Transition metal complexes pyridine-derived

A unique method to generate the pyridine ring employed a transition metal-mediated 6-endo-dig cyclization of A-propargylamine derivative 120. The reaction proceeds in 5-12 h with yields of 22-74%. Gold (HI) salts are required to catalyze the reaction, but copper salts are sufficient with reactive ketones. A proposed reaction mechanism involves activation of the alkyne by transition metal complexation. This lowers the activation energy for the enamine addition to the alkyne that generates 121. The transition metal also behaves as a Lewis acid and facilitates formation of 120 from 118 and 119. Subsequent aromatization of 121 affords pyridine 122. 

Transition metal complex-mediated hydroacylation of pyridine derivatives with aldehydes 99SL1. 

Transition metal complexes have been used in a number of reactions leading to the direct synthesis of pyridine derivatives from acyclic compounds and from other heterocycles. It is pertinent also to describe two methods that have been employed to prepare difficultly accessible 3-alkyl-, 3-formyl-, and 3-acylpyridines. By elaborating on reported194,195 procedures used in aromatic reactions, it is possible to convert 3-bromopyridines to products containing a 3-oxoalkyl function196 (Scheme 129). A minor problem in this simple catalytic process is caused by the formation in some cases of 2-substituted pyridines but this is minimized by using dimethyl-formamide as the solvent.196... 

In this chapter, we will focus on paramagnetic materials based on two pyridine substituted TTFs (Fig. 5) the TTF CH=CH py [59] and its trimethyl derivative Me/ITF CH=CH pv [51]. Owing to the presence of one pyridine group on each TTF, such ligands coordinate to one transition metal ion. Therefore, a large variety of transition metal complexes can, in principle, adapt pyridine substituted TTFs in... 

T. Yamamoto, T. Murauyama, Z.-H. Zhou, T. Ito, T. Fukuda, Y. Yoneda, F. Begum, T. Ikeda, S. Sasaki, H. Takezoe, A. Fukuda, and K. Kubota, -ir-Conjugated poly(pyridine-2,5-diyl), poly(2,2 -bipyridine-5,5 -diyl), and their alkyl derivatives. Preparation, linear structure, function as a ligand to form their transition metal complexes, catalytic reactions, //-type electrically conducting properties, optical properties, and alignment on substrates, J. Am. Chem. Soc., 116 4832-4845,... 

Effectively, this is another example of the addition of a functional aromatic compound to an alkene, as the Murai reaction, but the mechanism is different. Alkyl substituted pyridine derivatives are interesting molecules for pharmaceutical applications. The a-bond metathesis reaction is typical of early transition metal complexes as we have learnt in Chapter 2. 

Not only has binding of imidazoles and pyridines to Fe protoporphyrin IX been studied, as discussed in Section 4.1.2, but also photodissociation of axial ligands such as pyridines, imidazoles, or piperidines from six-coordinate, low-spin Fe porphyrins, in which the porphyrin is derived from protoporphyrin IX, or proto- or deuteroporphyrin IX dimethyl ester, has been investigated in nonaqueous solvents using picosecond transient absorption spectroscopy (see Photochemistry of Transition Metal Complexes). It has been shown that photodissociation leads to the formation of five-coordinate complexes, that is, only one ligand appears to be released upon excitation of the six-coordinate complex. ... 

Transition metal coordination of Cu(II) carboxylate groups and pyridine groups was employed as a means of coupling a telechelic butadiene-base polymer with a randomly functionalized styrenic polymer. Dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC) indicated partial miscibility of the two polymers and Fourier transform infrared (FTIR) spectroscopy demonstrated that interactions occurred on a molecular level. When compared with blends of PSVP and the free acid derivative of CTB, the compositions based on the transition metal complex had improved dimensional stability at elevated temperatures, though there remains some question as to the stability of the copper salt to hydrolysis. Electron spin resonance (ESR) spectroscopy showed that only the... 

Another approach of using transmetallation process is to transfer the organic moiety bound with early transition metal complexes to late transition metal complexes such as nickel to utilize the reactivity of the diorganonickel complexes to undergo reductive elimination. Various benzene and pyridine derivatives have been prepared by the methodology [100]. 

The scope of various pyridine derivatives with 1-hexene was examined with L45c-Sc/[Ph3C][B(C6F5)4] as the catalyst (Table 5.8). The asymmetric alkylation of 2-Me, 2-Et, 2- Pr, 2- Bu, and 2-phenyl-substituted pyridines 188 could also be achieved similarly in high yields (83-94%) and enantioselectivity (up to 94 6 er) (entries 1-5). Notably, the C—H bond activation reaction occurred selectively at the pyridine unit rather than at the phenyl group in the case of 2-phenylpyridine, which is in contrast with the reactions catalyzed by late transition metal complexes. The iodo, bromo, and chloro substituents in the picoline substrates are well compatible (entries 6-8). No alkylation reaction was observed with unsubstituted pyridine or quinoline, probably due to the poisoning effect of the N atom of pyridine to the metal center. 

A related class of compounds has been derived by using porphyrins connected to polypyridines such as 2,2 -bipyridine, 1,10-phenantholine and 2,2 6, 2"-terpyridine. These chelating ligands form thermodynamically more stable and inert transition metal complexes than the pyridine ligand, and such porphyrins have been extensively explored for the assembly of photochemically active supramolecular systems, especially by Sauvage et The oblique... 

Luminescent ionic transition-metal complexes for light-emitting electrochemical cells (pyridine, phenanthroHne, pyrazole, imidazole, triazole derivatives as Hgands) 12AG(E)8178. 

Chiral transition-metal complexes have also been featured in the following reports " of asymmetric carbonyl reductions hydrogenation of / -aryl- -ketoesters 0 using H2 and iridium-bearing spiro pyridine-aminophosphine ligand rhodium in a theoretical study of catalysis involving amino acid-derived ligands and in... 

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