derivatives as coligands to form oxovanadium(IV) and cis-dioxovanadium(V) complexes. With benzimidazole and N-methylimidazole, the products are oxovanadium(IV) complexes, viz. [VOL(3)(BzIm)].0.5CH(3)CN (1a) and [VOL(N-MeIm)(2)] (L = L(3), 1b; L = L(2), 1c), respectively. In both 1a,b, the O and S donor atoms of the tridentate ligand are cis to the terminal oxo group (in the "equatorial" plane) and mutually trans, but the N donor atom is respectively cis and trans to the oxo atom, as revealed from X-ray crystallography. When imidazole or 4-methylimidazole is used as the ancillary ligand, the products obtained are water-soluble cis-dioxovanadium(V) complexes [VO(2)L(R'-ImH)] (L = L(3) and L(2), R' = H and Me, 2a-d). These compounds have zigzag chain structures in the solid state as confirmed by X-ray crystallographic investigations of 2a,d, involving an alternating array of LVO(2)(-) species and the imidazolium counterions held together by Coulombic interactions and strong hydrogen bonding. Complexes 2a-d are stable in water or methanol. In aprotic solvents, viz. CH(3)CN, DMF, or DMSO, however, they undergo photochemical transformation when exposed to visible light. The putative product is a mixed-oxidation divanadium(IV/V) species obtained by photoinduced reduction as established by EPR, electronic spectroscopy, and dynamic (1)H NMR experiments.     

Glycine- and sarcosine-based models of vanadate-dependent haloperoxidases in sulfoxygenation reactions

Reaction of R-styreneoxide with glycine-tert-butylester yielded amino alcohols of the general formula NR1R2R3, where R1 = CH2COOtBu and R2 = R3 = 2-phenyl-2-hydroxyethyl (H2LA); R2 = 2-phenyl-2-hydroxyethyl and R3 = 1-phenyl-2-hydroxyethyl (H2LB); R2 = H and R3 = 2-phenyl-2-hydroxyethyl (HLC); and R2 = H and R3 = 1-phenyl-2-hydroxyethyl (HLD). The corresponding reaction with sarcosine-tert-butylester and subsequent hydrolysis provided the zwitterion +NH(CH3){CH2CHPh(OH)}(CH2CO2-), HLE* (asterisk refers to unprotected carboxylate). Reaction of these ligands with VO(OiPr)3 in CH2Cl2 gave the oxovanadium(V) complexes [VOL(OiPr)2] and [VOL2(OiPr)] (for LC and LD) or, when reacted in the presence of MeOH, [VOL'(OMe)], where L' represents the methyl ester of LA, LB, and LE. The crystal and molecular structures of R-HLC, S-HLD, R,S-HLE* x H2O, and lambda-[VO(R,S-LB')OMe] have been determined. The complex [VOLB'(OMe)] contains vanadium in a distorted trigonal-bipyramidal array (tau = 0.72), the oxo group in the equatorial plane, and methoxide and N in the apical positions, and thus, it structurally models the active center of vanadate-dependent haloperoxidases. The structure and the bonding parameters, including a particularly long d(V-N) of 2.562 A, are backed up by DFT calculations. The isolated oxovanadium(V) complexes and the in situ systems L + VO(OiPr)3 catalyze the oxidation, by cumylhydroperoxide HO2R', of prochiral sulfides (MeSPh, MeSp-Tol, PhSBn) to chiral sulfoxides plus some sulfone. The best results with respect to enantioselectivity (enantiomeric excess (ee) = 38%) were obtained with the system VO(OiPr)3/LA, and the best selectivity with respect to sulfoxide (100%) was obtained with [VOLA(OiPr)]. The reaction with the hexacoordinated [VO(OMe)(HOMe)LD*] was very slow. Oxidation of PhSBn is faster than that of MeSPh and MeSpTol. Turn-over numbers are up to 60 mol of sulfoxide mol-1 of catalyst h-1 (-20 degrees C). The unspectacular ee apparently is a consequence of flexibility of the active catalyst in solution, as shown by the 51V NMR of the catalysts [VOL(OR)] and the oxo-peroxo intermediates [VOL(O2R')]. As shown by DFT calculations, the peroxo ligand coordinates in the tilted end-on fashion in the axial or equatorial position (energy difference = 17.6 kJ/mol).     

Lead and thallium tetrakis(imidazolyl)borates: modifying structure by varying metal and anion

We are using the coordinating anions tetrakis(imidazolyl)borate and tetrakis(4-methylimidazolyl)borate to construct new metal-organic framework structures. In this report, we are exploring materials similar in composition to the previously reported layered network structure Pb[B(Im)(4)](NO(3))(nH(2)O). The metal in this compound can be replaced with isoelectronic Tl(I), affording Tl[B(Im)(4)], and the borate can be modified by using 4-methylimidazole, resulting in Pb[B(4-MeIm)(4)](NO(3)) and Tl[B(4-MeIm)(4)]. Like the parent Pb[B(Im)(4)](NO(3))(nH(2)O), Tl[B(Im)(4)] and Tl[B(4-MeIm)(4)] are layered network structures but both lack anions or solvent molecules in the interlayer spacing. The material Pb[B(4-MeIm)(4)](NO(3)), however, exhibits a 3D network structure that lacks an open topology, resulting from the increased stereochemical activity (greater steric bulk toward other ligands) of the 4-methylimidazole ring. Both of the Tl(I) solids display longer M-N bonds than observed in the analogous Pb(II) compounds; these lengths account for the decreased effect of the stereochemical activity of the 4-methylimidazole ring in Tl[B(4-MeIm)(4)].     

Synthesis,structure, and spectroscopic,photochemical, redox,and catalytic properties of ruthenium(II) isomeric complexes containing dimethyl sulfoxide,chloro, and the dinucleating bis(2-pyridyl)pyrazole ligands

Two isomeric Ru(II) complexes containing the dinucleating Hbpp (3,5-bis(2-pyridyl)pyrazole) ligand together with Cl and dmso ligands have been prepared and their structural, spectroscopic, electrochemical, photochemical, and catalytic properties studied. The crystal structures of trans,cis-[Ru(II)Cl(2)(Hbpp)(dmso)(2)], 2a, and cis(out),cis-[Ru(II)Cl(2)(Hbpp)(dmso)(2)], 2b, have been solved by means of single-crystal X-ray diffraction analysis showing a distorted octahedral geometry for the metal center where the dmso ligands coordinate through their S atom. 1D and 2D NMR spectroscopy corroborates a similar structure in solution for both isomers. Exposure of either 2a or 2b in acetonitrile solution under UV light produces a substitution of one dmso ligand by a solvent molecule generating the same product namely, cis(out)-[Ru(II)Cl(2)(Hbpp)(MeCN)(dmso)], 4. While the 1 e(-) oxidation of 2b or cis(out),cis-[Ru(II)Cl(2)(bpp)(dmso)(2)](+), 3b, generates a stable product, the same process for 2a or trans,cis-[Ru(II)Cl(2)(bpp)(dmso)(2)](+), 3a, produces the interesting linkage isomerization phenomenon where the dmso ligand switches its bond from Ru-S to Ru-O (K(III)(O)(-->)(S) = 0.25 +/- 0.025, k(III)(O)(-->)(S) = 0.017 s(-1), and k(III)(S)(-->)(O) = 0.065 s(-1); K(II)(O)(-->)(S) = 6.45 x 10(9), k(II)(O)(-->)(S) = 0.132 s(-1), k(II)(S)(-->)(O) = 2.1 x 10(-11) s(-1)). Finally complex 3a presents a relatively high activity as hydrogen transfer catalyst, with regard to its ability to transform acetophenone into 2-phenylethyl alcohol using 2-propanol as the source of hydrogen atoms.     

Structure and conformation of bis(acetylacetonato)oxovanadium(IV) and bis(maltolato)oxovanadium(IV) in solution determined by electron nuclear double resonance spectroscopy

The structure and conformation of bis(acetylacetonato)oxovanadium(IV) [VO(acac)(2)] and bis(maltolato)oxovanadium(IV) [VO(malto)(2)] in frozen methanol have been determined by application of electron nuclear double resonance (ENDOR) spectroscopy. The positions of inner- and outer-sphere-coordinated solvent were assigned by ENDOR through use of selectively deuterated analogues of methanol. Similarly, the methyl and methylinyl proton resonance features of VO(acac)(2) were identified by site-selective deuteration. For VO(acac)(2), the ENDOR-determined metal-proton distances were best accounted for by a complex of tetragonal-pyramidal geometry, essentially identical to that determined by X-ray crystallography [Dodge, R. P.; Templeton, D. H.; Zalkin, A. J. Chem. Phys. 1961, 35, 55] but with an inner-sphere solvent molecule coordinated trans to the vanadyl oxygen and an axially positioned solvent molecule hydrogen-bonded to the vanadyl oxygen. In contrast to its trans conformation in crystals [Caravan, P.; et al. J. Am. Chem. Soc. 1995, 117, 12759], the VO(malto)(2) complex was found in a cis conformation whereby the donor oxygen atoms of one maltolato ligand occupied equatorial coordination sites. One of the donor oxygen atoms of the second maltolato ligand occupied the axial coordination site opposite the vanadyl oxygen atom, and the other an equatorial position. An inner-sphere-coordinated methanol molecule in the equatorial plane and a solvent molecule hydrogen-bonded to the vanadyl oxygen were also identified. No evidence for the trans isomer was observed.     

Potentiometric, spectroscopic, electrochemical and DFT characterization of oxovanadium(IV) complexes formed by citrate and tartrates in aqueous solution at high ligand to metal molar ratios: the effects of the trigonal bipyramidal distortion in bis-chelated species and biological implications

The complexation of VO(iv) ion with citrate (L(3-)), d-, l- and dl-tartrate (L(2-)) at high ligand to metal molar ratios was studied in aqueous solution through the combined application of potentiometric, spectroscopic (UV-vis and EPR) and electrochemical (cyclic voltammetry) techniques. Unlike in equimolar solution, mononuclear and not dinuclear species are formed with the binding of carboxylate-COO(-) and alcoholate-O(-) donors yielding mono- and bis-chelated species with VOLH, VOL, VOLH(-1) and VOL(2)H(-2) composition; for tartrates also the "sugar-like" (O(-), O(-)) coordination is involved in the vanadium binding at basic pH values giving rise to the formation of VOL(2)H(-3) and VOL(2)H(-4) complexes. Among the species formed, VOL(2)H(-2) is characterised by a strong distortion towards the trigonal bipyramid with the two V-O(alcoholate) bonds in the equatorial and the two V-O(carboxylate) bonds in the axial positions. The geometry and electronic absorption spectra of such complexes were simulated by DFT methods and it was found that in aqueous solution the distortion follows the steric hindrance of the substituents on the alpha-carbon atom and the hydrophobicity of the ligands. The results were compared with those displayed by simple alpha-hydroxycarboxylates (glycolate, 2-hydroxyisobutyrate, 2-ethyl-2-hydroxybutyrate and benzilate). The trigonal bipyramidal distortion was correlated with the values of: i) Deltalambda = lambda(2) - lambda(3), where lambda(2) and lambda(3) are the central bands in the electronic absorption spectrum; ii) |A(x) - A(y)|, where A(x) and A(y) are the (51)V hyperfine coupling constants along the x and y axes in the anisotropic EPR spectrum; iii) the half-wave potential E(1/2) of oxidation of VO(iv) to the corresponding VO(2)(v) species in the cyclic voltammogram. Finally, a discussion on the possible form of VO(iv)-citrate complexes in blood serum is presented, where it is found that the most relevant species under physiological conditions should be [VO(citrH(-1))](2-).     

Structural models of vanadate-dependent haloperoxidases and their reactivity

Vanadium(V) complexes with hydrazone-based ONO and ONN donor ligands that partly model active-site structures of vanadate-dependent haloperoxidases have been reported. On reaction with [VO(acac)₂] (Hacac = acetylacetone) under nitrogen, these ligands generally provide oxovanadium(IV) complexes [VO(ONO)X] (X = solvent or nothing) and [VO(acac)(ONN)], respectively. Under aerobic conditions, these oxovanadium(IV) species undergo oxidation to give oxovanadium(V), dioxovanadium (V) or μ-oxobisoxovanadium(V) species depending upon the nature of the ligand. Anionic and neutral dioxovanadium(V) complexes slowly deoxygenate in methanol to give monooxo complexes [VO(OMe)(MeOH)(ONO)]. The anionic complexes [VO₂(ONO)]^- can also be convertedin situ on acidification to oxohydroxo complexes [VO(OH)(HONO)]⁺ and to peroxo complexes [VO(O₂)(ONO)]^-, and thus to the species assumed to be intermediates in the haloperoxidases activity of the enzymes. In the presence of catechol (H₂cat) and benzohydroxamic acid (H₂bha), oxovanadium (IV) complexes, [VO (acac)(ONN)] gave mixed-chelate oxovanadium(V) complexes [VO(cat)(ONN)] and [VO(bha)(ONN)] respectively. These complexes are not very stable in solution and slowly convert to the corresponding dioxo species [VO₂(ONN)] as observed by⁵¹V NMR and electronic absorption spectroscopic studies.     

Molybdenum- and tungsten(II) monometallic 3-(2-pyridyl)pyrazole and bimetallic 3-(2-pyridyl)pyrazolate complexes

Molybdenum and tungsten complexes containing the pypzH (3-(2-pyridyl)pyrazole) ligand as a chelating bidentate are prepared: [Mo(CO)(4)(pypzH)], cis-[MoBr(η(3)-allyl)(CO)(2)(pypzH)], cis-[MoCl(η(3)-methallyl)(CO)(2)(pypzH)], [MI(2)(CO)(3)(pypzH)] (M = Mo, W) from [Mo(CO)(4)(NBD)] or the adequate bis(acetonitrile) complexes. The deprotonation of the molybdenum allyl or methallyl complexes affords the bimetallic complexes [cis-{Mo(η(3)-allyl)(CO)(2)(μ(2)-pypz)}](2) or [cis-{Mo(η(3)-methallyl)(CO)(2)(μ(2)-pypz)}](2) (μ(2)-pypz = μ(2)-3-(2-pyridyl-κ(1)N)pyrazolate-2κ(1)N). The allyl complex was subjected to an electrochemical study, which shows a marked connection between both metallic centres through the bridging pyridylpyrazolates.     

Characterization of the Potent Insulin Mimetic Agent Bis(maltolato)oxovanadium(IV) (BMOV) in Solution by EPR Spectroscopy

Bis(maltolato)oxovanadium(IV) (abbreviated BMOV or VO(ma)(2)) has been characterized by electron paramagnetic resonance (EPR) spectroscopy in CH(2)Cl(2), H(2)O, MeOH, and pyridine at both room and low temperatures. Spin Hamiltonian parameters for mono- and bis(maltolato)oxovanadium(IV) complexes [VO(ma)](+) (=[VO(ma)(H(2)O)(n)()](+), n = 2 or 3) and VO(ma)(2) (Hma = 3-hydroxy-2-methyl-4-pyrone, maltol) have been obtained by computer simulation (SOPHE). Configurations of solvated vanadyl/maltol complexes, VO(ma)(2)S, in solution (S = solvent) are proposed on the basis of a comparison of their hyperfine coupling constants with those obtained for related vanadium(IV) compounds in the literature. Whereas at room temperature pyridine coordinates to VO(ma)(2) in a position cis to the oxo ligand (cis isomer), in H(2)O or in MeOH solvated and unsolvated cis and trans adducts of VO(ma)(2) are all formed, with the cis isomer dominant. As expected, the coordinating ability was found to be in the order py > H(2)O approximately MeOH > CH(2)Cl(2). In aqueous solutions at room temperature and neutral pH, cis- and trans-VO(ma)(2)(H(2)O) complexes are present as major and minor components, respectively.     

Structural characterization and DFT study of V(IV)O(acac)2 in imidazolium ionic liquids

We report the structural characterization of vanadyl acetylacetonate in imidazolium room temperature ionic liquids--bbimNTf(2), bmimNTf(2), C(3)OmimNTf(2), bm(2)imNTf(2), bmimPF(6), bmimOTf, bmimBF(4), bmimMeCO(2), bmimMeSO(4), bmimMe(2)PO(4) and bmimN(CN)(2)--and organic solvents. The complex was characterized by visible electronic (Vis) and EPR spectroscopies. VO(acac)(2) shows solvatochromism in the selected ionic liquids and behaves as in organic solvents, evidencing coordination of the ionic liquid anion in the solvents with higher coordinating ability. The Lewis basicity order obtained for the IL anions was: PF(6)(-) < NTf(2)(-) < OTf(-)≈ MeCO(2)(-) < MeSO(4)(-) < BF(4)(-)≈ N(CN)(2)(-) < Me(2)PO(4)(-). The solvent effect on the spectroscopic data was tentatively examined using linear solvation energy relationships based on the Kamlet-Taft solvent scale (α, β and π*), however no suitable correlation was found with all data. The EPR characterization showed the presence of two isomers in bmimOTf, bmimMeCO(2) and bmimMe(2)PO(4), suggesting coordination of the ionic liquid anions in both equatorial and axial positions. The full geometry optimization of cis-/trans-VO(acac)(2)(OTf)(-) and cis-/trans-VO(acac)(2)(OTf)(mmim) structures was done at the B3P86/6-31G* level of theory. The calculations confirm that the anion OTf(-) is able to coordinate to VO(acac)(2) with the trans isomer being more stable than the cis by 4.8 kcal mol(-1).     

Inorganic heterocyclic bis(phosphines): syntheses and structures of a 1,2-bis(diazasilaphosphetidino)ethane and its nickel,molybdenum, and rhodium complexes

Synthesis and characterization of a new, highly electron-rich, chelating bis(phosphine), based on the ethanediyl-linked inorganic heterocycle [Me(2)Si(mu-N(t)Bu)(2)P], are reported. Treatment of nickel chloride with this bis(phosphine) afforded square-planar cis-[[Me(2)Si(mu-N(t)Bu)(2)PCH(2)](2)NiCl(2)], which features isometric nickel-chloride (2.2220(8) A) and nickel-phosphorus (2.1572(8) A) bonds. The ligand reacted with cis-[(piperidine)(2)Mo(CO)(4)] to form colorless cis-[[Me(2)Si(mu-N(t)Bu)(2)PCH(2)](2)Mo(CO)(4)], which has distorted octahedral geometry and long Mo-P bonds (2.5461(18) A). Because of its potential applications in hydrogenation catalysis cis-[[Me(2)Si(mu-N(t)()Bu)(2)PCH(2)](2)Rh(COD)]BF(4) was synthesized. This square-planar, cationic rhodium(I) complex, having symmetrical Rh-P (2.250(2) A) and Rh-C (2.305(6) A) bonds, is structurally related to bis(phospholano)- and bis(phosphetano)rhodium species.     

Formation of μ-dinitrogen (salen)osmium complexes via ligand-induced N···N coupling of (salen)osmium(VI) nitrides

Treatment of [N(n)Bu(4)][Os(VI)(N)Cl(4)] with a stoichiometric amount of H(2)L (L = N,N'-bis(salicylidene)-o-cyclohexylenediamine dianion) in the presence of PF(6)(-) or ClO(4)(-) in MeOH affords [Os(VI)(N)(L)(OH(2))](PF(6)) 1a and [Os(VI)(N)(L)(CH(3)OH)](ClO(4)) 1b, respectively. The structure of 1b has been determined by X-ray crystallography and the Os≡N bond distance is 1.627(3) ?. In the presence of a N-donor heterocyclic ligand in CH(3)CN, 1a reacts at room temperature to afford the mixed-valence μ-N(2) (salen)osmium species [(X)(L)Os(III)-N≡N-Os(II)(L)(X)](PF(6)), 2-14 (X = py 2; 4-Mepy 3; 4-(t)Bupy 4; pz 5; 3-Mepz 6; 3,5-Me(2)pz 7; Im 8; 1-MeIm 9; 2-MeIm 10; 4-MeIm 11; 1,2-Me(2)Im 12; 2-Meozl 13; 4-MeTz 14). These complexes are formed by ligand-induced N···N coupling of two [Os(VI)≡N](+) to give initially [Os(III)-N(2)-Os(III)](2+), which is then reduced to give the more stable mixed-valence species [Os(III)-N(2)-Os(II)](+). Cyclic voltammograms (CVs) of 2-14 show two reversible couples, attributed to Os(III,III)/Os(III,II) and Os(III,II)/Os(II,II). The large comproportionation constants (K(com)) of (5.36-82.3) × 10(13) indicate charge delocalization in these complexes. The structures of 3 and 14 have been determined by X-ray crystallography, the salen ligands are in uncommon cis-β configuration. Oxidations of 4 and 14 by [Cp(2)Fe](PF(6)) afford the symmetrical species [(X)(L)Os(III)-N≡N-Os(III)(L)(X)](PF(6))(2) (X = 4-(t)Bupy 15; 4-MeTz 16). These are the first stable μ-N(2) diosmium(III,III) complexes that have been characterized by X-ray crystallography.     

First metallamacrocyclic complexes of Pt(iv) with 3,3,3',3'-tetraalkyl-1,1'-phenylenedicarbonylbis(thioureas): synthesis by direct or electrolytic oxidative addition of I(2), Br(2) and Cl(2)

Elemental I(2) and Br(2) cleanly react with the 3:3 Pt(ii) metallamacrocycle of 3,3,3',3'-tetra(n-butyl)-1,1'-terephthaloylbis(thiourea)(cis-[Pt(II)(3)(L(p)(1)-S,O)(3)]3), in chloroform at room temperature, to yield oxidative addition products; (195)Pt NMR studies reveal that a stepwise oxidative addition readily occurs to each of the Pt(ii) centres in the metallamacrocycle to yield the mixed valence species cis-[Pt(II)(2)Pt(IV)I(2)(L(p)(1)-S,O)(3)] and cis-[Pt(II)Pt(IV)(2)I(4)(L(p)(1)-S,O)(3)], and the fully oxidised cis-[Pt(IV)(3)I(6)(L(p)(1)-S,O)(3)] in solution, depending on the mole ratio I(2):3. Similar results are obtained on treatment of solutions of 3 with elemental Br(2). Treatment of the corresponding 2:2 Pt(ii) complex of 3,3,3',3'-tetraethyl-1,1'-isophthaloylbis(thiourea)(cis-[Pt(II)(2)(L(m)(1)-S,O)(2)]4) with iodine, results in facile oxidative addition to yield cis-[Pt(IV)(2)(L(m)(1)-S,O)(2)I(4)], with a trans-Pt(iv)-iodo arrangement. Molecules in the crystal structure of 5 have their trans-Pt(iv)-iodo axes essentially aligned, with very close intermolecular iodide contacts (3.775(1)A), resulting in chains of weakly bound metallamacrocycles in the solid. An alternative electrolytic synthesis method, using a simple two-compartment glass cell containing 4 and a chosen halide salt in dichloromethane, led to the formation of cis-[Pt(IV)(2)(L(m)(1)-S,O)(2)Br(4)] 6 and cis-[Pt(IV)(2)(L(m)(1)-S,O)(2)Cl(4)] 7, completing characterization of a series of first-reported trans-Pt(iv)-X (X=I, Br, Cl) metallamacrocyclic complexes.     

Oxidation of p-chlorotoluene and cyclohexene catalysed by polymer-anchored oxovanadium(IV) and copper(II) complexes of amino acid derived tridentate ligands

3-Formylsalicylic acid (Hfsal), covalently bound to chloromethylated polystyrene (PS) and cross-linked with 5% divinylbenzene reacts with d,l-alanine and l-isoleucine to give the Schiff-base tridentate ligands PS-H(2)fsal-d,l-Ala and PS-H(2)fsal-l-Ile, respectively. These anchored ligands upon reaction with VOSO(4) and Cu(CH(3)COO)(2).H(2)O form the complexes PS-[VO(fsal-d,l-Ala)(H(2)O)], PS-[Cu(fsal-d,l-Ala)(H(2)O)], PS-[VO(fsal-l-Ile)(H(2)O)] and PS-[Cu(fsal-l-Ile)(H(2)O)]. The structures of these immobilized complexes have been established on the basis of scanning electron micrographs, spectroscopic (infrared, electronic and EPR), thermogravimetric and elemental analysis studies. The oxidation of p-chlorotoluene and cyclohexene has been investigated using these complexes as the catalysts in the presence of H(2)O(2) as the oxidant. Reaction conditions have been optimised by considering the concentration of the oxidant, the amount of catalyst used and the temperature of the reaction mixture. Under the optimised conditions, p-chlorotoluene gave a maximum of 14% conversion using PS-[VO(fsal-d,l-Ala)(H(2)O)] as the catalyst, with the main products having a selectivity order of: p-chlorobenzaldehyde > p-chlorobenzylalcohol > p-chlorobenzoic acid > 2-methyl-5-chlorophenol > 3-methyl-6-chlorophenol. The oxidation of cyclohexene with PS-[VO(fsal-d,l-Ala)(H(2)O)] proceeds with 79% conversion, which is followed by PS-[VO(fsal-l-Ile)(H(2)O)] with 77% conversion, and the oxidation of cyclohexene by Cu-based catalysts occurs with considerably lower conversions (29-32%). The selectivity of the products follows the order: 2-cyclohexene-1-ol > cyclohexene oxide > cyclohexane-1,2-diol > 2-cyclohexene-1-one. Recycling studies indicate that these catalysts can be reused at least three times without any significant loss in their catalytic potential. However, EPR studies indicate that while the polymer supported V(iv)O-complexes do not change after being used, the EPR spectra of the Cu-complexes show significant changes. The corresponding non-polymer bound complexes [VO(fsal-d,l-Ala)(H(2)O)], [Cu(fsal-d,l-Ala)(H(2)O)], [VO(fsal-l-Ile)(H(2)O)] and [Cu(fsal-l-Ile)(H(2)O)] have also been prepared in order to compare their spectral properties and catalytic activities. The non-polymer bound complexes exhibit lower conversion, along with lower turn-over frequency as compared to their polymer-bound analogues. Several EPR, (51)V NMR and UV-vis studies have been undertaken to detect the intermediate species, and outlines for the mechanisms of the catalytic reactions are proposed.     

Side-on bound complexes of phenyl- and methyl-diazene

Treatment of trans-[FeCl(2)(dmpe)(2)] with phenylhydrazine and 1 equiv of base afforded the side-on bound phenylhydrazido complex cis-[Fe(η(2)-NH(2)NPh)(dmpe)(2)](+). Further deprotonation of the phenylhydrazido complex afforded the side-on bound phenyldiazene complex cis-[Fe(η(2)-HN═NPh)(dmpe)(2)] as a mixture of diastereomers. Treatment of cis-[RuCl(2)(dmpe)(2)] with phenylhydrazine or methylhydrazine afforded the end-on bound phenylhydrazine or methylhydrazine complexes cis-[RuCl(η(1)-NH(2)NHR)(dmpe)(2)](+) (R = Ph, Me). Treatment of the substituted hydrazine complexes with base afforded the side-on bound phenylhydrazido complex cis-[Ru(η(2)-NH(2)NPh)(dmpe)(2)](+) as well as the phenyldiazene and methyldiazene complexes cis-[Ru(η(2)-HN═NR)(dmpe)(2)] (R = Ph, Me). cis-[RuCl(η(1)-NH(2)NHR)(dmpe)(2)](+) (R = Ph, Me), cis-[M(η(2)-NH(2)NPh)(dmpe)(2)](+) (M = Fe, Ru) and cis-[Ru(η(2)-HN═NPh)(dmpe)(2)] were characterized structurally by X-ray crystallography. cis-[Ru(η(2)-HN═NPh)(dmpe)(2)] is the first side-on bound phenyldiazene complex to be structurally characterized. In the structure of cis-[Ru(η(2)-HN═NPh)(dmpe)(2)], the geometry of the coordinated diazene fragment is significantly nonplanar (CNNH angle 137°) suggesting that the complex is probably better described as a Ru(II) metallodiaziridine than a Ru(0) diazene π-complex.     

Organoplatinum complexes containing bis(diphenylphosphino)amine as ligand: uncommon case of N-H . . . I-Pt hydrogen bonding

The complex [PtMe(2)(dppa)], 1a, dppa = Ph(2)PNHPPh(2), which has previously been prepared as a mixture with the dimeric form [Pt(2)Me(4)(micro-dppa)(2)], was synthesized in pure form by the reaction of [PtCl(2)(dppa)] with MeLi. The aryl analogue [Pt(p-MeC(6)H(4))(2)(dppa)], 1b, was prepared by replacement of SMe(2) in cis-[Pt(p-MeC(6)H(4))(2)(SMe(2))(2)] with dppa. The reaction of the chelate complexes 1 with one equiv. of dppa afforded the complexes [PtR(2)(dppa-P)(2)], R=Me, 2a and R=p-MeC(6)H(4) 2b. The reaction of [PtR(2)(dppa)], 1, with neat MeI gave the organoplatinum(iv) complexes [PtR(2)MeI(dppa)], R=Me, 5a and R=p-MeC(6)H(4), 5b. The structure of 5a, determined by X-ray crystallography, indicated that the complex undergoes self-assembly by intermolecular N-H . . . I-Pt hydrogen bonding. MeI was also double oxidatively added to organodiplatinum(ii) complex cis,cis-[Me(2)Pt(micro-SMe(2))(micro-dppa)PtMe(2)], to give diorganoplatinum(iv) complex [Me(3)Pt(micro-dppa)(micro-I)(2)PtMe(3)], 4. The aryl analogue organodiplatinum(ii) complex cis,cis-[(p-MeC(6)H(4))(2)Pt(micro-SMe(2))(micro-dppa)Pt(p-MeC(6)H(4))(2)], 3b, was prepared by the reaction of cis-[Pt(p-MeC(6)H(4))(2)(SMe(2))(2)] with half equiv. of dppa, but 3b refused to react with MeI, probably because of the steric effects of the aryl ligands. The tetramethyl complex [PtMe(4)(dppa)], 6, was prepared either by reaction of 5a with MeLi or by replacement of SMe(2) in [Pt(2)Me(8)(micro-SMe(2))(2)] with dppa. All the complexes were fully characterized in solution by multinuclear NMR ((1)H, (13)C, (31)P and (195)Pt) methods and their coordination compared with that of the corresponding known dppm complexes.     

Coordination of 9-ethylguanine to the mixed-ligand compound alpha-[Ru(azpy)(bpy)Cl2] (azpy = 2-phenylazopyridine and bpy = 2,2'-bipyridine). An unprecedented ligand positional shift, correlated to the cytotoxicity of this type of [RuL2Cl2] (with L = azpy or bpy) complex

The striking difference in cytotoxic activity between the inactive cis-[Ru(bpy)(2)Cl(2)] and the recently reported highly cytotoxic alpha-[Ru(azpy)(2)Cl(2)] (alpha indicating the isomer in which the coordinating Cl atoms, pyridine nitrogens, and azo nitrogens are in mutual cis, trans, cis orientation) encouraged the synthesis of the mixed-ligand compound cis-[Ru(azpy)(bpy)Cl(2)]. The synthesis and characterization of the only occurring isomer, i.e., alpha-[Ru(azpy)(bpy)Cl(2)], 1 (alpha denoting the isomer in which the Cl ligands are cis related to each other and the pyridine ring of azpy is trans to the pyridine ring of bpy), are described. The solid-state structure of 1 has been determined by X-ray structure analysis. The IC(50) values obtained for several human tumor cell lines have indicated that compound 1 shows mostly a low to moderate cytotoxicity. The binding of the DNA model base 9-ethylguanine (9-EtGua) to the hydrolyzed species of 1 has been studied and compared to DNA model base binding studies of cis-[Ru(bpy)(2)Cl(2)] and alpha-[Ru(azpy)(2)Cl(2)]. The completely hydrolyzed species of 1, i.e., alpha-[Ru(azpy)(bpy)(H(2)O)(2)](2+), has been reacted with 9-EtGua in water at room temperature for 24 h. This resulted in the monofunctional binding of only one 9-EtGua, coordinated via the N7 atom. The product has been isolated as alpha-[Ru(azpy)(bpy)(9-EtGua)(H(2)O)](PF(6))(2), 2, and characterized by 2D NOESY NMR spectroscopy. The NOE data show that the 9-EtGua coordinates (under these conditions) at the position trans to the azo nitrogen atom. Surprisingly, time-dependent (1)H NMR data of the 9-EtGua adduct 2 in acetone-d(6) show an unprecedented positional shift of the 9-EtGua from the position trans to the azo nitrogen to the position trans to the bpy nitrogen atom, resulting in the adduct alpha'-[Ru(azpy)(bpy)(9-EtGua)(H(2)O)](PF(6))(2) (alpha' indicating 9-EtGua is trans to the bpy nitrogen). This positional isomerization of 9-EtGua is correlated to the cytotoxicity of 1 in comparison to both the cytotoxicity and 9-EtGua coordination of cis-[Ru(bpy)(2)Cl(2)], alpha-[Ru(azpy)(2)Cl(2)], and beta-[Ru(azpy)(2)Cl(2)]. This positional isomerization process is unprecedented in model base metal chemistry and could be of considerable biological significance.     

N,N-coordinated pi radical anions of S-methyl-1-phenyl-isothiosemicarbazide in two five-coordinate ferric complexes [Fe III(L Me*)(2)X] (X = CH3S-, Cl-)

The reaction between [Fe(III)(dmf)(6)](ClO(4))(3) and the ligand S-methyl-1-phenyl-isothiosemicarbazide, H(2)[L(Me)], and triethylamine (1:3:6) in methanol under an argon blanketing atmosphere at elevated temperatures (reflux) yields a purple solution from which upon cooling to 20 degrees C dark green crystals of [Fe(III)(L(Me)(*))(2)(SCH(3))] (1) were obtained in 15% yield. From a similar reaction mixture using FeCl(3) as starting material in the solvent acetone under anaerobic conditions at -80 degrees C, dark green crystals of [Fe(III)(L(Me)(*))(2)Cl] (2) were obtained in 21% yield. The structures of complexes 1 and 2 have been determined by single-crystal X-ray crystallography at 100 K. Both complexes are five-coordinate square base pyramidal ferric species containing two N,N-coordinated, monoanionic pi radicals, (L(Me)(*))(1)(-), of the parent S-methyl-1-phenyl-isothiosemicarbazide(2-) dianion in the basal positions whereas the axial position is occupied by methylthiolate in 1 and chloride in 2, respectively. The electronic structure of both species has been elucidated by their electronic spectra, magnetic properties, and X-band EPR and M?ssbauer spectra. Both possess an S(t) = (1)/(2) ground state which is attained via an antiferromagnetic coupling between the spins of an intermediate spin ferric ion (S(Fe) = (3)/(2)) and two ligand pi radical anions (S(rad) = (1)/(2)).