Vojtech Jancik

Oxo-molybdenum and oxo-tungsten complexes of Schiff bases relevant to molybdoenzymes

A series of octahedral dioxomolybdenum(VI) complexes of the type [MoO(2)L(2)] {L = 4-Ar-pent-2-en-ol; L(i-Pr2Ph) with Ar = 2,6-diisopropylphenyl (1); L(Me2Ph) with Ar = 2,6-dimethylphenyl (2), L(MePh) with Ar = 2-methylphenyl (3) and with Ar = phenyl (4)} and dioxotungsten(VI) compounds [WO(2)L(2)] {L(i-Pr2Ph) (5); L(Me2Ph) (6) and L(MePh) (7)} with Schiff bases have been synthesized as models for oxotransferases. Spectroscopic characterization in solution shows with the sterically encumbered ligands L(i-Pr2)Ph and L(Me2)Ph isomerically pure products whereas the ligand with only one substituent in ortho position at the aromatic ring L(MePh) revealed a dynamic mixture of three isomers as confirmed by variable temperature NMR spectroscopy. Single crystal X-ray diffraction analyses of compounds 1, 2, and 4 and showed them to be in the N,N-trans conformation consistent with the larger steric demand at nitrogen. Oxygen atom transfer (OAT) properties towards trimethylphosphine were investigated leading to the isolation of two mononuclear molybdenum(IV) compounds [MoO(PMe(3))(L(Me2Ph))(2)] (8) and [MoO(PMe(3))(L(MePh))(2)] (9) as confirmed by spectroscopic and crystallographic means. The kinetics of OAT between complex [MoO(2)(L(Me2Ph))(2)] (2) and PMe(3) was investigated by UV/Vis spectroscopy under pseudo-first-order conditions revealing single-step reactions with Eyring values of DeltaH(double dagger) = +60.79 kJ mol(-1) and DeltaS(double dagger) = -112 J mol(-1) K(-1) and a first-order dependence of phosphine consistent with a slow nucleophilic attack of the phosphine showing the octahedral geometries of this system to be unfavorable for OAT. Compound 1 showed no OAT reactivity towards PMe(3) emphasizing the influence of sterical properties. Furthermore, the reactivity of the reduced compounds [MoO(PMe(3))(L(Me2Ph))(2)] (8) and [MoO(PMe(3))(L(MePh))(2)] (9) towards molecular oxygen was investigated leading, in the case of 8, to the substitution of PMe(3) by O(2) under formation of the peroxo compound [MoO(O(2))(L(Me2Ph))(2)] (10). In contrast, the analogous reaction employing 9 led to oxidation forming the dioxo compound [MoO(2)(L(MePh))(2)] (3).

Lanthanide(III) Complexes with 4,5-Bis(diphenylphosphinoyl)-1,2,3-triazolate and the Use of 1,10-Phenanthroline As Auxiliary Ligand

New lanthanide complexes with 4,5-bis(diphenyl)phosphoranyl-1,2,3-triazolate (L(-)), LnL(3).nH(2)O (1-8) and LnL(3)(phen).nH(2)O (9-16) (Ln = La, Ce, Nd, Sm, Eu, Gd, Tb, Er), have been prepared and spectroscopically characterized. The structures of LnL(3).nH(2)O (Ln = La, Ce, Nd, Sm and Gd) were determined by X-ray crystallography. The metal centers exhibit a distorted trigonal dodecahedron coordination environment with two symmetrically O,O-bidentate ligands and one unsymmetrically O,N- ligand attached to the metal; two oxygen atoms from neighboring dimethyl sulfoxide (DMSO) molecules complete the coordination sphere. This unsymmetrical ligand coordination behavior was also identified in solution through (31)P{(1)H} NMR studies. Photoluminescence spectroscopy experiments in CH(2)Cl(2) for both types of complexes containing Eu(III) (6, 14) and Tb(III) (7, 15) exhibit strong characteristic red and green emission bands for Eu(III) and Tb(III), respectively. Furthermore, NdL(3) (phen).5H (2)O (11) displays emission in the near-infrared spectral region ((4)F(3/2) --> (4)F(9/2) at 872 nm and (4)F(3/2) --> (4)F(11/2) at 1073 nm). The complexes containing 1,10-phenantroline exhibit higher quantum yields upon excitation at 267 nm, indicating that this auxiliary ligand promotes the luminescence of the complexes; however, luminescence lifetimes (tau) in this case are shorter than those of the LnL(3).nH(2)O series.

Structural Variety of Alkali Metal Compounds Containing P−E−M (E = S, Se; M = Li, Na, K) Units Derived from Nitrogen Rich Heterocycles

The preparation of novel alkali metal chalcogenides supported by multidentate nitrogen rich ligands is reported. Treatment of the ligand precursors [H{(4,5-(P(E)Ph(2))(2)tz}] (E = S (1a), Se (1b)) with organolithium reagents or elemental sodium and potassium in tetrahydrofuran (THF) leads to the isolation of 2-7 in high yields. These compounds were characterized by elemental analysis, IR spectroscopy, mass spectrometry, solution and solid-state multinuclear NMR spectroscopy, and single crystal X-ray diffraction analysis. In the solid state, 2, 4, and 5 are dimers that contain bimetallic six-membered (M(2)N(4)) rings (M = Li, Na). In 3, the discrete monomer [Li{4,5-(P(Se)Ph(2))(2)tz}(thf)(2)] (tz = 1,2,3-triazole) contains a five-membered CPSeLiN ring which adopts an envelope conformation. The polymeric arrangement [K{4,5-(P(S)Ph(2))(2)}tz](infinity) in 6 displays different bonding modes based on the hapticity of the ligand upon binding to the potassium atom. In compounds 2-6, the presence of secondary bonding features the alkali metal chalcogen bonds.

Cyclic alumosiloxanes and alumosilicates: exemplifying the Loewenstein rule at the molecular level.

The cyclic alumosiloxane [{LAl(μ-O)(Ph(2)Si)(μ-O)}(2)] (3) and alumosilicate [{LAl(μ-O){((t)BuO)(2)Si}(μ-O)}(2)] (4) were obtained by reaction of the appropriate R(2)Si(OH)(2) precursor (R = Ph, O(t)Bu) with [{LAl(H)}(2)(μ-O)] (1), providing a nice illustration of the Loewenstein rule at work at the molecular level.

A Structurally Diverse Series of Aluminum Chloride Alkoxides [ClxAl(μ-OR)y]n (R = nBu, cHex, Ph, 2,4-tBu2C6H3)

A diverse series of aluminum chloride alkoxides, [Cl(x)Al(mu-OR)(y)](n) (R = (n)Bu, (c)Hex, Ph, 2,4-(t)Bu(2)C(6)H(3)), was synthesized using the reactions of dichlorethylalane (EtAlCl(2)) with cyclohexanol ((c)HexOH), n-butanol ((n)BuOH), and phenols (PhOH and 2,4-(t)Bu(2)C(6)H(3)OH). Eight molecular products were isolated and structurally characterized. The dimeric [Cl(2)Al(mu-O(c)Hex)(2)AlCl(2)] (1) was the smallest oligomer isolated among the cyclohexanolate derivatives. The adduct of 1 with cyclohexanol is a dinuclear molecule [Cl(2)(HO(c)Hex)Al(mu-O(c)Hex)(2)AlCl(2)] (2) which represents a possible intermediate in the conversion reaction leading to the formation of a trinuclear bicyclic [ClAl{(mu-O(c)Hex)(2)AlCl(2)}(2)] (3). Two polymorphic forms of 3 were isolated. Further coordination of cyclohexanol to the Lewis acidic five-coordinate aluminum atom in 3 provided [Cl(HO(c)Hex)Al{(mu-O(c)Hex)(2)AlCl(2)}(2)] (4) with octahedrally coordinated central aluminum. Compound 4 could be regarded as a precursor to the well-known Mitsubishi (tridiamond) tetranuclear species. The reactions of EtAlCl(2) with less sterically demanding (n)BuOH yielded a cyclic trimer, [Cl(2)Al(mu-O(n)Bu)](3) (5), and a unique trinuclear ionic species, [Cl(2)Al{(mu-OH)(mu-O(n)Bu)AlCl(HO(n)Bu)(3)}(2)]Cl (6) with a linear Al(mu-O)(2)Al(mu-O)(2)Al core. In the reactions with phenols, the aromatic groups preferentially stabilized dimeric structures of [Cl(2)Al(mu-OR)(2)AlCl(2)] (R = Ph, 7; 2,4-(t)Bu(2)C(6)H(3), 8). Since these compounds could be considered as intermediates in the nonhydrolytic condensation reactions of metal halides with metal alkoxides, a mixture of EtAlCl(2) with (c)HexOH was used as a precursor for the nonaqueous synthesis of alumina by alkylhalide elimination.

Facile Synthesis of Zero-, One-, and Two-Dimensional Vanadyl Pyrophosphates

Crystallization of Na(2)VOP(2)O(7) from its aqueous solution results in formation of a one-dimensional inorganic polymer {Na(2)VO(H(2)O)P(2)O(7)·7H(2)O}(n) (1). When this polymer is dehydrated at elevated temperatures this polymer undergoes a phase transition to form the two-dimensional framework β-Na(2)VOP(2)O(7), which although previously reported had been difficult to access. Exchanging lithium for sodium via ion-exchange chromatography results in formation of a discrete, cyclic, tetramer species, Li(8)[VOP(2)O(7)(H(2)O)·4H(2)O](4) (2). Isolation of crystalline β-Li(2)VOP(2)O(7) using a dehydration procedure analogous to the one employed for the sodium derivative was unsuccessful. In contrast, we show that β-K(2)VOP(2)O(7) can be obtained from the amorphous phase K(2)VOP(2)O(7)·nH(2)O (n = 0-7) upon thermal dehydration.

Molecular gallosilicates and their group 4 multimetallic derivatives.

Reaction between the silanediol (HO)(2)Si(OtBu)(2) and gallium amides, LGaCl(NHtBu) and LGa(NHEt)(2) (L = [HC{C(Me)N(Ar)}(2)](-), Ar = 2,6-iPr(2)C(6)H(3)), respectively, resulted in the facile isolation of molecular gallosilicates LGaCl(μ-O)Si(OH)(OtBu)(2) (1) and LGa(NHEt)(μ-O)Si(OH)(OtBu)(2) (2). Compound 2 easily reacts with 1 equiv of water to form the unique gallosilicate-hydroxide LGa(OH·THF)(μ-O)Si(OH)(OtBu)(2) (3). Compounds 1-3 contain the simple Ga-O-SiO(3) framework and are the first structurally authenticated molecular gallosilicates. These compounds may be used not only as models for gallosilicate-based materials but also as further reagents because of the presence of reactive functional groups attached to both gallium and silicon atoms. Accordingly, seven molecular heterometallic compounds were obtained from the reactions between compound 3 and group 4 amides M(NMe(2))(4) (M = Ti, Zr) or M(NEt(2))(4) (M = Ti, Zr, Hf). Hence, by tuning the reactions conditions and stoichiometries, it was possible to isolate and structurally characterize the complete 1:1 and 2:1 series (4-10). Completely inorganic cores of types M-O-Ga-O-Si-O and spiro M[O-Ga-O-Si-O](2) were obtained and characterized by common spectroscopic techniques.

Soluble, reactive and stable – unique aluminosilicate ligands and a heterobimetallic derivative [LAl(SLi)(μ-O)Si(OLi·2thf)(OtBu)2]2

The heterobimetallic aluminosilicate [LAl(SLi)(micro-O)Si(OLi.2thf)(O(t)Bu)(2)](2) was prepared from the LAl(SH)(micro-O)Si(OH)(O(t)Bu)(2) (L = [HC{C(Me)N(Ar)}(2)](-), Ar = 2,6-di-(i)Pr(2)C(6)H(3)) ligand, which can also be hydrolyzed to LAl(OH.thf)(micro-O)Si(OH)(O(t)Bu)(2)- leading to the first aluminosilicate-dihydroxide soluble in organic solvents.

Is hexachloro-cyclo-triphosphazene aromatic? Evidence from experimental charge density analysis.

Experimental charge density studies of hexachloro-cyclo-triphosphazene (1) and the boat conformation of octachloro-cyclo-tetraphosphazene (2 a) were performed to unambiguously describe the origin of the electron delocalization in the P3 N3 ring in 1. The obtained results were compared to DFT studies in the solid state and the gas phase. Electron density analysis revealed a highly polarized nature of the P-N bonds and a modular structure of the P3 N3 and P4 N4 rings, which can be separated into independent Cl2 PN units with a perfect transferability between the compounds. Further analysis of the source function experimentally proves the presence of negative hyperconjugation involving both out-of-plane and in-plane nitrogen electrons as well as electrons of the chlorine atoms. Finally, these results discard the presence of pseudoaromatic delocalization in the nearly planar P3 N3 ring.

Redetermination of 1-cyclo­hexyl-3-(2-furo­yl)thio­urea

The title compound, C12H16N2O2S, was synthesized from furoyl isothiocyanate and cyclohexylamine in dry acetone, and the crystal structure redetermined. The thiourea group is in the thioamide form. The structure [Otazo-Sánchez et al. (2001 ▶). J. Chem. Soc. Perkin Trans. 2, pp. 2211–2218] has been redetermined in order to establish the intra- and intermolecular interactions. The trans–cis geometry of the thiourea group is stabilized by intramolecular hydrogen bonding between the carbonyl and cis-thioamide groups, resulting in a pseudo-S(6) planar ring which makes a dihedral angle of 3.24 (6)° with the 2-furoyl group and a torsion angle of −84.3 (2)° with the cyclohexyl group. There is also an intramolecular hydrogen bond between the furan O atom and the other thioamide H atom. In the crystal structure, molecules are linked by intermolecular N—H⋯O hydrogen bonds, forming chains along [010].