Janusz Zachara

Reactivity of Various Four‐Coordinate Aluminum Alkyls towards Dioxygen: Evidence for Spatial Requirements in the Insertion of an Oxygen Molecule into the Al−C Bond

The interaction of dioxygen with various tetrahedral aluminum alkyls, (tBu)3Al.OEt2 (1), tBu2Al(mu-OtBu)2AltBu2 (6), (tBu)2Al(mesal) (2) [mesal=methyl salicylate anion], R2Al(mu-pz)2AlR2 [pz=deprotonated pyrazole, R= Me (3a), Et (3b), and tBu (3c)], R2Al(mu-3,5-Me2pz)2AIR2[3,5-Me2pz = deprotonated 3,5-dimethylpyrazole, R= Me (4a), and Et (4b)], and Et2B(mu-pz)2AlEt2 (5), has been investigated. We were particularly interested in the effect of steric hindrances both caused by the metal-bonded substituents and those that result from the nature of the bifunctional ligand used in the oxygenation reaction. In the reaction of 1 with O2, only the formation of the monoalkoxide compound6 was observed. The latter di-tert-butyl compound as well as all planar aluminapyrazoles, that is, the tert-butyl derivative 3c and lower alkylaluminum derivatives with the more demanding 3,5-dimethylpyrazoyl ligands 4a and 4b, are stable under an atmosphere of dry oxygen and ambient conditions. Inspection of the space-filling representation of these compounds has undoubtedly shown that the bulky tert-butyl groups or pyrazolyles ligands, respectively, provide steric protection for the metal center from the dioxygen attack. In contrast, the dialkylaluminum derivatives of pyrazole, 3a and 3b, and the diethylaluminum bis(1-pyrazolyl)borate complex 5, all with the metal center eclipsed with respect to the plane defined by the four nitrogen atoms, react smoothly with O2 to form the alkyl(alkoxy)aluminum complexes. In the reaction of 5 with O2 for example, the Et-B bonds remained intact, and the dimeric five-coordinate compound [Et2B(mu-pz)2 Al(mu-OEt)Et]2 (9) was isolated in good yield. The interaction of mononuclear di-tert-butyl chelate complex 2 with O2 at -15 degrees C gives (tBuOO)(tBuO)Al(mu-OtBu)2Al(mesal)2 (7) in high yield, and the presence of the alkylperoxo moiety is a particularly significant point in the resulting product. All the compounds have been characterized spectroscopically, and the structures of 3c, 4a, 6, 7, and 9 have been confirmed by X-ray crystallography. Structural features of 1-6 are discussed and are considered in relation to the possible approach pathways of the O2 molecule to the four-coordinate metal center. This analysis and the observed apparent dissimilarity in the reactions of model four-coordinate aluminum alkyls with O2 clearly show that the stereoelectronic prerequisites are responsible for the fundamentally different reactivity.

X-RAY STRUCTURE ANALYSIS OF DIAQUOBIS(2-PYRAZINECARBOXYLATO) MANGANESE(II), COBALT(II), NICKEL(II), COPPER(II) AND ZINC(II) COMPLEXES

Abstract The crystal structures of diaquobis (2-pyrazinecarboxylato) manganese(II) and isostructural diaquobis(2-pyrazinecarboxylato) cobalt(II), nickel(II), copper(II) and zinc(II) have been determined using single crystal X-ray intensity data. The former complex is orthorhombic (space group Fdd2), with unit cell dimensions a = 15.418(1), b 23.537(3)A, c = 6.940(4)A, the latter compounds are monoclinic (space group P21/c) with unit cell dimensions a = 5.241(1)A, b = 11.108(1)A, c = 10.286(2)A, β = 99.54(1)deg for the cobalt complex. All structures show monomeric molecules consisting of a metal ion chelated by two oxygen atoms belonging to two monodentate carboxylic groups and two heteronitrogen atoms of two pyrazinic acid molecules and two water molecules. In the case of manganese dipyrazinate dihydrate the coordination polyhedron around the manganese ion is a distorted octahedron with the water molecules cis, while in the remaining compounds the octahedra are fairly regular with two water molecules abov...

A tautomeric equilibrium between functionalized 2-formylphenylboronic acids and corresponding 1,3-dihydro-1,3-dihydroxybenzo[c][2,1]oxaboroles

Functionalized 2-formylphenylboronic acids undergo an unprecedented tautomeric rearrangement in solution to form corresponding 1,3-dihydro-1,3-dihydroxybenzo[c][2,1]oxaboroles. X-Ray analyses of selected examples revealed diverse solid-state molecular structures from a planar open form with a hydrogen-bonded carbonyl group (X = 3-F) through a twisted conformer showing a weak carbonyl–boron interaction (X = 3,5-Br2) to a cyclic oxaborole derivative (X = 3-Br). Variable-temperature 1H NMR spectroscopy was used to determine equilibrium constants as well as enthalpies and entropies of tautomerization in a mixed solvent [D6]acetone–D2O (95 : 5). A computational approach to the process by DFT (B3LYP) and MP2 methods has also been performed.

Intramolecular etherification of five-membered cyclic carbonates bearing hydroxyalkyl groups

We report a new one-pot synthetic route to tetrahydrofuran derivatives, which were unexpectedly produced under basic conditions by intramolecular etherification of substituted five-membered cyclic carbonates. For alcohols with vicinal hydroxyl groups, and additional OH groups at the β-position, intramolecular etherification leading to 3-hydroxytetrahydrofuran derivatives was observed. These reactions were studied for compounds having from 2 to 6 hydroxyl groups per molecule, and the mechanism was proposed. The developed method provides a new environmentally friendly approach to the synthesis of five-membered cyclic ether derivatives under non-acidic conditions.

On the Crystal Engineering of Organogallium Alkoxides Derived from Primary‐Amine Alcohols − Relationships between Hydrogen Bonding and Donor−Acceptor Bonds

The crystal structure analysis of model organogallium amine-alkoxides Me2Ga(OCH2CH2CH2NH2) (2) and [Me2Ga{μ-OCH2CH(CH3)NH2}]2 (3), demonstrate how hydrogen bonding can effectively compete with metal−ligand coordination preferences in determining the molecular and crystal structure and how conformational changes in a ligand and increased steric bulk on the carbon atom adjacent to the amine group can impart on a network morphology and molecular aggregations.

Chelating Ruthenium Phenolate Complexes: Synthesis, General Catalytic Activity, and Applications in Olefin Metathesis Polymerization

Cyclic Ru-phenolates were synthesized, and these compounds were used as olefin metathesis catalysts. Investigation of their catalytic activity pointed out that, after activation with chemical agents, these catalysts promote ring-closing metathesis (RCM), enyne and cross-metathesis (CM) reactions, including butenolysis, with good results. Importantly, these latent catalysts are soluble in neat dicyclopentadiene (DCPD) and show good applicability in ring-opening metathesis polymeriyation (ROMP) of this monomer.

Reactions of nickelocene with methyl-, ethyl- and vinyl-lithium compounds. Hydrogen elimination and cyclopentadienyl ring hydrogenation

Abstract It has been shown that bis(cyclopentadienyl)(μ-cyclopentadiene)dinickel, (NiCP)2(η-C5H6), and (η5-cyclopentadienyl) (η3-cyclopentenyl)nickel, CpNi(η3-C5H7), are formed in the reaction of nickelocene with methyl-lithium and with 1-phenyl-2-methyl-propenyl-lithium. The compound (NiCp)2(μ-C5H6) can be only formed as a result of the reduction of the cyclopentadienyl ring bonded to the nickel atom whereas the formation of CpNi(η3-C5H7) can be explained by the further hydrogeneration of cyclopentadiene formed in the earlier reaction steps. (NiCp)2(μ-C5H6) has been fully characterised spectrometrically and its X-ray structure determined. It crystallises in the orthorhombic system, space group Pnma, with four molecules per unit cell.

Synthesis and molecular structure of AlMe[OC(OMe) C6H4-o-O]2. The first structurally characterized five-coordinated simple alky☆

Abstract The interaction of AlMe 3 with 2 equiv. of OC(OMe)C 6 H 4 - o -OH leads to the formation of the mononuclear, five-coordinated aluminiu

13C and 19F NMR study on the structure and conformation of tricarbonylchromium complexes of biphenyl derivatives

Abstract The 13 C and 19 F NMR spectra of 2,2′-difluoro-4,4′-dimethylbiphenyl (BIP), 4,5-difluoro-9,10-dihydrophenanthrene (PHE) and their tricarbonylchromium complexes are reported. The 13 C- 19 F couplings between carbonyl carbons and aromatic fluorine were used to determine the structure and conformation of the investigated complexes. To support the conclusions obtained, the structure of one of the BIP complexes was established by X-ray crystallography.

The first structurally characterized trinickel cluster with an open structure: Crystal and molecular structure of CpPh]Ni(μ-η2η2-PhCCPh)NiCp

Reaction of nickelocene with methyllithium in the presence of diphenylacetylene at the molar ratio of reactants 1:1:2 produces a trinickel cluster with an open structure. The cluster contains a bent arrangement of nickel atoms. Two of the alkyne units are linked via a carboncarbon bond to produce a nickelacyclopentadienyl ring, while the third alkyne unit remains independently coordinated to the cluster via two π -bonds. Two Cp groups are bonded to two terminal nickel atoms. The cluster crystallizes from methylene chloride with solvent molecules in a monoclinic crystal system and P 2 1 / n space group. Corresponding unit cell parameters were determined as: a =12.4385(13) A; b =24.994(3) A; c =13.9657(14) A; β =91.457(8)°; V =4340.4(8) A 3 ; Z =4.