Reactivity consequences of electronic and spin state effects in organometallic chemistry

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I propose an integrated synthetic, mechanistic, and computational study to probe selectively the effects of electronic configuration and spin state on the stoichiometric reactions fundamental to organometallic catalysis.  Careful interplay of metal properties and ligand design will allow for the synthesis of compounds wherein steric and/or electronic modification to the periphery of the ligand sphere will adjust the orbital splitting and pairing energies at the metal centre, either inductively or by adjusting the coordination geometry, thereby selectively tuning the spin state energies of the compound.  This will allow for the synthesis of pairs or series of compounds with identical metals and oxidation states in similar coordination environments, but differing ground state spin, permitting a systematic mechanistic study of how the spin state of a complex alone affects the thermodynamics and kinetics of the reactions that make up organometallic catalytic cycles.The rational design of catalysts for synthetic organic and industrial applications continues to be a principal focus of organometallic chemistry.  The spin state of the catalyst has the potential to play a critical role, in that the presence of unpaired electrons or the need to cross over between surfaces of different spin can have a profound and often unexpected effect on the energies, mechanisms, and rates of reactions.  An increasing number of recently developed catalytic systems, particularly those in the area of alkene polymerization, employ mid-valent compounds of first-row metals such as Cr, Fe, and Co, yielding catalysts or catalyst precursors that not only have paramagnetic ground states, but also may cross between different spin surfaces during the catalytic cycle.  An increasing body of work suggests that spin crossover phenomena will prove to play an enormous role in organometallic catalysis.  The principal goal of this research is therefore the first systematic study to isolate and investigate the means by which spin state alone can affect and control organometallic reactivity generally, and to demonstrate specific instances in which this control might be exploited.Two well-defined systems of relevance to alkene polymerization chemistry are currently under investigation.  These are bis(oxazolinyl)pyridine dialkyl iron(II) (traditional Ziegler-Natta polymerization), and bis(amidinate) and bis(beta-ketoamine) monoalkyl cobalt(III) complexes (atom transfer and organometallic radical polymerization).  Both are five-coordinate, 16 valence electron systems with six d-shell electrons, but in each case there are multiple possible ground state spins, with the most likely configurations being the open-shell quintet and closed-shell singlet.  In each case, the ligands are easily modified to bear a variety of electron donating/withdrawing groups of varying steric profile, which affords control of the exhibited spin properties.  This will permit a side-by-side comparison of fundamental organometallic reactions, whereby one reaction takes place on a single diamagnetic spin surface, while the other takes place on either a wholly paramagnetic surface or requires a crossover from one spin state to another.  Reactions such as coordination, insertion, and beta-elimination are of relevance to Z-N polymerization mechanisms, while single-electron and atom transfer reactions are important in ATRP and OMRP.  Computational studies employing DFT will both guide the choice of systems for experimental investigation, and serve to interpret and support the mechanistic results.This approach of investigation is well suited to the resources associated with current undergraduate research at UBC Okanagan, but will easily be applied to longer-term studies as our graduate programme develops.  The proposed target compounds are a few simple synthetic steps from commercially available and inexpensive materials.  The ligand systems are easily modified, allowing a wide range of compounds to be developed quickly.  The integrated nature of the study will give students experience with organic and organometallic synthesis and characterization, mechanistic studies using UV-visible and NMR spectroscopic techniques, and computational methods.  Despite their relatively simple basis, I believe these studies have dramatic implications, and will yield results that will greatly enhance the rational design of open-shell paramagnetic transition-metal catalysts.