FULLERENE ACETYLENE HYBRIDS - TOWARDS A NOVEL CLASS OF MOLECULAR CARBON ALLOTROPES

The synthesis and complete characterization of 17 new fullerene-acetyl ene covalent derivatives is described. Reaction of 3-bromo-1,5-bis(tri methylsilyl)penta-1,4-diyne (5) with C-60 gave bis-protected diethynyl methanofullerene 4 in 56% yield. Unsymmetrically bis-protected diethyn ylmethanofullerene 6 was synthesized in 53% yield from tosylhydrazone 7 and C-60 Proto-desilylation of 4 and 6 gave the corresponding free a lkynes 3 and 8 in 83% and 69% yield, respectively. partial deprotectio n of 4 afforded mono-protected fullerene 9 in 35% yield. Oxidative het ero-coupling reactions of 3 and 8 under Hay conditions with various mo nosubstituted acetylenes gave the butadiynylmethanofullerenes 10-13 in yields varying from 25-49%. Home-coupling of 8 produced dumbbell-shap ed fullerene 14, the first dimeric fullerene that could be fully chara cterized. The X-ray crystal structure analysis of 14 revealed little o r no electronic interaction between the two fullerene spheres. Additio n of lithium trimethylsilylacetylide to C-60 gave access to 1-substitu ted-2-(trimethylsilylethynyl)fullerenes. The acidity of hydrofullerene 16, synthesized in 58% yield, was studied as a function of base and s olvent. Reaction of lithiated fullerene 17 with various electrophiles is discussed. Alcohol 25 was prepared in 57% yield by reaction of 17 w ith formaldehyde. Under strongly basic conditions, 25 eliminates forma ldehyde to give 16 in quantitative yield Oxidation of 25 afforded alde hyde 27 in 53% yield, a rather unstable compound that is easily conver ted to hydrofullerene 16. Conversion of 25 to the corresponding tosyla te could be performed in 40% yield. (C) 1996 Elsevier Science Ltd