Saturated bridges

Figure C3.2.9. Both nearest neighbour and nonnearest neighbour coupling interactions mediate superexchange between tire temrinal pi-electron groups of rigid dienes witlr saturated bridging units. From [31],...

Figure 17. Three dyads possessing Zn(ll) porphyrin donor and Fe(lll) porphyrin acceptor linked by (from top to bottom) H-bonded bridge, a partially unsaturated bridge and a saturated bridge.1341...

Systems that do not meet all the above specifications, but the use of which is acceptable because of their convenience or the lack of suitable alternatives are the bridging nomenclature, system 4, method b (in which saturated bridging groups are permitted), the spiro method, 6a, ii (in which the components may be fully unsaturated or saturated and retain their original numberings), and system 7 for assemblies of identical cyclic components. 

A specialized system of nomenclature has been developed, principally by Smith,16 for naming skeletons consisting of aromatic residues linked in various ways by saturated bridges. Those skeletons containing benzene residues only are termed cyclophanes, and names for heteroaromatic analogues are based on the name of the heterocycle with the termination -ophane. The numbers of atoms in the bridges are indicated in square brackets, and the orientation of substitution on the aromatic residue(s) is shown in parentheses. A few simple examples are given (149-151), with alternative names. 

Similar observations were made in Refs. [86, 119] with molecules containing methoxybenzene chromophore as D and dicyanoethylene acceptor fragment as A linked with hydrocarbon saturated bridge and in Refs. [115, 116] with D-L2-A molecules containing acceptors linked to the donors via two bridges, so that the acceptor is held in a relatively rigid, capped position over the donor. 

UV spectra of the norporphins 2 and 3 are very similar to those of OEiBC(14) and OEBC(13). A hypsochromic o.iift of 2 and 3 points to a deviation from planarity in the hydroporphyrins (86PAC153). Similar steric interactions of substituents at the saturated bridge of hydroporphyrins have been observed in OEC (69TL1145). 

Scheme 30. Saturated-bridged bis(diazenium) and bis(hydrazine) intervalence compounds.

Figure 5. Long-range ET. Direct overlap between the donor and acceptor orbitals is negligible, and ET occurs by an indirect mechanism involving electron tunneling through the orbitals of the intervening medium, e.g., solvent molecules (upper) or a covalently linked saturated bridge (lower).

Table 1. Photophysical data of dinuclear complexes containing saturated bridging ligands. 

Gross and coworkers demonstrated that both Cf Hi2+ isomers reside in distinct potential wells and can be characterized by CID in both sector-field and FT-ICR mass spectrometers. The mass spectrometric experiments were in line with calculation in that the ionized bicyclic isomer appears to be more stable than 4-vinylcyclohexene ions, and with the radiolytic results in that a closely related bicyclic isomer, viz. ionized bicy-clo[2.2.2]octene, is not easily formed upon ionization of the other CgHn hydrocarbons. The retro-Diels-Alder reaction ionized bicyclo[2.2.2]octa-2,5-dienes leading to expulsion of the initially saturated bridge as an alkene gives rise to the base peak in the El spectra . ... 

---