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Michael Bolte

Publications and source records attributed to Michael Bolte.

At least 19 recordsLinked to original sources
PubMed2006

2-Hydroxy-3-(3-oxobutyl)naphthalene-1,4-dione.

The title compound, C14H12O4, forms crystals which appear monoclinic but are actually twinned triclinic. The asymmetric unit consists of two similar molecules, which differ only in the conformation of the 3-oxobutyl side chain. The molecular conformation is characterized by an intramolecular O-H...O hydrogen bond between the hydroxy group and the adjacent carbonyl O atom. The crystal structure is stabilized by O-H...O hydrogen bonds connecting the molecules into zigzag chains running along the b axis.

Crystallography, X-Ray↗
PubMed2006

Hydrogen- and fluorine-bridged disilyl cations and their use in catalytic C-F activation.

The hydrogen-bridged disilyl cation 6 with an 1,8-naphthalenediyl backbone was synthesized and was characterized by NMR spectroscopy and X-ray crystallography, supported by quantum mechanical computations. The SiHSi linkage is symmetrical, corresponding to a single minimum potential, and the structural parameters are in agreement with the presence of a two electron-three center bond in 6. Treatment of disilyl cation 6 with alkyl fluorides yields the disilylfluoronium ion 10. The SiFSi group in the disilyl fluoronium ion 10 is symmetrical with an average SiF bond length of 175.9(8) and a bent angle beta = 130 degrees . Both cations catalyze the hydrodefluorination reaction of alkyl and benzyl fluorides to give alkanes.

Journal Article↗
PubMed2006

Modular approach to tridentate N,O,N' ligands using pyrazolylborate chemistry.

Two anionic tridentate N,O,N' chelators, [pz(Ph)B(mu-pz)(mu-O)B(Ph)pz](-) (3(-)) and [pz(Ph)(Ph)B(mu-pz)(mu-O)B(Ph)pz(Ph)](-) (4(-)), as well as the corresponding complexes [Fe(3)(py)Cl], [Fe(3)Cl(2)] and [Cu(3)Cl], have been synthesised and structurally characterised by X-ray crystallography (pz: pyrazolyl, pz(Ph): 3-phenylpyrazolyl, py: pyridine). Since our synthesis approach takes advantage of the highly modular pyrazolylborate chemistry, inexpensive and relatively resistant N,O,N' ligands of varying steric demand are readily accessible. The complexes [Fe(3)(py)Cl] and [Fe(3)Cl(2)] possess a distorted trigonal-bipyramidal configuration with the pyrazolyl rings occupying equatorial positions and the oxygen donor being located at an apical position. The complex [Cu(3)Cl] crystallises as chloro-bridged dimers featuring Cu(II) ions with ligand environments that are intermediate between a square-planar and a trigonal-bipyramidal geometry.

Journal Article↗
PubMed2006

Unusual conformations of 1,3-dialkoxythiacalix[4]arenes in the solid state.

The structures of three syn-1,3-dialkoxythiacalix[4]arenes with unusual conformations in the solid state are reported. The pinched cone conformation of syn-2(2),4(2)-dihydroxy-1(2),3(2)-bis(prop-2-enyloxy)thiacalix[4]arene, C30H24O4S4, (3a), is stabilized by two intramolecular hydrogen bonds, remarkably formed from both OH groups to the same ether O atom. In syn-2(2),4(2)-dihydroxy-1(5),2(5),3(5),4(5)-tetranitro-1(2),3(2)-bis(prop-2-enyloxy)thiacalix[4]arene acetone disolvate, C30H20N4O12S4.2C3H6O, (3b1), the molecule is found in the 1,3-alternate conformation. The crystallographic C2 symmetry is due to a twofold rotation axis running through the centre of the calixarene ring. The hydroxy groups cannot form intramolecular hydrogen bonds as in (3a) and both are bonded to an acetone solvent molecule. The molecule of the pseudo-polymorph of (3b1) in which the same compound crystallized without any solvent, viz. (3b2), is located on a crystallographic mirror plane. Only one of the two hydroxy groups forms a hydrogen bond, and this is with a nitro group of a neighbouring molecule as acceptor. Molecular mechanics calculations for syn-1,3-diethers suggest a preference of the 1,3-alternate over the usual cone conformation for thiacalix[4]arene versus calix[4]arene and for para-nitro versus para-H derivatives.

Calixarenes↗
PubMed2006

Bis(mu6-cis-2,4,6,8,10,12,14,16-octamethylcyclooctasiloxane-2,4,6,8,10,12,14,16-octolato)octakis[(dimethylformamide)copper(II)] dimethylformamide solvate enclosing a pyrazine molecule.

The title compound, [Cu8(C8H24O2Si)2(C3H7NO)8].C4H4N2.C3H7NO, features a sandwich-like cage enclosing a pyrazine molecule, both situated on a centre of inversion. In addition, the crystal structure contains one dimethylformamide molecule which is disordered over a centre of inversion. The copper layer, containing eight atoms, is located between two siloxanolate fragments. The whole structure of Cu atoms and siloxanolate rings is distorted by the pyrazine molecule, leading to an oval form. As a result, the angles between the Cu atoms differ at the copper layer. The difference in the angles could lead to some deviations in the Cu-Cu exchange interactions within the copper ring, which is of interest for molecular magnetism.

Journal Article↗
PubMed2006

Disodium 2,5-bis(phenylamino)terephthalate decahydrate, an intermediate in the industrial synthesis of quinacridone pigments.

The title compound, 2Na+.C20H14N2O4(2-).10H2O, is an intermediate in the industrial synthesis of red and violet quinacridone pigments. The structure is remarkable for two reasons. First, one of the Na+ ions is surrounded octahedrally by five water molecules and a phenyl group, although the crystal contains many more water molecules than are required for complete coordination of both Na+ ions with six water molecules each. Secondly, although the anion has almost exact molecular inversion symmetry, it is positioned on a general position; this is one of the very few exceptions to the observation of Kitajgorodskij [Advances in Structure Research by Diffraction Methods--Fortschritte der Strukturforschung mit Beugungsmethoden (1970), Vol. 3, pp. 173-247] that molecules with inversion centres always lie on crystallographic inversion centres.

Journal Article↗
PubMed2005

A chloro-bridged dimanganese complex and an oxo-bridged dititanium complex of a ditopic bis(pyrazol-1-yl)borate ligand.

The synthesis and crystal structure analysis of the ditopic p-phenylene-bridged bis(pyrazol-1-yl)borate [[p-C6H4(Bpz2tBu)2]Li2] (LLi2; pz=pyrazol-1-yl) is described. A salt metathesis reaction between LLi2 and MnCl2 in THF leads to the dinuclear complex [L[Mn(THF)]2(mu-Cl)2] featuring a central diamond MnII-(mu-Cl)2-MnII core (X-ray crystal structure analysis). Treatment of LLi2 with 2 equiv of [Ti(NMe2)3Cl] gives the dinuclear titanium compound [L[Ti(NMe2)3]2]. Upon reaction of LLi2 with [Ti(NMe2)2Cl2] and water, the mu-oxo-bridged dititanium species [L[Ti(NMe2)Cl]2(mu-O)] is obtained in excellent yield (X-ray crystal structure analysis).

Boron Compounds↗
PubMed2005

Conformational properties of cyanomethoxy calix[4]arenes.

O-Alkylation of the dinitro calix[4]arene 2, easily available by selective ipso-nitration of the di-cyanomethyl ether 1, with allylbromide (DMF/Cs2CO3) gave tetraethers 3 and 4 with anti- and syn-orientations of the two allyl ether residues. The two possible stereoisomers of in the partial cone and 1,2-alternate conformation exist as an equilibrium mixture which could be quantitatively analysed by 1H NMR spectroscopy. The temperature dependence of this equilibrium leads to deltaH0 = -7.6 to -9.7 kJ mol(-1) in different solvents (tetrachloroethane, benzene, dimethylsulfoxide). Since 3(1,2-alt) could be obtained in pure form, its isomerisation to the equilibrium mixture with 3(paco) could be followed also kinetically. An activation energy of E(a) = 110.5 kJ mol(-1) was found for this reaction in DMSO-d6. The results were confirmed by similar studies with tetraethers 5 and 6 obtained by O-allylation of 1, although exact thermodynamic and kinetic studies were not possible in this case, since the NMR signals of the respective isomers were strongly overlapping. Single crystal X-ray structures were obtained for 2, 3(1,2-alt), 4(paco) and 5(1,2-alt).

Journal Article↗
PubMed2005

Enantioselective Brønsted acid catalyzed transfer hydrogenation: organocatalytic reduction of imines.

The first enantioselective Brønsted acid catalyzed reduction of imines has been developed. This new organocatalytic transfer hydrogenation of ketimines with Hantzsch dihydropyridine as the hydrogen source offers a mild method to various chiral amines with high enantioselectivity. The stereochemistry of the chiral amines can be rationalized by a stereochemical model derived from an X-ray crystal structure of a chiral BINOL phosphate catalyst. [reaction: see text]

Journal Article↗
PubMed2005

A joint experimental and theoretical study of cation-pi interactions: multiple-decker sandwich complexes of ferrocene with alkali metal ions (Li+, Na+, K+, Rb+, Cs+).

A systematic study of cation-pi interactions between alkali metal ions and the cyclopentadienyl ring of ferrocene is presented. The alkali metal (Li+, Na+, K+, Rb+, Cs+) salts of the ditopic mono(pyrazol-1-yl)borate ligand [1,1'-fc(BMe2pz)2]2- crystallize from dimethoxyethane as multiple-decker sandwich complexes with the M+ ions bound to the pi faces of the ferrocene cyclopentadienyl rings in an eta5 manner (fc = (C5H4)2Fe; pz = pyrazolyl). X-ray crystallography of the lithium complex reveals discrete trimetallic entities with each lithium ion being coordinated by only one cyclopentadienyl ring. The sodium salt forms polyanionic zigzag chains where each Na+ ion bridges the cyclopentadienyl rings of two ferrocene moieties. Linear columns [-CpR-Fe-CpR-M+-CpR-Fe-CpR-M+-](infinity) (R = [-BMe2pz]-) are established by the K+, Rb+, and Cs+ derivatives in the solid state. According to DFT calculations, the binding enthalpies of M+-eta5(ferrocene) model complexes are about 20% higher as compared to the corresponding M+-eta6(benzene) aggregates when M+ = Li+ or Na+. For K+ and Rb+, the degree of cation-pi interaction with both aromatics is about the same. The binding sequence along the M+-eta5(ferrocene) series follows a classical electrostatic trend with the smaller ions being more tightly bound.

Journal Article↗
PubMed2005

Magnetic properties of two double-layer structures built from hydroxynaphthoic acids and manganese.

Double-layer structures consisting of alternating polar and non-polar layers have been prepared using Mn2+ ions and o-hydroxynaphthoic acids. The polar layers contain the Mn2+ ions, carboxylate groups, hydroxy groups and water molecules. The non-polar layers are built up from the naphthalene moieties. In catena-poly[[diaquamanganese(II)]bis(mu-3-hydroxy-2-naphthoato-kappa2O:O')] (also called manganese 3-hydroxy-2-naphthoate dihydrate), [Mn(C11H7O3)2(H2O)2]n, (I), the Mn2+ ions are connected by carboxylate groups to form two-dimensional networks. This compound shows distinct antiferromagnetic interactions and long-range ordering at low temperature. In contrast, tetraaquabis(1-hydroxy-2-naphthoato-kappaO)manganese(II), [Mn(C11H7O3)2(H2O)4], (II), which lacks a close linkage between the Mn2+ ions, reveals purely paramagnetic behaviour. In (II), the Mn2+ ion lies on an inversion centre.

Journal Article↗
PubMed2005

Synthesis of huge macrocycles using two calix[4]arenes as templates.

Macrocycles with up to 100 atoms have been synthesised using two calix[4]arenes as templates: first, (3,5-dialkenyloxy)phenyl groups are attached to the wide rim of a calix[4]arene via urea links, then the alkenyl groups are connected via a metathesis reaction using a tetratosylurea calix[4]arene for their correct prearrangement and finally the urea functions are cleaved to detach the newly formed macrocycles.

Journal Article↗