Mark R. Mason

From minerals to materials: synthesis of alumoxanes from the reaction of boehmite with carboxylic acids

Reaction of pseudo-boehmite, [Al(O)(OH)]n, with carboxylic acids (RCO2H) results in the formation of the carboxylatoalumoxanes, [Al(O)x(OH)y(O2CR)z]n where 2x + y + z = 3 and R = C1–C13. The physical properties of the alumoxanes are highly dependent on the identity of the alkyl substituents, R, and range from insoluble crystalline powders to powders which readily form solutions or gels in hydrocarbon solvents, from which films may be readily spin-coated. The physical and chemical changes that occur during the reaction of boehmite with carboxylic acids, and the resulting alumoxanes, have been characterized by scanning electron and transmission electron microscopy (SEM and TEM), IR and multinuclear NMR spectroscopy, and thermogravimetric/differential thermal analysis (TG/DTA). The carboxylatoalumoxanes reported herein are spectroscopically similar to analogues prepared from small molecule precursors. Based on the IR and NMR spectra of the alumoxanes as well as comparison with the aluminium carboxylate compounds [Me2Al(µ-O2CR)]2 and Al(O2CR)(salen)(R = CH3, n-C5H11), a model structure of the alumoxanes is proposed, consisting of a boehmite-like core with the carboxylate substituents bound in a bridging mode. Furthermore, the alumoxane particles appear as rod or sheet-like particles, not linear polymers. This is proposed to be due to the destruction of hydrogen bonding within the mineral as hydroxide groups are removed and replaced with acid functionalities. All of the alumoxanes decompose under mild thermolysis to yield alumina. Mass spectral studies indicate that upon thermolysis the volatile decomposition products are water and the carboxylic acid.

Di- and triindolylmethanes: molecular structures and spectroscopic characterization of potentially bidentate and tridentate ligands

Abstract4-Bromophenyldi(3-methylindol-2-yl)methane (2) and 2-methoxyphenyldi(3-methylindol-2-yl)methane (3) were prepared by sulfuric-acid-catalyzed reactions of 3-methylindole with 4-bromobenzaldehyde and o-anisaldehyde, respectively. Di(3-methylindol-2-yl)phenylmethane (1) and tri(3-methylindol-2-yl)methane (4) were similarly prepared as described previously. Spectroscopic data (1H, 13C NMR) and the X-ray crystal structures for 1⋅C2H5OH and 2–4 are reported. The molecular structure of 1⋅C2H5OH shows hydrogen bonding of both indolyl NH protons to the oxygen of an ethanol molecule. Crystal data for 1⋅C2H5OH: Orthorhombic, Pca21, a = 23.9782(17) Å, b = 8.4437(7) Å, c = 11.3029(9) Å, V = 2288.4(3) Å3, R1 = 0.0597. Crystal data for 2: Orthorhombic, P212121, a = 8.911(3) Å, b = 9.584(4) Å, c = 24.040(11) Å, V = 2053.0(14) Å3, R1 = 0.0454. Crystal data for 3: Monoclinic, P21/c, a = 9.737(2) Å, b = 25.035(6) Å, c = 9.359(2) Å, β = 114.853(4)○, V = 2070.2(8) Å3, R1 = 0.0511. Crystal data for 4: Trigonal, R3, a = 14.2214(10) Å, c = 9.6190(10) Å, V = 1684.8(2) Å3, R1 = 0.0425.

Hydroformylation of 1-hexene in supercritical carbon dioxide using a heterogeneous rhodium catalyst. 3. Evaluation of solvent effects

The heterogeneously catalyzed hydroformylation of 1-hexene in supercritical carbon dioxide is demonstrated as an alternative to homogeneous catalysis through the use of a rhodium–phosphine catalyst tethered to a silica support. Reaction over the heterogeneous catalyst in supercritical CO2 is compared with the use of this catalyst in liquid-phase toluene, and toluene expanded with CO2. Likewise, the performance of the tethered catalyst is compared with a homogeneous rhodium–phosphine catalyst, and shown to be equally effective under identical reaction conditions. Comparable reaction rates were obtained using the heterogeneous rhodium catalyst in supercritical CO2 and CO2-expanded toluene, both of which were superior to the reaction rate with the heterogeneous catalyst in liquid-phase toluene. Initial aldehyde selectivity obtained with the heterogeneous species was also comparable to that obtained with the homogeneous catalyst, but decreased over the course of the reaction. These results demonstrate the value of using phase behavior, and the importance of understanding this behavior in the development and analysis of greener solvent/catalyst systems.

Molecular Phosphates, Phosphonates, Phosphinates, and Arsonates of the Group 13 Elements

Acids of phosphorus and arsenic form cyclic and cage compounds upon reaction with group 13 element alkyls. The molecular products obtained not only have a structural relationship to secondary building units in phosphate and arsenate materials, but these molecular species may act as models of and precursors to the solid state materials. The synthesis, characterization, reactivity and potential applications of these compounds are reviewed.

Hydroformylation of 1-hexene in supercritical carbon dioxide using a heterogeneous rhodium catalyst. 1. Effect of process parameters

Abstract The hydroformylation of 1-hexene in supercritical carbon dioxide is catalyzed with a heterogeneous rhodium catalyst that is active, selective, and stable for the formation of heptanal. The aldehyde yield and regioselectivity can be affected through changes in catalyst support structure, CO2 solvent pressure, and reaction temperature. A complex reaction pathway model is described that allows determination of rate constants, which are in turn, evaluated as a function of temperature and pressure. Analysis reveals an activation volume of −474 cm3/mol and activation energy of 31.9 kJ/mol for the hydroformylation pathways.

Alkylaluminophosphonate-catalyzed ring-opening homopolymerization of epichlorohydrin and propylene oxide

Reactions of an aluminum alkyl, AlR3 (R=Me, Et, iBu, tBu), with a phosphonic acid, R′P(O)(OH)2 (R′=H, Me, tBu, Ph), in molar ratios of 3:1, 2:1, and 1:1 were conducted in toluene–THF. Resulting aluminophosphonate solutions were screened for catalytic activity for the ring-opening homopolymerization of epichlorohydrin (ECH) and propylene oxide (PO). A highly active catalyst solution, 3a, was obtained from reaction of tBu3Al with MeP(O)(OH)2 in a 2:1 molar ratio in toluene–THF. A more active catalyst, 3b, was obtained by removing volatiles, specifically THF, from solutions of 3a and reconstituting with toluene. Catalyst 3a polymerized ECH at 60°C in 1–3 h to an elastomer with molecular weight, Mn, of 103 000 and polydispersity, Mw/Mn, of 1.9. Catalyst 3b yielded poly-ECH with Mn of 130 000 and Mw/Mn of 1.9 within 15 min. Catalysts 3a and 3b polymerized PO to oily oligomers with Mn of 3588 and 4046 and Mw/Mn of 1.1 and 1.2, respectively. Known dimeric and tetrameric aluminophosphonates such as [tBu2AlO2P(OSiMe3)Ph]2 and [RAlO3PR′]4 (R=Me, R′=Me; R=tBu, R′=Me, Ph) do not account for the observed activity of the catalyst solutions. Comparisons of catalytic activity with that for well-defined catalysts and a structural analogy of alkylaluminophosphonates to cyclic and cage tert-butylaluminoxanes are presented.

Synthesis and Calorimetric, Spectroscopic, and Structural Characterization of Isocyanide Complexes of Trialkylaluminum and Tri-tert-butylgallium

Addition of tert-butylisocyanide or 2,6-dimethylphenylisocyanide to a solution of trialkylaluminum or trialkylgallium results in formation of complexes R(3)M·C≡N(t)Bu (M = Al, R = Me (1), Et (2), (i)Bu (3), (t)Bu (4); M = Ga, R = (t)Bu (9)) or R(3)M·C≡N(2,6-Me(2)C(6)H(3)) (M = Al, R = Me (5), Et (6), (i)Bu (7), (t)Bu (8); M = Ga, R = (t)Bu (10)), respectively. Complexes 1, 4, 5, and 8-10 are isolated as solids, whereas the triethylaluminum and triisobutylaluminum adducts 2, 3, 6, and 7 are viscous oils. Complexes 1-10 were characterized by NMR ((1)H, (13)C) and IR spectroscopies, and the molecular structures of 4, 5, and 8-10 were also determined by X-ray crystallography. The frequency of the C≡N stretch of the isocyanide increased by 58-91 cm(-1) upon complexation, consistent with coordination of the isocyanide as a σ donor. Enthalpies of complex formation for 1-10 were determined by isothermal titration calorimetry. Enthalpy data suggest the following order of decreasing Lewis acidity: (t)Bu(3)Al ≫ (i)Bu(3)Al ≥ Me(3)Al ≈ Et(3)Al ≫ (t)Bu(3)Ga. In the absence of oxygen and protic reagents, the reported complexes do not undergo insertion or elimination reactions upon heating their benzene-d(6) solutions to 80 °C.

Sterically crowded aryloxide compounds of aluminium: hydrides and homoleptic aryloxides

Interaction of [AlH3(NMe3)] and [AlH2Cl(NMe3)] with HOR1(R1= C6H2But2-2,6-Me-4) allows for the isolation of [AlH2(OR1)(NMe3)]1 and [AI(H)Cl(OR1)(NMe3)]2 respectively. Compound 1 exists in both mono- and di-meric forms in the solid state. The reaction of 1 with NH2But results in ligand redistribution to give [AIH(OR1)2(NH2But)]3. Similarly, multiple recrystallisation of 1 from Et2O allows for the isolation of [AIH(OR1)2(OEt2)]4, while addition of HOR2(R2= C6H3Ph2-2,6) to 1 yields the mixed aryloxide complex [AIH(OR1)(OR2)(NMe3)]5. Interaction of compound 1 with benzophenone results in the formation of the bridged dimer [{AIH(OR1)(µ-OCHPh2)}2]6. The reaction of 3 molar equivalents of HOR1 with LiAlH4 yields, in addition to [{Li(OR1)(OEt2)}2], compound 4, which reacts futher with H2O, HOR1 or NH2C6H2Cl3-2,4,6 to give [{AI(µ-OH)(OR1)2}2]7, [AI(OR1)3]8 or [AI(OR1)2(NHC6H2Cl3-2,4,6)]13 respectively. Compounds 8 and 13 form stable Lewis acid–base complexes [Al(OR1)3L][L = MeCN 9, pyridine (py)10, OPPh311 or OC(C5H9)But-4 12] and [Al(OR1)2(NHC6H2Cl3-2,4,6)L](L = Et2O 14, py 15 or 3,5-dimethylpyridine 16). The presence of a slow ligand exchange for compound 9 and 12 was investigated by 1H NMR spectroscopy. The molecular structures of 1, 3, 4, 8 and 12 have been confirmed by X-ray crystallography.

Metallo-ligands containing terminal oxygen donors bonded to a manganese–carbonyl moiety

The reactions of [Mn(CO)5Br] with [M(salen)][M = Co, Cu, Zn, Pd, Ni, or Sn; salen =N,N′-ethylenebis(salicylideneiminate)], [Co(salphen)][salphen =N,N′-o-phenylenebis(salicylideneiminate)], or [Co(salchd)][salchd =N,N′-cyclohexane-1,2-diylbis(salicylideneiminate)] in a variety of solvents resulted in the substitution products having the general formula [(ML)Mn(CO)3Br](L = salen, salphen, or salchd). The reaction of 4-ethyl-5-methyl-3,6-diazaocta-3,5-diene-1,8-dithiolatonickel(II), [NiL′], with [Mn(CO)5Br] resulted in the substitution product [(NiL′)Mn(CO)3Br]. These complexes were characterized by i.r. and electronic spectra and magnetic and cyclic voltammetry measurements. Chemical and physical data indicate that the metallo-ligand moieties of these bimetallic complexes bond weakly to the Mn(CO)3Br moiety.