Other Phanes

Initially, the phane concept was intended solely for supercyclic systems, namely, cyclophanes. During elaboration of the new all-encompassing cyclophane nomenclature it became more and more obvious that its basic principles apply equally well to extended linear assemblies of chain and ring segments. Such superchains can then be treated exactly like cyclophanes, except that their names end with the morpheme... phane after the numerical term denoting the length of the superchain. 

A further extension of this system consists in the inclusion of spiro components and appears particularly advantageous in the case of multilayered polyspiro systems of the following type  

To close this chapter and in anticipation of subsequent discussions it should be kept in mind that the new assembly names obtained along the lines of phane nomenclature can now be used as parent names for the multifarious ways of substitution by functional groups in the same way as the more conventional parent names of old. 

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The original trade name Cellophane is frequently misused generically, as other brand names for regenerated cellulose film also exist (Rayophane, Dio-phane, etc.). 

This and the nickel analogue are shock-sensitive and violently explosive. Other metal complexes (except cobalt) decompose slowly liberating the dimethyldiphos-phane which tends to ignite when old sample bottles are opened. 

A large variety of polymers has been considered. In the beginning, polystyrene and styrene/ divinylbenzene copolymers (Merrifield resins) were by far the most used.73 Then others were tested such as polyvinyls,47-50,61-64 polyacrylates,72 4,75 and cellulose.76,77 Most commonly, diphenylphos-phane groups were grafted on the polymeric support, either directly or via one CH2 group. 

Thus in the past decades, almost all types of phanes have been prepared and structures and reactions have been investigated in detail. One remaining interest in the chemistry is to replace the C-C bridge(s) of phanes with bonds of other elements, in particular of Group 14 heavy elements such as Si, Ge, and Sn. 

Before going into a detailed account of the chemistry of phanes, the author will touch on 3,4,7,8-tetrasilacycloocta-l,5-diyne briefly, since the compound illustrates the importance of a—it mixing. The ionization potential of the Si-Si bond is estimated by photoelectron spectroscopy to be 8.69 eV (9). Thus, the HOMO level of the Si-Si is comparable to most HOMOs of tt systems. Consequently, the Si-Si bond can conjugate efficiently with carbon-carbon double and triple bonds, benzene rings, and other tt systems. Most Si-Si bonds are stable enough to construct sophisticated structures by themselves and with organic molecules (10). 

After warming the reaction mixture to 20°C the cyclotriphosphane 111 and 113 are formed, instead of the expected n-tetraphosphane 110. Formation of 111 probably results from 1,3-elimination of n-BuP(SiMe3)2 (113) from compound 110. This preliminary step to the cyclization reaction, shown in Eq. (21h), could not be demonstrated, but nevertheless its formation according to Eq. (21a) and Eq. (19) is plausible. As is also shown by mass spectroscopic investigations, the n-tetraphosphanes exhibit a considerable tendency toward the formation of cyclotriphosphanes by means of 1,3-elimination of simpler phos-phanes RP(SiMe)2 44). The isomeric n-tetraphosphane 112 on the other hand, is stable in the same reaction solution. 

The hydrocarbon 25 has been partially resolved by asymmetric complexation with Newman s reagent [TAPA ( )-a(2,4,5,7-tetranitro-9-fluorenylideneaminooxy)prop-ionic acid] thereby establishing its chiral Z)2-structure 53). Similarity, the naphthaleno-phane 27b could be resolved by chromatography on silicagel coated with (—)-TAPA 49) and recently also by HPLC on optically active poly(triphenylmethyl methacrylate)49a) which also proved to be very useful for the optical resolution of many other axial and planarchiral aromatic compounds 49b>. 

Absolute configurations (chiralities) of phanes — together with those of several other planar chiral structures — have been compiled in the Atlas of Stereochemis-stry 25) (for previous surveys see Refs. 10) and I00)). 

Optical activity caused by restricted rotation of other types. Substituted paracyclo-phanes may be optically active and 20, for example, has been resolved.57 In this case chirality... 

A broad, structureless fluorescence emission is observed for [2.2], [3.3], and [4.4] paracyclophane, but only structured monomer emission is seen in [4.5] and [6.6] paracyclophane. The fluorescence properties of the [2.3], [2.4], [3.4], [3.6], [4.6], [5.5], and [5.6] paracyclophanes have not been reported, although the latter three would be expected to yield only monomer emission. The UV absorption spectra of all of the above paracyclophanes have been reported, and all [m.n] phanes for which both m and n are 4 have absorption spectra that are identical to 1,4-bis (4 -ethylphenyl)butane, the open-chain analog. The UV absorption spectra of other paracyclophanes become increasingly red-shifted and broadened in the order [3.6], [3.4], [2.4], [3.3], [2.3], and [2.2] paracyclophane. 

Other bridged derivatives are also known, examples being illustrated by the metacyclo-phane derivative (37) (74T2633), the thia crown ether (38) (74AG126) and the isomeric and separable cyclophanes (39) and (40) (74TL799). 

One example of an aromatic molecule with markedly different singlet and triplet-state photochemistry is provided by [2.2]paracyclo-phane.203 Irradiation at wavelengths above 2700 A or photosensitization with acetone yields p-ethylbibenzyl as the sole product. This must be a triplet product because the reaction is quenched by naphthalene. Direct irradiation of the paracyclophane at 2537 A and lower wavelengths produces other products. 

P H, P4H, P H, and P7H3 coul b isolated in pure form so far, whereas tne other phosphanes have been obtained oi y as mixtures. As the detailed structures are mostly unknown, a P-NMR spectroscopic investigation was initiated. Beginning with tetraphos-phane(6), the structural situation of the open-chain phosphanes becomes more and more complex due to the existence of co ti u-tional and configurational isomers. The low temperature P H -NMR spectrum of P4H could be simulated very satisfactorily by the... 

Complexes 16a,b are thus versatile molecular clips to control the organization of -conjugated systems in supramolecular assemblies having a [2.2]paracyclo-phane topology. The elucidation of the electronic properties of these novel n-stacked molecular assemblies and the use of other ditopic conjugated systems to construct novel metallo[2.2]paracyclophane are under active investigations. 

Several pyridinophanes have been synthesized in which the two pyridine rings are stacked one-on-top-of the other and are held together with four bridges. Cyclo-phanes 74 (24%) and 75 (22%) have been synthesized as shown in Scheme VI, and the single crystal X-ray analyses 37138) indicate that the heteroaromatic rings exist in the boat conformation with an inter-ring distance in both cases of 2.64 A. Both cyclophanes are relatively strong bases and should be able to complex transition metals to date no such studies have been published 39). 

Vogtle and Klieser [86] succeeded in the first four-(and fivefold) bridging of the benzene ring by cyclization of tetrakis(bromomethyl)benzene (93) with the corresponding tetrathiol 94. Whilst the combination CS2CO3/DMF led to the isomeric phanes 97 in a total yield of 10%, cyclizations with other solvent/base combinations such as e.g. K2CO3/DMF only produced the dithia compound 98 [86]. 

Besides photochemical desulfurization, sulfone pyrolysis allows for the broadest range of applications. The compounds which have been synthesized belong to classes as different as heterophanes, multilayered phanes, nonbenzenoid phanes, molecules containing molecular cavities or phenylenicen . The pyrolysis of sulfones in the gas phase in comparison with other methods has many advantages ... 

Haenel et al. for their studies of exciplex-interactions used a [3.2](l,4)naphtha-lenophane, the aromatic planes of which are inclined towards each other about 10° to 20° because of the different lengths of the bridges [22]. Pyrolysis of the mono-sulfone in the gas phase yielded a 1 3 mixture of the syn- and a ti-phanes 6 and 7a/b, respectively, that could be separated by chromatography. 

The ability of fluoro-2 -phosphanes to transform silyl ethers into fluorides was first observed during a study of the reactions of phosphorus pentafluoride and its derivatives R PF5 (n = 1, 2, 3 R = hydrocarbon group) with trimethylsilyl ethers. Subsequently, this reaction was proposed as a new method for the preparation of C-F compounds from silyl ethers or silicic acid esters with fluoro-A -phosphanes. Pentafluorophenyl-substituted fluoro-A -phos-phanes were found to react similarily, Other workers found that tctrafluoro(phenyl)-A -phos-phane. which was chosen as the most convenient reagent with regard to reactivity and stability, gave considerable amounts of elimination products, especially with primary and cyclic alcohols. Good yields of fluorinated products are obtained when stable carbocations can be formed at the site of substitution, such as in tertiary alcohols, but 2-phcnylethanol. benzyl alcohol and diphcnylmethanol, on the other hand, give only poor yields of fluorinated products ethers and polymers are the main products. ... 

When perflluoro(2-methylpropene) reacts with tributylphosphane in acetonitrile at — 30"C, the reaction does not stop with the formation of fluoro-2 -phosphanes, and, as a result of a series of transformations, perfluorodiene 3 and conjugated cross-triene 4 are formed. When the reaction is carried out with triphenylphosphane in acetonitrile without cooling triene 4 is obtained in 67 % yield.On the other hand, the reaction of perfluoro(2-methylpropcnc) with tributylphosphane in diethyl ether at — 70 C leads to the corresponding fluoro-A -phos-phane treating this compound with potassium fluoride dihydrate in tetraglyme gives 1,1,1,3-tetrafluoro-2-(trifluoromethyl)hept-3-ene in 75% yield,... 

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