Robert J. Baker

Fluorine–Fluorine Interactions in the Solid State: An Experimental and Theoretical Study

The solid state structures of three compounds that contain a perfluorinated chain, CF(3)(CF(2))(5)CH(2)CH(CH(3))CO(2)H, CF(3)(CF(2))(5)(CH(2))(4)(CF(2))(5)CF(3) and {CF(3)(CF(2))(5)CH(2)CH(2)}(3)P═O have been compared and a number of C-F···F-C and C-F···H-C interactions that are closer than the sum of the van der Waals radii have been identified. These interactions have been probed by a comprehensive computational chemistry investigation and the stabilizing energy between dimeric fragments was found to be 0.26-29.64 kcal/mol, depending on the type of interaction. An Atoms-in-Molecules (AIM) study has confirmed that specific C-F···F-C interactions are indeed present, and are not due simply to crystal packing. The weakly stabilizing nature of these interactions has been utilized in the physisorption of a selected number of compounds containing long chain perfluorinated ponytails onto a perfluorinated self-assembled monolayer, which has been characterized by IRRAS (Infrared Reflection Absorption Spectroscopy).

New reactivity of the uranyl(VI) ion.

The chemistry of the uranyl ion ([UO(2)](2+)) has evolved remarkably over the past few years, with unexpected reactivity observed that challenge our understanding of this ion, and of actinides in general. This review highlights some recent advances in the field, focussing on the organometallic chemistry of the uranyl moiety, which is not well developed in comparison to lower oxidation states of uranium. The use of uranyl as a catalyst is highlighted and the newly developed supramolecular chemistry is described. The uranyl oxygen atoms have been considered as inert, but recent work has shown that is not necessarily the case and is discussed herein. Finally, reduction to the [UO(2)](+) ion will be discussed.

The reactivity of gallium(I) and indium(I) halides towards bipyridines, terpyridines, imino-substituted pyridines and bis(imino)acenaphthenes

“GaI” reacts with 2,2′-bipyridine (bipy) to give salts of composition [Ga(bipy)3][I]3, [{(bipy)2Ga}2(μ-OH)2]2[Ga2I6][I]6 or [{(bipy)2Ga}2(μ-OH)2][I]4, depending upon the reaction conditions. “GaI” also reacts with 4′-phenyl-2,2′∶6′,2″-terpyridine (Phterpy) to give the salt [GaI2(Phterpy)][I]. When “GaI” is treated with the imino-substituted pyridines RNC(H)Py, Pyu2006=u20062-pyridyl, Ru2006=u2006Ar (C6H3Pri2-2,6) or But, a reductive coupling of the CN functionality occurs to give the diamido-digallium(III) complexes [{I2Ga[η2-(Py)(NR)C(H)]}2]. In contrast, InCl reacts with ArNC(H)Py to give an adduct, [InCl3(THF){η2-ArNC(H)Py}], via disproportionation of the metal halide. Similarly, the reaction of the bis(imino)pyridine, 2,6-{ArNC(Me)}2(NC5H3), bimpy, with “GaI” affords the salt [GaI2(bimpy)][GaI4]. Finally, the reaction of bis(2,6-diisopropylphenylimino)acenaphthene (ArBIAN) with “GaI” leads to a paramagnetic Ga(III) complex [GaI2(ArBIAN)˙]. The X-ray crystal structures of all prepared complexes are reported.

Structural and spectroscopic studies of carbene and N-donor ligand complexes of Group 13 hydrides and halides

Abstract The syntheses of two Group 13 complexes of the sterically demanding carbene, 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene, (IPr), are reported, vis. [MX3(IPr)] M=Al, X=H; M=In, X=Br; both of which have been structurally characterised. Also reported is the crystal structure of the imidazolium salt [IPrH][InBr4], formed by the presence of adventitious water in the preparation of the [InBr3(IPr)] adduct. The preparation of the complex [InBr3(IMes)], IMes=1,3-bis(2,4,6-trimethylpheny)imidazol-2-ylidene, is described as are details of its crystal structure analysis. In addition, two indium tribromide adducts of nitrogen donor ligands, namely a bulky diazabutadiene and quinuclidine have been investigated. The crystal structures of N,N′-1,4-bis(2,6-diisopropylphenyl)diazabutadiene indium tribromide and bis(quinuclidine)indium tribromide are reported.

Synthesis and characterisation of the first carbene and diazabutadiene–indium(ii) complexesElectronic supplementary information (ESI) available: synthetic details. See http://www.rsc.org/suppdata/cc/b2/b202532a/

The reactions of IMes [:CN(Mes)C2H2N(Mes), Mes = mesityl] and DAB [(ArN=CH)2, Ar = C6H3Pri2-2,6] with indium(I) halides have afforded the first carbene and diazabutadiene indium(II) complexes, [In2Br4(IMes)2] and [In2Cl2(DAB.)2], both of which have been crystallographically characterised.

New Mechanism for the Ring-Opening Polymerization of Lactones? Uranyl Aryloxide-Induced Intermolecular Catalysis

The uranyl aryloxide [UO2(OAr)2(THF)2] (Ar = 2,6-(t)Bu2-C6H2) is an active catalyst for the ring-opening cyclo-oligomerization of ε-caprolactone and δ-valerolactone but not for β-butyrolactone, γ-butyrolactone, and rac-lactide. (1)H EXSY measurements give the thermodynamic parameters for exchange of monomer and coordinated THF, and rates of polymerization have been determined. A comprehensive theoretical examination of the mechanism is discussed. From both experiment and theory, the initiation step is intramolecular and in keeping with the accepted mechanism, while computational studies indicate that propagation can go via an intermolecular pathway, which is the first time this has been observed. The lack of polymerization for the inactive monomers has been investigated theoretically and C-H···π interactions stabilize the coordination of the less rigid monomers.

Synthesis, structural and theoretical studies of an iron-gallium(I) heterocycle complex: Analogies with N-heterocyclic carbene chemistry

The first iron complex of an anionic gallium N-heterocyclic carbene analogue, [Fe(CO)4{Ga[N(Ar)C(H)]2}]− Ar = C6H3Pri2-2,6, has been prepared and shown to have an unusual polymeric structure in the solid state; theoretical studies have pointed toward minimal Fe → Ga back-bonding in this complex.

Physical Characterization and Reactivity of the Uranyl Peroxide [UO2(η2-O2)(H2O)2]·2H2O: Implications for Storage of Spent Nuclear Fuels

The unusual uranyl peroxide studtite, [UO(2)(η(2)-O(2))(H(2)O)(2)]·2H(2)O, is a phase alteration product of spent nuclear fuel and has been characterized by solid-state cyclic voltammetry. The voltammogram exhibits two reduction waves that have been assigned to the U(VI/V) redox couple at -0.74 V and to the U(V/IV) redox couple at -1.10 V. This potential shows some dependence upon the identity of the cation of the supporting electrolyte, where cations with larger ionic radii exhibit more cathodic reduction potentials. Raman spectroelectrochemistry indicated that exhaustive reduction at either potential result in a product that does not contain peroxide linkers and is likely to be UO(2). On the basis of the reduction potentials, the unusual behavior of neptunium in the presence of studtite can be rationalized. Furthermore, the oxidation of other species relevant to the long-term storage of nuclear fuel, namely, iodine and iodide, has been explored. The phase altered product should therefore be considered as electrochemically noninnocent. Radiotracer studies with (241)Am show that it does not interact with studtite so mobility will not be retarded in repositories. Finally, a large difference in band gap energies between studtite and its dehydrated congener metastudtite has been determined from the electronic absorption spectra.

Ring-Opening Polymerization of Epoxides Catalyzed by Uranyl Complexes: An Experimental and Theoretical Study of the Reaction Mechanism

A comprehensive computational study on the ring-opening polymerization of propylene oxide catalyzed by uranyl chloride [UO(2)Cl(2)(THF)(3)] and the uranyl aryloxide [UO(2)(OAr)(2)(THF)(2)] (Ar = 2,6-(t)Bu(2)C(6)H(3)) is reported. The initiation and propagation steps have been probed and significant differences between the two catalysts discovered. The initiation step involving uranyl chloride is an intermolecular process because the orientation of the lone pair on the initiating chloride nucleophile is optimally oriented toward the empty σ*-antibonding orbital of the epoxide, which lowers the activation barrier by 22 kcal mol(-1). Thus, initiation is orbitally controlled. Propagation occurs through a dimeric species, and low-temperature fluorescence spectroscopy has been used to probe this experimentally. In contrast the initiation step for the uranyl aryloxide catalyzed mechanism is intramolecular because of the steric constraints imposed by the bulky substituents on the aryl ring and the fact that the lone pair on the nucleophile is able to approach the propylene oxide coordinated to the same uranium center. Thus, initiation is principally sterically controlled. Propagation is, however, intermolecular, and this can be traced to steric effects. Experimental evidence in the form of fluorescence spectroscopy and diffusion NMR has been used to explore the propagation process in solution.

Reactions of a carbene stabilised indium trihydride complex, [InH3{CN(Mes)C2H2N(Mes)}] Mes = mesityl, with transition metal complexes

The reactivity of the carbene stabilised indium trihydride complex, [InH3(IMes)] IMes = 1,3-dimesitylimidazol-2-ylidene, toward a variety of transition metal complexes has been investigated. The study has shown that the InH3 complex can act as a carbene and/or hydride transfer reagent to transition metal centres but does not yield heterobimetallic materials. Two new complexes, [Cp2Ti(μ-Cl)2Zn(IMes)Cl] and [CpNi(H)(IMes)], have resulted from this work, both of which have been spectroscopically and structurally characterised.