The catalytic synthesis and electronic properties of poly(arylmethylgermanes)

Polygermanes are inorganic polymers in which the conjugation of σ-electrons along the polymer backbone gives rise to interesting electronic properties. This thesis describes a catalytic route for the synthesis of poly(arylmethylgermanes) containing a variety of substituents. In contrast to traditional synthetic methods, demethanative coupling using a ruthenium catalyst is a mild route for the preparation of these materials in moderate to high yields. The mechanism for demethanative coupling of dimethylarylgermanes is proposed to involve generation of an active bis(germyl) species, σ-methyl migration to yield a germyl(germylene)complex, and germyl to germylene migration to form a new Ge-Ge bond. The polymerization exhibits more chain growth character than that observed in the polymerization of GeMe3H due to the increased stability of intermediate aryl germyl ruthenium complexes. Unlike poly(permethylgermane), (MeGePh)n has been shown to have a linear rather than a branched backbone. The polymers have been analyzed by 1H NMR and GPC, using both traditional polystyrene and static light scattering methods for molecular weight determination. In addition, the electronic properties have been studied using electronic absorption and fluorescence emission spectroscopy. It has been shown that electron donating substituents on the aryl ring have a pronounced effect on both absorption and emission. The emission spectrum of the polygermane containing the dimethylaminophenyl group is surprisingly broad and red-shifted relative to other poly(arylmethylgermanes). It is proposed that the broad emission arises from a localized excited state which may be caused by branch points in the polymer backbone. Several monomers do not undergo catalytic coupling, including germanes with p-cyanophenyl, 3-pyridyl, and 9-anthracyl substituents. In the latter case, reaction of GeMe2H(9-anth) with (PMe3)4RuMe2 results in the stoichiometric formation of (PMe3)4Ru(η2-9-GeMe 2-anthrac-8-yl) which has been structurally characterized in addition, reaction of GeMe2HCl with (PMe3)4RuMe 2 leads to the formation of a new ruthenium complex, (PMe3) 4Ru(Cl)(GeMe2Cl). The proposed mechanism involves a rate limiting nucleophilic displacement of chloride from germanium by a methyl group on the 18 e– Ru complex to yield an intermediate ruthenium complex, (PMe3)4Ru(Me)(Cl). Subsequent phosphine dissociation, Ge-H addition, and methane loss leads to the observed product