Lynn M. Mihichuk

Brønsted acidity and the medium: fundamentals with a focus on ionic liquids.

Fundamental aspects of Brønsted acidity in ionic liquid systems, in relation to those of simple protic molecules in the gas phase, pure protic molecules in the condensed phase and solutions of protic molecules in molecular systems, are presented. The variety of acidities possible, beyond those observed in aqueous systems, is emphasised and discussed in terms of differences of solvent levelling, ionisation, dissociation, homo-/hetero-conjugate ion speciation and the stabilisation of proton-transfer products from solvent to solvent. It is argued that data regarding aqueous systems do not necessarily explain acid/base behaviour in other liquids satisfactorily. Methods of measuring acidity are reviewed, particularly by spectrophotometry and electrochemistry and recommendations proffered for estimating speciation and acidity of ionic liquids of various complexities.

Computational Study of Tungsten(II)-Catalyzed Rearrangements of Norbornadiene

Rearrangements of norbornadiene (NBD, C7H8) to various alkylidenes, via a hypothetical 7-coordinate tungsten(II) complex W(CO)3I2(NBD), were studied using density-functional theory computations. An extensive search for intermediates and transition states of rearrangement was made. The theoretical method (basis sets and level of DFT) used was justified by new benchmark studies which compare optimized structural parameters to those from crystal structures of several different tungsten complexes. Transition-metal-catalyzed rearrangements of NBD are not as well-known as those of norbornene and are considerably more complicated than had been thought. This work predicts a large variety of intermediates which may be feasible targets for experimental synthesis. All the rearrangement paths to alkylidenes found here feature high activation energies of over 45 kcal mol(-1), implying that self-initiation for the ring-opening metathesis polymerization of NBD via tungsten(II) complexes must occur via an alternative mechanism.

Reactions of Co(II) cobaloximes with organohaloarsines and the crystal structure of an arsine derivative of a Co(II) cobaloxime

Abstract The Co(II) cobaloximes (B)Co(dmgH) 2 (B = phosphine or phosphite; dmgH = dimethylglyoximato monoanion) react with (R 1 )(R 2 AsX (X = Cl: R 1 = R 2 =CH 3 ; R 1 =CH 3 , R 2 =C 6 H 5 ; R 1 =R 2 =C 6 H 5 . X = I: R 1 =R 2 =CH 3 to give in all cases XCo(dmgH) 2 B. In addition, for X = Cl, R 1 =CH 3 , R 2 =C 6 H 5 and X = Cl, R 1 =R 2 =C 6 H 5 , compounds of the formulae C 15 H 23 AsClCoN 4 O 5 ·H 2 O and C 20 H 25 AsClCoN 4 O 5 , respectively, were obtained. A crystal structure analysis of the former shows it to be either (CH 3 )(C 6 H 5 )As(OH)Co(dmgH) 2 Cl·H 2 O or (CH 3 )(C 6 H 5 As(O)Co(dmgH)(dmg)Cl·H 2 O. The crystals (at −100 °C) are orthorhombic, Space group Pnam, a = 14.273(3), b = 11.154(3), c = 12.995(4) A. The structure is disordered, but the molecule can be identified from its superimposed images. It consists of a Co atom bonded equatorially to two bidentate dmgH ligands (av. Co-N = 1.90(2) A) with a Cl atom above this plane (Co-Cl = 2.286(3) A) and the As atom of the (CH 3 )(C 6 H 5 As (O or OH) group below it (Co-As = 2.311 or 2.320(2) A).