Professor of Chemistry
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I have extensive experience in the study of ring systems containing catenated C-N-S and C-N-Se sequences, including those that incorporate transition metals. We are engaged in a detailed study of the electrochemistry of such compounds, since their redox behaviour is a key factor for conductivity and magnetic properties. We have used cyclic voltammetry and a.c. voltammetry in the study of these highly-reactive inorganic ring systems. The compounds necessitate handling under full vacuum, and we have innovative cell-designs which make this possible and practical. Many of the ring systems which we study form thermally stable free-radicals. Many more radicals are accessible via electrochemical generation. We have long wanted routine access to electron paramagnetic resonance for the characterization of radicals produced chemically and electrochemically in our work. This has recently become possible with the installation of a Bruker EMX 10/12 EPR spectrometer at the University of Calgary, of which I am one of the major users.One exciting aspect of there search program is a consideration of the fate of unpaired electrons on main-group rings when these interact with a transition metal fragment (e.g. by oxidative addition), where the metal may have been either diamagnetic or paramagnetic to start. We anticipate the discovery of entirely new classes of molecular magnets from this approach. Finally, we routinely employ computational methods for the interpretation of the electrochemical and EPR properties of many of the ring systems we have studied (extended Hückel, semi-empirical, and, to a lesser extent, density functional methods have been used). For example, we have provided the first sensible rationalization for the extreme variations in the reduction potentials of a series of closely related, high-valent, Mo and W complexes.
2. Coordination chemistry of imides,
amidines, biguanidines and related nitrogen ligands with super-bulky substituents:
So-called "super-bulky" substituents were originally developed in order to stabilize low-coordinate main-group elements of the 3rd period and beyond, allowing, to name one famous example, Yosifuji to isolate the first compound containing a P=P double bond. They have since found extensive application in many areas of main group chemistry, including some of the 2nd period elements, e.g. boron.2 Chemists who incorporate these substituents have always been aware that their large bulk may have created some perturbation on the bonds they were investigating, but in any case had no choice; lowering the bulk only slightly could lead to decomposition of the thermodynamically stable, but kinetically unstable bond, usually via a polymerization reaction. In view of these facts, it is surprising that more attention has not been given to making analogous compounds using these substituents with the elements that do not intrinsically need them for kinetic stabilization, e.g. the second-period elements such as C, N and O. Here direct comparison between analogous crowded and non-crowded molecule sought to be possible, and the influence of the steric bulk should be evident, and indeed often quantifiable.
It is our contention that the use of super-bulky substituents on these elements will also lead to unique patterns of reactivity, and in this work we have studied the application of one such group, the 2,6-diisopropylphenyl substituent, to N,N'-disubstituted amidine ligands. Somewhat less bulky substituents (trimethylsilyl4, cyclohexyl5) have already found extensive application in amidinate metal complexes. We demonstrate that the super-bulky substituent does not prevent the synthesis of the ligands themselves, which have been prepared by fairly straight forward modifications of classical amidine synthetic procedures, nor do they fail to react with transition elements. Nevertheless, the course of the reactions with, for exmple, Mo(CO)6 differs significantly from that previously found for analogous non-bulky amidines, such as N,N'-diphenylbenzamidine, which was investigated many years ago by Cotton and Kilner. In particular, whereas heating diphenylbenzamidine together with Mo(CO)6 produced aquadruply-bonded dimolybdenum complex, we find that analogous reactions of the diisopropylphenyl amidines produced two kinds ofproducts, an N-coordinated LMo(CO)5 complex and/or a half-sandwich LMo(CO)3 complex in which one of the aryl rings of the ligand is p-complexed to Mo(CO)3. The Cotton reaction is completely blocked, and there is no evidence of any metal complex in a higher oxidation state than Mo(0). Further developments of this idea are currently in progress
3. Bio-Inorganic chemistry:
I have two nascent research projects in the bio-inorganic and bio-medical area. The first is the adaptation of some of the bulky ligands developed under (2) to act as carriers for radioimaging agents such as radioactive Ga and Gd isotopes. The other is the study of the active ingredient in "Ruthenium Red" which acts as a calcium-channel block in nerve cells. Commercial ruthenium red, as used by biologists in staining tissue for electron microscopy, is a complex mixture of a variety of mono, bi, and tri-molecular ruthenium coordination complexes. The project, which will require collaboration with neuroscientists, aims to prepare chemically pure samples of each component, and their hydrolysis products as produced under physiological conditions, and screen each for their Ca-channel blocking effect. The complexes to be studied are extremely interesting in their own right, especially the bi andtri-molecular complexes, which promise to have rich electrochemical properties.
4. Synthesis of reactive small molecules:
I am involved in collaborative research with Prof. N.Moazzen-Ahmadi of the Department of Physics, University of Calgary. Reactive precursor molecules are prepared, either off-line (e.g. C3O2, diacetylene) or on-line (C5O2), and are subsequently subjected to an electrical discharge. In this way highly-unstable, reactive small molecules, such as linear CCO can be prepared in the gas phase in a flow cell, and the rovibrational spectra are measured using diode laser infra-red spectroscopy. My contribution to this work is largely the preparation of the precursor compounds.
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