Syntheses and Physical Properties of Several Polyphenylenes Containing Mixed Linkages

Fourteen macrocyclic polyphenylenes, including the following ten new compounds, were synthesized by intra- or intermolecular homo-coupling of di-Grignard compound and by cross-coupling of two kinds of di-Grignard compounds with copper(II) chloride: m,m,o,p,o-pentaphenylene; o,o,p,o,o,p-, m,o,p,m,o,p-, o,p,o,p,o,p-, m,o,p,o,p,o-, m,o,m,o,m,o-, and m,m,m,o,m,o-hexaphenylene; m,o,p,p,o,m,p-, and m,m,m,m,p,o,p-heptaphenylene; and m,o,o,m,o,o,m,o,o,m,o,o-dodecaphenylene. 1H NMR spectra of the polyphenylenes, compared with those of open-chain analogues, provide valuable information on the nonplanar spacial relationship of constituting phenylene rings. UV spectra of the compounds containing p-phenylene ring(s) suggest that the lack or decrease in intensity of K-band above ca. 260 nm or a marked shift of that band provides useful conformational information. Empirical Hückel molecular orbital calculations of longest-wavelength absorption bands of twelve polyphenylenes were also carried out. The calculations furnish additional bases for their conformational aspects deduced from their spectral data and Dreiding stereomodels. IR spectra indicate that lack of intense band(s) near 700 cm−1 may generally be regarded as a piece of plausible evidence for the macrocyclic structure containing no m-phenylene ring. Stabilities of the polyphenylenes to electron bombardment are also discussed.