Effect of polyfluorination on ring inversion barriers for cyclooctatetraenes. Transition-metal compounds of unsaturated, polyfluorinated cycloaliphatics. Crystal and molecular structures of [Fe(.eta.-C5R5)(.eta.1-heptafluorocycloocta-1,3,5,7-tetraenyl)(CO)2] (R = H, Me), {[Fe(.eta.-C5H5)(CO)2]2(.mu.2-(1.eta.,5.eta.)-hexafluorocycloocta-1,3,5,7-tetraenediyl)], and [Mn((3.eta.)-heptafluorotricyclo[4.2.0.02,5]octa-3,7-dienyl)(CO)5]