Nortricyclenes, structure

With the heavier elements of group V, the [Ey] Zintl ion with a nortricyclene structure (Figure 10.1) is exceptionally stable, and numerous derivatives P7R3 and AsyRj with R = alkyl have been synthesized over the years from these Zintl ions. ... 

Olah believes that the only structure corresponding to the data of Raman laser and NMR C spectra is that of protonated nortricyclene. At —70 C the cyclo-propyl carbons C , and C are averaged as a result of rapid 6,1,2-hydride shift (E = 5.9 + 0.2kcal/mole A = 10 s ).Ifthe protonated nortricyclene structure is comer-protonated, the C, and C are averaged as follows ... 

Si INEPT-INADEQUATE NMR spectroscopy afforded further evidence for the nortricyclene structure of 7 as the coupling constants (Fig. 4) are consistent with the proposed atom arrangement. 

On the basis of the available evidence at that time, and knowledge that the nortricyclene structure had been proposed for the 2,5-norbornadiene-sulfur dioxide copolymer, it was suggested that the 61A-MA copolymer also contained nortricyclene residues 65, arising from an intramolecular cycli-... 

Based on this additional information, a revised initiation and propagation mechanism was offered to account for the 61A- and 61B-MA copolymer structure 66. As shown, MA is envisioned as being incorporated as part of a six-membered bicyclic structure 66 along the backbone of the polymer molecule.The Pledger and Butler study does not exclude the chance that a small amount of nortricyclene structure could still be part of the 61A-or 61B-MA copolymers. 

Polymerization of norbornadiene with cationic catalysts (e.g., AICI3) occurs readily at various temperatures leading to saturated polymers [139]. Thus, at low temperatures, soluble polymers having 2,6-disub-stituted nortricyclene structure were primarily obtained while at higher temperatures insoluble polymers with cross-linked structures, as a result of addition polymerization of the two double bonds, were formed [Eq. (70)]. 

The above assumes that C protonation is not excluded for steric reasons. Thus N protonation takes place with derivatives of dehydroquinuclidine and the alkaloids neostrychnine and trimethylconkurchine (( ). N protonation was also believed to occur in the case of 2-N-hexamethyleneimino-bicyclo[l,2,2]-2-heptene, which was believed to give the nortricyclene derivative (6) on protonation with perchloric acid. Later work, however, showed the salt to be the results of C protonation (15) and to have structure 7. 

The non-classical ion may exist as edge or face protonated nortricyclene, represented by structure [9], as an alternative. This species is not a resonance structure of [7] or [8]. If it is a discrete intermediate, one might expect to be able to detect the displaced proton via a suitably designed exchange experiment. 

In 1972 Olah revised his ideas of the structure of the norbornyl ion and its analogues under the stable ion conditions. While earlier he practically identified the static 2-norbornyl ion with the corner-protonated nortricyclene 5 a and denoted its structure by the formula 5a in he considers two possible ways of protonating the cyclopropane ring —- on the C—C bond and on C—H bond to form, in the case of protonating the cyclopane itself, the C-cycloproponium (edge-protonated) ion with structure II or the H-cycloproponium (corner-protonated) ion with structure I. 

As nortricyclenes and adamantanes are structurally closely related we were able to obtain members of both classes from hexa-fimctional heptasUanes by reactions with nucleophiles and reductive elimination respectively. Products were characterized by means of X-ray diffraction and a combination of ab-initio calculations and NMR spectroscopy [4]. 

By reduction of la with lithium naphthalenide at -70 °C in THF the nortricyclene-analogue cage 7 is formed. Its structure was determined by a combination of ab-initio methods and NMR spectroscopy as no crystals suitable for X-ray diffraction could be obtained. Calculated NMR shifts were obtained with the GIAO method at RHF level using 6-3IG basis sets and are reported relative to the calculated shift of tetramethylsilane. 

Additional work, comparing the copolymerization of both 61A and 61B with MA, failed to substantiate the thought that a nortricyclene moiety was part of the copolymer structures. 

The technique of mass spectroscopy is of considerable value in the study of mechanism with compounds of known structure but it remains qf little value in the determination of structure of bridged compounds of unknown structure. Spectra have been recorded of bicyclo[2,2,l]heptanols, acetates of bicyclo[2,2,l]heptanols, trimethylstannylnorbomenes, nortricyclenes, adamantanes, and dimethanonaphthalenes. ... 

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