Synthesis of Polyphenylene Dendrimers Related to “Cubic Graphite”

Four large, 6-fold symmetric, polyphenylene hydrocarbons have been prepared by short syntheses that chiefly employed alkyne trimerization, palladium-catalyzed coupling, and Diels−Alder reactions. The two largest of these molecules, hexakis[4‘-(pentaphenylphenyl)biphenyl-4-yl]benzene (4, C294H198) and hexakis[4‘-(2,3,4,5-tetraphenylphenyl)biphenyl-4-yl]benzene (5, C258H174) are substructures of “phenylogous cubic graphite”, and the other two, hexakis(2‘,3‘,4‘,5‘,6‘-pentaphenylbiphenyl-4-yl)benzene (26, C258H174) and hexakis(2‘,3‘,4‘,5‘-tetraphenylbiphenyl-4-yl)benzene (25, C222H150) are strongly pitched, six-bladed molecular propellers. The X-ray crystal structure of compound 26 has also been determined; dendrimer 26 is at present the largest crystallographically characterized hydrocarbon.