Biomedical subjects
Publications and source records attributed to Claire Wilson.
Reactions of tetrahedral Cu(I) and Ag(I) cations with 2,3,4,5-tetra(4-pyridyl)thiophene allows targeted construction of coordination frameworks with zeolite-like, 4(2).8(4), topologies.
In the presence of enantiopure MTBH(2)(monothiobinaphthol, 2-hydroxy-2[prime or minute]mercapto-1,1[prime or minute]-binaphthyl; 0.2 eq.) quantitative allylation of ArC([double bond]O)Me takes place with impure Sn(CH(2)CH[double bond]CH(2))(4)(prepared from allyl chloride, air-oxidised magnesium and SnCl(4)) to yield tert-homoallylic alcohols in 85-92% ee. In the same process highly purified, or commercial, Sn(CH(2)CH[double bond]CH(2))(4) yields material of only 35-50% ee. The origin of these effects is the presence of small amounts of the compounds, EtSn(CH(2)CH[double bond]CH(2))(3), ClSn(CH(2)CH[double bond]CH(2))(3) ClSnEt(CH(2)CH[double bond]CH(2))(2) in the tetraallyltin sample and the presence of traces of water (which inhibits achiral background reactions). All the triallyl and diallyl species enhance the stereoselectivity in the catalytic allylation reaction, the chlorides more so than the ethyl compound. Hydrolysis of ClSnEt(CH(2)CH[double bond]CH(2))(2) affords crystallographically characterised Sn(4)(mu(3)-O)(mu(2)-Cl)(2)Cl(2)Et(4)(CH(2)CH[double bond]CH(2))(4). Reaction of this latter compound with MTBH(2) leads to the most potent catalyst.
The remarkable luminescence properties of the platinum(II) complex of 1,3-di(2-pyridyl)benzene, acting as a terdentate N=C=N-coordinating ligand cyclometalated at C2 of the benzene ring ([PtL(1)Cl]), have been investigated, together with those of two new 5-substituted analogues [PtL(2)Cl] and [PtL(3)Cl] [HL(2) = methyl-3,5-di(2-pyridyl)benzoate; HL(3) = 3,5-di(2-pyridyl)toluene]. All three complexes are intense emitters in degassed solution at 298 K (lambda(max) 480-580 nm; phi(lum) = 0.60, 0.58, and 0.68 in CH(2)Cl(2)), displaying highly structured emission spectra in dilute solution, with lifetimes in the microsecond range (7.2, 8.0, and 7.8 micros). On the basis of the very small Stokes shift, the highly structured profiles, and the relatively long lifetimes, the emission is attributed to an excited state of primarily (3)pi-pi character. At concentrations >1 x 10(-)(5) M, structureless excimer emission centered at ca. 700 nm is observed. The X-ray crystal structure of [PtL(2)Cl] is also reported.
The asymmetric binuclear complex [(dppe)Ni(mu-'S, S')Ni(L)](PF6)2 [L = (N, N'-diethyl-3,7-diazanonane-1,9-dithiolato)2-] shows a reversible one-electron reduction to afford a mixed-valent Ni(II) x Ni(I) species; the reduced complex has been characterised by EPR spectroscopy and mimics the redox active Nip site in the active A-cluster of acetyl coenzyme A synthase.
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Single crystals of magnesium diiodide have been grown and the structure solved for the first time from single-crystal X-ray diffraction data. This study confirms that MgI(2) is isostructural with CdI(2) (C6 or 2H structure type). The space group is P-3m1 with the Mg atom on a site with 3m symmetry (Wyckoff site 1a) and the I atom on a site with m symmetry (Wyckoff site 2d). Trends in the 2H structures of dihalides are discussed briefly.
Reaction of the mononuclear nickel-thiolate complex [Ni(L1)(dppe)] with CH2Cl2 affords the novel pentanuclear complex [Ni5Cl2(L1)4(dppe)2], while [Ni(L1)(dcpe)] reacts with CH2Cl2 to give the binuclear species [Ni2Cl2(L2)(dcpe)2] in which two L1 units are linked by a methylene group derived from CH2Cl2.
The synthesis of new Pt(II) diimine complexes bearing perfluorinated thiolate ligands, Pt(II)(NN)(4-X-C(6)F(4)-S)(2), where NN = 2,2'-bipyridine or 1,10-phenanthroline and X = F or CN, is reported, together with an investigation of the nature and dynamics of their lowest excited states. A combined UV-vis, (spectro)electrochemical, resonance Raman, and time-resolved infrared (TRIR) study has suggested that the HOMO is mainly composed of thiolate(pi)/S(p)/Pt(d) orbitals and that the LUMO is largely localized on the pi*(diimine) orbital, thus revealing the [charge-transfer-to-diimine] nature of the lowest excited state. An enhancement of the thiolate ring vibrations, C-F vibrations, and the vibration of the CN-substituent on the thiolate moiety was observed in the resonance Raman spectra, whereas no such enhancement was seen for the nonfluorinated analogues. Thus, the introduction of fluorine substituents on the thiolate moiety probably leads to a more pronounced contribution of the intrathiolate modes to the HOMO compared to the analogous complexes with nonfluorinated thiolates. Furthermore, the introduction of the p-CN group into the thiolate moiety has allowed the dynamics of the lowest excited state of Pt(bpy)(4-CN-C(6)F(4)-S)(2) to be monitored by picosecond TRIR spectroscopy. The dynamics of the lowest [charge-transfer-to-diimine] excited state are governed by ca. 2-ps vibrational cooling and 35-ps back electron transfer.
Model studies are presented that suggest the mechanism of the lanthanide(III) salt catalysed mono acylation of symmetrical diols proceeds via chelation of the diol and the anhydride to the lanthanide salt, followed by an 'intramolecular' acyl transfer.
The complexation of palladium(II) by a unique family of [2+2] diiminodipyrromethane macrocycles yields compounds that adopt structures reminiscent of Pac-Man porphyrins.
The homohexanuclear complexes [Ni2[Ni(L1)]4](BF4)4 x MeCN, 1, [Pd2(Pd(L2)]4](BF4)4, 2, and the heteropentanuclear aggregate [Cu2[Ni(L3)]3](PF6)2, 3, all adopt a 'pinwheel' type structural motif via thiolate bridging between square-planar Ni(II) or Pd(II) and between trigonal planar Cu(I) centres, respectively.
The ionic Diels-Alder reaction, whereby an alpha,beta-unsaturated acetal in combination with a Lewis or Bronsted acid forms an equilibrium concentration of an activated dienophile, has been developed to provide an enantioselective synthesis of cis-decalins. Cyclohex-2-enone type chiral acetals of (2R,3R)-butane-2,3-diol have been screened against Lewis and Brønsted acids with a variety of dienes and are efficient for the synthesis of a limited subset of cis-decalin structures. Diastereoselectivities of 73% and 82% have been found for the asymmetric ionic Diels-Alder reaction between the chiral acetal derivatives of cyclohex-2-enone (6) and 2-methylcyclohex-2-enone (18) with 2,3-dimethyl-1,3-butadiene (7). Terminal substituents on the diene partner in general render the system unreactive. However a synthetically useful cis-decalin 31, derived from the reaction of 2-methylcyclohex-2-enone and Z-3-t-butyldimethyl-silyloxypenta-1,3-diene has been prepared in enantiomerically pure form in 74% isolated yield using this asymmetric ionic Diels-Alder protocol.
The tetradentate imino-carboxylate ligand [L](2)(-) chelates the equatorial sites of Ni(II) to give the complex [Ni(L)(MeOH)(2)] in which a Ni(II) center is bound in an octahedral coordination environment with MeOH ligands occupying the axial sites. Lanthanide (Ln) and Group II metal ions (M) template the aggregation of six [Ni(L)] fragments into the octahedral cage aggregates (M[Ni(L)](6))(x)(+) (1: M = Sr(II); x = 2,2: M = Ba(II); x = 2, 3: M = La(III); x = 3, 4: M = Ce(III); x = 3, 5: M = Pr(III); x = 3, and 6: M = Nd(III); x = 3). In the presence of Group I cations, however, aggregates composed of the alkali metal-oxide cations template various cage compounds. Thus, Na(+) forms the trigonal bipyramidal [Na(5)O](3+) core within a tricapped trigonal prismatic [Ni(L)](9) aggregate to give ((Na(5)O) subset [Ni(L)](9)(MeOH)(3))(BF(4))(2).OH.CH(3)OH, 7. Li(+) and Na(+) together form a mixed Li(+)/Na(+) core comprising distorted trigonal bipyramidal [Na(3)Li(2)O](3+) within an approximately anti-square prismatic [Ni(L)](8) cage in ((Na(3)Li(2)O) subset [Ni(L)](8)(CH(3)OH)(1.3)(BF(4))(0.7))(BF(4))(2.3).(CH(3)OH)(2.75).(C(4)H(10)O)(0.5), 8, while in the presence of Li(+), a tetrahedral [Li(4)O](2+) core within a hexanuclear open cage [Ni(L)](6) in ((Li(4)O) subset [Ni(L)](6)(CH(3)OH)(3))2ClO(4).1.85CH(3)OH, 9, is produced. In the presence of H(2)O, the Cs(+) cation induces the aggregation of the [Ni(L)(H(2)O)(2)] monomer to give the cluster Cs(2)[Ni(L)(H(2)O)(2)](6).2I.4CH(3)OH.5.25H(2)O, 10. Analysis by electronic spectroscopy and mass spectrometry indicates that in solution the trend in stability follows the order 1-6 > 7 > 8 approximately 9. Magnetic susceptibility data indicate that there is net antiferromagnetic exchange between magnetic centers within the cages.
The key step in an attempted biomimetic synthesis of the indole-diterpene mycotoxin emindole SB delivers the pentacyclic compound resulting from 6-endo cyclisation instead of the product arising by the 5-exo reaction required in the putative biosynthetic pathway.
The meso-disubstituted dipyrrolide ligand (L) has promoted the formation of a unique tetranuclear iron(II) compound that contains both diazaferrocenyl and distorted-tetrahedral iron centres.
Four new series of non-disklike complexes of general formula [MCl(2)(L(n))] based upon substituted 2,6-bis(3',4',5'-trialkoxyphenyliminomethyl)pyridine ligands (L(n)) and with M=Zn(II), Co(II), Mn(II), and Ni(II) have been prepared and examined for liquid crystallinity. A complete analysis of the thermal behavior by polarized-light optical microscopy, differential scanning calorimetry, and small-angle Xray scattering revealed a rich and varied mesomorphism. Moreover, the high thermal stability of the compounds leads to rather extended mesomorphic ranges. The nature and thermal stability of each mesophase depend on both the length of the six terminal alkoxy chains, n (n=8, 10, 12, 14, 16), and on the metal ions. As demonstrated by small-angle Xray diffraction experiments, the mesomorphism of these complexes is solely of the columnar type. One compound shows an oblique columnar phase, while most of them show a hexagonal columnar phase, Col(h), and several types of rectangular columnar phase, Col(r). Xray single-crystal structures obtained for three methoxy derivatives confirm the 1:1 metal-ligand stoichiometry of the complexes, in which the metal is pentacoordinate with a distorted, trigonal bipyramidal geometry. The crystalline structures also reveal the existence of some columnar organization in the solid state, the columns resulting from an alternated stacking of the complexes in one direction. By combining these results with those obtained from dilatometry experiments, a model for the molecular organization within the mesophases is proposed in which an antiparallel arrangement of the metallomesogens is retained in the mesophase.
A series of structurally related binuclear metallacycles [Cd(NO(3))(2)L](2), where L is an angular exo-bidentate ligand, have been synthesized. Each metallacycle contains two coordinatively unsaturated, chiral metal centers within a single molecule, and the assembly of these metallacycles into polymeric framework structures has been studied systematically for the first time. Stereoselective homochiral association of [Cd(NO(3))(2)L](2) leads to the formation of helical coordination polymers, whereas meso type association results in nonhelical chain structures. The type of stereoselective aggregation depends on the conditions of self-assembly as well as on ligand functionality. Both helical and nonhelical polymeric complexes have been isolated for the metallacycle [Cd(NO(3))(2)(2,4'-pyacph)](2) (2,4'-pyacph = 2,4'-(4-ethynylphenyl)bipyridyl). Homochiral association results in the formation of helical [Cd(NO(3))]( infinity ) chains which link the binuclear [Cd(NO(3))(2)(2,4'-pyacph)](2) metallacycles into racemic two-dimensional sheets which contain both P and M [Cd(NO(3))]( infinity ) helices. In contrast, meso-association leads to the formation of nonhelical one-dimensional chains. It is shown that the product of homochiral association is predominately formed at room temperature and that of meso-association is generated at elevated temperatures. Thus, it may be concluded that the homochiral association appears to be energetically less favorable than the meso-association, a conclusion that has been confirmed by theoretical calculations of the crystal lattice energy. Several high-yield syntheses of bipyridyl-type ligands used for metallacyclic assembly are also reported.