SYNTHESIS, CHEMICAL AND PHYSICAL-PROPERTIES, X-RAY CRYSTAL-STRUCTURE, AND THEORETICAL CALCULATIONS OF 9-[1-(2,4,6-CYCLOHEPTATRIENYLIDENE)]XANTHENE

The title heptafulvalene (3) was synthesized in high yield by treatment of (9/9-xanthyl)tropylium tetrafluoroborate (II) with either methanol, N,N-diisopropylethylamine, or dimethyl sulfoxide (DMSO). A single-crystal X-ray diffraction structure determination and MNDO, AMI, PM3 semiempirical molecular orbital and molecular mechanics theoretical calculation studies indicate that the geometry of title compound 3 is distorted into a nonplanar “S” shape around the exocyclic double bond connecting the two rings. This is due to the nonbonded steric interactions occurring between the peri hydrogens on the xanthyl portion of the molecule and those at the 2-and 7-positions on the cycloheptatrienyl ring. UV-visible spectral studies and the lack of reactivity toward lithium aluminum hydride clearly indicate polyolefin character and a minimal polar nature for compound 3. These results are in good agreement with the low dipole moment calculated by the semiempirical methods. © 1990, American Chemical Society. All rights reserved.