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ABSTRACT: The new tripodal ligand tris(2-(2-picolylcarbamoyl)-pyridin-6-yl)methanol (L1) was synthesized via a Pd-catalyzed amidocarbonylation reaction in good yield (64%). The ligand readily forms mononuclear 1:1 complexes with both Fe(II) and Zn(II), which were characterized by x-ray crystallog. Continuous Shape Mapping calcns. also were performed which confirm the ligands ability to enforce near-perfect trigonal prismatic coordination environments upon each of these metal ions. [on SciFinder(R)]
Polyhedron. 01/2012; 31:457-462.
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ABSTRACT: The thermodynamic factors underlying the use of ferroceneboronic esters as electrochemical or colorimetric fluoride ion sensors have been investigated through the synthesis of a range of systematically related derivatives differing in the number/nature of the boronic ester substituents and in the nature of ancillary ligands. Thus, if the shift in electrochemical potential associated with the conversion of one (or more) boronic ester group(s) to anionic boronate(s) on fluoride binding is sufficient to allow oxidation of the resulting host/guest complex by dioxygen, colorimetric sensing is possible. In practice, while monofunctional systems of the type CpFe[eta(5)-C(5)H(4)B(OR)(2)] offer selectivity in fluoride binding, electrochemical shifts in chloroform solution are insufficient to allow for a colorimetric response. Two chemical modification strategies have been shown to be successful in realizing a colorimetric sensor: (i) the use of the more strongly electron-donating Cp(*) ancillary ligand (which shifts the oxidation potential of both the free receptor and the resulting fluoride adduct cathodically by ca. -400 mV) and (ii) receptors featuring two or more binding sites and consequently a larger fluoride-induced electrochemical shift. Thus, in the case of [eta(5)-C(5)H(4)B(OR)(2)](2)Fe [(OR)(2) = OC(H)PhC(H)PhO, 2(s)], the binding of 2 equiv of fluoride gives an electrochemical shift (in chloroform) of -960 mV (cf. -530 mV for the corresponding monofunctional analogue, 1(s)). Related tris- and tetrakis-functionalized systems are also shown to be oxidized as the bis(fluoride) adducts, presumably because of fast oxidation kinetics, relative to the rate of the (electrostatically unfavorable) binding of a third equivalent of fluoride. Furthermore, the rate of sensor response (as measured by UV/vis spectroscopy) is found to be strongly enhanced by the presence of pendant (uncomplexed) three-coordinate boronic ester functions (e.g., a rate enhancement of 1-2 orders of magnitude for 3(s)/4(s) with respect to 2(s)) and/or delocalized aromatic substituents.
Inorganic Chemistry 03/2008; 47(3):793-804. · 4.60 Impact Factor
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Manuel Iglesias,
Dirk J. Beetstra,
James C. Knight, Li-Ling Ooi,
Andreas Stasch,
Simon Coles,
Louise Male,
Michael B. Hursthouse,
Kingsley J. Cavell,
Athanasia Dervisi,
Ian A. Fallis
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ABSTRACT: The addn. of arom. formamidines to dihaloalkanes proceeds in air under mildly basic conditions and in polar solvents to afford the corresponding amidinium salts in high yields. To demonstrate the wide scope of this methodol., several five-, six-, and seven-membered satd. N-heterocyclic amidinium salts were prepd. Some free carbenes also were isolated as stable white solids, and for the 1st time the solid state structures of free seven-membered N-heterocyclic carbenes were detd. The syntheses and characterization of their Ag(I) halide complexes are also described and the x-ray structures for 4 complexes detd. On the basis of NMR data the Ag halide species form either neutral, Ag(NHC)X, or ionic, [Ag(NHC)2][AgX2] complexes in soln. A feature of the expanded ring carbenes is the extremely large NCN angle (≥120°) and the consequential steric impact of the N-substituents on the metal center. For the free seven-membered ring carbenes the 13C NMR shifts are 258-260 ppm, well down field from those obs
Organometallics. 01/2008; 27:3279-3289.
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ABSTRACT: A simple, one-step synthesis of multinuclear Lewis acids can be driven with high selectivity towards either macrocyclic or polymeric arrays by appropriate choice of backbone framework.
Dalton Transactions 09/2007; · 3.84 Impact Factor
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ABSTRACT: The synthesis of the benzyl phosphinothioether derivatives Ph(2)PCH(2)CH(Et)SR and their corresponding palladium complexes are reported, where R = CH(2)Ph, R = CH(2)-3,5-Me-C(6)H(3) and R = 1-CH(2)C(10)H(7)(5). Crystallographic data obtained for the complexes Pd(3)Cl(2) and Pd(4)Cl(2) show intra- and inter-molecular pi-pi interactions between the aromatic rings on the P and S substituents, and NOE experiments for Pd(4)Cl(2) show that these interactions persist in solution. The performance of the phosphinothioether palladium complexes in aryl-aryl cross-coupling reactions is compared with that of the corresponding complex of the parent phosphinothiolato ligand Ph(2)PCH(2)CH(Et)S(-)(1). High turnover numbers up to 2000000 are reported for the coupling of bromobenzene, using the palladium dimer [Pd(1)I](2) as the catalyst precursor. Kinetic studies show a linear dependence of the reaction on catalyst loading. The effect of other variables on the cross-coupling reaction, such as temperature, solvent and base, is also reported.
Dalton Transactions 01/2007; · 3.84 Impact Factor
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ABSTRACT: A general synthetic route to 5-alkylidene-1,3-dioxane-4,6-diones, which are a family of axially chiral alkenes, is described. Conformational issues are explored and the platinum-binding properties of these species are discussed. That these alkenes exist as stable enantiomers is established by their partial kinetic resolution upon reaction with cysteine.
Organic & Biomolecular Chemistry 11/2006; 4(20):3822-30. · 3.70 Impact Factor
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ABSTRACT: Novel, well-defined, coordinatively unsaturated NHC palladium(0) and nickel(0) complexes have been synthesized and fully characterized. Mixed N-heterocyclic carbene−olefin complexes, M0(NHC)n(DMFU)m (where M = Ni, Pd, NHC = 1,3-dimesitylimidazolin-2-ylidene, and DMFU = dimethyl fumarate; for Pd n = 1, m = 2 and n = 2, m = 1; for Ni n = 1, m = 1, 2 and n = 2, m = 1) have been prepared, including a dimeric Ni complex in which the DMFU acts as a bridging ligand, via the double bond and one carbonyl oxygen. The bis-NHC complexes of Ni0 and Pd0 undergo facile ligand exchange equilibria in solution in the presence of excess olefin (DMFU), leading to mono-NHC−M0−(olefin) complexes. This exchange is driven by the formation of an NHC−olefin coupling product. The dimeric Ni complex is labile in solution and can be used in situ, to provide a source of the L−Ni0 moiety. The complexes M0(NHC)n(DMFU)m (M = Pd, n = 1, m = 2; M = Ni, n = 1, m = 1, 2 and n = 2, m = 1) could be isolated as pure crystalline compounds in the solid state, and molecular structures were obtained.
07/2006;
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ABSTRACT: Primary and secondary phosphine piano-stool complexes of the type [eta(5)-CpFeL3]+ (L = phenylphosphine, 3, (alpha-methyl)vinylphosphine, 4, allylphosphine, 5, (2-methylpropenyl)phosphine, 5b, allyl(phenyl)phosphine, 6) are described. The alkenyl phosphine complexes, 5 and 6, react by intramolecular hydrophosphination to give the corresponding [eta(5)-CpFe]+ complexes of 1,5,9-triphosphacyclododecane (12-aneP3R3, 2, R = H), 9 and 10 respectively. Alkylation of the secondary phosphines in 9 is achieved by hydrophosphinations with ethene to give the 12-aneP3R3 (R = Et) derivative 11. These complexes are also obtained by reaction of suitable [eta(5)-CpFe]+ containing precursor complexes with the corresponding free 12-aneP3R3 macrocycle as is the related [eta(5)-Cp*Fe]+ derivative, 8. Direct substitution of acetonitrile in [Fe(CH3CN)6][BF4]2 by 12-aneP3Et3, leads to the macrocycle piano-stool complex, [(12-aneP3Et3)Fe(CH3CN)3][BF4]2, 7. The crystal structures of selected primary phosphine, eta(5)-Cp, eta(5)-Cp* complexes and 7, allow a comparison of steric influences upon key macrocycle ring closure reactions and hence an insight into parameters required for the formation of smaller ring sizes by template based methods.
Dalton Transactions 02/2006; · 3.84 Impact Factor
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ABSTRACT: The synthesis, spectroscopic and structural characterization of the aryloxy and amino functionalized chloroboryl complexes (eta(5)-C(5)R(5))Fe(CO)(2)B(OMes)Cl (R = H, 2a ; R = Me, 3a) and (eta(5)-C(5)H(5))Fe(CO)(2)B(N(i)Pr(2))Cl (7a) are reported. Compound 2ais shown to be a versatile substrate for further boron-centred substitution chemistry leading to the asymmetric boryl complexes (eta(5)-C(5)H(5))Fe(CO)(2)B(OMes)ER(n) [ER(n) = OC(6)H(4)(t)Bu-4, 2c; ER(n) = SPh, 2d] with retention of the metal-boron bond. The reactivities of 2a, 3a and 7a towards the halide abstraction agent Na[BAr(f)(4)] have also been examined, in order to investigate the potential for the generation of cationic heteroatom-stabilized terminal borylene complexes. The application of this methodology to the mesityloxy derivatives and gives rise to B-F containing products, presumably via fluoride abstraction from the [BAr(f)(4)](-) counter-ion. By contrast, amino-functionalized complex 7a is more amenable to this approach, and the thermally robust terminal aminoborylene complex [(eta(5)-C(5)H(5))Fe(CO)(2)B(N(i)Pr(2))][BAr(f)(4)] (9) can be isolated in ca. 50% yield. The reactivity of 9towards a range of nucleophilic and/or unsaturated reagents has been examined, with examples of addition, protonolysis and metathesis chemistries having been established.
Dalton Transactions 02/2006; · 3.84 Impact Factor
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Advanced Synthesis & Catalysis 01/2006; 348(1‐2):175 - 183. · 6.05 Impact Factor
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Angewandte Chemie International Edition 01/2006; 44(45):7457-60. · 13.45 Impact Factor
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ABSTRACT: The title hydrated 2,2'-bipyridine-6,6'-dicarboxylate-Cd(II) complex crystallizes in orthorhombic space group Pcab; Z = 8. The divalent Cd ion is seven-coordinate, and the coordination polyhedron can best be described as slightly distorted pentagonal-bipyramidal. [on SciFinder(R)]
Acta Crystallographica, Section E: Structure Reports Online. 01/2006; E62:m3306-m3308.
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Angewandte Chemie International Edition 12/2005; 44(46):7546-9. · 13.45 Impact Factor
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Sook Wah Yee,
Laetitia Jarno,
Mohamed Sayed Gomaa,
Carole Elford, Li-Ling Ooi,
Michael P Coogan,
Richard McClelland,
Robert Ian Nicholson,
Bronwen A J Evans,
Andrea Brancale,
Claire Simons
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ABSTRACT: The potent inhibitory activity of novel 2-benzyltetralone and 2-benzylidenetetralone derivatives vs liver microsomal retinoic acid metabolizing enzymes and a MCF-7 CYP26A1 cell assay is described. In the liver microsomal assay, the 2-biphenylmethyl-6-hydroxytetralone derivatives 16a and 16b were found to be potent inhibitors (IC50 = 0.5 and 0.8 microM) compared with the broad spectrum P450 inhibitor ketoconazole and the retinoid mimetic R115866 (IC50 = 18.0 and 9.0 microM, respectively). In the MCF-7 CYP26A1 cell assay, the 2-(4-hydroxybenzyl)-6-methoxytetralone 5 and unsaturated benzylidene precursor 6 were found to be the most potent (IC50 = 7 and 5 microM, respectively), which was comparable with liarozole (7 microM) but considerably less active than R115866 (IC50 = 5 nM). With a CYP26A1 homology model, the tetralones were shown to be positioned in a hydrophobic tunnel with additional interactions, e.g., transition metal coordination and hydrogen-bonding interactions with GLY300, observed for the potent 4-hydroxyphenyl substituted inhibitors.
Journal of Medicinal Chemistry 12/2005; 48(23):7123-31. · 5.25 Impact Factor
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ABSTRACT: Transition metal complexes containing ligands featuring three-coordinate, halide-functionalized gallium or indium donors represent key precursors to unsaturated cationic species of the type [LnM(EX)]+ via halide abstraction chemistry. Two routes to these three-coordinate systems have been demonstrated: (i) salt elimination, such as the reaction between Na[Cp*Fe(CO)2] and Mes*GaCl2 or Mes*InBr2 (Mes* = C6H2tBu3-2,4,6, supermesityl) to generate Cp*Fe(CO)2E(Mes*)X (3a, E = Ga, X = Cl; 5, E = In, X = Br), and (ii) insertion of a gallium(I) or indium(I) halide into a metal−halogen or metal−metal bond followed, where necessary, by substitution by a sterically bulky anionic nucleophile. Crystallographic studies have confirmed the presence of the target trigonal planar ligand systems both in gallyl/indyl complexes of the type LnM-E(Aryl)X and in halide-functionalized gallane- and indane-diyl systems of the type (LnM)2EX.
10/2005;
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ABSTRACT: Halide abstraction chemistry offers a viable synthetic route to the cationic two-coordinate complexes [{Cp*Fe(CO)2}2(μ-E)]+ (7, E = Ga; 8, E = In) featuring linear bridging gallium or indium atoms. Structural, spectroscopic, and computational studies undertaken on 7 are consistent with appreciable Fe−Ga π-bonding character; in contrast, the indium-bridged complex 8 is shown to feature a much smaller π component to the metal−ligand interaction. Analogous reactions utilizing the supermesityl-substituted gallyl or indyl precursors of the type (η5-C5R5)Fe(CO)2E(Mes*)X, on the other hand, lead to the synthesis of halide-bridged species of the type [{(η5-C5R5)Fe(CO)2E(Mes*)}2(μ-X)]+, presumably by trapping of the highly electrophilic putative cationic diyl complex [(η5-C5R5)Fe(CO)2E(Mes*)]+.
10/2005;
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Angewandte Chemie International Edition 09/2005; 44(33):5282-4. · 13.45 Impact Factor
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Angewandte Chemie International Edition 07/2005; 44(23):3606-9. · 13.45 Impact Factor
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ABSTRACT: Condensation of 2-alkyl- or 2-aryl-3-aminoquinazolin-4-ones with benz[1,3]oxazin-4-ones gives the unsymmetrical 2,2' disubstituted 3,3' biquinazoline-4,4'-diones. The reaction is tolerant to a range of heteroatom and unsaturated functionality in the quinazolinone 2-position. However, treatment of 3-amino-2-hydroxymethyl-3H-quinazolin-4-ones with benz[1,3]oxazinone at high temperatures gave 4H-3-oxo-1,9a,10-triazaanthracen-9-ones, an unreported fused heterocyclic system, a more direct synthesis of which, replacing benzoxazinones with orthoesters is presented.
Organic & Biomolecular Chemistry 04/2005; 3(6):1134-9. · 3.70 Impact Factor
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ABSTRACT: The reactivities of the highly electrophilic boranes ClB(C(6)F(5))(2) (1) and [HB(C(6)F(5))(2)](n) (2) towards a range of organometallic reagents featuring metals from Groups 7-10 have been investigated. Salt elimination chemistry is observed 1 between and the nucleophilic anions eta(5)-C(5)R(5))Fe(CO)(2)](-)(R = H or Me) and [Mn(CO)(5)](-), leading to the generation of the novel boryl complexes (eta(5)-C(5)R(5))Fe(CO)(2)B(C(6)F(5))(2)[R = H (3) or Me (4)] and (OC)(5)MnB(C(6)F(5))(2) (5). Such systems are designed to probe the extent to which the strongly sigma-donor boryl ligand can also act as a pi-acceptor; a variety of spectroscopic, structural and computational probes imply that even with such strongly electron withdrawing boryl substituents, the pi component of the metal-boron linkage is a relatively minor one. Similar reactivity is observed towards the hydridomanganese anion [(eta(5)-C(5)H(4)Me)Mn(CO)(2)H](-), generating a thermally labile product identified spectroscopically as (eta(5)-C(5)H(4)Me)Mn(CO)(2)(H)B(C(6)F(5))(2) (6). Boranes 1 and 2 display different patterns of reactivity towards low-valent platinum and rhodium complexes than those demonstrated previously for less electrophilic reagents. Thus, reaction of 1 with (Ph(3)P)(2)Pt(H(2)C=CH(2)) ultimately generates EtB(C(6)F(5))(2) (10) as the major boron-containing product, together with cis-(Ph(3)P)(2)PtCl(2) and trans-(Ph(3)P)(2)Pt(C(6)F(5))Cl (9). The cationic platinum hydride [(Ph(3)P)(3)PtH](+) is identified as an intermediate in the reaction pathway. Reaction of with [(Ph(3)P)(2)Rh(mu-Cl)](2), in toluene on the other hand, appears to proceed via ligand abstraction with both Ph(3)P.HB(C(6)F(5))(2) (11) and the arene rhodium(I) cation [(Ph(3)P)(2)Rh(eta(6)-C(6)H(5)Me)](+) (14) ultimately being formed.
Dalton Transactions 01/2005; · 3.84 Impact Factor
