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

A series of nitro-substituted phosphine-containing cyclophanes (2-4) w as prepared by base-promoted condensation of various nitrated derivati ves of 1,3,5-tris(bromomethyl)benzene with tris(2-mercaptophenyl)phosp hine under conditions of high dilution. The mononitro cyclophane 2 was reduced with TiCl3 in THF-EtOH to give the corresponding amino deriva tive 5. The C-13 NMR spectra of these compounds exhibit ''through-spac e'' spin-spin coupling between the phosphorus and the substituted basa l aromatic ring, and in their P-31 NMR spectra the phosphorus resonanc es are anomalously far downfield. The nitro-substituted phanes are col ored, probably due to charge-transfer absorptions between the phosphin e 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, respective ly, 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 en antiomers showed a very high molecular ellipticity at 332 nm of 120 00 0 deg.cm2.dmol-1.