Bipyridyl system

Comparable compounds have recently been described by Weidenbruch et al., starting from cyclotrisilanes as a source for di-organylsilylenes [10]. Whether these complexes are formed by electron donation from the nitrogen lone pairs to silicon with subsequent electron transfer from silicon to the bipyridyl system or by a [4+1]cycloaddition process involving the diazadiene fragment is still uncertain. 

Nevertheless, positions and differences of Ej and E2 allow some qualitative interpretations. The vinylene bridge in 5,6-position seems to be inert not only in ii, which resembles the 4,4 -bipyridyl system i/(c.f. 3.1) but also 13B2 and 13B3 which behave similar to the 2,2 -bipyridyl systems 2B2 and 2B3. In 13B3 the vinylene group prevents the two pyridyl units from distortion by the Ca-brit e between the nitrogen atoms compared to 2B3. Thus its Ksem stays closer to that of 13B2. 

Hydrogen bonding can be used to orient systems in co-crystals such that subsequent reaction can occur. This is demonstrated in the co-crystals of resorcinol and bipyridyl systems, which are oriented such that irradiation of the sample produces a cyclobutane (Scheme 12) <2000JA7817>. 

Several other systems have been investigated in this context. An important condition that has to be satisfied while choosing system, is that the free energy of photochemical steady state under sun light illumination should be greater than that when it is dark. Methylene blue and Fe2+, Co-EDTA complex and thionine, and excited tri-bipyridyl complex of Ru2+ and Fe2+ are a few systems that satisfy this condition. The equilibrium in dark with the bipyridyl system is... 

The E of the bipyridyl system is 1.2 V and that of the Fe2+/ Fe3+ system 0.7. The equilibrium is shifted to the left. When the system is illuminated the excitation reaction occurs as... 

Bipyridinium chlorochromate (4) is a mild, air stable nonhygroscopic oxidant. It is weaker than PCC, and thus 2-4 equiv. are required to obtain good yields of carbonyl compounds. The bipyridyl system acts as an internal buffer, permitting the ready oxitktion of alcohols in sul trates with acid labile groups. Bipyridinium chlorochromate will also oxidize sulfides to sulfoxides and sulfones." ... 

Nocera and co-workers (259) reported an amidinium functionalized ruthen-ium(II) bipyridyl system (138) binding 3,5-dinitrobenzoate (259). On binding the carboxylate anion, the chemical shift of the amidinium protons changes by >2.0 ppm (in DMSO). Electron-transfer kinetics in dichloromethane were investigated in order to elucidate the role of proton motion within the salt bridge... 

Hydroxyglutaric acid forms a ternary anionic complex with Fe and The complexes TiCl2L2 (L = ethyl-4-nitrobenzoylpyruvate, ethyl-4-phenylbenzoyl-pyruvate, ethyl-2,4-dimethoxybenzoylpyruvate, or ethyl-2-naphthylpyruvate) have been prepared.There has been a spectroscopic study of complex formation in the Ti -salicylate-aa-bipyridyl system,and a reinvestigation of the reaction between Ti and salicylic acid in concentrated sulphuric acid. The coloured TiO salicylic acid complex formed in the latter system is formulated as a 7t-compIex rather than a chelate. 

Complex formation in the Ti -salicylate-aa -bipyridyl system has been studied. 

Carbonyl and other Low Oxidation State Compounds.— The full report of the polaro-graphic study of redox phenomena in the vanadium-bipyridyl system has been pub-... 

Cu(II) ions have been used to assemble tetra- and octavalent V-acetyl galactosy-lamide dendrons (Fig. 35). The carbohydrate epitopes were first attached to a bipyridyl system using linker of different length. Tetracoordination of the Cu(II) core produced the glycodendrimers which were characterized using proton and carbon NMR, MALDI-Tof mass spectrometry, and UV-VIS spectroscopy [233],... 

Scheme 7.2.17 contains another very interesting bipyridyl system, namely the ruthenium(II) complex of 2,2 -bipyridine. In this complex the d-orbitals of the ruthenium ion and the 7t-orbitals of the bipyridine are similar in energy and mix. As a result, there is almost no redox quenching of the excited singlet and triplet states and the compound fluoresces strongly, which is very unusual for a transition metal complex. It cannot only be used to produce hydrogen with the aid of viologen, but the oxidation product ruthenium(III) bipyridinate is such a... 

The synthesis of both orellanine and orelline was elaborated almost simultaneously by two independent teams from Germany and Italy. In both cases the key intermediate step, entailing the coupling reaction to the bipyridyl system, was carried out using the general method elaborated by Tiecco et al. (308). In the procedure described by Dehmlow and Schulz (298,307) (Scheme 47), 2-chloro-3,4-dimethoxypyridine was coupled in the... 

Chen SN, Wu WY, Tsai FY (2008) Hiyama reaction of aryl bromides with arylsiloxanes catalyzed by a reusable palladium(II)/cationic bipyridyl system in water. Tetrahedron 64(35) 8164-8168... 

E. L. Kopp etal. Catalytic activity of Et3Al-2,2 bipyridyl systems. Izvest. Akad. Nauk S.S.S.R., Ser, khim., 1977, 26, 2055. 

Aliferis, T., latrou, H., and Hadjichristidis, N. (2004) Living polypeptides. Biomacromolecules, 5,1653-1656. Angot, S., Murthy, K.S., Taton, D., and Gnanou, Y. (2000) Scope of the copper halide/bipyridyl system associated with calixarene-based multihalides for the synthesis of well-defined polystyrene and poly(meth)acrylate stars. 

They also reported the synthesis of the Af-heterocycles 10a,ll-dihydro-i0//-indolo[l,2- ]indoles using Cu(OTf)2/2,2 -bipyridyl system and Mn02 as oxidant. When TEMPO is added to the reaction mixture, aminooxygenation product indolines could be obtained in good yields with O2 as oxidant [59] (Scheme 8.23). 

A NaBH4-cobalt(ll)-a,a -bipyridyl system reduces azidosteroids to amines under conditions which NaBH4 alone is ineffective. Earlier workers had found that this system is stronger than NaBH4 for reduction of nitrobenzene to aniline. 

FIGURE 13. Di-boronate esters based on 1,2,4,5-tetrahydroxybenzene coodinatively interact with bipyridyl systems to form zigzag linear polymers (Reprinted with permission from Ref. 38. Copyright 2007 Wiley-VCH Verlag GmbH Co. KGaA.)... 

The [M(CN)3(0)(bipy)] anions, M = Mo or W, are formed from the respective [M(CN)g] anions plus 2,2 -bipyridyl by photoaquation of cyanide followed by thermal substitution by the bipy. [M(0)(CN)5] intermediates were characterized as their Cs" " salts the tungsten product was characterized by X-ray crystal-structure determination. An investigation of the analogous [W(CN)g] plus 1,10-phenanthroline photoreaction over a wide pH range suggested the intermediacy of [HW(CN)7(OH2)] (presumably [W(CN)6(CNH)(OH2)] -) in acid, [W(CN)7(OH)] - in base, prior to the formation of the penta- and tri-cyano complexes analogous to those characterized in the bipyridyl systems just mentioned. 

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