Publications
54 results found
O'Hare D, Ashley A, 2011, Process for producing methanol using heterolytic cleavage of hydrogen by a frustrated Lewis pair.
A process for methanol prodn. comprises heterolytic cleavage of hydrogen by a frustrated Lewis pair comprising a Lewis acid and a Lewis base; and the hydrogenation of CO2 with the heterolytically cleaved hydrogen to form methanol, whereby the Lewis acid and Lewis base could be sep. mols. or sep. moieties of the same mol. Thus, reacting H2 with an equimolar ratio of 2,2,6,6-tetramethylpiperidine and B(C6F5)3 gives salt [TMPH][HB(C6F5)3] in which the hydrogen mol. has undergone heterolytic fission; in the second step CO2 is reduced using H2 activated by this frustrated Lewis acid-base pair to give formate, decompn. of which results in methanol. [on SciFinder(R)]
Ransom P, Ashley AE, Brown ND, et al., 2011, Synthesis, characterization, and polymerization studies of ethylenebis(hexamethylindenyl) complexes of zirconium and hafnium., Organometallics, Vol: 30, Pages: 800-814, ISSN: 0276-7333
The chem. of a series of ansa-bridged ethylene-bis(hexamethylindenyl)zirconium and hafnium complexes has been explored. Treatment of EBI*Li2·THF0.38 with MCl4·THF2 (M = Zr, Hf) gives rac-EBI*MCl2 (rac-2, rac-3) and meso-EBI*MCl2 (meso-2, meso-3) (M = Zr and Hf), resp. The rac- and meso- isomers can be sepd. by fractional crystn. meso-EBI*ZrMe2 (meso-4) can be prepd. by alkylation of meso-2 with MeLi·LiBr. The mol. structures of rac- and meso-2 and rac- and meso-3 have been detd. by single-crystal x-ray crystallog. A comprehensive structural comparison between these compds. and related ansa metallocenes has been carried out. Rac- and meso-2 and rac- and meso-3 in the presence of modified methylaluminoxane (MMAO) are very active catalyst precursors for the polymn. of ethene to give high-d. polyethene (HDPE) with mol. wts. (Mw) in the range 100000-220000 and polydispersities (Mw/Mn) of ca. 2.6. The activities of both catalyst precursors rac- and meso-2 are some of the highest reported in the literature, at 61800 and 38200 kgPE/mol met/h/bar, resp. [on SciFinder(R)]
Aguirre-Etcheverry P, Ashley AE, Balazs G, et al., 2010, Synthesis, Structure, and Ligand Exchange Reactions of Tetramethyleneethane Complexes of Cobalt., Organometallics, Vol: 29, Pages: 5847-5858, ISSN: 0276-7333
The synthesis of (η3:η3-TME)[Co(CO)3]2 (1) was achieved using 2,3-bis(bromomethyl)-1,3-butadiene (TMEBr2) as the tetramethyleneethane (TME) ligand precursor and Na[Co(CO)4]. Soln. NMR studies suggested an η3:η3-configuration, which has been confirmed in the solid state by single-crystal x-ray diffraction studies. The series of complexes (η3:η3-TME)[Co(CO)2PR3]2 (R = Me, 2; R = Et, 3; R = n-Bu, 4; R = Ph, 5; R = OPh, 6) were also synthesized by ligand exchange reactions, demonstrating that only one carbonyl may be exchanged for a phosphine group on each metal center. The η3:η3-configuration of the tetramethyleneethane ligand in these complexes was detd. by crystallog. studies. The effect of the electron-donating properties of PR3 was studied by cyclic voltammetry (CV) and IR spectroscopy. The greatest degree of electron donation was seen when R = Et (3) and lowest when R = Ph (5) or R = OPh (6). Electronic communication between the metal centers was obsd. by CV. The chem. oxidn. of 1 resulted in a highly unstable species that decompd. to {[(CO)2Co]TME[Co(CO)3]}+[BF4]- (1+d), detd. by its crystal structure. The synthesis of (η4:η4-TME)[CoCp*]2 (7) has been achieved using a dipotassium 2,3-bis(methylene)-1,3-butanediyl (TMEK2) synthon. NMR studies suggested that 7 adopts an unusual η4:η4-configuration, which was confirmed with the aid of crystallog. studies. DFT calcns. were performed in order to rationalize the bonding for 1, 7, and hypothetical (η4:η4-TME)[CoCp]2 (8). The large energy difference between the two coordination isomers 1 and 1a confirmed the η3:η3-configuration. For isomers 7/7a and 8/8a, the energy difference between the two isomers (ca. 15 kJ mol-1) is in favor of the η4:η4-configuration. For complexes 1+ and 8+, the calcns. suggested complete delocalization on the system when one electron was removed. [on SciFinder(R)]
Chadwick FM, Ashley A, Wildgoose G, et al., 2010, Bis(permethylpentalene)uranium., Dalton Trans., Vol: 39, Pages: 6789-6793, ISSN: 1477-9226
The reaction of Li2(C14H18)(TMEDA)x (C14H18 = permethylpentalene, Pn*) with UCl4 yields U(η8-C14H18)2, (UPn*2) an analog of CePn*2 and U{η8-C8H4(1,4-SiiPr3)2}2. The UPn*2 mol. is structurally characterized via a variety of techniques, its magnetism is probed in the soln. and solid phase and the redox properties were studied using cyclic voltammetry. UPn*2 is reducible and the reduced species reacted with N2 to form a stable complex. An analogous complex was not found under Ar. [on SciFinder(R)]
Ransom P, Ashley A, Thompson A, et al., 2009, Synthesis, structure and characterisation of rac and meso-ansa-bridged permethylindenyl cobalt complexes., J. Organomet. Chem., Vol: 694, Pages: 1059-1068, ISSN: 0022-328X
Disodium ethylene-bis-hexamethylindenyl, {(C9Me6)2C2H4}Na2 (EBI*Na2), has been prepd. in good yield by the reaction of lithium heptamethylindenyl with cyanogen bromide followed by treatment with sodium naphthalenide. EBI*Na2 reacts with anhyd. Co(acac)2 to give a mixt. of rac and meso-ethylene-bis-hexamethylindenyl cobalt(II) (EBI*Co). The isomers can be sepd. by fractional crystn. and the rac-isomer has been structurally characterized. Oxidn. of the reaction mixt. yields both rac and meso-ethylene-bis-hexamethylindenyl cobalt(III) which have both been structurally characterized. [on SciFinder(R)]
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