Elucidating New Reactivity Modes of Organometallics and Investigating Their Impact on Catalysis

Triscatecholate binding has been widely studied in the context of biological systems, supramolecular chemistry, and weak aggregate interactions. However, the utilization of the triscatecholate binding motif for the preparation of metalloligands remains unexplored. Herein, we report the synthesis, structural characterization, and functional studies of a triscatecholate ligand with an appended pyridyl residue as a candidate for such applications. Our findings reveal that the selective formation of cis-triscatecholate-based metalloligands is influenced by electronic effects on the catecholate anions, enabling the targeted synthesis of Al(III), Ga(III), and In(III) triscatecholate metalloligands capable of binding Zn(II) and Ru(II) at the appended pyridyl moiety for applications in catalysis. This triscatecholate-based metalloligand has also been investigated in its application to ruthenium-catalyzed olefin metathesis, wherein the size of its respective phosphonium counteraction was found to influence the olefin geometry of the metathesis product. Non-covalent interactions, such as bulk steric effects of counterions, are a coveted means by which to elicit novel reactivity in organometallic species. The discovery of a steric-based noncovalent influence in olefin metathesis led to further investigation of metathesis systems. A further work hoping to apply a frustrated-Lewis pair approach to controlling olefin metathesis with (PCy3)2Cl2Ru=CHPh (Grubbs I, GI) and tris(pentafluorophenyl) borane B(C6F5)3 was envisioned; however, the discovery of a novel halide abstraction pathway of GI with tris(pentafluorophenyl) borane B(C6F5)3 was elucidated. This halide abstraction pathway was unconventional for olefin metathesis and was applied to module the polymeric properties of recalcitrant olefins in ring-opening metathesis polymerization (ROMP) reactions. Dihydrofuran (DHF) was one of the monomeric units explored for their propensity to undergo this type of polymerization process. In doing so, it was found that this material was instead undergoing a different polymerization process rather than ROMP. To further tailor the reactivity of this system, a series of diimine and pyridine imine type ligands with pendant Lewis acids were synthesized.