SYNTHESIS, MOLECULAR-STRUCTURE, AND PROPERTIES OF IN-PHOSPHAPHANES WITH SUBSTITUTED BASAL AROMATIC RINGS

A series of nitro-substituted phosphine-containing cyclophanes (2-4) was prepared by base-promoted condensation of various nitrated derivatives of 1,3,5-tris(bromomethyl)benzene with tris(2-mercaptophenyl)phosphine under conditions of high dilution. The mononitro cyclophane 2 was reduced with TiCl3 in THF-EtOH to give the corresponding amino derivative 5. The C-13 NMR spectra of these compounds exhibit ''through-space'' spin-spin coupling between the phosphorus and the substituted basal aromatic ring, and in their P-31 NMR spectra the phosphorus resonances are anomalously far downfield. The nitro-substituted phanes are colored, probably due to charge-transfer absorptions between the phosphine and the nitroarene base. The X-ray crystal structures of cyclophanes 4 and 5 reveal a pronounced inward pyramidalization of the phosphines such that the phosphorus atoms are 2.98 and 2.92 angstrom, respectively, from the centers of the basal rings. These cyclophanes are rigid, molecular propellers, and compound 2 was chromatographically resolved on a chiral HPLC column. The circular dichroism spectra of the pure enantiomers showed a very high molecular ellipticity at 332 nm of 120 000 deg.cm2.dmol-1.