1,1‘,3,3‘,6,6‘,8,8‘-Octachloro-9,9‘-bifluorenylidene and Perchloro-9,9‘-bifluorenylidene, Two Exceedingly Twisted Ethylenes

Abstract

The syntheses of 1,1',3,3',6,6',8,8'-octachloro-9,9'-bifluorenylidene (1), its precursors, and the byproduct 3,3',5,5'-tetrachloro-4-(trichloromethyl)biphenyl (5) are described. Accurate structural X-ray data on 1 and on perchloro-9,9'-bifluorenylidene (2) are reported and discussed. Because of chlorine overcrowding, the dihedral angles between their two identical fluorenylidene moieties are abnormally large, the central-ethylene twist angles being 55 and 66 degrees, respectively. Significant out-of-plane carbon-chlorine bond bending is likewise exhibited. Their ESR spectra and magnetic measurements prove that they are singlet species. The exceptionally large bathochromic displacements of their UV-vis absorption spectrum with respect to that of their parent hydrocarbon are mainly attributed to bond bending and molecular warping.

Synthesis of an Extremely Bent Acyclic Allene (A “Carbodicarbene”): A Strong Donor Ligand

“…The former option can be effected by steric congestion, as in the symmetrical compound C 1 (twist angle = 668; d C=C = 1.39 ), [11] whereas the latter is a result of p-bond polarization, as in C 2 (twist angle = 868; d C=C = 1.47 ). [12] The steric approach cannot be extended to allenes because the termini are too remote for significant interactions.…”

The Effects of Fluorine and Chlorine Substituents across the Fjords of Bifluorenylidenes: Overcrowding and Stereochemistry

“…Table 2 gives the relative energies of a series of homodesmotic reactions of the studied BFs. Table 3 gives representative optimized geometrical parameters of the twisted conformations of the various BFs under study [at the B3LYP/ 6-311++G(d,p) level] and the respective experimental parameters of Z11ЈF2, [24] Z11ЈCl2, [31] and 1,3,6,8,1Ј,3Ј,6Ј,8Ј-octachlorobifluorenylidene (13681Ј3Ј6Ј8ЈCl8) [26] derived from their molecular (X-ray) structures. The following geometrical parameters were included: pure ethylenic twist angle [4] (ω) around C 9 =C 9Ј , defined as the average of the two torsion angles C 9a -C 9 -C 9Ј -C 9aЈ and C 8a -C 9 -C 9Ј -C 8aЈ ; folding dihedral angle of the tricyclic (fluorenylidene) moiety (A-B), defined as the dihedral angle between the leastsquare planes of the atoms C 1 , C 2 , C 3 , C 4 , C 4a , C 9a and C 5 , C 6 , C 7 , C 8 , C 8a , C 4b ( Figure 2) of the benzene rings and reflecting the nonplanarity of the tricyclic moieties; twisting dihedral angle between the fluorenylidene moieties (AEB-CFD), defined as the dihedral angle between the leastsquare planes of all the untagged and all the tagged carbon atoms; pyramidalization angles [4] (χ) at C 9 and C 9Ј , defined as the improper torsion angle C 9a -C 9 -C 9Ј -C 8a subtracted from 180°, bond lengths r(…”

“…For comparison, in 13681Ј3Ј6Ј8ЈCl8 and in perchlorobifluorenylidene, ω = 55°a nd 66°, respectively. [26] Surprisingly, the two diastereomers E11ЈF2 and Z11ЈF2 have identical twists, ω = 37.1°. By contrast, in E11ЈCl2 and Z11ЈCl2, ω = 40.6°and 42.7°, respectively.…”

“…The structures of perchlorobifluorenylidene and 1,3,6,8,1Ј,3Ј,6Ј,8Ј-octachlorobifluorenylidene, in which all four positions at the fjord regions are occupied by chlorine atoms, have been described. [26] For comparison, fluorine and chlorine atoms were also introduced not in the fjord regions of BF (positions 3, 3Ј, 6, and 6Ј). In these substituted bifluorenylidenes overcrowding was not expected to be affected.…”

Overcrowded 5,10,15‐Trisubstituted Derivatives: Synthesis of 5,10,15‐Tri(fluorenylidene)truxene

“…[19,20] Chlorinated derivatives 1, 1Ј,3,3Ј,6,6Ј,8,8Ј-octachloro-9,9Ј-bifluorenylidene (5c) and perchloro-9,9Ј-bifluorenylidene (5d) are very twisted molecules with a dihedral angle of 55°and 60°, respectively. [21] Twisted CϭC bonds have also been observed for other alkenylidenefluorenes. [22,23] Chiral, twisted olefins have received much attention in the context of the construction of molecular motors and switches.…”