William M. Cleaver

Oxidation and hydrolysis of tris-tert-butylgallium

Abstract The oxidation of GaBu3t with oxygen leads to the formation of [Bu3tGa(μ-OOBut)]2 (1). The thermolysis of 1 yields the alkoxide complex [Bu2tGa(μ-OBut)]2 (2), which may also be prepared directly from GaBu3t and ButOH. The reaction of [ButGaCl(μ-Cl)]2 (3) with oxygen does not result in its oxidation, but may be used in its purification due to the oxidation of the GaBu3t impurities. The hydrolysis of GaBu3t in thf solution, in which it exists as the solvated complex 4, results in the formation of the monomeric hydroxide complex Bu2tGa(OH)(thf) (5). In contrast, the use of non-coordinating solvents results in the trimeric hydroxide [Bu2tGa(μ-OH)]3 (6). Compound 6 is also isolated from the reaction of Bu2tGaCl(thf) (7) with KOH in refluxing thf. The solid state pyrolysis of 6 gives the polymeric oxide [ButGa(O)]x (8). All the compounds have been characterized by NMR, IR and mass spectroscopy, while the structures of 1, 2 and 3 have been confirmed by X-ray crystallography. Compound 1 crystallizes in the monoclinic space group C2/m with a = 16.375(2), b = 11.323(2), c = 8.895(2) A and β = 116.710(12)°, Z = 2, R = 0.042 and Rw, = 0.038. Compound 2 crystallizes in the orthorhombic space group Pbca with a = 15.0072(17), b = 9.8399(8), c = 18.3840(15) A, Z = 4, R = 0.037 and Rw = 0.041. Compound 3 crystallizes in the monoclinic space group P21/c with a = 6.816(4), b = 6.743(5), c = 17.062(10)A and β = 95.87(4)°, Z = 2, R = 0.042, Rw = 0.049.

Alcoholysis of tri-tert-butylgallium: synthesis and structural characterization of [(But)2Ga(μ-OR)]2

Abstract Compounds of the type [(But)2Ga(μ-OR)]2, where R = Me (1), Et (2), Prn (3), Pri (4), Bun (5), Bui (6), Bus (7), But (8), n-C5H11 (9), CH2CH2Pri (10), C(H)Et2 (11), CH2But (12), n-C6H13 (13), cyclo-C6H13 (14), Ph (15), CH2Ph (16), have been synthesized and characterized by 1H and 13C NMR and IR spectroscopy, and mass spectrometry. All the compounds are dimeric. The molecular structure of compounds 1, 3, 9, 11, 12, 13 and 15 have been determined by X-ray crystallography. The geometry of the Ga2O2 core is found to be independent of the substituents at oxygen, but steric interactions with the gallium-tert-butyl groups do modify the conformation adopted by the alkoxide group. The crystal packing of [(But)2Ga(μ-OR)]2 for substituents with carbon chains of five or lower is dependent on the packing of the organometallic [(But)2Ga(μ-O)2Ga(But)2] core, while for longer carbon chains the amphiphilic inter-molecular interactions dominate the packing

Dimethylaluminium alkoxides: a physico-chemical investigation

Compounds of the type [Me2Al(µ-OR)]x(R = Me, Et, Prn, Pri, Bun, Bui, Bus, But, n-C5H11, CH2CH2Pri, CH2But, n-C6H13, n-C8H17, n-C10H21 or n-C12H25) have been synthesised and studied by 1H, 13C, 17O and 27Al NMR, IR and mass spectrometry. With the exception of R = CH2CH2Pri, all the compounds with branched-chain alkoxide substituents are purely dimeric (x= 2), while the former and the n-alkyl derivatives exist in solution as an equilibrium between dimeric (x= 2) and trimeric (x= 3) forms. Equilibrium constants and ΔH and ΔS for the trimer–dimer equilibria in solution were obtained for R = Prn. These results, and the NMR spectroscopic data, are interpreted on the basis of steric interactions and ring strain. The kinetics of conversion of [Me2Al(OPrn)]3 into [Me2Al(OPrn)]2 has been investigated, ΔH‡ and ΔS‡ determined, and the identity of the reaction intermediates probed by NMR and mass spectrometry. Ab initio molecular orbital calculations have been carried out on the model compounds [H2Al(µ-OH)]2 and [H2Al(µ-OH)]3. Their relative energies and calculated structures are considered in relation to experimental data.

UV excimer laser photochemistry of hybrid organometallic compounds of gallium.

The gas phase ultraviolet (UV) excimer laser induced photolysis of the gallium-alkyls Ga(t-C4H9)n− (CH3)3−n (n=0, 1, 2, 3) was studied, using photolysis wavelengths of 308, 248, and 193 nm. The photofragments Ga, GaH, and GaCH3 were detected by laser ionization time-of-flight mass spectroscopy, while the hydrocarbon products CH4, C2H6, HC(CH3)3 and H2C=C(CH3)2 were identified using Fourier transform infrared (FTIR) spectroscopy. The formation of the GaH photofragment, and a high olefin-to-alkane product ratio, for Ga(t-C4H9)2(CH3) and Ga(t-C4H9)3 are interpreted to indicate a β-hydrogen elimination process. However, β-hydrogen elimination only occurs after fission of the weakest Ga-C bond, thus no β-hydride elimination is observed for Ga(t-C4H9)(CH3)2. Detection of C2H6 for Ga(CH3)3 and Ga(t-C4H9)(CH3)2, but not for Ga(t-C4H9)2(CH3), shows that under our experimental conditions the formation of ethane is as a result of the reductive elimination of the methyl groups, and is not due to the recombination of two free methyl radicals.

Hybrid organometallic compounds of gallium: UV excimer laser photochemistry of Ga(t-C4H9)n(CH3)3-n (n = 0, 1, 2, 3)

Abstract The gas-phase ultraviolet (UV) excimer laser induced photolysis of the gallium-alkyls Ga(t-C4H9)n(CH3)3-n (n = 0, 1, 2, 3) was studied, using photolysis wavelenghts of 308, 248 and 193 nm. The photofragments Ga, GaH and GaCH3 were detected by laser ionization time-of-flight mass spectroscopy, while the hydrocarbon products CH4, C2H6, HC(CH3)3 and H2C=C(CH3)2 were identified using Fourier transform infrared (FTIR) spectroscopy. The formation of the GaH photofragment, and a high olefin-to-alkane product ratio, for Ga(t-C4H9)2(CH3) and Ga(t-C4H9)3 is interpreted to indicate a β-hydrogen elimination process. However, β-hydrogen elimination only occurs after fission of the weakest Ga-C bond, thus no β-hydride elimination is observed for Ga(t-C4H9)(CH3)2.