Diels -Alder reactions between fullerene[60] and various pentacenes

The reaction of fullerene[60] with pentacene and various 6,13-disubstituted pentacenes has been studied and the formation of cis-bisfullerene[60] adducts has been achieved. The reaction of fullerene[60] with pentacene was studied with the goal of preparing cis-1 and trans-2 bisfullerene[60] adducts. Instead, the solution phase Diels-Alder reaction between fullerene[60] and pentacene yields a C 2v symmetric monoadduct, 3, in 59% yield.*. Semi-empirical PM3 calculations suggest that fullerene[60] should react favorably with 6,13-disubstituted pentacenes such that molecules similar to 1 and 2 would form. Several 6,13-disubstituted pentacenes were synthesized and subsequently reacted with fullerene[60] resulting in the formation of various cis-bisfullerene[60] adducts in high yield. The reactions are completely regioselective, cycloadditions occurring exclusively across the 5,14- and 7,12-positions of the pentacene backbone, and highly cis-stereoselective as well. The corresponding trans-bisfullerene[60] adducts are not detected above trace levels. The reactions proceed through the formation of CS symmetric monoadducts, some of which form in high yield and are easily isolated. 6,13-Diethynyl substituted pentacenes are especially prone to CS monoadduct formation in good yield. NMR spectroscopy in conjunction with mass spectrometry and X-ray structure analysis has enabled a thorough characterization of the products.*. A combination of experimental data, model compound studies, and computational results suggest that favorable pi-stacking interactions between fullerene[60] moieties in the ground state and in transition states are responsible for the high cis-stereoselectivities observed in these reactions whether they be run under kinetically controlled or thermodynamically controlled conditions. Electrochemistry of two bisfullerene[60] adducts has been studied. Separate I electron reductions for each fullerene[60] moiety on one of the bisfullerene[60] adducts, are resolved at low negative potential. Bisfullerene[60] adducts are also susceptible to chemical reductions and reactions with Zn dust in 2 different solvents have been studied