Radicals and Metal Derivatives

Photolysing silanes in chlorinated solvents gives silyl radicals. 

While NO2 cleaves the iodomethyl group from R2SnCH2l (R Me,Et,Ph), CN gives R2SnCH2 and R Sn and provides a simple route to (R,SnCH,),Hg. Calculations indicate that radical cations Me,SnR  

RCu and Me,SiCl accelerate and improve 1,4-addition reactions with 187 

Thermal alkynes can be disilylated with Me SiLi or PhMe2SiLi and MnCl2/MeMgI give alkenes as an isomeric mixture, whereas with RjSnLi (R=Me,Bu) under the same conditions only the ( )-isomer was formed. With Bu SnM (M=MgMe,AlBt2,Zn) terminal alkynes, enol 

R 2=9-fiuorenyl or 9-xanthenyl M = Si, Ge, Sn) can be generated from the C—H or C—halogen compound or a ketone, and R3M. All are in equilibrium with their dimers, which possess the quinonoid structure and give diaryl methanes in acid [equation (10)].  

germyl, and stannyl radicals will add to p-diones, the unsymmetrical ones (18) and (19) giving a mixture of adducts. In the case of (19) attack occurs predominantly at the carbonyl group removed from the methyl group. The stannyl radical (PhMe2CCH2)3Sn shows hindered rotation about the Sn—C bond, and like other tin radicals, has a non-planar structure. The radical anions formed 

A recipe for the synthesis of radical ions isoelectronic with that of l,4-bis(tri-methylsilyl)benzene is reported for the elements B, C, N and Al, Si, P. All the ions, both cations and anions, persist at room temperature and e.s.r. parameters reflect the structural differences. The two pyrazine derivatives have larger ring-proton and smaller methyl-proton coupling constants, and higher g factors than the three benzene derivatives.  

The properties of HMPT, DME, and TMED complexes of RgSiLi (R= Me and Et) were investigated, and Et3MK-18-crown-6 (M=Si, Ge) prepared in solution. Silyl-sodium and -potassium compounds result from cleavage of Si—H and Si—Si bonds using NaH or KH in DME, in sharp contrast to the reactions of McgSiLi derivatives with arenes just mentioned.  

Germyl- and stannyl-sodium and -potassium derivatives can be prepared by the same method. They readily couple with organic halides and with a-enones, though the reaction with tertiary halides is less satisfactory than that with primary and secondary ones. MegSnLi couples with substituted 2-cyclohexenyl 

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Over the past 10 years, our understanding of enzymes which effect the difficult chemical process of C6H bond cleavage has increased dramatically (Stubbe, 1989 Klinman, 1996). We know that nature employs both metal ions and reactive organic cofactors, such as radicals and quinones, derived by post-translational modification of aminoacids in the polypeptide chain of the enzyme. The two enzymes to be described in the present review are good examples galactose oxidase employs copper and a tyrosine covalently cross-linked to a cysteine to stabilize a radical whilst amine oxidases employ copper and tyrosine-derived quinones. There is subtle interplay between the roles played by copper in the biogenesis of these novel cofactors and in the catalytic cycle of the oxidases. 

Acetyl-acetic acid—CH,—CO—CH,—COOH is produced as the ethylic ether of a sodium derivative by the action of metallic Na upon ethyl acetate. The acid itself may be obtained as a very unstable, acid liquid, soluble in water in all proportions. It is the type of a great number of similarly constituted acids, containing other radicals and their derivatives, and is extensively used in the preparation of synthetic products of great variety, as, for instance, in the manufacture of antipyrin (q. v.). 

Chemical Properties. Higher a-olefins are exceedingly reactive because their double bond provides the reactive site for catalytic activation as well as numerous radical and ionic reactions. These olefins also participate in additional reactions, such as oxidations, hydrogenation, double-bond isomerization, complex formation with transition-metal derivatives, polymerization, and copolymerization with other olefins in the presence of Ziegler-Natta, metallocene, and cationic catalysts. All olefins readily form peroxides by exposure to air. 

Pyridine has been phenylated with the following free-radical sources benzenediazonium chloride with aluminum trichloride the Gomberg reaction " phenylhydrazine and metal oxides A -nitroso-acetanilide dibenzoyl peroxide phenylazotriphenylmethane di-phenyliodonium hydroxide and electrolysis of benzoic acid. ° Although 2-phenylpyridine usually accounts for over 50% of the total phenylated product, each of the three phenyl derivatives can be obtained from the reaction by fractional recrystallization of the... 

Dihydro-l,3-diborolenes are accessible as pentaorgano derivatives " and serve as ideal precursors of the diborolyl radieal. The formation of the radical and its interaction with a metal center is formally described as a metal oxidation. The resulting 2,3-dihydro-1,3-diborolyI ligand is either a three-electron donor or an anionic four-electron donor. l,3,4,5-Tetraethyl-2-methyl-2,3-dihydro-l,3-diborole reacts with [T -CpNi(CO)2] or (T7 -Cp>2Ni in hot mesitylene to yield a sandwich complex and a triple-decked complex ... 

Other selected examples include tris(tetramethylethylene diamine-sodium)-9,9-dianthryl 143,154 alkali metal salts of 9,10-bis(diisopropylsilyl)anthracene 144,155 as well as the closely related naked 9,10-bis(trimethylsilyl)anthra-cene radical anion 145.156 This chemistry is further extended to the solvent-shared and solvent-separated alkali metal salts of perylene radical anions and dianions 146, 147,156 while other examples focus on alkali metal salts of 1,2-diphenylbenzene and tetraphenylethylene derivatives, where reduction with potassium in diglyme afforded contact molecules with extensive 7r-bonding, [l,2-Ph2C6H4K(diglyme)] 148.157 Extensive 7r-coordination is also observed in (1,1,4,4 tetraphenylbutadiene-2,3-diyl)tetracesiumbis(diglyme)bis(methoxyethanolate) 149.158... 

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