Jiří Fusek

Syntheses of the B(8)-hydroxy- and B(8,8′)-dihydroxy-derivatives of the bis(1,2-dicarbollido)-3-cobalt(1-)ate ion by its reductive acetoxylation and hydroxylation: molecular structure of [8,8′-μ-CH3C(O)2(1,2-C2B9H10)2-3-Co]0 zwitterion determined by X-ray diffraction analysis

Preparative routes to 8-hydroxy-bis(1,2-dicarbollido)-3-cobalt(1-)ate ( 2 ) and 8,8′-dihydroxy-bis(1,2-dicarbollido)-3-cobalt(1-)ate ( 3 ) ions are reported by the reductive acetoxylation of the parent bis(dicarbollido)cobaltate ion ( 1 ) followed by hydrolysis of the intermediates. The essential reagent is acetic anhydride, and strong acids are required as catalysts. For the hydroxyderivative ion 2 the simultaneous presence of acetic acid brings benefit, whereas it is detrimental for the formation of the dihydroxyderivative 3 . Reaction intermediate leading to the dihydroxy derivative is the already reported [8,8′-μ-CH 3 C(O) 2 (1,2-C 2 B 9 H 10 ) 2 -3-Co] 0 zwitterion. This compound was adequately characterised for the first time and its molecular structure as determined by X-ray diffraction analysis is presented. Both B-hydroxylated bis(dicarbollido)-ions can be alternatively obtained on the direct hydroxylation of the parent ion by hot 60–80% sulphuric acid. Optimised synthetic procedures and the main physicochemical properties (MS, TLC, HPLC, 1 H- and 11 B-NMR) of the species are presented. The probable reaction course of the reductive acetoxylation is discussed.

A convenient route to carbon-substituted derivatives of nido-5,6-C2B8H12

Abstract An alternative route to the parent nido -5,6-C 2 B 8 H 12 dicarbaborane is reported together with a convenient synthesis of its carbon-substituted derivatives. The method is based on reactions between 4-(Me 2 S)- arachno -B 9 H 13 and alkynes R 1 R 2 C 2 (where R 1 R 2 =H,H; Me, Me; Ph,H, and Ph,Ph) in toluene at reflux. The characteristic reaction mode is a dicarbon insertion into the 9-vertex arachno cluster to produce a series of the 5,6-R 1 R 2 - nido -5,6-C 2 B 8 H 10 species combined with concomitant elimination of one {BH} vertex. The products were characterised by high-field 1 H and 11 B NMR spectroscopy and mass spectrometry associated with [ 11 B– 11 B]-COSY and 1 H{ 11 B(selective)} measurements that permitted complete assignments of all resonances to individual cluster {BH} units.

Alkoxohydridoaluminates: multinuclear NMR study of sodium hydrido-(2-methoxyethoxo) aluminates

Abstract 23 Na, 27 Al, and 1 H NMR spectra were obtained on benzene solutions of varying sodium alkoxohydridoaluminate compositions, Na + H x Al − (OR) 4− x , where x = 2 to 0, and OR = OCH 2 CH 2 OCH 3 . An extensive series was prepared by titration of initial Na + H 2 Al(OR) 2 − , (SDMA), x = 2, by 2-methoxyethanol, HOCH 2 CH 2 OCH 3 . The NMR data presented enabled the refinement of the structure of SDMA, sodium dihydrido-bis(2-methoxyethoxo)aluminate, proposed formerly as an individual compound. The preparation of the analogous ‘mono-hydrido aluminate’, Na + HAl − (OR) 3 , x = 1, as an individual compound, for reason of excellent selective reducing ability, failed. NMR data revealed that alcoholysis of the SDMA by 2-methoxyethanol (in molar ratio Na + H 2 Al − (OR) 2 : HOCH 2 CH 2 OCH 3 = 1:1) does not result in in the desired individual Na + HAl − (OR) 3 , but in an equilibrium mixture of the Na + salt of H 2 Al − (OR) 2 , HAl − (OR) 3 and Al − (OR) 4 aluminate anions. The inherently ionic sodium alkoxohydridoaluminate are stabilized in solvents of low dielectric constant and low donation strength—in benzene—via different types of aggregate: SDMA via higher, weaker ionic aggregates, and mixture of Na + salt of HAl − (OR) 3 , HAl − (OR) 3 and Al − (OR) 4 aluminate anions via ion-paired predominantly trimeric aggregates. These different types of aggregation were recognized on the basis of apparent molecular weight and conductivity measurements on the system. Multinuclear NMR data were used for discussion of these different types of aggregate in more detail.

71Ga NMR studies of mixtures of gallium trichloride and trimethylgallium

Abstract 71 Ga NMR spectra of solutions of GaCl 3 and Me 3 Ga, and of binary mixtures of GaCl 3 Me 3 Ga, in n-heptane have been recorded. The resonance signals for both Me 3 Ga and GaCl 3 are unchanged on dilution over the temperature range 20–100°C. Mixtures of GaCl 3 and Me 3 Ga show only one resonance signal, whose chemical shift is determined predominantly by the nature of the coordination at gallium, indicating rapid chemical exchange of the species involved. The results of studies of methanolysis and hydrolysis, and of adduct formation, are also discussed. The 71 Ga resonances of several possible external standards in the temperature range 20–100°C are also reported. The 71 Ga NMR signal of a solution of GaCl 4 − in 6 M aqueous hydrochloric acid, for which δ( 71 Ga) = 250 ± 0.5 ppm downfield from the signal of a 1 M solution of [Ga(H 2 O) 6 ] 3+ [ClO 4 ] 3 − in 1 M HClO 4 , is recommended as a temperature-independent external standard for gallium NMR studies.

71Ga NMR spectroscopy of solutions of gallium tribromide in aromatic solvents

Abstract The 71 Ga NMR spectra of solutions of gallium tribromide in different aromatic solvents have been recorded, and dependences of chemical shift on concentration, temperature and solvent observed. Such effects are absent in the corresponding solutions of Me 3 Ga. The 71 Ga chemical shift changes are consistent with the dissociation of the dimeric form of gallium tribromide to the monomer, as observed in the gas phase, but a study of effect of added H 2 O or Et 2 O indicates that solutions of gallium tribromide contain no monomeric species and the changes are best accounted for in terms of rapid chemical exchange between two different dimeric forms of gallium tribromide, one closed and the other half-open. With increasing solvating power of the aromatic solvent, the equilibrium between these dimeric structures favours the half-open solvated species.

Synthesis, characterisation and properties of magnesium di(ε-caprolactamate)

Abstract The various synthetic routes to the magnesium di(e-caprolactamate), CL2Mg, were investigated, primarily to establish reproducibility of the route and purity of the products. The reactions of e-caprolactam, CL, with diethylmagnesium, Et2Mg, in diethyl ether have proved to be the most favourable preparative method. The products, primarily CL2Mg and CLnMg, the later representing CL2Mg solvated with (n−2) CL, were characterised by IR, Raman, mass and NMR spectroscopies, including methods of thermal analysis (TGA and DSC), and colligative properties of their benzene solutions were studied as well. A particular attention was paid to the reactions of the products with water.