Syntheses and spectral characteristics of seven polyphenyls containing highly branched para-phenylene ring(s)

Seven polyphenyls, including four new compounds, 2, 2', 6'- (2) and 3, 2', 6'-triphenyl-p-terphenyl (3), 3', 5'-diphenyl-p-quaterphenyl (4), and 2-phenyl-3'-(2-biphenylyl)-p-terphenyl (7), were synthesized by the Ullmann coupling reaction of aryl iodide (s) or by the Kharash-type coupling reaction of aryl Grignard reagent with an aryl iodide catalyzed by bis (acetylacetonato)-nickel (II). Infrared spectral studies of the polyphenyls showed that the range of 730-770 cm-1, generally accepted as the position of the out-of-plane C-H bending bands of the phenyl ring, should be widened slightly to 730-786 cm-1. The high frequency bands were confirmed to be correlated closely to the overcrowding by terminal rings in the complex structures. Proton magnetic resonance spectral studies indicated that the characteristic spectral features of the branched polyphenyls were fully consistent with their conformational aspects deduced from stereomodels. In the ultraviolet spectral studies the polyphenyls containing highly branched p-phenylene ring (s) showed intense K-bands or shoulders at locations very similar to those of the corresponding linear polyphenyls containing the same number of p-phenylene rings.