Stilbene, nickel complexes

The electrochemistry of cobalt-salen complexes in the presence of alkyl halides has been studied thoroughly.252,263-266 The reaction mechanism is similar to that for the nickel complexes, with the intermediate formation of an alkylcobalt(III) complex. Co -salen reacts with 1,8-diiodo-octane to afford an alkyl-bridged bis[Co" (salen)] complex.267 Electrosynthetic applications of the cobalt-salen catalyst are homo- and heterocoupling reactions with mixtures of alkylchlorides and bromides,268 conversion of benzal chloride to stilbene with the intermediate formation of l,2-dichloro-l,2-diphenylethane,269 reductive coupling of bromoalkanes with an activated alkenes,270 or carboxylation of benzylic and allylic chlorides by C02.271,272 Efficient electroreduc-tive dimerization of benzyl bromide to bibenzyl is catalyzed by the dicobalt complex (15).273 The proposed mechanism involves an intermediate bis[alkylcobalt(III)] complex. 

Many transition-metal complexes have been widely studied in their application as catalysts in alkene epoxidation. Nickel is unique in the respect that its simple soluble salts such as Ni(N03)2 6H20 are completely ineffective in the catalytic epoxidation of alkenes, whereas soluble manganese, iron, cobalt, or copper salts in acetonitrile catalyze the epoxidation of stilbene or substituted alkenes with iodosylbenzene as oxidant. However, the Ni(II) complexes of tetraaza macrocycles as well as other chelating ligands dramatically enhance the reactivity of epoxidation of olefins (90, 91). 

The trany-stilbene ligand 0-Ph2PC6H4CH==CHC6H4PPh2-0 reacts with nickel(II) halides to give red air-stable nickel(II) complexes according to Scheme 15.1334... 

Alkyl phenyl telluriums and diaryl telluriums react with Grignard reagents in THF or diethyl ether in the presence of catalytic amounts of nickel- or cobalt-phosphane complexes. Tellurium is precipitated. The organic groups combine to form in most cases all three possible coupling products in ratios determined by reaction conditions . The reaction of ( Z,)-phenylethenyl phenyl tellurium and phenyl magnesium bromide formed almost exclusively ( Zj-stilbene in quantitative yield. ( ZJ-Ethoxycarbonylethenyl phenyl tellurium and phenyl magnesium bromide reacted differently ( Fj-ethoxycarbonyl-(phenyl)-ethene and diphenyl tellurium were produced. Tellurium was not formed. ... 

Reagents. The lithium metal, containing a maximum of 0.05% sodium, was obtained from the Lithium Corporation of America. Bis(l,5-cycloocta-diene)nickel [(Cod)2Ni)] was prepared by a modification of a known procedure (13). This complex was used to prepare tetrakis(triethylphosphine)nickel [(Et3P)4Ni]. Tetraphenylcyclobutadienenickel(II) bromide dimer was synthesized from stilbene-free diphenylacetylene (14). 

In order to assess the efficiency of a light stabilizer in its coupling with a phenolic antioxidant, multifunctional hindered amine light stabilizer or some complexes of tetramethylpiperidine with nickel were synthesized [48]. These products were successfiiUy used for the stabUization of monofilament polypropylene and the usage range was expanded to low density polyethylene. For the PVC stabilization, some stilbene compounds such as 4-chloro-a-cyan-3-methyl-stilben (9) were also efficiently used [49]. 

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