Isostructural salts of the same complex showing contrasting thermal spin-crossover mediated by multiple phase changes.

Two salts of [FeL2](2+) (L = 2,6-bis[5-methyl-1H-pyrazol-3-yl]pyridine) are isostructural under ambient conditions but show different thermal spin-crossover behaviour, involving a variety of crystallographic phase changes.

Solid-phase methodology for synthesis of O-alkylated aromatic oligoamide inhibitors of α-helix-mediated protein-protein interactions.

Rapid access to rigid rods: A method is described for the synthesis of 3-O-alkylated aromatic oligobenzamide foldamers that could be used for assembly of libraries of α-helix mimetic inhibitors of protein-protein interactions (see scheme; Fmoc=9-fluorenylmethoxycarbonyl).

Carbophilic 3-component cascades: access to complex bioactive cyclopropyl diindolylmethanes.

Naturally occurring indole-3-carbinol and 3,3-diindolylmethane show bioactivity in a number of disparate disease areas, including cancer, prompting substantial synthetic analogue activity. We describe a new approach to highly functionalised derivatives that starts from allene gas and proceeds via the combination of a three-component Pd(0)-catalysed cascade with a one-pot, three-component carbophilic Pt(II) cascade linked to a stereoselective acid-catalysed Mannich-Michael reaction that generates complex cyclopropyl diindolylmethanes which show selective activity against prostate cancer cell lines.

2-O-alkylated para-benzamide α-helix mimetics: the role of scaffold curvature.

The design and synthesis of a new 2-O-alklyated benzamide α-helix mimetic is described. Comparison with regioisomeric 3-O-alkylated benzamides permits a preliminary evaluation of the role that mimetic curvature has in determining molecular recognition properties.

Suppression of the Jahn-Teller distortion in a six-coordinate copper(II) complex by doping it into a host lattice.

The electronic structures of [Cu(terpy)(2)](2+) and [Cu(bpp)(2)](2+) (bpp = 2,6-di[pyrazol-1-yl]pyridine) are different, when doped into [M(bpp)(2)][BF(4)](2) (M(2+) = Fe(2+) or Zn(2+)). The [Cu(terpy)(2)](2+) dopant is a typical pseudo-Jahn-Teller elongated copper(II) center. However, the [Cu(bpp)(2)](2+) sites show EPR spectra consistent with a tetragonally compressed {d(z(2))}(1) configuration.

Tetrakis(methylimidazole) and tetrakis(methylimidazolium) calix[4]arenes: competitive anion binding and deprotonation.

Neutral tetrakis(methylimidazole) (1) and the novel cationic tetrakis(methylimidazolium) (2) calixarenes have been prepared and their solid-state and solution behaviour examined. The neutral imidazole forms a mono-zwitterion at elevated temperature, a feature that has been observed both in solution and in the solid-state. The cationic imidazolium exhibits a range of hydrogen bond interactions with anions, with the titration curves upon binding to basic anions suggesting sequential binding to both the upper and lower rims.

Mechanistic studies on a sulfoxide transfer reaction mediated by diphenyl sulfoxide/triflic anhydride.

Sulfoxides are frequently used in organic synthesis as chiral auxiliaries and reagents to mediate a wide variety of chemical transformations. For example, diphenyl sulfoxide and triflic anhydride can be used to activate a wide range of glycosyl donors including hemiacetals, glycals and thioglycosides. In this way, an alcohol, enol or sulfide is converted into a good leaving group for subsequent reaction with an acceptor alcohol. However, reaction of diphenyl sulfoxide and triflic anhydride with oxathiane-based thioglycosides, and other oxathianes, leads to a different process in which the thioglycoside is oxidised to a sulfoxide. This unexpected oxidation reaction is very stereoselective and proceeds under anhydrous conditions in which the diphenyl sulfoxide acts both as oxidant and as the source of the oxygen atom. Isotopic labelling experiments support a reaction mechanism that involves the formation of oxodisulfonium (S-O-S) dication intermediates. These intermediates undergo oxygen-exchange reactions with other sulfoxides and also allow interconversion of axial and equatorial sulfoxides in oxathiane rings. The reversibility of the oxygen-exchange reaction suggests that the stereochemical outcome of the oxidation reaction may be under thermodynamic control, which potentially presents a novel strategy for the stereoselective synthesis of sulfoxides.

Iron(II) complexes of new hexadentate 1,1,1-tris-(iminomethyl)ethane podands, and their 7-methyl-1,3,5-triazaadamantane rearrangement products.

New iron(II) podand complexes have been prepared, by condensation of 2-(aminomethyl)-2-methyl-1,3-diaminopropane with 3 equiv of a heterocyclic aldehyde in the presence of hydrated Fe[BF(4)](2) or Fe[ClO(4)](2) as templates. The 2-(aminomethyl)-2-methyl-1,3-diaminopropane is prepared in situ by deprotonation of its trihydrochloride salt. The chloride must be removed from these reactions by precipitation with silver, to avoid the formation of the alternative 2,4,6-trisubstituted-7-methyl-1,3,5-triazaadamantane condensation products, or their FeCl(2) adducts. The crystal structures of two 2,4,6-tri(pyridyl)-7-methyl-1,3,5-triazaadamantane-containing species are presented, and contain two different geometric isomers of this tricyclic ring with three equatorial, or two equatorial and one axial, pyridyl substituents. Both structures feature strong C-HX (X = Cl or F) hydrogen bonding from the aminal C-H groups in the triazaadamantane ring. Five iron(II) podand complexes were successfully obtained, all of which contain low-spin iron centres.

Intrinsically thermochromic fluorans.

A Suzuki coupling strategy has been employed to access a series of novel fluorans substituted with a phenolic moiety. These fluorans display good thermochromism in methyl stearate and obviate the need for traditional complex formulations containing acidic colour developers.

Do glycosyl sulfonium ions engage in neighbouring-group participation? A study of oxathiane glycosyl donors and the basis for their stereoselectivity.

Neighbouring-group participation has long been used to control the synthesis of 1,2-trans-glycosides. More recently there has been a growing interest in the development of similar strategies for the synthesis of 1,2-cis-glycosides, in particular the use of auxiliary groups that generate sulfonium ion intermediates. However, there has been some debate over the role of sulfonium ion intermediates in these reactions: do sulfonium ions actually engage in neighbouring-group participation, or are they a resting state of the system prior to reaction through an oxacarbenium ion intermediate? Herein, we describe the reactivities and stereoselectivities of a family of bicyclic thioglycosides in which an oxathiane ring is fused to the sugar to form a trans-decalin-like structure. A methyl sulfonium ion derived from one such glycosyl donor is so stable that it can be crystallised from ethanol, yet it reacts with complete stereoselectivity at high temperature. The importance of a ketal group in the oxathiane ring for maintaining this high stereoselectivity is investigated using a combination of experiment and ab initio calculations. The data are discussed in terms of S(N)1 and S(N)2 type mechanisms. Trends in stereoselectivity across a series of compounds are more consistent with selective addition to oxacarbenium ions rather than a shift between S(N)1 and S(N)2 mechanisms.

Stereoselective glycosylations using oxathiane spiroketal glycosyl donors.

Novel oxathiane spiroketal donors have been synthesised and activated via an umpolung S-arylation strategy using 1,3,5-trimethoxybenzene and 1,3-dimethoxybenzene. The comparative reactivity of the resulting 2,4,6-trimethoxyphenyl (TMP)- and 2,4-dimethoxyphenyl (DMP)-oxathiane spiroketal sulfonium ions is discussed, and their α-stereoselectivity in glycosylation reactions is compared to the analogous TMP- and DMP-sulfonium ions derived from an oxathiane glycosyl donor bearing a methyl ketal group. The results show that the stereoselectivity of the oxathiane glycosyl donors is dependent on the structure of the ketal group and reactivity can be tuned by varying the substituent on the sulfonium ion.

Spin-crossover in [Fe(3-bpp)2][BF4]2 in different solvents--a dramatic stabilisation of the low-spin state in water.

The temperature of spin-crossover in [Fe(3-bpp)(2)][BF(4)](2) (3-bpp = 2,6-di{pyrazol-3-yl}pyridine) tends to increase in associating solvents. In particular, T(½) shifts to 60-70 K higher temperature in water compared to organic solvents.

New insights into the aggregation of silver pyrazolides using sterically hindered bidentate pyrazole ligands.

Recrystallisation of Ag[L(1)] (HL(1) = 3{5}-[pyrid-2-yl]-5{3}-tert-butylpyrazole) in the presence of halide anions leads to two polymorphs of [Ag(3)(µ-Br)(µ-L(1))(2)], which differ in their mode of supramolecular association, and the cluster [Ag(10)(µ-L(1))(8)]Cl(2). In contrast, Ag[L(2)] (HL(2) = 3{5}-[isoquinol-1-yl]-5{3}-tert-butyl-pyrazole) crystallises as a cyclic tetrameric molecule.

Two heptacopper(II) disk complexes with a [Cu(7)(µ(3)-OH)(4)(µ-OR)(2)](8+) core.

The reaction of CuX(2) (X(-) ≠ F(-)) salts with 1 equiv of 3-pyridyl-5-tert-butylpyrazole (HL) in basic methanol yields blue solids, from which disk complexes of the type [Cu(7)(µ(3)-OH)(4)(µ-OR)(2)(µ-L)(6)](2+) and/or the cubane [Cu(4)(µ(3)-OH)(4)(HL)(4)](4+) can be isolated by recrystallization under the appropriate conditions. Two of the disk complexes have been prepared in crystalline form: [Cu(7)(µ(3)-OH)(4)(µ-OCH(2)CF(3))(2)(µ-L)(6)][BF(4)](2) (2) and [Cu(7)(µ(3)-OH)(4)(µ-OCH(3))(2)(µ-L)(6)]Cl(2)·xCH(2)Cl(2) (3·xCH(2)Cl(2)). The molecular structures of both compounds as solvated crystals can be described as [Cu⊂Cu(6)(µ-OH)(4)(µ-OR)(2)(µ-L)(6)](2+) (R = CH(2)CF(3) or CH(3)) adducts. The [Cu(6)(µ-OH)(4)(µ-OR)(2)(µ-L)(6)] ring is constructed of six square-pyramidal Cu ions, linked by 1,2-pyrazolido bridges from the L(-) ligands and by basal, apical-bridging hydroxy or alkoxy groups, while the central Cu ion is bound to the four metallamacrocyclic hydroxy donors in a near-regular square-planar geometry. The L(-) ligands project above and below the metal ion core, forming two bowl-shaped cavities that are fully (R = CH(2)CF(3)) or partially (R = CH(3)) occupied by the alkoxy R substituents. Variable-temperature magnetic susceptibility measurements on 2 demonstrated antiferromagnetic interactions between the Cu ions, yielding a spin-frustrated S = (1)/(2) magnetic ground state that is fully populated below around 15 K. Electrospray ionization mass spectrometry, UV/vis/near-IR, and electron paramagnetic resonance measurements imply that the heptacopper(II) disk motif is robust in organic solvents.

Benzopentalenonaphthalenones from the intramolecular capture of a merocyanine derived from a naphthopyran.

Novel, highly coloured benzopentalenonaphthalenones result from a cascade process initiated by the thermally-induced ring-opening of diarylmethanol substituted 2H-naphtho[1,2-b]pyrans in the presence of acid.

Asymmetric general base catalysis of the phospho-aldol reaction via dimeric aluminium hydroxides.

Dimeric aluminium hydroxide complexes containing the (R,R)-N,N'-bis(2'-hydroxy-3'-organobenzyl)-trans-1,2-diaminocyclohexane ligand backbone effect catalysis of the phospho-aldol reaction under ambient, aerobic conditions at catalyst loadings of 0.5 mol% to afford enantioselectivities of ca. 65%.

The influence of a 1,1-diarylvinyl moiety on the photochromism of naphthopyrans.

1,1,3-Triarylpent-4-en-1-yn-3-ols, efficiently obtained in two steps from 1,1,3-triarylprop-2-yn-1-ols by a Meyer-Schuster rearrangement and subsequent addition of lithium trimethylsilylacetylide, react with either a 1- or 2- naphthol to afford photochromic 1,1-diarylvinyl substituted naphtho[1,2-b]- or naphtho[2,1-b]-pyrans respectively. Irradiation of solutions of these naphthopyrans results in reversible electrocyclic ring-opening to afford photomerocyanines which possess an extended conjugated system and show a bathochromically-shifted λ(max) relative to the non-vinyl substituted analogues.

An unusual discontinuity in the thermal spin transition in [Co(terpy)2][BF4]2.

Single crystal and powder samples of [Co(terpy)(2)][BF(4)](2) are low spin below 100 K but show a typically gradual thermal spin-transition on warming, centred near 270 K. However, the spin-crossover exhibits an unusual and pronounced discontinuity above room temperature, when the material is ca. 87% high-spin. A crystallographic study at nine temperatures between 30-375 K showed that the discontinuity is not caused by a phase transition or by changes in anion disorder. Rather, it may reflect the steric consequence of small changes in the nearest neighbour interactions between the cations as the spin transition progresses.

On the prebiotic potential of reduced oxidation state phosphorus: the H-phosphinate-pyruvate system.

H-Phosphinic acid and pyruvic acid, both plausible prebiotic chemicals, react selectively in water to build structural complexity including amide bond formation under remarkably mild conditions and oxidative coupling of P(1) compounds to condensed pyrophosphorus compounds.