Publications
54 results found
Chadwick FM, Cooper RT, Ashley AE, et al., 2014, Early Transition Metal Permethylpentalene Complexes for the Polymerization of Ethylene, ORGANOMETALLICS, Vol: 33, Pages: 3775-3785, ISSN: 0276-7333
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- Citations: 13
Lawrence EJ, Oganesyan VS, Hughes DL, et al., 2014, An Electrochemical Study of Frustrated Lewis Pairs: A Metal-Free Route to Hydrogen Oxidation, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, Vol: 136, Pages: 6031-6036, ISSN: 0002-7863
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- Citations: 43
Doyle LR, Heath A, Low CH, et al., 2014, A Convenient Synthetic Protocol to 1,2-Bis(dialkylphosphino)ethanes, ADVANCED SYNTHESIS & CATALYSIS, Vol: 356, Pages: 603-608, ISSN: 1615-4150
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- Citations: 10
Ashley AE, O'Hare D, 2013, FLP-mediated activations and reductions of CO<inf>2</inf> and CO, Topics in Current Chemistry, Vol: 334, Pages: 191-218, ISSN: 0340-1022
This chapter reviews the published work to date on the interaction of CO2 and CO with frustrated Lewis pairs (FLPs). The ability of FLP-derived systems reversibly to bind and release CO2 is a dramatic and exciting development, offering new routes to sequester this environmentally important molecule. Furthermore, in combination with FLPs' documented ability to cleave H2 heterolytically, new CO2 hydrogenation chemistry has been uncovered. Novel tandem catalytic processes involving FLPs are beginning to be developed which allow the chemical functionalisation of CO2. Structure-function relationships which affect the thermal stability of FLP-CO2 adducts are highlighted, alongside an insight towards the future design of successful FLP-mediated CO2 hydrogenation catalysts. © Springer-Verlag Berlin Heidelberg 2013.
Cooper RT, Chadwick FM, Ashley AE, et al., 2013, Synthesis and Characterization of Group 4 Permethylpentalene Dichloride Complexes, ORGANOMETALLICS, Vol: 32, Pages: 2228-2233, ISSN: 0276-7333
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- Citations: 26
Lawrence EJ, Oganesyan VS, Wildgoose GG, et al., 2013, Exploring the fate of the tris(pentafluorophenyl)borane radical anion in weakly coordinating solvents, DALTON TRANSACTIONS, Vol: 42, Pages: 782-789, ISSN: 1477-9226
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- Citations: 53
Ashley AE, O'Hare D, 2013, FLP-Mediated Activations and Reductions of CO<sub>2</sub> and CO, FRUSTRATED LEWIS PAIRS II: EXPANDING THE SCOPE, Vol: 334, Pages: 191-217, ISSN: 0340-1022
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- Citations: 50
Zaher H, Ashley AE, Irwin M, et al., 2013, Structural and theoretical studies of intermolecular dihydrogen bonding in [(C<sub>6</sub>F<sub>5</sub>)<sub>2</sub>(C<sub>6</sub>Cl<sub>5</sub>)B]-H•••H-[TMP], CHEMICAL COMMUNICATIONS, Vol: 49, Pages: 9755-9757, ISSN: 1359-7345
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- Citations: 24
Herrington TJ, Thom AJW, White AJP, et al., 2012, Novel H<sub>2</sub> activation by a tris[3,5-bis(trifluoromethyl)phenyl]borane frustrated Lewis pair, DALTON TRANSACTIONS, Vol: 41, Pages: 9019-9022, ISSN: 1477-9226
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- Citations: 64
O'Hare D, Ransom P, Ashley A, 2011, Olefin metallocene polymerization catalysts.
The present invention relates to novel metallocene catalysts of formula (I), wherein R1-12 = hydrocarbyl, carbocyclyl, heterocyclyl; Q = bridging group; X = Zr, Ti, Hf; and Y = halo, halide, phosphated or sulfonated anion, C1-6 alkyl, C1-6 alkoxy, aryl, aryloxy, optionally substituted halo, nitro, amino, Ph, C1-6 alkoxy, tri(C1-4)alkylsilyl. The present invention also provides processes for making these catalysts and their use in olefin polymn. reactions. [on SciFinder(R)]
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)]
Ashley AE, Thompson AL, O'Hare D, 2009, Non-Metal-Mediated Homogeneous Hydrogenation of CO2 to CH3OH., Angew. Chem., Int. Ed., Vol: 48, Pages: 9839-S9839/4, ISSN: 1433-7851
The selective hydrogenation of CO2 to methanol was carried out using an FLP [frustrated Lewis pairs]-based nonmetal-mediated process at low pressures (1-2 atm). The first step is heterolytic activation of H and subsequent insertion of CO2 into a B-H bond of 2,2,6,6-tetramethylpiperidine [TMP] and B(C6F5)3 forming [TMPH][HB(C6F5)3].; introduction of CO2 produced the formatoborate complex [TMPH]-[HCO2B(C6F5)3]. Selective distn. at 100° resulted in decompn. of the intermediate complex with recovery of methanol. The process provides for utilization of CO2 greenhouse gas, solving problems related to storage of sequestered gas, with further benefit of prodn. of methanol as fuel and chem. feedstock. [on SciFinder(R)]
Ashley AE, Cowley AR, Green JC, et al., 2009, Synthesis and Characterisation of Low-Coordinate Transition-Metal Complexes Stabilised by Sterically Demanding Carbazolido Ligands., Eur. J. Inorg. Chem., Pages: 2547-2552, ISSN: 1434-1948
The synthesis and characterization of the homoleptic transition-metal complexes (1,8-Ph2-3,6-Me2C12H4N)2M (M = Cr, 1; M = Mn, 2; M = Fe, 3; M = Co, 4) are described. Formally two-coordinate, the solid-state structures of 2 and 3 reveal near-linear N-M-N geometries and significant bending of the flanking Ph groups towards the metal centers. Solid-state magnetic measurements reveal high spin metal centers in 1-4; computational calcns. for the model complexes M(1,8-Ph2C12H6N)2 (M = Cr-Co) confirm the presence of high-spin configurations within these bis-carbazolido compds. and an orbital ordering of δ < π < σ for these systems. [on SciFinder(R)]
O'Hare DM, Ashley AE, 2008, Process for preparation of substituted pentalene derivatives and their transition metal sandwich complexes.
A process for prepn. of 1-R1-2-R2-3-R3-4-R4-5-R5-6-R6-pentalenes (1; R1-R6 = C1-40 organyl, halo; preferably R1-R6 = C1-4 alkyl; preferably R5 = R5, R1 = R4, R3 = R6; more preferably R1-R6 are the same, R1-R6 = Me), 1-R1-2-R2-3-R3-4-R4-5-R5-6-R6-1,2-dihydropentalenes (2, same R), alkali and alk. earth salts of 1,2-dihydropentalenes MSx[1·H]n (M = Group IA, IIA metal, S = chelating solvent, preferably 1,2-dimethoxyethane, TMEDA; x = 0-8; n = 1,2) and Group IIIB-VIII transition metal complexes, comprising η3-η8 dihydropentalenide ligands, including sandwich, ansa-sandwich and binuclear sandwich compds., useful as catalysts for hydrogenation, Fischer-Tropsch reaction, hydroformylation, hydroamination, hydrosilylation, polymn., oxidn., cyclotrimerization, and cycloaddn. reactions, is described. The process comprises electrophilic alkylation of 3,7-dioxobicyclo[3.3.0]octane-2,4,6,8-tetracarboxylate ester, decarboxylation yielding the 2-R1-4-R3-6-R4-8-R6-bicyclo[3.3.0]octane-3,7-dione (3), dehydrogenation to the substituted 1,2,4,5-tetrahydropentalene-2,5-dione (4), redn. to 1,3,4,6-tetrahydropentalene-2(2H),5(5H)-dione (5), alkylation of the dione 5 by an organometallic reagent, preferably by RCeCl2 at -70°, yielding 1-R1-2-R2-3-R3-4-R4-5-R5-6-R6-1,2,3,4,5,6-hexahydropentalene-2,5-diol (6), dehydration of the diol 6, preferably by reaction with conc. H2SO4 to give the 1,2- or 1,4-dihydropentalenes (1a) followed by optional deprotonation, transmetalation, stannylation or complexation reactions. In an example, 1,2,3,4,5,6-hexamethyl-1,2-dihydropentalene (1aa)was prepd. in a multistep procedure starting from tetra-Me 3,7-dihydroxybicyclo[3.3.0]octa-2,6-diene-2,4,6,8-tetracarboxylate by MeI/K2CO3 methylation, decarboxylation, Br2 oxidn. to 2,4,6,8-tetramethylbicyclo[3.3.0]octa-2,5-diene-3,7-dione, Zn redn. to 2,4,6,8-tetramethylbicyclo[3.3.0]octa-1(5)-ene-3,7-dione and methylation by MeCeCl2 in a 60% yield. In another example, the iron complex [Fe2(CO)4
Ashley AE, Cooper RT, Wildgoose GG, et al., 2008, Homoleptic Permethylpentalene Complexes: "Double Metallocenes" of the First-Row Transition Metals., J. Am. Chem. Soc., Vol: 130, Pages: 15662-15677, ISSN: 0002-7863
The synthesis of the bimetallic permethylpentalene complexes Pn*2M2 (M = V, Cr, Mn, Co, Ni; Pn* = C8Me6) was accomplished, and all of the complexes were structurally characterized in the solid state by single-crystal x-ray diffraction. Pn*2V2 (1) and Pn*2Mn2 (3) show very short intermetallic distances that are consistent with metal-metal bonding, while the Co centers in Pn*2Co2 (4) exhibit differential bonding to each side of the Pn* ligand that is consistent with an η5:η3 formulation. The Pn* ligands in Pn*2Ni2 (5) are best described as η3:η3-bonded to the metal centers. 1H NMR studies indicate that all of the Pn*2M2 species exhibit D2h mol. symmetry in the soln. phase; the temp. variation of the chem. shifts for the resonances of Pn*2Cr2 (2) indicates that the mol. has an S = 0 ground state and a thermally populated S = 1 excited state and can be successfully modeled using a Boltzmann distribution (ΔH° = 14.9 kJ mol-1 and ΔS° = 26.5 J K-1 mol-1). The solid-state molar magnetic susceptibility of 3 obeys the Curie-Weiss law with μeff = 2.78 μB and θ = -1.0 K; the complex is best described as having an S = 1 electronic ground state over the temp. range 4-300 K. Paradoxically, attempts to isolate the double ferrocene equiv., Pn*2Fe2, led only to the isolation of the permethylpentalene dimer Pn*2 (6). Soln. electrochem. studies were performed on all of the organometallic compds.; 2-5 exhibit multiple quasi-reversible redox processes. D. functional theory calcns. were performed on this series of complexes to rationalize the obsd. structural and spectroscopic data and provide ests. of the M-M bond order. [on SciFinder(R)]
Ashley A, Balazs G, Cowley A, et al., 2007, Bis(permethylpentalene)cerium - another ambiguity in lanthanide oxidation state., Chem. Commun. (Cambridge, U. K.), Pages: 1515-1517, ISSN: 1359-7345
The title compd. Ce(η8-C8Me6)2 (1) exists in a valency close to Ce(III) with some Ce(IV) and provides an example of the Kondo effect in a discrete mol. Treating Li2(C8Me6)(TMEDA)0.19 with CeCl3 in THF, followed by treatment with 1,2-dichloroethane as mild oxidant gave 61% 1. The structure of 1 was detd. by x-ray crystallog. and also optimized geometries were calcd. by DFT-B3LYP methods. [on SciFinder(R)]
Ashley AE, Cowley AR, O'Hare D, 2007, The hexamethylpentalene dianion and other reagents for organometallic pentalene chemistry., Chem. Commun. (Cambridge, U. K.), Pages: 1512-1514, ISSN: 1359-7345
Novel permethylated pentalenide anions are reported which offer exciting new opportunities for the future development of organometallic pentalene chem. Thus, lithiation of 1,3,4,5,6-pentamethyl-2-methylene-1,2-dihydropentalene (Pn*) with LS-selectride in THF at room temp. gave 92% LiPn*H which on BuLi lithiation in the presence of TMEDA in hexane gave [Li2Pn*(TMEDA)x] (2a). Trimethylstannylation of 2a gave 98% [cis-trans-(Me3Sn)2Pn*] (3), whereas lithiation of 3 with MeLi in the presence of TMEDA in Et2O gave [Li2Pn*(TMEDA)2] (2b). The crystal structure of 2b and cis-3 were detd. [on SciFinder(R)]
Ashley AE, Balazs G, Cowley AR, et al., 2007, syn-Permethylpentalene iron and cobalt carbonyl complexes: proximity bimetallics lacking metal-metal bonding., Organometallics, Vol: 26, Pages: 5517-5521, ISSN: 0276-7333
Reaction of the pentalene synthon, 1,3,4,5,6-pentamethyl-2-methylene-1,2-dihydropentalene (Pn*') with Fe2(CO)9 or Co2(CO)8 led to the synthesis of binuclear pentalenyl-bridged [Fe2(CO)4(μ-CO)(μ-η5:η5-Pn*)] (1) and [Co2(CO)4(μ-η5:η5-Pn*)] (2), resp., in good yields. The complexes 1 and 2 were structurally characterized by x-ray crystallog. and are examples of syn-facial 34-electron dinuclear permethylpentalene complexes; 1 contains a μ-CO moiety with an unusual orientation, and NMR data indicate rapid terminal-bridging CO exchange. Theor. investigations support the structures found in the solid state and also suggest an absence of metal-metal bonding in these compds., despite the proximity of the metal centers. [on SciFinder(R)]
Ashley AE, Cowley AR, O'Hare D, 2007, Permethylpentalene chemistry., Eur. J. Org. Chem., Pages: 2239-2242, ISSN: 1434-193X
A rational soln.-phase synthesis of a permethylpentalene ligand precursor for use in organometallic chem. has been devised through the novel peripheral alkylation of the bicyclo[3.3.0]octane ring system. Tetramethylation of tetra-Me 3,7-dihydroxybicyclo[3.3.0]octa-2,6-diene-2,4,6,8-tetracarboxylate forms sterically encumbered I which exhibits fluxionality. Decarboxylation of I followed by facile double dehydrogenation using Br2 affords II. Nucleophilic addn. of the final two Me groups necessitates the use of an organocerium reagent and work-up yields the hexamethylated hydroxyfulvene. Dehydration of the latter is achieved using aprotic conditions (LiCl/DMSO) to afford the tetraene III, an exocyclic isomer of permethylpentalene. III incorporates a bicyclic vinylfulvene unit, avoiding an 8π anti-arom. structure. Both I and II were structurally characterized using X-ray anal. [on SciFinder(R)]
Moss J, Thomas J, Ashley A, et al., 2006, Bulk Synthesis of Octa- and Nonamethylfluorene (Flu''H and Flu*H) and the Characterization of the Organometallic Derivatives Flu*SnMe3, [(FeCp)2Flu*H][PF6]2, and [(FeCp)2Flu''H][PF6]2., Organometallics, Vol: 25, Pages: 4279-4285, ISSN: 0276-7333
The large-scale (47-63 mmol) synthesis of two highly methylated fluorene ligands is reported, and the synthesis and characterization of three organometallic derivs. are reported. Starting with 1,2,3,4-tetramethylbenzene, 1,2,3,4,5,6,7,8-octa- and 1,2,3,4,5,6,7,8,9-nonamethylfluorene (Flu''H and Flu*H, resp.) were synthesized in overall yields of >50%. Both fluorenes may be deprotonated at the 9 position to yield useful organometallic synthons; the Sn deriv., Flu*SnMe3, was synthesized by using this reagent, and its mol. structure was elucidated. The dinuclear Fe complexes, [(FeCp)2Flu*H][PF6]2 and [(FeCp)2Flu''H][PF6]2 were isolated, and their electrochem. properties ascertained. Electrochem. measurements on these complexes show the methylated fluorene ligand acts as a strong electron donor and acts to increase the electronic communication between the metal centers, in comparison with the non-methylated analogs. The solid-state structure of [(FeCp)2Flu''H][PF6]2 was detd. and, unlike the Sn complex, does not show a significantly twisted fluorenyl core. [on SciFinder(R)]
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