PubMed Health⌕ Search

Biomedical subjects

Mark E Light

Publications and source records attributed to Mark E Light.

At least 37 records · Page 2Linked to original sources
PubMed2005

The synthesis, structure and ethene polymerisation catalysis of mono(salicylaldiminato) titanium and zirconium complexes.

The silyl ethers 3-But-2-(OSiMe3)C6H3CH=NR (2a-e) have been prepared by deprotonation of the known iminophenols (1a-e) and treatment with SiClMe3 (a, R = C6H5; b, R = 2,6-Pri2C6H3; c, R = 2,4,6-Me3C6H2; d, R = 2-C6H5C6H4; e, R = C6F5). 2a-c react with TiCl4 in hydrocarbon solvents to give the binuclear complexes [Ti{3-But-2-(O)C6H3CH=N(R)}Cl(mu-Cl3)TiCl3] (3a-c). The pentafluorophenyl species 2e reacts with TiCl4 to give the known complex Ti{3-But-2-(O)C6H3CH=N(R)}2Cl2. The mononuclear five-coordinate complex, Ti{3-But-2-(O)C6H3CH=N(2,4,6-Me3C6H2)}Cl3 (4c), was isolated after repeated recrystallisation of 3c. Performing the dehalosilylation reaction in the presence of tetrahydrofuran yields the octahedral, mononuclear complexes Ti{3-But-2-(O)C6H3CH=N(R)}Cl3(THF) (5a-e). The reaction with ZrCl4(THF)2 proceeds similarly to give complexes Zr{3-But-2-(O)C6H3CH=N(R)}Cl3(THF) (6b-e). The crystal structures of 3b, 4c, 5a, 5c, 5e, 6b, 6d, 6e and the salicylaldehyde titanium complex Ti{3-But-2-(O)C6H3CH=O}Cl3(THF) (7) have been determined. Activation of complexes 5a-e and 6b-e with MAO in an ethene saturated toluene solution gives polyethylene with at best high activity depending on the imine substituent.

Journal Article↗
PubMed2004

'Twisted' isophthalamide analogues.

Steric interactions in 1,3-dicarboxamidoanthraquinones have been employed to 'twist' isophthalamide-like anion binding sites; the crystal structure of the fluoride complex of a bis-3,5-dichlorophenylamide derivative shows the receptor acting as a 'hydrogen-bonding corner' in a '2 + 2' fluoride containing molecular box.

Journal Article↗
PubMed2004

Mixed valence Mn(II)/Mn(III) [3 x 3] grid complexes: structural, electrochemical, spectroscopic, and magnetic properties.

Mn(II)9 grid complexes with a [Mn9(mu-O)12] core, obtained by self-assembly of a series of tritopic picolinic dihydrazone ligands with Mn(II) salts, have been oxidized by both chemical and electrochemical methods to produce mixed oxidation state systems. Examples involving [Mn(III)3Mn(II)6] and [Mn(III)4Mn(II)5] combinations have been produced. Structures are reported for [Mn9(2poap-2H)6](NO3)6.14H2O (1), [Mn9(2poap-2H)6](ClO4)10.10H2O (3), and [Mn9(Cl2poap-2H)6](ClO4)9.14H2O.3CH3CN (10). Structural studies show distinct contraction of the corner grid sites on oxidation, with overall magnetic properties consistent with the resulting changes in electron distribution. Antiferromagnetic exchange in the outer ring of eight metal centers creates a ferrimagnetic subunit, which undergoes antiferromagnetic coupling to the central metal, leading to S=1/2 (3) and S2/2 (10) ground states. Two moderately intense absorptions are observed on oxidation of the Mn(II) grids in the visible and near-infrared (1000 nm, 700 nm), associated with charge transfer transitions (LMCT, IVCT respectively). Compound 1 crystallized in the monoclinic system, space group P2 1/n, with a=21.308(2) A, b=23.611(2) A, c=32.178(3) A, beta=93.820(2) degrees . Compound 3 crystallized in the tetragonal system, space group I, with a=b=18.44410(10) A, c = 24.9935(3) A. Compound 10 crystallized in the triclinic system, space group P, with a=19.1150(10) A, b=19.7221(10) A, c=26.8334(14) A, alpha=74.7190(10) degrees, beta=77.6970(10) degrees, gamma=64.7770(10) degrees. The facile oxidation of the Mn(II)9 grids is highlighted in terms of their potential use as molecular based platforms for switching and data storage.

Journal Article↗
PubMed2004

Reactivity of the bis(pentafluorophenyl)boranes ClB(C6F5)2 and [HB(C6F5)2]n towards late transition metal reagents.

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.

Journal Article↗
PubMed2004

Di- and tri-alkylphosphine adducts of S-donor palladacycles as catalysts in the Suzuki coupling of aryl chlorides.

The reaction of tricyclohexylphosphine with the S-based palladacycle [(Pd(mu-OAc)(kappa2-S,C-C(6)H(4)CH(2)SMe))(2)] gives several products, regardless of stoichiometry, one of which, [Pd(kappa1-OAc)(eta1-C(6)H(4)CH(2)SMe)(PCy3)2], has been characterised crystallographically. Despite this, catalysts formed in situ from di- and tri-alkylphosphines and [(Pd(mu-OAc)(kappa2-S,C-C(6)H(4)CH(2)SMe))2] show excellent activity in the Suzuki coupling of a range of deactivated, non-activated and activated aryl chloride substrates.

Journal Article↗
PubMed2004

Anion binding properties of 5,5'-dicarboxamido-dipyrrolylmethanes.

A series of 5,5'-dicarboxamido-dipyrrolylmethanes have been synthesized and in some cases crystallographically characterized. Proton NMR titrations have revealed that these compounds, that contain only four neutral hydrogen bond donors and are acyclic, selectively bind anions in very competitive solvent media such as DMSO-d6/water mixtures.

Anions↗
PubMed2004

Syntheses, spectroscopic and molecular quadratic nonlinear optical properties of dipolar ruthenium(II) complexes of the ligand 1,2-phenylenebis(dimethylarsine).

Six new complex salts trans-[Ru(II)Cl(pdma)2L][PF6]n [pdma = 1,2-phenylenebis(dimethylarsine); L = (E,E,E)-1,6-bis(4-pyridyl)hexa-1,3,5-triene (bph), n= 1, 5; L =N-methyl-4-[(E)-2-(4-pyridyl)ethenyl]pyridinium (Mebpe+), n= 2, 7; L =N-methyl-4-[(E,E)-4-(4-pyridyl)buta-1,3-dienyl]pyridinium (Mebpb+), n= 2, 8; L =N-methyl-4-[(E,E,E)-6-(4-pyridyl)hexa-1,3,5-trienyl]pyridinium (Mebph+), n= 2, 9; L = bis(4-pyridyl)acetylene (bpa), n= 1, 10; L =N-methyl-4-[2-(4-pyridyl)ethynyl]pyridinium (Mebpa+), n= 2, 11] have been prepared. The electronic absorption spectra of 5 and 7-11 display intense, visible metal-to-ligand charge-transfer (MLCT) bands, with lambdamax values in the range 434-492 nm in acetonitrile. Cyclic voltammetric studies reveal reversible Ru(III/II) waves with E(1/2) values in the range 1.06-1.15 V vs. Ag-AgCl, together with irreversible L-based reduction processes. Along with a number of previously reported related compounds (B. J. Coe et al., J. Chem. Soc., Dalton Trans., 1996, 3917; 1997, 591; 2000, 797), salts 5 and 7-11 have been investigated by using Stark (electroabsorption) spectroscopy in butyronitrile glasses at 77 K. These studies have afforded dipole moment changes Deltamu12 for the MLCT transitions which have been used to calculate molecular static first hyperpolarizabilities beta0 according to the two-state equation beta0= 3Deltamu12(mu12)2/(Emax)2 (mu12 = transition dipole moment, Emax = MLCT energy). MLCT absorption and electrochemical data show that a trans-[Ru(II)Cl(pdma)2]+ centre is considerably less electron-rich than a [Ru(II)(NH3)5]2+ unit. Although the beta0 responses of the pdma complexes are only a little smaller than those of their [Ru(II)(NH3)5]2+ analogues, this result is partly attributable to unexpected changes in the relative mu12 values on freezing. Thus, substantial increases in mu12 for the arsine compounds act to partially offset the beta0-decreasing influence of their higher Emax values when compared with the analogous pentaammine species. Single crystal X-ray structures have been obtained for the salts 1(.)2.5MeCN, 4(.)2MeCN, 7 and 11, but only 1(.)2.5MeCN adopts a non-centrosymmetric space group (Fdd2) such as may show bulk NLO effects.

Journal Article↗
PubMed2004

Mild mono and double demethylation in dimethylsulfonium substituted ruthenacarborane complexes. A regioselective reaction.

Reaction of [RuCl(2)(eta(6)-C(6)H(6))](2) with [10-(CH(3))(2)S-7,8-nido-C(2)B(9)H(10)](-) or [9-(CH(3))(2)S-7,8-nido-C(2)B(9)H(10)](-) afforded the expected cationic complexes [Ru(eta(5)-n-(CH(3))(2)S-7,8-C(2)B(9)H(10))(eta(6)-C(6)H(6))](+)(n= 10, (1); 9, (3)), but also the unexpected neutral Ru(eta(5)-10-HS-7,8-C(2)B(9)H(10))(eta(6)-C(6)H(6))(2) or Ru(eta(5)-9-(CH(3))S-7,8-C(2)B(9)H(10))(eta(6)-C(6)H(6))(4) by double and mono demethylation of the (CH(3))(2)S moiety, respectively.

Journal Article↗
PubMed2004

Highly-functionalised difluorinated (hydroxymethyl)conduritol analogues via the Diels-Alder reactions of a difluorinated dienophile.

A difluorodienophile, synthesised using a Stille coupling reaction underwent tin(iv)-catalysed cycloaddition with three furans to afford oxa[2.2.1]bicycloheptenes in good yield. Reduction of ester and carbamate carbonyl groups and diol protection as the acetonide set the stage for palladium-catalysed hydrostannylation in two cases. Treatment of the stannanes with methyllithium triggered ring-opening to afford highly-functionalised difluorinated cyclohexenols which could be deprotected to afford (hydroxymethyl)conduritol analogues.

Journal Article↗
PubMed2003

Syntheses of selectively fluorinated cyclodecenones: the first deployment of the neutral oxy-Cope rearrangement in organofluorine chemistry.

Metallated haloalkenes were used to open epoxides in moderate to good yield. The homoallylic alcohols obtained underwent Swern oxidation to afford three gamma,gamma-difluorinated beta,gamma-enones, which reacted with either vinyllithium,2-lithio-2H-dihydropyran or another metallated haloalkene to afford substituted trans-1,2-divinylcyclohexanols of different degrees of stability. These intermediates underwent neutral thermal oxy-Cope rearrangements when heated in xylene in Ace tubes. The first-formed enols ketonised without loss of HF to afford a range of cyclodecenones in moderate to good yield; X-ray crystallography was used extensively for product characterisation. All substrates rearranged more rapidly than a cis/trans mixture of 1,2-divinylcyclohexanols.

Crystallography, X-Ray↗
PubMed2003

Thermal and sonochemical studies on the Diels-Alder cycloadditions of masked o-benzoquinones with furans: new insights into the reaction mechanism.

What does a Diels-Alder cycloaddition look like? This question is here addressed in the case of the increasingly significant cycloadditions of masked o-benzoquinones (MOBs), which serve as versatile dienes for the construction of complex and functionalized structures. So first, what the mechanism is not: It is not (by and large) a classical, concerted [4 + 2] cycloaddition. Experimental evidence is now supported by sonochemical studies, which were instrumental in elucidating the pathway. Reactions with furans are accelerated and improved under sonication, even when conducted at -10 degrees C. Variation of the acoustic energy, temperature, and solvent composition allows us to optimize the yields and provide insights into the mechanism. Ultrasound does not cause sonochemical switching, as an alternative radical pathway should be ruled out. Results are consistent with a polar mechanism as claimed recently in a theoretical study. Moreover, this also does justice to a series of seminal papers, largely ignored, that gave a clue to the crucial issue of furan regioselectivity based on a nucleophilic addition. Most effects caused by ultrasonic agitation are of mechanochemical nature and suggest the existence of a perfectly stirred reactor with enhanced mass transfer.

Journal Article↗
PubMed2003

Pentapyrrolic calix[4]pyrrole.

A new calix[4]pyrrole has been synthesised that contains a 3,4,5-trisbromopyrrole appended to a meso-position which shows enhanced anion affinity as compared to the parent meso-octamethylcalix[4]pyrrole macrocycle.

Calixarenes↗
PubMed2003

trans-Bis[1,2-bis(diphenylphosphino)ethane-kappa(2)P,P']bis[4-(trimethylsilyl)buta-1,3-diynyl]ruthenium(II) and trans-bis[1,2-bis(diphenylphosphino)ethane-kappa(2)P,P']bis(buta-1,3-diynyl)ruthenium(II).

The crystal structures of the title compounds, [Ru(C(7)H(9)Si)(2)(C(26)H(24)P(2))(2)] and [Ru(C(4)H)(2)(C(26)H(24)P(2))(2)], are described. The metal centre in both complexes has an octahedral coordination geometry, with mutually trans buta-1,3-diynyl ligands forming pseudo-linear ruthenium-centred polyyne chains.

Journal Article↗
PubMed2003

Anion-directed assembly: the first fluoride-directed double helix.

The crystal structures of anion complexes of two nitroaromatic functionalised isophthalamides are reported; the structures reveal assembly around anions in the solid-state and in the case of the fluoride complex of receptor 2, the formation of a double helix.

Journal Article↗