Photochemical reactions nickel complexes

The reaction between aryl halides and cuprous cyanide is called the Rosenmund-von Braun reactionP Reactivity is in the order I > Br > Cl > F, indicating that the SnAt mechanism does not apply.Other cyanides (e.g., KCN and NaCN), do not react with aryl halides, even activated ones. However, alkali cyanides do convert aryl halides to nitrilesin dipolar aprotic solvents in the presence of Pd(II) salts or copper or nickel complexes. A nickel complex also catalyzes the reaction between aryl triflates and KCN to give aryl nitriles. Aromatic ethers ArOR have been photochemically converted to ArCN. 

It has been found that certain 2 + 2 cycloadditions that do not occur thermally can be made to take place without photochemical initiation by the use of certain catalysts, usually transition metal compounds. Among the catalysts used are Lewis acids and phosphine-nickel complexes.Certain of the reverse cyclobutane ring openings can also be catalytically induced (18-38). The role of the catalyst is not certain and may be different in each case. One possibility is that the presence of the catalyst causes a forbidden reaction to become allowed, through coordination of the catalyst to the n or s bonds of the substrate. In such a case, the... 

Disilanaphthalenes can be prepared by the thermolysis of a disilacyclopropane in deuteriated benzene the reaction may be monitored by NMR spectroscopy <83JA7776>. A mechanism of formation is proposed which involves Si—Si bond rupture followed by C—Si bond formation via a silyl radical. Thermolysis of 2-(mesityl)-2-(phenylethynyl)hexamethyltrisilane also results in two isomeric 1,3-disilanaphthalenes <860M1518> but better yields are achieved if the reaction (either thermally or photochemically) is catalyzed by a nickel complex <86JA7417, 890M2050>. Nickel-... 

Works of Other Researchers. Before 1930 studies on coordination chemistry in Japan were almost exclusively concentrated in Yuji Shibata s laboratory, and only a few reports from other laboratories were published. For instance, Satoyasu limori (1885-1982), who later became the founder of radiochemistry in Japan, studied the replacement of CN- groups in the hexacyanoferrate(III) ion with water in 1915 (38) and photochemical reactions of cyano complexes of platinum and nickel and photochemical cells in 1918 (39). 

In recent years Ishikawa and coworkers have described some very complex photochemical rearrangements of compounds derived from nickel-catalyzed reactions of silacyclopropenes with silylalkynes. As depicted in equation 93, it was shown that the disilacyclohexadiene A could be photochemically converted to the same products as were formed from the silacyclobutene B. In the absence of a trapping reagent the silaindene C was formed as a major product, via the proposed intermediates shown141. In the presence of methanol, two adducts were isolated whose structures can be understood in terms of the reaction of methanol with one of the proposed intermediates. While the structures of the products are confirmed by the X-ray crystal structure data, the mechanisms of the reactions observed must be considered speculative at this time. 

Tervalent copper and nickel are involved in the autoxidation reactions of [Cu(H 3G4)] and [Ni(H 3G4)] respectively. In the case of nickel, decomposition of [Ni(H 3G4)] proceeds by decarboxylation of the terminal carboxy-group adjacent to the peptide nitrogen. - With copper, decomposition of [Cu-(H sG4)] proceeds through a carbon-centred free radical produced by abstraction of a hydrogen atom from the peptide backbone. Bulky carbon substituents assist the stabilization of the higher-oxidation state ions, and a study of the stabilities of leucyl tripeptide complexes with copper(ii) and nickel(u) has been reported. Copper(iii) and nickel(iii) tripeptide complexes of a-aminoisobutyric acid are thermally stable but are readily decomposed by photochemical pathways. Resonance Raman and other studies with copper(iii) peptide complexes have also been reported. ... 

Nickel dimethyl complexes NiMe2(PRs)2 decompose readily in solution, either thermally or photochemically, providing an efficient method for the generation of Ni(0) complexes. The complex NiMe2(dtbpe) undergoes reductive elimination in benzene at 50-60 °C, giving rise to a binuclear Ni(0) 7r-arene complex. Careful thermolysis in THF-/ 8 over several days at 20 °G affords a 1 2 1 mixture of the ethylene complex 159, the hydride 160, and ethane (Scheme 47). If the reaction is carried out in the presence of ethylene, equimolecular amounts of 159 and ethane are formed. These results can be explained by assuming that the decomposition process involves the formation of a complex. In contrast with this behavior, the bis(carbene) dimethyl complex 45 decomposes... 

The d phosphine and phosphite complexes of zerovalent nickel, palladium and platinum possess long-lived emissive excited states in both fluid solution and in the solid state.The lifetimes of the Ni and Pd complexes are in the 1.39-5.38 ps range, with the platinum complex Pt(PPh3)4 having the shorter excited state lifetime of 0.07 //s because of spin-orbit coupling. These long lifetimes allow for bimolecular reactions to occur, and under photochemical conditions chlorobenzene will add to the complex Pd(PPh3)3 (Ref. 75) ... 

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