James H. Cameron

Synthesis of iron(II) C2-capped strapped porphyrin complexes and their reaction with dioxygen

The synthesis of potentially quinquedentate ligands based on a C2-capped porphyrinate ligand, the ‘C2-capped strapped’ ligands, is described where the ‘strapping’ groups contain a pyridine function. The iron(II) complexes of the ligands undergo reversible oxygenation at room temperature in toluene solution, and show good stability to autoxidation. Interestingly the products of decomposition are not µ-oxo dimers but are iron(III) species which can be directly reduced back to the active iron(II) form. The affinities of the complexes for dioxygen have been determined. The relatively low affinities of these new complexes are ascribed to inhibition of the motion of the iron(II), which must occur on the binding of O2. This is due to the locking of the complex in a ‘domed’ configuration, enhanced by the strapping group, and to unfavourable steric interactions of the strapping group with the parent porphyrin.

Tridentate coordination of dioxomolybdenum(VI) with some potentially quinquedentate (N2O3) Schiff base ligands

Abstract Three complexes of molybdenum(VI) 4–6 have been prepared and characterised using potentially quinquedentate ligands derived from Schiff base condensations using 1,3-diamino-2- hydroxypropane. From NMR spectroscopic evidence it is clear that the ligands bind to the metal ion in a terdentate manner, leaving two of the possible ligand donor atoms uncoordinated. This represents a new coordination mode for monomeric complexes of these ligands with a transition metal ion. In solution, the sixth coordination site of the MoO 2 2+ ion is occupied by a solvent molecule while in the solid state, the 13 C NMR spectrum of 4 suggests that the sixth coordination site of MoO 2 2+ is occupied by a phenolic oxygen, probably via an intermolecular interaction between the complexes.

Lyotropic liquid crystalline cellulose derivatives in blends and molecular composites

Solutions of cellulose tricarbanilate (CTC) in methyl acrylate (MA) and methyl methacrylate (MMA) were prepared. The MA and MMA monomers were subsequently polymerised to produce a series of molecular composites, in which the amount of CTC and the degree of substitution (DS) of the tricarbanilate groups were varied. The CTC solutions were studied using polarised microscopy and indicated isotropic behaviour in solutions with a CTC concentration of less than 33 wt%. Solutions of 33–45 wt% CTC were found to have a nematic texture and a chiral nematic texture was detected on shearing of 45 wt% solutions. The mechanical properties and morphologies of the composites were investigated using dynamic mechanical thermal analysis (DMTA), tensile testing and scanning electron microscopy. Tensile testing measurements illustrated the reinforcing behaviour of the CTC on the composite, with the initial modulus increasing by up to 250% at 45 wt% CTC. Scanning electron microscope (SEM) micrographs for composites with <45 wt% CTC revealed a one-phase system. DMTA measurements indicated the existence of a double Tg at DS of the tricarbanilate of less than 3, with a single Tg for composites containing cellulose with degrees of carbanilate substitution equal to 3. The 45 wt% CTC composite showed a broad relaxation process at 350 K and another relaxation at higher temperature (490 K) corresponding to the glass transition of the CTC itself. This result, which is indicative of phase separation, is consistent with the SEM micrographs showing distinctive layered structures within the film.

Preparation and characterisation of some new asymmetric tetraaza macrocyclic complexes of nickel(II)

The synthesis of a new neutral, asymmetrically substituted nickel(II) tetraaza macrocyclic complex has been performed via the template condensation of an asymmetric, acyclic precursor with 1,3-propanediamine. The peripheral aromatic nitro group of this asymmetric macrocycle undergoes catalytic reduction with hydrogen to produce the corresponding aromatic primary amine complex. The asymmetric nature of these materials is clearly demonstrated with the aid of 1H and 13C NMR spectroscopy. The synthesis of a new 15-membered macrocycle is also described. Deacylation of this macrocycle gives either the neutral macrocycle or the related asymmetric, monoprotonated macrocyclic salt, depending upon the reaction conditions.

Electrochemically controlled dissociation of dioxygen from a µ-peroxo cobalt(III) dimer

The electrochemistry of the µ-peroxo dimer of a cobalt Schiff-base complex, [{CoIII(salen)(dmso)}2O2][salen =N,N′-ethylenebis(salicylideneiminate), dmso = dimethyl sulfoxide], has been studied in solution in dmso. Controlled-potential oxidative electrolysis of the dimer is a two-electron process and resulted in its dissociation, with release of dioxygen to the solution and formation of [CoIII(salen)(dmso)2]+. Reduction of the cobalt(III) complex produced the corresponding cobalt(II) complex. The various redox and co-ordination states of the process were characterised by spectroelectrochemistry. The results provide conclusive evidence that electrochemical oxidation can be used as a mechanism for release of O2 from a dioxygen-containing complex.

Thiazyl chloride: an experimental and theoretical study of the valence shell HeI photoelectron spectrum

Abstract High level (CASSCF-MRCI) ab initio calculations are used to investigate the structural, electronic and vibrational properties of the electronic ground state of thiazyl chloride (NSCl) and of the low-lying electronic states of NSCl + . A new high resolution HeI photoelectron spectrum of NSCl has been recorded in the 10–16 eV energy region. From the results of the calculations, the first band is assigned to the (1) 2 A ′ state of NSCl + . The second one corresponds to the (2) 2 A ′ and (1) 2 A ″ states which are quasi-degenerate. Despite the high resolution, the two first bands show no vibrational fine structure. For the first one, Franck–Condon analysis shows that it is due to the overlapping of two vibrational progressions involving the S–Cl stretching and the NSCl bending modes. In the case of the second band, it is explained by the highly repulsive character of the potential energy surfaces of two states of NSCl + in the Franck–Condon region of the neutral molecule. For the third band, which shows vibrational peaks, the calculation of Franck–Condon factors permits the determination of the adiabatic ionisation energy of the (3) 2 A ′ electronic state of NSCl + at 13.798 eV. Finally, the fourth band, which is due to three different ionic states with vibrational progressions, is too complicated to be assigned quantitatively.

STRUCTURAL CONTROL OF REACTIVITY IN SOME NEW CYCLIDENE COMPLEXES

Abstract The crystal structure of a monoalkylated cyclidene complex of nickel(II) is reported. The asymmetric nature of this structure supports the results of earlier structural work in solution using NMR spectral evidence, and highlights the importance of steric control of the reactions of cyclidene molecules. The crystal structure of a new cyclidene, bearing chiral side chains, is also reported. This species shows extreme selectivity in its reactivity, refusing to alkylate with groups larger than methyl. The lack of reactivity of this cyclidene with the larger alkyl groups is ascribed to the sterically congested nature of the starting material. The structural studies show how careful choice of cyclidene substituents allows for control of the nature of the products of alkylation reactions.

Spectroelectrochemistry of iron complexes of the C2-capped porphyrin ligand

Abstract The coordination chemistry of iron complexes of C 2 -capped porphyrin ligand has been examined by spectroelectrochemistry. In solution, in dimethylsulphoxide (DMSO), the chloride ion of [Fe 111 (C 2 cap)Cl] remained bound to iron(III). In the presence of 1-methylimidazole (1-MeIm) the Cl − ion is substituted by OH − , generated by reaction of 1-MeIm with trace amounts of water in the system. Controlled potential reduction of [Fe 111 (C 2 cap)(OH)] in DMSO solution produced the six-coordinate iron(II) complex [Fe 11 (C 2 cap)(1-MeIm)(DMSO)], with the DMSO ligand bound within the capping group. Reduction of [Fe 111 (C 2 cap)Cl], in solution in CH 2 Cl 2 containing 1-MeIm, produced the five coordinate iron(II) species, Fe 11 (C 2 cap)(1-MeIm).

Non-symmetrical tetraaza macrocyclic complexes of nickel(II) and their binding to synthetic polymer supports

The synthesis and characterisation of a family of new tetraaza macrocyclic complexes of nickel(II) have been performed, via reaction of a nucleophilic macrocycle with various acid chlorides, or via peripheral functionalisation of suitable macrocycles. The new complexes have an asymmetric distribution of the peripheral groups on the macrocyclic rings and this is reflected in the appearance of their NMR spectra. Some of the new complexes have been incorporated into the structure of synthetic polymers, either via copolymerisation with a chosen comonomer, in this case styrene, or via reaction with a suitably functionalised, performed polymer.

Polymer-supported cobalt(II) tetraaza macrocyclic complexes and their reaction with dioxygen

Four cobalt(II) tetraaza macrocyclic complexes of the ‘lacunar cyclidene’ type have been prepared, including two new, unbridged, examples. The reactions of these complexes with oxygen have been investigated, either in solution, in a mixture of acetonitrile–pyridine (4 : 1 v/v), or when dispersed in the matrix of a copolymer containing 4-vinylpyridine (vpy), dissolved in dichloromethane. Three different copolymers have been used as supporting matrices (vpy content in parentheses); vpy–styrene (6.2), –methyl methacrylate (5.2) and –butyl methacrylate (15.2%). The oxygenation reactions have been studied both by ESR spectroscopy of frozen solutions and by electronic spectroscopy at or near room temperature. The presence of the polymeric supports has a marked influence on both the formation of Co–O2 adducts and their stability with respect to autoxidation. The polymer-supported ‘copoly complex’ oxygen adducts have much greater lifetimes than those of the O2 dioxygen adducts of the same complexes ‘free’ in solution. The results are discussed in terms of the complex structure, polymer type and the temperature of the reaction.