Rational design of new transition metal complexes for use in molecular imprinting-based catalysis

Tetrahedral titanium (IV) complexes of structure (ArO)TiCl₂ were shown to be active catalysts for the Diels-Alder reaction between N-acryloyloxazolidinone and cyclohexadiene. Polymerizable analogues of these complexes (vinyl groups attached to aryloxide ligands) were designed, synthesized and immobilized onto macroporous polymer supports and subsequently converted to active catalysts once inside the polymer matrix. This treatment revealed insoluble polymer monoliths that were capable of catalyzing the aforementioned Diels-Alder reaction with rates competitive to those in solution (only 3–5 times slower). Octahedral titanium (IV) Lewis acid/Lewis base adducts were then studied to access polymerizable transition state analogues (TSAs) which, in combination with the molecular imprinting technology, would seek to provide asymmetric induction through outer-sphere stereocontrol. Initial experiments involved the study of titanium Lewis acids with a variety of P- and N-containing bidentate Lewis bases. Competition experiments were carried out between various Lewis acid/Lewis base adducts to determine which complexes formed the strongest interactions. The results of these studies were then applied to the synthesis of a TSA for the Ti-catalyzed Diels-Alder reaction. To this end, an asymmetric synthesis of a rigid C₂-symmetric bis(ferrocenyl)diamine base was designed and the bidentate ligand was shown to form a strong adduct with the Lewis acidic (ArO)TiCl₂ (ArO = 2,6-dimethylphenol).{09}A polymerizable version of this adduct was realized and immobilized onto a macroporous support, however, attempts to activate the polymer were problematic due to comproportionation reactivity. Therefore, efforts were focused on the synthesis of a polmerizable bis(aryloxide) ligand which could control comproportionation to some degree through the chelate effect.; Studies were also directed toward the rational design and synthesis of square planar platinum(II) complexes that could serve as TSAs for late metal catalysis. The synthesis of polymerizable and enantiopure diphosphines based on the McOBiphep scaffold were realized in order to combine inner sphere stereocontrol with the outer sphere elements invoked through molecular imprinting. P ₂Pt(II) BINOLate complexes were then synthesized, immobilized onto solid supports and were shown (upon subsequent activation) to be active catalysts for the glyoxylate ene reaction. However, control of asymmetry was shown to arise solely through the catalyst's inner sphere. In order to mimic the transition state (outer sphere stereocontrol) of the glyoxylate ene reaction, a BINOL ligand substituted in the 4,4′-positions was synthesized (e.g., 4,4′-Ph₂BINOL) and complexed to platinum. Unfortunately, the new ligand design offered no benefit over unsubstituted BINOL in the glyoxylate ene reaction. In order to create a more homogenous outer sphere within a macroporous polymer matrix, studies were also applied toward the design, synthesis, and Pt(II) coordination chemistry of a BINOL imprinting ligand with polymerizable and cleavable acetal units in the 6,6 ′ positions.