Complexes of carbonyl compounds with RnAIX3n compounds : IV. The evidence for the formation of cyclic complexes chloroaluminium compounds

Reasonably stable 1 : 2 complexes are formed by carbonyl compounds with chloroaluminium compounds, usually in equilibrium with a 1: 1 complex, however with trimethylaluminium only a 1 : 1 complex is formed. In the case of complexes with an excess of MeAlCl₂, a disproportionation reaction occurs. Possible structures are discussed in light of PMR and IR spectroscopy, dipole moments and molecular weight determination. The previously proposed cyclic six-membered ring is the most reliable structure for the 1 : 2 complex.     

The study of coordinative interaction in the organoaluminium derivatives of substituted phenols

Intramolecular coordination in dimethylaluminium phenoxides (with an ortho-substituted ring) was investigated. Only strongly donating groups in the phenoxy ring (COOMe) displayed strong intramolecular coordination. All compounds investigated formed donor-acceptor complexes with hexamethylphosphoramide (HMPA). Dimethylaluminium methylsalicilate coordinated HMPA without splitting the intramolecular carbonyl oxygen—aluminium bond, which suggests formation of the pentacoordinated aluminium atom.     

Reactions of Me2Al-i-Bu and Me2AlCCMe with primary and secondary amines

The elimination reaction which takes place in complexes of dimethylisobutylaluminium or dimethylpropynylaluminium and N-methylaniline, di-n-butylamine or octylamine was investigated. The abilities of methyl, isobutyl and propynyl groups to take part in elimination reactions were different. A radical exchange reaction was observed.     

Phenoxyaluminium compounds : VII. Reactions of organoaluminium compounds with hindered phenols

Reactions of Me₃Al, i-Bu₃Al, Me₂AlCl and Me₂AlCCMe with 2,6-di-t-butyl-4-methylphenol have been studied at different molar ratios of the reactants.It is found that in the reaction with the phenol, trimethylaluminium forms monomeric methylaluminium diphenoxide; triisobutylaluminium gives both monomeric mono- and di-phenoxyaluminium (depending on molar ratios of the reactants) and dimethylchloroaluminium forms dimeric methylphenoxyaluminium chloride.It is found that methylpropynylaluminium phenoxide is unstable and disproportionates in hydrocarbon solutions.The mechanisms of some of these reactions are suggested.     

Phenoxyaluminium compounds : V. Homolytic cleavage of the aluminium—oxygen bond of organoaluminium phenoxides in the presence of oxygen

Oxydation reactions of monomeric alkylaluminium diphenoxides were studied. It was stated that during the oxidation a homolytic cleavage of the aluminium—oxygen bond takes place with the formation of two free radicals stable at room temperature. On the basis of ESR spectra it was found that one of these is the 2,6-di-t-butyl-4-alkylphenoxy radical. The second, more stable radical contains aluminium and the 2,6-di-t-butyl-4-alkylphenoxy group.     

Complexes of carbonyl compounds with RnAlX3-n compounds: III. The stoichiometry of complexes of ketones with aluminium trichloride

Acetophenone and p-methylacetophenone complex with aluminium trichloride; $\text{1}\text{1}$ and $\text{1}\text{2}$ complexes are formed in equilibrium in benzene solution. A 6-membered ring structure is proposed for the $\text{1}\text{2}$ complex.     

Alkynylaluminum compounds III. Synthesis and structure of the complexes of dimethylpropynylaluminum with dipropynylberyllium and dipropynylmagnesium

Complexes of formula Me₄(MeCC)₄Al₂M (M  Be; Mg) have been synthesized. The low conductance and features indicate that the bonding is mainly covalent; σ-bonding of four alkynyl groups to Be or Mg atoms is suggested with the aluminum atoms coordinated through a combination of σ and π orbitals of the alkynyl groups.     

Short-term changes in delta(13)C and delta(15)N signatures of water discharged from grazed grasslands

The composition of dissolved organic matter (DOM) in a soil is the product of a variety of soil processes. Changes in the composition of DOM in water discharged from soil should, therefore, give an important insight into modifications in these soil processes. We hypothesise that these processes in soils, under different grassland management regimes, would be affected to different extents by the short-term disturbance of a storm event and that evidence of this could be detected in delta(13)C and delta(15)N signatures in drainage and surface runoff waters. During a storm event we collected discharge waters from 1 ha grassland lysimeters, with or without artificial drainage, which received contrasting fertiliser inputs, and delta(13)C and delta(15)N signatures were determined. Changes in (13)C enrichment during the storm event were clearly identifiable, as were differences between plots for (13)C and (15)N, illustrating that this technique has potential to be a useful tool for identifying and investigating short- and long-term changes in soil organic matter dynamics. Copyright 1999 John Wiley & Sons, Ltd.     

Magnetic behavior of the oxide spinels: Li0.5Fe2.5−2x Al x Cr x O4

In order to study the effect of substitution of Fe³⁺ by Al³⁺ and Cr³⁺ in Li_0.5Fe_2.5O₄ on its structural and magnetic properties, the spinel system Li_0.5Al _x Cr _x Fe_2.5?2x O₄ (x=0.0, 0.2, 0.4, 0.5, 0.6 and 0.8) has been characterized by X-ray diffraction, high field magnetization, low field ac susceptibility and ⁵⁷Fe Mossbauer spectroscopy. Contrary to the earlier reports, about 50% of Al³⁺ is found to occupy the tetrahedral sites. The system exhibits canted spin structure and a central paramagnetic doublet was found superimposed on magnetic sextet in the Mössbauer spectra (x>0.5).     

Phenoxyaluminium compounds IV. syntheses and structures of monomeric (2,6-DI-t-Butyl-4-methylphenoxy)aluminium compounds

The preparations of monomeric dialkyl(2,6-di-t-butyl-4-methylphenoxy)aluminium (alkyl = methyl, i-butyl) and i-butylbis(2,6-di-t-butyl-4-methyl-phenoxy)aluminium are described and their reactions, PMR and ESR spectra are reported.