## LSU Historical Dissertations and Theses

1989

Dissertation

#### Degree Name

Doctor of Philosophy (PhD)

George R. Newkome

#### Abstract

A new class of specifically shaped, highly branched molecules was prepared where the branches emanate from tetrahedral carbons. This class of molecules has been named arborols because of their topological similarity to the "Leeuwenberg" model for tropical trees. The arborols were synthesized a layer (or tier) at a time to generate cascade spheres, where the number of terminal groups per sphere increases exponentially. Initially, molecules possessing a single cascade sphere attached to simple hydrocarbon chains were prepared to develop synthetic methods and provide proof-of-concept. Several series of dumbbell shaped, two-directional arborols were prepared, where two cascade spheres are connected via a hydrocarbon backbone of varying length (3 to 13 carbons). The molecules were named (m) -n- (m) arborols, where m denotes the number of terminal hydroxyl moieties, and n denotes the length of the hydrocarbon backbone. Some of these arborols (m = 6: 8 $\leq$ n $\leq$ 13; m = 9: 10 $\leq$ n $\leq$ 13) formed aqueous gels at concentrations of ca. 0.3-10%. Gel formation was determined to be a function of cascade sphere size and chain length. The generalized cascade sphere synthesis was applied to benzyl halides. A three-directional arborol possessing a central benzene core was prepared. The three symmetrically placed spheres formed a triad, which was readily visualized via transmission electron microscopy; their aggregation properties of aqueous solutions were studied by dynamic light scattering. The synthetic procedure was then used to modify commercially available poly(vinylbenzyl chloride) to demonstrate the potential for polymer modification. Triethyl methanetricarboxylate was utilized as a malonate equivalent to permit the preparation of a series of bis(thioether) tetradentate ligands, which would be difficult to prepare by other means. Preliminary attempts to prepare the cyclometalated Pd(II) complexes of these new ligands failed. The synthesis and X-ray crystal structure analysis of a cyclometalated Rh(III) complex of methyl 3-(2-pyridyl)-2-carbomethoxypropanoate revealed the presence of a metal-carbonyl oxygen bond. Variable temperature $\sp{\rm 1}$H NMR spectra indicated the presence of an equilibrium process where an ester carbonyl from one ligand displaces the coordinated ester carbonyl of the other ligand.

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