Asymmetric Synthesis of Mono- and Dinuclear Bis(dipyrrinato) Complexes

The diastereoselective syntheses of Zn(II) bis(dipyrrinato) helicates is reported, involving ligands templated
by the incorporation of homochiral binol within the linker joining the two dipyrrinato units. The most
diastereoselective formation of dinuclear bis(dipyrrinato) helicates to date is reported. The formation of
either mononuclear or dinuclear helicates can be tuned by varying the length of the linker between the
dipyrrinato units and by varying the complexation procedure. The neutral dipyrrinato helicates were
readily analyzed by HPLC to ascertain diastereoselectivity, and circular dichroism studies revealed the
helical nature of the complexes. The molar ellipticities of the helicates produced by diastereoselective
complexation are very large in the visible region and typically correspond to binol moieties in the UV
region. Extensive X-ray crystallographic investigations further confirmed the helicity of the mononuclear
Zn(II) helicates and identified significant interlayer displacement and bending within crystals.