Radicals, Anions, and Metal Derivatives

BuN(0 )OMR3 decay compared, and intramolecular H-transfer of o-(bromophenyl)Mc2Si ethers by radical means used in rapamycin-di synthesis283. 

Cp TiX3 with (Mc3Sn)3N gives (Cp TiXNSnMe3 2 while RNHSnMe3 and 

Sifylcuptates RCuO -Me3SiI cmiv is Y S-unsatuiated acids to allyUc o, unsaturated esters, dimethylphenylsilylcuprate conjugate addition t PhSO to unsatuiated esters and allene 

Q Rh(H)2(SiMe3)2 with BuLi then N-methyl-2-clil(HX yTidinium salts gives the 

6-Bis(dimethylaminomethyl)phenyl-lithium (ULi) reacts with its 1-silyl derivative LSiH3 to give th [4+4]-coordinated silicon derivative L2SiH2, with Si—N 312 pm if trans to Si-H and 289.5 pm if trans to Si-C l . With I2, the 5 coordinate monocation L2SiH+ results while 

2HX gives the 6 coordinate cation L2Si. Bis(8-dimethylaniinonaphthyl)sUane is deprotonated by I2 to give the 5 coordinate cation stabilised by p-t-BuLLi reacts 

The first observation of a primary radical cation t-Bu3SiH - results from the direct radiolysis of the silane, others giving radicals through secondary processes, and calculations support a D3jj structure for the [M2Meg] - radical cations (M=Si - Pb), while silyl radicals add to CgQ and are 

3Sn (R=Me,Ph) bridges 2,3- in B q, and SnCl2 with nido 10-vertex carborane 

Silanes dehydiocouple through Si-Ti intermediates and the structures and vibrational spectra of a range of hydi osilyl-W complexes have been analysed, while Me3SiCo(CO)4 ring opens 

The [( n -naphthalene)2Ti(SnMe3)2l complex shows Ti-Sn 286.9 pra, a little shorter than that in the Ti(-I) derivative [Cy3SnTi(CO)g] (Ti-Sn 292.1 pm) , stannyl-Cr anions give carbene complexes with R2CX2, heterobimetallic complexes with Mo-Sn units show 7- 

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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... 

The name dithiolenes was chosen to describe these compounds without prejudice towards one of the limiting structures. The equally descriptive name dithienes has been coined for the same reason, but it is now rarely used. The less fortunate description of dithiolenes as dithiolato complexes is found occasionally, but it does have a much more restricted meaning (see Section 16.5.2.4) and should be avoided for the neutral species. Nevertheless, Chemical Abstracts refers to dithiolenes as bis[l,2-ethenedithiolato(2—)] complexes of the respective central metal, for example the parent nickel complex (4) is listed as nickel, bis[l,2-ethenedithiolato(2—)-5,S ]- however, depending on the date of the CA issue, its tetraphenyl derivative will be found either under bis[a,a -stilbenedithiolato(2 — )]-nickel or as bis[ 1,2-diphenyl-1,2-ethenedithiolato(2 -)-S,S"]-nick-el. Even less appropriate are the CA names for the radical anions and dianions of the dithiolenes, which are referred to as metallates(—) and metallates(2 —) of the respective ligands the dianion of the parent nickel dithiolene thus is found as bis[l,2-ethenedithiolato(2—)]-nickelate(2—), a name which has little to do with the electronic structure of the compound. 

New kinetic regularities at polymerization of vinyl monomers in homophase and heterophase conditions in the presence of additives of transition metal salts, azonitriles, peroxides, stable nitroxyl radicals and radical anions (and their complexes), aromatic amines and their derivatives, emulsifiers and solvents of various nature were revealed. The mechanisms of the studied processes have been estabhshed in the whole and as elementary stages, their basic kinetic characteristics have been determined. Equations to describe the behavior of the studied chemical systems in polymerization reactions proceeding in various physicochemical conditions have been derived. Scientific principles of regulating polymer synthesis processes have been elaborated, which allows optimization of some industrial technologies and solving most important problems of environment protection. 

The path for the formation of the Grignard reagent is believed to involve transfer of an electron from the sea of electrons present in the metal into the lowest unoccupied molecular orbital (LUMO) of the alkyl (aryl) halide. The radical anion/ surface-metal cation can continue with the transfer of a second electron or, depending on steric and electronic circumstances, an alkyl (aryl radical) and halogen anion can be produced. Coupling and elimination products occasionally accompany reduction and those products can be rationalized as being derived from free radicals. The halide anion remains associated with the surface as it does with most reactions in solvents that cannot support ionic materials. The alkyl radical would be free from that constraint. 

Two classes of charged radicals derived from ketones have been well studied. Ketyls are radical anions formed by one-electron reduction of carbonyl compounds. The formation of the benzophenone radical anion by reduction with sodium metal is an example. This radical anion is deep blue in color and is veiy reactive toward both oxygen and protons. Many detailed studies on the structure and spectral properties of this and related radical anions have been carried out. A common chemical reaction of the ketyl radicals is coupling to form a diamagnetic dianion. This occurs reversibly for simple aromatic ketyls. The dimerization is promoted by protonation of one or both of the ketyls because the electrostatic repulsion is then removed. The coupling process leads to reductive dimerization of carbonyl compounds, a reaction that will be discussed in detail in Section 5.5.3 of Part B. 

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