The first optically active polygermanes: preferential screw sense helicity of enantiopure chiral-substituted aryl polygermanes and comparison with analogous polysilanes

摘要

Circular dichroism and ultraviolet spectroscopic studies of meta and para poly[methyl {(S)- 2-methylbutylphenyl} germane]s, the first enantiopure chiral substituted polygermanes, indicate that the polymer main chains are induced to adopt preferential screw sense helical conformations and the values of the Kuhn dissymmetry ratio (g(abs), = Deltaepsilon/epsilon) at - 70degreesC were evaluated as - 0.34 x 10(-4) and - 0.38 x 10(-4), respectively for the polymers above. The analogous polysilanes have g(abs), values of - 0.76 x 10(-4) and 0.81 x 10(-4), which indicate a greater preferential screw sense selectivity. It is suggested that the origin of the lower screw sense selectivity in the polygermanes lies in the longer E-E bond in the backbone, leading to reduced steric interaction between the preferential screw sense-inducing enantiopure chiral side chain moieties. (C) 2003 Elsevier Science B.V. All rights reserved. [References: 49]