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The oxidations of alkyl 4-nitrophenyl, and dialkyl, sulfides and sulfoxides by dimethyldioxirane in acetone occur by concerted mechanisms but the sulfides respond differently from the sulfoxides to variation in the alkyl group. The reactions of the sulfides are inhibited by the steric effects of alkyl groups and these predominate over their inductive effects. By contrast, the reactions of these limited sets of sulfoxides are insensitive to alkyl steric effects but there is an indication of steric acceleration when a broader set of sulfoxides is considered. This behaviour is rationalised in terms of the differences in dipolar charge and its solvation between the ground state and transition state for the two types of substrate. The oxidations of cyclic sulfides and sulfoxides also exhibit contrasting behaviour. The reactivity of the sulfides is insensitive to ring strain but is explicable in frontier orbital terms whereas that of the sulfoxides is partly dependent upon the change in ring strain between reactant and product on oxidation, a difference rationalised in terms of the relative positions of the transition states in the reaction coordinates of the two oxidations. The reactivity of 4-, 5- and 6-membered cyclic sulfoxides is also dependent on a ring-size related property of the transition state. Calculations at the B3-LYP/6-31G* level of density functional theory on both ground states and transition states, including simulation of solvation by acetone, strongly support the mechanistic conclusions reached in this and earlier work.

The oxidation of phenolic substrates with H2O2 catalysed by [MnIV2(μ-O)3(TMTACN)2](PF6)21, (TMTACN, 1,4,7-trimethyl-1,4,7-triazacyclononane) has been investigated by use of ESI mass spectrometry. The role of the phenols as one-electron reductants and as co-ligands in the stabilisation and reaction of an intermediate OMnV species has been analysed and the presence of a variety of manganese species in solution has been explained. Our results lead to a proposed mechanism for the catalytic oxidation of phenols in this system.

A kinetic and mechanistic study is reported of the oxidation of a number of azonaphthol dyes with hydrogen peroxide in aqueous solution, catalysed by some mono and dinuclear manganese(IV) complexes of 1,4,7-trimethyl-1,4,7-triazacyclononane (Me3TACN). The results of UV-Vis investigations, augmented by EPR and ESI-MS studies, are described for a series of experiments in which concentrations, pH and ionic strength have been varied. The reactions are characterised by an induction period followed by a relatively rapid oxidation. For the dinuclear manganese complex 2, these are consistent with an initial perhydrolysis of the manganese complex involving both the dye anion and HO2-, to give mononuclear manganese species and the operation of a catalytic cycle incorporating MnIIIL(OH)3, O = MnVL(OH)2 and MnIVL(OH)3 (L = Me3TACN) (cf. the reactions of peroxidase enzymes). ESI-MS results provide evidence for the formation and reaction (with the dye) of MnIVL(OH)3. With the mononuclear manganese complex MnIVL(OMe)3, there is a short lag-phase attributed to perhydrolysis by HO2- followed by the same catalytic cycle.

This paper reports a study of the dimerisation of ester radicals arising from the thermolysis and photolysis of di-tert-butyl peroxide (DTBPO) and dicumyl peroxide [DCPO, bis(α,α-dimethylbenzyl) peroxide] in neopentyl butanoate and a selection of structurally related neopentyl esters, in the temperature range 298 to 438 K. The acyl moieties of these esters were chosen to incorporate a variety of structural types to provide mechanistic information about the reactions. At 438 K, the thermolyses of DTBPO and DCPO in neopentyl butanoate give six ester radical dimers (three pairs of diastereoisomers). The two major diastereoisomers threo- and meso-dineopentyl 2,3-diethylbutanedioate have been prepared and the crystal structure of the meso compound determined. Interestingly, the dimer product distribution is independent of the peroxide used. By contrast, at 298 K more than twice as many dimers are observed and the product distributions from the two peroxides are no longer the same. Similar results are also observed for the other neopentyl esters. Evidence is presented to show that the ester radicals arise from hydrogen atom abstraction from the esters by alkoxyl and methyl radicals; the latter being formed by the fragmentation of the alkoxyls. At 438 K the dimer product distributions are determined predominantly by a thermodynamically controlled equilibrium of ester radicals prior to dimerisation. Lowering the temperature leads to the increased importance of kinetic effects in determining the product distribution.

Chloromethylated poly(styrene) and chloropropylated silica gel have been reacted with α,ω-diamines to give diamine modified catalyst supports which have then been covalently attached to iron(III) tetrakis(pentafluorophenyl)porphyrin (FeTF5PP). In this way the diamino groups provide a simple linker/spacer unit between the support and the catalyst. The diamino-silica has been further modified using trimethylsilyl chloride and by acetylation or acid washing. The polarities of the modified inorganic and organic supports have been measured using Reichardt’s dye. Spectroscopic studies reveal that with all the supported catalysts, except that on acid washed diamino-silica where the amines are protonated, the diamino groups reduce the iron(III) porphyrin to iron(II). The supported iron porphyrins have been used to catalyse the oxidation of ethylbenzene by dioxygen. These reactions give the same three products, 1-phenylethyl hydroperoxide, 1-phenylethanol and acetophenone, as the analogous homogeneous oxidation using FeTF5PP, suggesting that they proceed by the same mechanism, however, in general they are slower. The overall product yields are limited by the stability/activity of the iron porphyrin and these in turn are very dependent on the length of the linker, the catalyst loading and the microenvironment provided by the support. The role of the diamino groups in the oxidations is discussed.

The successful synthesis of 5,10,15,20-tetrakis[(R,R)-2,6-bis(1-phenylbutoxy)phenyl]porphyrin, with (R)-1-phenylbutoxy substituents on each of the eight ortho-positions, by a 2+2 approach viameso-[(R,R)-2,6-bis(1-phenylbutoxy)phenyl]dipyrromethane rather than a one-pot condensation of (R,R)-2,6-bis(1-phenylbutoxy)benzaldehyde with pyrrole, is described. The synthesis has also been modified using meso-(pentafluorophenyl)dipyrromethane to prepare four further chiral porphyrins containing one, two (cis and trans) and three pentafluorophenyls in place of the bis(phenylbutoxy)phenyl groups. The cross-coupling of the two dipyrromethanes with pentafluorobenzaldehyde gave as one of the products the unexpected cis-disubstituted 5,10-bis(pentafluorophenyl)-15,20-bis[(R,R)-2,6-bis(1-phenylbutoxy)phenyl]porphyrin. It seems likely that the formation of the latter compound involves the acid-catalysed reversion of the dipyrromethane synthesis. Both faces of each of the porphyrins are chiral and equivalent in this way the wasteful formation and time-consuming separation of atropisomers is avoided. Four iron(III) and one manganese(III) complex of these porphyrins have been prepared. The 1H and 19F NMR spectra of the series of porphyrin ligands reveal some interesting structure- and symmetry-dependent splitting patterns and trends which are used to confirm the identities of the compounds. In particular, the 1H NMR couplings of the β-pyrrole hydrogens are very diagnostic of the substitution patterns of the meso-aryl groups on the porphyrin ring.

Manganese(III) complexes of tetra-anionic and tetra-cationic porphyrins have been immobilised on counter-charged, surface-modified silica supports and on organic ion-exchange resins. The reactions of these supported manganese(III) porphyrin systems and analogous uncharged homogeneous systems have been examined using cyclooctene and (E)- and (Z)-4-methylpent-2-ene epoxidations, with iodosylbenzene (PhIO) as the oxygen donor. Comparisons using the manganese porphyrin systems as catalysts for the epoxidation of cyclooctene in acetonitrile reveal that, in low turnover reactions (maximum 136 turnovers), they all give an essentially quantitative yield of epoxide although the heterogeneous reactions are significantly slower than the homogeneous analogues. In large scale repeat-use experiments, however, the supported catalysts are clearly superior, giving markedly better yields. The epoxidations of (E)- and (Z)-4-methylpent-2-ene with all the catalysts show a very high stereoretention, with the (Z)-alkene reacting faster than the (E)-isomer. The sterically hindered manganese(III) 5,10,15,20-tetrakis(2,6-dichloro-3-sulfonatophenyl)porphyrin (MnTDCSPP) shows the highest selectivity for the (Z)-isomer; by contrast the supported manganese(III) 5,10,15,20-tetrakis[2,3,5,6-tetrafluoro-4-(trimethylammonio)phenyl]porphyrin on Dowex (MnTF4TMAPP–Dowex) reacts with the two alkenes at effectively the same rate. The mechanism of the epoxidations and the influence of the porphyrin ligand and support on the substrate selectivity are discussed.

Six neopentyl esters have been selected, as models for pentaerythrityl esters used as lubricants, to study the selectivity of hydrogen abstraction by alkoxyl radicals. Kinetic and product data for the reactions of two oxygenated radicals, tert-butoxyl and cumyloxyl, with the six neopentyl esters between 408 and 438 K have been determined. They show that attack by the radicals occurs at the α- and subsequent positions on the acyl moiety as well as at the alkyl group. The selectivity of the reactions is discussed in terms of bond dissociation, steric and polar effects.

The oxidation of ethylbenzene with dioxygen catalysed by iron(III) porphyrins in a solvent free system has been studied over the temperature range 30–110 °C. The time dependence of the formation of the three main products, 1-phenylethanol, acetophenone and 1-phenylethyl hydroperoxide, and the fate of the iron porphyrin are interpreted in terms of a free radical autoxidation mechanism. The yields of the oxidation products are determined by the rate of reaction and by the lifetime of the catalyst. Catalyst degradation is shown to involve reaction of the porphyrin ligand with 1-phenylethoxyl and 1-phenylethylperoxyl radicals. The disadvantages of increased induction periods and longer reaction times of the oxidations observed at lower reaction temperatures are counter balanced by increased catalyst turnovers. Less extensive studies on the oxidations of toluene, cumene, (2-methylpropyl)benzene and tert-butylbenzene support the overall mechanism proposed for ethylbenzene. A comparative study using the catalysts iron(III) 2,3,7,8,12,13,17,18-octachloro-5,10,15,20-tetrakis(2,6-dichlorophenyl)porphyrin and iron(III) tetrakis(pentafluorophenyl)porphyrin and five of its derivatives reveals that halogenation of the β-pyrrole positions markedly increases the activity of the catalysts but not the stability of the porphyrin towards degradation. The highest yields were obtained with the μ-oxodimer of iron(III) tetrakis(pentafluorophenyl)porphyrin and iron(III) tetrakis(4-dimethylamino-2,3,5,6-tetrafluorophenyl)porphyrin.

EPR experiments involving the attack of oxygen-centred free radicals on polysaccharides in aqueous solution reveal two sources of regioselectivity in C–H abstraction. For SO4−˙ (derived from one-electron reduction of S2O82−), hydrogen-atom abstraction is encouraged by SOMO–σ* interactions involving β-C–O bonds which eclipse the orbital of the unpaired electron at the developing radical centre. In addition, for a series of cyclodextrins, the reactivity observed with SO4−˙ points to the selective reaction of the latter within the cyclodextrin cavity; these findings are in contrast to those obtained with ˙OH (from H2O2).

The autoxidation of six esters, neopentyl butanoate, 2,2-dimethylpropanoate, 3,3-dimethylbutanoate, 2,2-dimethylbutanoate, 2-methylbutanoate and 1,1-[2H2]-neopentyl butanoate, has been studied at 438 K. The reaction products were determined for each system and key reactions leading to the formation and further reactions of the primary products have been identified.Primary products include a range of hydroperoxides which lead to the formation of keto- and hydroxy-esters. Large amounts of neopentanol and the parent carboxylic acid are formed from each ester. It is shown that these are principally oxidation, and not hydrolysis, products.The relative rates of autoxidation of the first five esters mirror the relative rates of attack that occur on reaction with alkoxyl radicals; the sites of attack are on both the alkyl and acyl groups, with the α-alkyl hydrogen atoms on the ester showing particular vulnerability compared to the acyl hydrogen atoms. The analysis of products from the deuterated ester supports this conclusion. p

A systematic synthesis designed to connect a metalloporphyrin to a metal carbonyl moiety is demonstrated through a zinc tetraphenyl porphyrin substituted with Re(CO)3(4′-methyl-2,2′-bipyridyl)Br via an amide bond; the emission and excited state absorption spectra are dominated by porphyrin transitions.

The axial ligand of a series of iron(III) 5,10,15,20-tetramesitylporphyrin phenolate complexes was found to exchange with added carboxylic acids and alcohols. The rates of axial ligand exchange with carboxylic acids were found to be dependent on acidity of the carboxylic acid, basicity of the phenolate, and the steric bulk of both the carboxylic acid and the phenolate axial ligand. The rates of axial ligand exchange with alcohols were found to be dependent on the nucleophilicity of the alcohol, leaving group ability of the phenolate, and the steric bulk of both the alcohol and the phenolate axial ligand. Different mechanisms for ligand exchange are proposed for carboxylic acids and alcohols.

A selection of 5-substituted salicylaldehydes have been reacted with cis,cis-triaminocyclohexane to prepare a series of tri-imine and tri-amine ligands; cyclic voltammetry has been used to show that the electronic effect of the substituent has a marked and systematic effect on the MnIII/MnIV and MnIII/MnII redox potentials of their manganese complexes.

Drinking water treatment typically uses strong oxidants such as chlorine which are capable of converting Cr(III) to Cr(VI). The rates and extent of Cr(III) oxidation by chlorine are not well established. Cr(III) oxidation experiments were therefore conducted in distilled deionized water and New York City tap water dosed initially with Cr(III) and supplemented with sodium hypochlorite to increase free chlorine residual. Reaction progress was monitored using capillary electrophoresis which quenched reactions and allowed for quantification of Cr(VI). Three different forms of Cr(III) were used as reactants: a Cr(III) nitrate salt, Cr(III)-EDTA, and Cr(III) hydroxide. Rates of Cr(VI) production for all three forms of Cr(III) were rapid, on the order of hours. However, oxidation rates slowed and a plateau in Cr(VI) concentrations was reached. This resulted in less than 100% conversion of Cr(III) to Cr(VI) even at relatively high chlorine doses (10 to 100 mg L(-1) as Cl(2)). The loss of free chlorine due to a non-Cr chlorine demand, the precipitation of Cr(III) to Cr(OH)(3)(s), and the partial oxidation of Cr(III) to intermediate oxidation states (i.e. Cr(IV) and Cr(V)) were examined and eliminated as possible explanations for this behavior. Consumption of chlorine via reaction with intermediate oxidation states of Cr is therefore offered as a possible explanation for the plateau in Cr(VI) concentrations.

The photochemical and electrochemical properties of a Zn-porphyrin appended rhenium(I) tricarbonyl bipyridine 3-Me-pyridine complex have been investigated; visible-light sensitisation of electron transfer results in ligand substitution at a site remote from the chromophore.

Relative rate constants have been measured for the oxidation of aryl methyl sulfides and sulfoxides by dimethyldioxirane in acetone, in mixtures of acetone with aprotic co-solvents of both higher and lower relative permittivity, and in aqueous acetone mixtures. Correlation analyses of the effects of substituents in the different solvents show that, with one exception, reactions take place via a single step mechanism in which the formation of the new SO bond and the elimination of acetone occur concertedly. The exception was oxidation of the sulfides in aqueous acetone containing the highest proportion of water of those studied (20% v/v). Here, the behaviour of the reaction is consistent with a two-step mechanism in which the oxidant reversibly attacks the sulfide to form an open-chain sulfonium betaine that subsequently fragments to sulfoxide and acetone. There is no evidence for the participation of an intermediate dioxathietane as has been found in the case of sulfide oxidations by (trifluoromethyl)methyldioxirane in CH(2)Cl(2) and similar aprotic solvents. It is not justified to generalise a mechanism involving a betaine, with or without a derived dioxathietane, to the reactions of dimethyldioxirane in acetone.

The oxidations of methyl 4-nitrophenyl sulfide and sulfoxide by dimethyldioxirane, in acetone and mixtures of acetone with water, methanol, acetonitrile and hexane, have been followed by UV-Vis spectroscopy to monitor the decay of the substrates. The data show that, under all the conditions studied, both oxidations obey second-order kinetics. Grunwald-Winstein and Kamlet-Taft analyses of the influence of solvents on the second-order rate constants have been used to obtain mechanistic information on the two reactions. Activation parameters for the two oxidations in acetone and aqueous acetone have been calculated from rate constants for reactions in the temperature range 283-313 K and compared with those from sulfide and sulfoxide oxidations with other oxidants. For sulfoxide oxidations in acetone and 1-20% v/v water in acetone, the results support a concerted nucleophilic displacement by sulfur of oxygen from dimethyldioxirane with the rate being dependent on the solvent's polarity. Sulfide oxidations in acetone and 1-5% v/v water in acetone also proceed by a concerted mechanism. However, in the most polar solvent system studied, 20% v/v water in acetone, the mechanism changes in favour of a two-step reaction involving a betaine intermediate. Importantly, the sulfide oxidation shows a different solvent dependence to that of the sulfoxide, with the rate of oxidation being determined by the hydrogen bond donor capacity and electron-pair donicity of the solvent.

The supramolecular array formed by co-crystallisation of 1,2-diaminoethane and benzoic acid is investigated by neutron diffraction; the system self-assembles into an unusual layered structure composed of two-dimensional hydrogen-bonded networks sandwiched between layers of edge-to-face stacked aromatic systems; the number of hydrogen-bond donors and acceptors is balanced in the structure.

The bis-azo dye Direct Blue 1 (Chicago Sky Blue 6B) has been studied in solution and on cellophane and cotton surfaces using NMR, resonance Raman, infrared, and UV–visible spectroscopy. The data indicate that Direct Blue 1 is present as the hydrazone tautomer in all of these media, with distinct changes in the spectra with medium showing that the dye is affected by interactions with its environment. In DMF and DMSO solutions, the dye is present as a monomer that is internally hydrogen-bonded. It is also monomeric at low concentrations in aqueous solution, with subtle changes in the Raman spectra from those in DMF and DMSO being attributed to external hydrogen bonding with water. Direct Blue 1 is also present as a hydrazone monomer at low concentrations on cellophane and cotton: the Raman spectra indicate that there is hydrogen bonding with cellulose, and the UV–visible spectra indicate that it experiences an apolar environment which is attributed to its adsorption onto cellulose surfaces.

A selection of alkenes has been epoxidised with iodosylbenzene, catalysed by three related iron(III) tetraarylporphyrins: 1*, 2* and 3* with four 2,6-di(1-phenylbutoxy)phenyl groups, with one pentafluorophenyl and three 2,6-di(1-phenylbutoxy)phenyl groups and with two pentafluorophenyl and two 2,6-di(1-phenylbutoxy)phenyl groups, respectively. 1* is very sterically hindered and prone to self-oxidation which makes it a relatively poor epoxidation catalyst. Introducing the smaller pentafluorophenyl groups, in place of 2,6-di(1-phenylbutoxy)phenyl, increases catalyst reactivity, stability and selectivity. This change allows easier access of the substrates to the active oxidant and also, by decreasing the electron density on the porphyrin ligand, increases the reactivity of the oxoiron intermediate and its stability towards self-oxidation. A family of five homochiral catalysts, 1, 2 and 3, [the analogues of 1*, 2* and 3*, prepared from (R,R)-2,6-di(1-phenylbutoxy)benzaldehyde] and catalyst 4 with three pentafluorophenyl and one (R,R)-2,6-di(1-phenylbutoxy)phenyl group and 5 the manganese(III) analogue of 3 have been used to epoxidise three prochiral alkenes. All the reactions give low enantioselectivities. Using styrene as the substrate, (S)-styrene epoxide is the major enantiomer obtained with all the catalysts except 1 which leads to the (R)-styrene epoxide being preferred. In contrast cis-hept-2-ene and 2-methylbut-2-ene give the same major epoxide enantiomer with all the catalysts. The dependence of the ee values on catalyst and substrate structure, temperature and solvent is examined and discussed.

The host–guest interaction between cyclam and 4-tert-butylbenzoic acid has been investigated by NMR titration, X-ray diffraction, neutron diffraction and semi-empirical MO calculation; the product represents a system preassembled for metal-ion complexation.

A series of free base and zinc porphyrins, mono meso-substituted with a pyridyl group via an amide link, have been prepared by stepwise functionalisation of free base tetraphenylporphyrin, H2tpp. Four [W(CO)5L] (L = pyridyl-porphyrin) complexes have been synthesised; [M{tpp-NHCO-py-W(CO)5}], where M = 2H or Zn, one phenyl group is substituted at the 4-position and the pyridine is substituted at the 3- or 4-position. The spectroscopic data of the [W(CO)5L] complexes have been compared with those of the porphyrin ligands alone and with those of the model compounds, [W(CO)5(3-H2NCO-py)] and [W(CO)5(4-H2NCO-py)]. The UV-Vis spectra of the model compounds show that the MLCT and LF absorption bands overlap and no emission is observed at room temperature in solution. The UV-Vis absorption and emission spectra of the porphyrins with peripheral W(CO)5 are dominated by porphyrin bands. Time-resolved emission was observed from the porphyrin moiety in the [W(CO)5L] complexes and fitted to mono-exponential kinetics to give lifetimes of ≤10 ns for the zinc porphyrins and of ca. 22 ns for the free base porphyrins. Transients characteristic of the porphyrin 3(π–π*) excited state have been observed by time-resolved absorption and their decay kinetics have been fitted to an appropriate rate law. Long wavelength photolysis of [W(CO)5(3-H2NCO-py)] and [W(CO)5(4-H2NCO-py)] in THF resulted in conversion to [W(CO)5(THF)]. The [W(CO)5L] complexes behaved similarly with photolysis at λ > 395 nm but were photostable with λ > 495 nm.

The neutron diffraction structure of a 17-membered macrocyclic ligand incorporating an O2N3-donor set has been determined in order to investigate whether the C–C bond in the –OCH2CH2O– atom string remains short as found in the corresponding X-ray structure of this compound; the evidence suggests that the short bond found by X-ray diffraction in this as well as in many other polyether compounds is largely an artefact with the ‘real’ component of the shortening being quite minor.