ALBERT

Notes: Summary Copolymerization of diphenylacetylene having a hexaphenylbenzene group, 1-[p-(pentaphenyl)phenyl]-2-phenylacetylene (1), with a few other diphenylacetylene derivatives (i.e., diphenylacetylene, 1-phenyl-2-[p-(trimethylsilyl)phenyl] acetylene, 1-phenyl-2-[p-n-octylphenyl]acetylene, (2a–c, respectively) and properties of the formed copolymers were investigated. No polymer was obtained in homopolymerization of 1 with TaCl5-n-Bu4Sn catalyst owing to steric hindrance. On the other hand, copolymerization with 2a–c proceeded at various feed ratios to give copolymers in moderate yields. Copoly(1/2a) (feed ratio 25/75) was soluble in toluene and CHCl3 and its weight-average molecular weight (M w) was ca. 31×104 and relatively high. Copoly(1/2b) and copoly(1/2c) (both feed ratios 5/95) were soluble in common organic solvents, and had a large M w up to ca. 1×106. These copolymers were yellow to orange solids. Oxidative cyclodehydrogenation of hexaphenylbenzene groups in copoly(1/2a) was attempted in order to convert them into more conjugated groups.

Notes: The π-bond configurations, the conformations, and the dynamic behaviour of dibenzo [c,j]octalene (2) and of benzo [c]octalene (3) have been investigated by 13C-NMR. spectroscopy at different temperatures. Dibenzooctalene was found to present π-bond fixation in the octalene unit as in 2b; with this π-bond fixation the molecule is not planar and takes two different conformations which are rapidly interconverted by inversion of one cyclooctatetraene ring. Monobenzooctalene (3) also presents π-bond fixation in the octalene unit but exists as two valence isomers, 3b and 3c. Isomer 3c dominates the dynamic equilibrium. With this π-bond configuration, the molecule is chiral but undergoes several isodynamic processes, namely inversion of the cyclooctatriene and/or of the cyclooctatetraene ring. The valence isomer 3b can have two different conformations which are rapidly interconverted by inversion of one cyclooctatetraene ring. The interconversion 3c ⇌ 3b implies the occurrence of a π-bond shift process; this process affects the 13C-NMR. lineshape above 50°.

Notes: The dianions of phenanthrene and 1,2,3,4-dibenzocyclooctatetraene have been prepared by metal reduction of the neutral compounds and characterized via the study of their 1H- and 13C-NMR. spectra. A description of the charge distribution can be achieved which is consistent with both MO-models and the spin density distribution of the corresponding radical anions. Thus, the dianion of 1,2,3,4-dibenzocyclooctatetraene appears as a π-bond delocalized species having its excess charge mainly localized in the eight membered ring.

Notes: Metal reduction of the polycycle 2 yields a surprisingly stable dianion with intact molecular framework. This conclusion can be drawn from reoxidation experiments and from an analysis of the 1H-NMR. spectrum. The excess charge turns out to be distributed over both the π- and σ-fragments of the molecule. The relative stabilities of ionic species derived from 1, 2 and 3 are considered.

Notes: [2+2]-Cycloadditions and -cycloreversions in radical anions. An ESR. spectroscopic study for 2,2′-disubstituted diphenyl derivativesThe radical anions derived from the polycyclic olefins 1, 2 and 3 are shown by ESR. spectroscopy to undergo [π2+π2]-cycloaddition reactions even at low temperatures. Similarly, facile cleavage by [σ2+σ2]-cycloreversion processes is observed for the radical anions of the corresponding cyclobutane species. This reactivity, which is in marked contrast with the thermal stability of the neutral parent compounds, is discussed taking into account the molecular geometry and the spin density distribution.

Notes: The rearrangement products obtained upon reduction of 1,6-methano[10]-annulene (1) and its 11-halogen derivatives have been studied by ESR. and, in part, by ENDOR. spectroscopy. These derivatives comprise 11,11-difluoro- (2), 11-fluoro- (3), 11,11-dichloro- (4) and 11-bromo-1,6-methano[10]annulene (5), as well as the 2,5,7,10-tetradeuteriated compounds 2-D4 and 3-D4. The studies of the secondary products in question have been initiated by the finding that the radical anion of 11,11-dimethyltricyclo[4.4.1.01,6]undeca-2,4,7,9-tetraene (12), i.e., the prevailing valence isomer of 11,11-dimethyl-1,6-methano[10]annulene, undergoes above 163 K a rearrangement to the radical anion of 5,5-dimethylbenzocycloheptene (14). A rearrangement of this kind also occurs for the radical anion of the parent compound 1, albeit only above 323 K. The lower reactivity of 1\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} relative to 12\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} is rationalized by the assumption that the first and rate determining step in the case of 1\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} is the valence isomerization to the radical anion of tricyclo[4.4.1.01,6]undeca-2,4,7,9-tetraene (1a). In the reducing medium used in such reactions (potassium in 1,2-dimethoxyethane), the final paramagnetic product of 1\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} is not 5H-benzocycloheptene (15), but the benzotropylium radical dianion (). This product () is also obtained from the radical anions of the halogen-substituted 1,6-methano[10]annulenes, 2 to 5, in the same medium. The temperatures required for the conversion of 2\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} and 3\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} into lie above 293 and 243 K, respectively, whereas the short-lived species 4\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} and 5\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} undergo such a rearrangement already at 163 K. The stability of the four halogen-substituted radical anions thus decreases in the sequence 2\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} 〉 3\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} 〉 4\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} ≈ 5\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document}. Replacement of 2\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} and 3\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} by 2-D4\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} and 3-D4\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document}, respectively, leads to 1,4,5,8-tetradeuteriobenzotropylium radical dianion (). Experimental evidence and theoretical arguments indicate that the rearrangements in question are initiated by a loss of one (3\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} and 5\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document}) or two (2\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document} and 4\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document}) halogen atoms. Such a reaction step must involve the intermediacy of the radical 19 · (see below) which rapidly isomerizes to the benzotropylium radical 16:. Support for the transient existence of 19. is provided by the thermolysis of 1,6-methano [10]annulene-11-t-butylperoxyester (6) which yields 16. in a temperature dependent equilibrium with a mixture of its dimers (162).In the hitherto unreported ESR. spectra of 2\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document}. and 3\documentclass{article}\pagestyle{empty}\begin{document}$ 1^{\ominus \atop \dot{}} $\end{document}, the coupling constants of the ring protons differ considerably from the analogous values for the radical anions of other 1,6-bridged [10]annulenes. These differences strongly suggest that the fluoro-substitution substantially affects the character of the singly occupied orbital.