2,2 -Bipyridinium, bridged

Fig. 27 Elecriochemical synthesis of supramolecular porphyrin arrays by nucleophilic attack of pyridine and bipyridine derivatives to porphyrin C-atoms at me o-positions leading to formation of C-N(pyridinium) bonds generating a a meio-bipiridinium OEP b a cw-few-bipyridinium OEP c a mew-pyridinium bridged feii-porphyrin d a few-bipyridinium bridged OEP multiarray and e trans-bis- yndimma (POM) bridged OEP arrays...

That electrosynthesis reaction was shown to be vesy effective and used to prepare porphyrin dimCTS using ww-pyridylporphyrins as nucleophiles (Fig. 27c), as demonstrated by Ruhlmann et al. [146] starting with ZnOEP and 5,10,15-tritolyl-20-(4-pyridyl)poiphyrin (4-H2TTP) or 5,10,15-tritolyl-20-(3-pyridyl)-porphyrin (3-H2TTP) isomer. The dimers were characterized spectroscopically and electrochemically showing that the redox potentials shifted anodically (150-250 mV) as a consequoice of the electron-withdrawing effect of the bipyridinium bridge on the pOTphyrin n-system. 

DR. ALBERT HAIM (State University of New York at Stony Brook) Dr. Meyer considered plots of optical transition energy versus 1/D(optical) minus 1/D(static) for various types of systems, some of which were binuclear and clearly delocalized. If instead, one considers a ruthenium(II) pentaamine bound to N-methyl-4,4,-bipyridinium, is this in any way different from the bridging situation In some instances there was a similar dependence for both the mononuclear systems and the binuclear systems. But some of these mononuclear systems did not seem to behave similarly. Is there any connection between whether that simple linear relationship works or not and whether the system is localized or delocalized ... 

The high affinity of ammonium cations for tetra-bridged phosphorus(IV) P=0 cavitands was used to complex bis-ammonium guests. The highly insoluble NjAT-dimethyl-bipyridinium dication [paraquat " ] was readily dissolved in chloroform solution in presence of 12b in a 2 1 host-guest ratio. 

There has been considerable interest in diquaternary salts of 2,2 -bipyr-idine. Simple 1,1-dialkyl-2,2 -bipyridinium salts are obtained by reaction of 2,2 -bipyridine with excess of an alkyl halide or dialkyl sulfate and related processes, - " and dialkyl diquaternary salts of substituted 2,2 -bipyridines are obtained likewise. " Bridged diquaternary salts are formed by reaction of 2,2 -bipyridines with 1,2-dibromoethane. Thus the parent compound alfords 6,7-dihydrodipyrido-[l,2-a 2, T-c]pyrazinediium... 

The far IR spectra of the [Znd4]2- anion in salts with the 1,10-phenanthrolinium and 2,2-bipyridinium cations have been reported.1039 The anion in the former salt appears to be tetrahedral, while that in the latter is believed to be halogen-bridged. 

We will review here work wherein several types of species incorporate the Ir-bis-terpy unit and derivatives. The search for multicomponent arrays, including metal-based photoactive centres in combination with electron donor and acceptor components, was started a couple of decades ago, and one of the first systems, compound 14+, was studied by Meyer et al. (Fig. 1) [5]. In this multicomponent system, the electron donor phenothiazine (PTZ) and the bridged 2,2/-bipyridinium (DQ) units are linked to the photoactive unit by flexible methylene connections. In this early example, excitation at the Ru-based chromophore ultimately yields a PTZ+-DQ" CS state which lives 165 ns and for which the transiently stored energy is 1.29 eV. 

The thiophene-bridged 4,4 -bipyridinium salts 149 and 150 can be prepared by alkylation of bis-bipyridinium cations <1999T4709>. The order of alkylation is crucial. Whereas in the thiophene derivative the xylene core is introduced in the last step, it is not possible to obtain the benzothiophene derivative in the same way due to the less stable bis-cation. Therefore, the benzothiophene unit is introduced in the last ring-closing step. 

CDs form complexes not only with non-ionic polymers but also with ionic polymers, such as linear polymers consisting of bipyridinium (viologen) bridged by polymethylene chains (Scheme 5) [ 128]. The methylene peaks split in two upon addition of a-CD, although these peaks did not change upon addition of y-CD. These peaks are broadened upon addition of P-CD. These results indicate that a-CD stays at one of the methylene chains on the H... 

A few examples of higher nuclearity aggregates composed of [EXs] are known. In the structure of [2,2 -bipyridinium][SbCl5] (36) (51), a tetrameric arrangement is found, as shown in K. Each [SbCls] " unit is linked to two others through approximately linear chlorine bridges that are somewhat asymmetric, the relevant distances being 2.804/ 3.218 and 2.836/3.054 A. 

The corresponding 2,2 -bipyridinium salt occurs predominantly in the anti conformation, but the cis conformation can be enforced by a connection of the nitrogen atoms via an ethylene bridge (diquat). Only the latter compound gives stable radicals upon reduction (Scheme 7.2.20) 378 nm e = 30,000) (Sum-... 

Further diverse systems have been developed and used in the investigation of intramolecular SET processes. These include styrene/amide-spacer/amine diads, 9-aminoacridine/polyether-spacer/benzoate ester diads, l-(4-cyano-phenyl)-4-(cyanomethylene)piperidine, 7i-donor/polyoxyethylene/Zn(II)por-phyrin/N,N -dimethyl-4,4 -bipyridinium systems, naphthalene/porphyrin/ quinone cyclophanes and their anthracene analogues, pyropheophytin-naphthoquinone diads, rigid donor/bridge/acceptor systems, anilide-substi-... 

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