Metal-induced transformations

Chander Mohan was born in 1975 at Dhariwal, Punjab, India. He received his B.Pharm. and M.Tech.(Pharm.) in bulk drugs from Guru Nanak Dev University and the National Institute of Pharmaceutical Education and Research (NIPER), Mohali. After that he worked as senior chemist at Dr. Reddy s Research Foundation, Hyderabad. He then joined Professor M. P. Mahajan s research group in 2002 for his doctoral studies. His research is focused on the synthesis and chemical transformation of C-5/C-6-substituted pyrimidinones. His research interests include synthesis of medicinally important molecules, transition metal-induced transformations in organic synthesis, reaction mechanism and total synthesis of natural products. 

Influence of Benzopyrene Pretreatment on Metal Induced Transformation. The induction of cancer by metal carcinogens is thought to be independent of microsomal enzyme activation. These conclusions are not based upon experimental evidence as such, but on an idea that has developed from at least two observations 1) carcinogenic metals and their com-... 

During the first third of the nineteenth centuiy, several systematic obseiwations led researchers to conclude that the mere presence of metals induced chemical transformations in fluids that would otherwise not have occurred. Early on, Thenard had... 

To date, only one example of a combination of a photochemically induced transformation with a transition metal-catalyzed reaction has been found in the literature. This hv/Pd°-promoted process allows the synthesis of five-membered cyclic y-keto esters 5-119 from 5-iodoalkenes 5-117 in the presence of CO and an alcohol 5-118 as a nucleophile (Scheme 5.24) [41]. The yields are high, and differently substituted iodoalkenes can be employed. 

Substitution of cyclopropane rings with the alkenyl group permits unique ring transformations based on metal coordination interaction with four -electrons. The transition-metal-induced ring-opening rearrangement also results in the formation of metallacycles. Further elaboration is attained by insertion and reductive elimination. 

In view of the extensive and fruitful results described above, redox reactions of small ring compounds provide a variety of versatile synthetic methods. In particular, transition metal-induced redox reactions play an important role in this area. Transition metal intermediates such as metallacycles, carbene complexes, 71-allyl complexes, transition metal enolates are involved, allowing further transformations, for example, insertion of olefins and carbon monoxide. Two-electron- and one-electron-mediated transformations are complementary to each other although the latter radical reactions have been less thoroughly investigated. 

Anaerobic conditions are traditionally a major concern when dealing with microbial-induced transformations of wastewater in a collection system. The problem is primarily associated with the risk of hydrogen sulfide and odorous organic compounds. The corresponding problems appear as concrete and metal corrosion, health-related impacts and malodors. Such in-sewer process-related problems have been reported as early as over 50 years ago (Parker, 1945a, 1945b Pomeroy and Bowlus, 1946). 

Haushalter RC, O Connor CM, Haushalter JP et al (1984) Synthesis of new amorphous metallic spin-glasses Ct2SnTe4, Mu2SnTe4, Ee2SnTe4, Co2SnTe4 - solvent induced metal-insulator transformations. Angew Chem hit Ed 23(2) 169-170... 

The formation of the latent image should be considered as a photo-induced transformation of the dielectric molecular silver phase into the metallic one." (230). During chemical sensitization the silver halide grains pass into a nonequilibrium... 

Other current investigations concerning cycloadditions of nitrosoalkenes are directed towards employment of more complex dienophiles, e. g. NjM-bis-tri-methylsilyl enamines [380, 381] or 2,5-dihydrooxepines [382]. Furthermore, interest focuses on exploring the scope of subsequent reactions of the cycloadducts, such as stereoselective halogenation [383], ds-dihydroxylation [384] and numerous reductive [385] as well as acid or transition metal induced [386] transformations of 5,6-dihydro-4H-l,2-oxazines. 

To date, only one example of a combination of a photochemically induced transformation with a transition metal-catalyzed reaction has been found in the literature. 

When the simple oxide involves a transition metal, other transformations than structure changes are possible at high pressures, in particular, changes in spin state. As early as 1960, Fyfe suggested that a pressure-induced high-spin->low-spin transition in Fe might have important consequences for the interior of the Earth, and this theme was later devel-... 

Metal alkylidyne complexes undergo a variety of oxidation and reduction reactions as well as redox-induced transformations of the alkylidyne ligands. A method for the direct transformation of Fischer-type carbyne complexes into Schrock-type alkylidyne complexes was developed in our laboratory. Bromine oxidation of the /ra/7, -carbyne bromo tetracarbonyl complexes 49 of molybdenum and tungsten in the presence of dimethox-yethane affords the dme-stabilized alkylidyne tribromo metal complexes 50 [Eq. (42)] (81). For alkyl-substituted complexes (R = Me, CH2CMe3)... 

The assay system described in the present study should be useful in screening potential metal carcinogens for their ability to induce transformation. However, further work is required to demonstrate and validate that each of the various metals induce neoplastic transformation in tissue culture. A statistically significant number of transformed colonies induced by exposure of cells to each of the metal compounds must be cloned and derived into cell lines. The tumorigenic potency of these various cell lines must be tested in nude mice. 

Jcfrgensen (20) has analyzed a number of spectra of hexacoordinated transition metal ions in relation to pressure. In K20sBrg the peaks at 22.200 cm and at 16.750 cm are shifted distinctly to lower energy with increasing pressure at the same time the spUtting increases drastically. Spectroscopic changes occur as a result of the pressure induced transformation of tetrahedral cobalt(U)-complexes in solution into octahedral arrangements (21, 22), and indeed are used as evidence for this transformation. 

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