Pyridine-gold

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. 

A variety of gold(III) complexes of carboxamido substituted heterocyclic ligands are obtained by reaction of [AuCh] with the appropriate ligands, these include [Au (N,N )Cl2j (HN,N =picolinamide) (IS) [70], [Au(N,N, N")Cl]Cl [N,N H,N" = N-(8-quinolyl)pyridine-2-carboxamide (16), N-(8-quinolyl)glycine-2-carboxamide (17) or N-(8-quinolyl)-L-alanine-2-carboxamide (18)] [71] (Figure 2.11). 

Cinellu, M.A., Zucca, A., Stoccoro, S., Minghetti, G., Manassero, M. and Sansoni, M. (1995) Synthesis and characterization of gold(III) adducts and cyclometallated derivatives with 2-substituted pyridines. Crystal structure of [Au NC5H4(CMe2C6H4)-2 Cl2]. Journal of the Chemical Society, Dalton Transactions, (17), 2865. 

Fuchita, Y, leda, H. and Yasutake, M. (2000) First intramolecular aromatic substitution by gold(III) of a ligand other than pyridine derivatives. 

D. T, Burns, K., Titus, D.D., Girard, G.R., Reiff, W.M. and Mascavage, L.M. (2003) Dichloro (pyridine-2-carboxamido-N 1, N2)gold(III), a bis-nitrogen aurocycle syntheses, gold-197 Mossbauer spectroscopy, and X-ray crystal structure. Inorganica Chimica Acta, 346, 1. 

Annibale, G., Canovese, L., Cattalini, L., Marangoni, G., Michelon, G. and Tobe, M.L. (1984) Displacement by chloride of pyridine-2-carboxylate from dichloro (pyridine-2-carboxylato) gold(111) in acidic solution the position of ring opening. Journal of the Chemical Society, Dalton Transactions, (8), 1641. 

Shieh, S.-J., Hong, X., Peng, S.-M. and Che, C.-M. (1994) Synthesis and crystal structure of a luminescent onedimensional phenylacetylide-gold(I) polymer with 2,6-bis(diphenylphosphino) pyridine as ligand. Journal of the Chemical Society, Dalton Transactions, 3067-3068. 

As well as the adsorption of halogen atoms or molecules, the adsorption of halide anions to gold surfaces has been extensively studied and a comprehensive review of the area has been published by Magnussen [168]. The degree of specific adsorption to gold surfaces increases in the order F < Cl < Br < 1 with only weakly specifically adsorbed. The presence of halide anions can also affect the electrodeposition of organic molecules such as pyridine on Au surfaces with chloride and bromide solutions suppressing the formation of ordered N-bonded pyridine layers [169]. 

Metal nanotube membranes with electrochemically suitable ion-transport selectivity, which can be reversibly switched between cation-permeable and anion-permselective states, have been reported. These membranes can be viewed as universal ion-exchange membranes. Gold nanotube molecular filtration membranes have been made for the separation of small molecules (< 400 Da) on the basis of molecular size, eg. separation of pyridine from quinine (Jirage and Martin, 1999). 

Carbene complexes have also been prepared by transmetallation reactions. Lithiated azoles react with gold chloride compounds and after protonation or alkylation the corresponding dihydro-azol-ylidene compounds, e.g., (381) or (382), are obtained.22 9-2264 Silver salts of benz-imidazol have also been used to obtain carbene derivatives.2265 Mononuclear gold(I) carbene complexes also form when trimeric gold(I) imidazolyl reacts with ethyl chlorocarbonate or ethyl idodate.2266,2267 The treatment of gold halide complexes with 2-lithiated pyridine followed by protonation or alkylation also yields carbene complexes such as (383).2268 Some of these carbene complexes show luminescent properties.2269-2271... 

Some gold(I) derivatives have been obtained with other type of /V-donor ligands as acetonitrile the compound [Au(NCMe)2]+ can be obtained by halide-catalyzed electrolysis of gold metal in MeCN.2412 This cation is very moisture sensitive and thermally labile, but the more stable cation [Au(NCPh)2]+ has been obtained by oxidation of gold with the nitrosyl cation in benzonitrile.2413 From EXAFS spectroscopic studies it has been suggested that the solvated gold(I) cations are tetra-coordinate in pyridine or acetonitrile solutions.2414 Other gold(I) complexes have been... 

The results clearly showed the importance of directionality. 4-lhiopyridine is an excellent promoter, while the 2 isomer shows no activity. After adsorption the 4 isomer has the pyridine nitrogen direction out into solution while the 2 isomer points the N back towards the electrode where it is available for adsorption to the gold rather than the cytochrome c. 

Creighton J.A., Blatchford C.B., Albrecht M.C., Plasma resonance enhancement of Raman-scattering by pyridine adsorbed on silver or gold sol particles of size comparable to the excitation wavelength, J. Chem. Soc. Faraday Trans. 1979 2 790-798. 

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