Coordination chemistry of p-block element Lewis acceptors: Applying principles of transition metal chemistry to non-metal elements

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The synthesis and characterization of new compounds represents a fundamental foundation in the discovery of new reagents, catalysts and materials exhibiting new properties with potential function in society for production of commodity chemicals, electrolytes, conducting polymers, flame retardants, elastomers, pharmaceuticals and biomedical materials. The emerging importance of p-block elements such as silicon, germanium, tin, phosphorus, antimony, bismuth, sulfur and selenium in these discoveries has prompted the development of new versatile synthetic methods for the compounds of these elements. The Burford NSERC Discovery Grant has previously supported the development of new synthetic methods to compounds featuring homoatomic and heteroatomic bonds between phosphorus and all elements of group 15. This research is changing the way in which chemists understand the chemistry of non-metal elements in general. The discovery of a new direction in coordination chemistry involving phosphorus ligands on phosphorus Lewis acceptors has now been extrapolated to other p-block elements to provide a vastly diverse and rapidly evolving coordination chemistry for the p-block elements as Lewis acceptors. Chemical structure and reactivity that is well developed for transition metal elements (d-block) can now be extrapolated to the p-block elements with realisation of new structure, bonding and reactivity, including patterns that are not evident at transition metal Lewis acceptors. Our recent discoveries include series of cationic compounds that represent coordination complexes of group 14 and 15 Lewis acceptor centers, new catena-phosphorus compounds, and redox chemistry involving cationic complexes of phosphines on arsenic, antimony and bismuth. The proposed research offers a systematic evolution of the coordination chemistry for the tetrael (group 14), pnictogen (group 15), and chalcogen (group 16) elements exploiting all oxidation states and cationic molecular charges. In addition, catenation chemistry previously developed for the pnictogens will be extrapolated to the teraels and chalcogens, and the reactivity and potential catalytic behaviour of the highly charged cations of non-metal elements will be assessed. Our research has confirmed that the presence of a cationic charge (positive charge) in a molecule featuring a heavy (n > 3) p-block element augments the strength of all bonds in the molecule as well as enhancing the Lewis acidity of the molecule. The proposal describes approaches to evolve synthetic reactions to form coordination complexes that are analogous to the classic complexes of transition metals. Features such as multi-ligand interaction and coordination numbers of up to six are evident, as well as ligand exchange reactivity and variable oxidation state. The presence of a stereochemically active lone pair at a Lewis acceptor site represents a new direction for coordination chemistry.