Biomedical subjects
Publications and source records attributed to Alexander J Blake.
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.
N-Amination of 3-amino-5-tert-butylpyrazole 11 with hydroxylamine-O-sulfonic acid gave the 1,5-diaminopyrazole 12 with good regiochemical control. The reactions of 12 with certain electrophiles (e.g. acetic anhydride, DMF acetal, aromatic aldehydes, methoxymethylene Meldrum's acid) took place at one (or both) of the amino groups and no cyclised products were obtained. Reaction of 12 with carbon disulfide followed by alkylation under basic conditions provided the pyrazolo[1,5-b]1,2,4-triazole 26 which is a useful photographic magenta coupler. Reactions of 12 with 1,2- and 1,3-dicarbonyl compounds (diketones and ketoesters) provided new pyrazolo[1,5-b]1,2,4-triazines 29, 30, 42 and 43 and the first derivatives of the pyrazolo[1,5-b]1,2,4-triazepine system 31 and 35-36. The X-ray crystal structure of the pyrazolotriazepine 33 is reported.
The efficient syntheses of novel planar chiral 1,3-diamines and 1,3-amino ethers with an oxy or amino function directly bound to the cyclopentadienyl ring of ferrocene has been developed. The key reaction is the Cu2O promoted substitution of (pR)-N,N-diisopropyl-2-iodoferrocenecarboxamide with either phthalimide or AcOH to introduce nitrogen or oxygen functionality onto the cyclopentadienyl ring. The enantiomerically pure iodoferrocene derivative is available from the known enantioselective ortho-lithiation of N,N-diisopropylferrocenecarboxamide with n-BuLi-sparteine. In the course of these studies the synthesis of a novel C2 symmetric C-2 dimer of N,N-dimethyl-1-ferrocenylethylamine was characterised by single crystal X-ray diffraction.
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.
A homobimetallic supramolecular helicate has been used to template the formation of a polyiodide network which adopts an infinite cross-linked double helical structure, topologically analogous to DNA.
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.
The trans-trans conformations adopted by the derivatized bis(bidentate) chelating N(4)-donor ligand 3,6-bis(pyrazol-1-yl)-4-[2-(4-thiamorpholino)ethanesulfanyl]pyridazine, C(16)H(19)N(7)S(2), and an intermediate in its formation, 3,6-dichloro-4-[2-(4-thiamorpholino)ethanesulfanyl]pyridazine, C(10)H(13)Cl(2)N(3)S(2), contrast with the cis-cis conformation found previously for 3,6-bis(thiophen-2-yl)pyridazine [Ackers, Blake, Hill & Hubberstey (2002). Acta Cryst. C58, o640-o641], which places all four heteroatoms on the same side of the molecule.
Hexanuclear cage complexes [M6L6X](X)5 [M = Cu(I), Ag(I); L = 6,6'-bis(4-ethynylpyridine)2,2'-bipyridine; X = BF4-, SbF6-] have been prepared using a self-assembly approach; these architectures encapsulate anions in the solid-state and are fluxional in solution.
A homobimetallic supramolecular helicate has been prepared from a new multimodal ligand, and used to template the formation of two polyiodide networks, one containing an unprecedented figure-of-eight polyiodide helix, the other dominated by peripheral C-H...I polyiodide chain interactions.
The asymmetric unit of ([4,7-bis(2-aminoethyl)-1,4,7-triazacyclononan-1-yl]acetato)zinc(II) triaqua(mu-[4,7-bis(2-aminoethyl)-1,4,7-triazacyclononan-1-yl]acetato)lithium(I)zinc(II) chloride diperchlorate, [Zn(C(12)H(26)N(5)O(2))][LiZn(C(12)H(26)N(5)O(2))(H(2)O)(3)]Cl(ClO(4))(2), obtained from the reaction between the lithium salt of 4,7-bis(2-aminoethyl)-1,4,7-triazacyclononane-1-acetate and Zn(ClO(4))(2), contains two Zn(II) complexes in which each Zn(II) ion is six-coordinated by five N-atom donors and one O-atom donor from the ligand. One carboxylate O-atom donor is not involved in coordination to a Zn(II) atom, but coordinates to an Li+ ion, the tetrahedral geometry of Li+ being completed by three water molecules. The two complexes are linked via a hydrogen bond between a primary amine N-H group and the carboxylate-O atom not involved in coordination to a metal.
Lithium niobium disulfide, Li(0.63)NbS(2), has been prepared by a metathesis reaction between physically separated solid reactants, i.e. separated reactant metathesis (SRM). Single-crystal data were collected at reduced temperature [150 (2) K], yielding a refined Li content of y = 0.63 (6). The Li content in the crystalline samples was also determined analytically by flame photometry. The compound crystallizes in hexagonal space group P6(3)/mmc (No. 194), with Li(+) ions situated in octahedral sites between NbS(2) layers.
The reactions between meso-disubstituted dipyrromethanes and titanium and zirconium amides and alkyls have generated the first examples of dipyrrolide complexes of Group 4 metals.