SYNTHESIS AND CHARACTERIZATION OF A SERIES OF MONODISPERSE, 1,3,5-PHENYLENE-BASED HYDROCARBON DENDRIMERS INCLUDING C276H186 AND THEIR FLUORINATED ANALOGS

The convergent synthesis of a series of monodisperse aromatic dendrimers having molecular diameters of 15-31 angstrom is described. These materials consist of 4, 10, 22, or 46 benzene rings linked symmetrically by sigma-bonds. Increasingly large dendrimer arms are prepared stepwise via palladium-catalyzed coupling of arylboronic acids to 3,5-dibromo-1-(trimethylsilyl)benzene. The aryltrimethylsilane is subsequently converted to a new arylboronic acid by reaction with boron tribromide followed by hydrolysis. Coupling of arylboronic acid dendrimer arms to 1,3,5-tribromobenzene or 1,3,5-tris(3,5-dibromophenyl)benzene is the final step in the synthesis. A series of dendrimers consisting of 4, 10 and 22 phenyl rings symmetrically arranged in which the outer phenyl rings are fluorinated is synthesized by a similar sequence of reactions. The largest hydrocarbon dendrimer is soluble to the extent of 190 g/L in toluene and is stable to 500-degrees-C. Depending upon their thermal history, dendrimers having more than 10 phenyl rings can be crystalline or amorphous. Enthalpies and entropies of fusion and glass-transition temperatures where applicable have been measured. These materials are single molecules having high symmetry and thermal stability and utility as standards in size-exclusion chromatography.