Groups I, II, and III

One-electron transfer processes are rather common in the reactions of Group I and II organometallic reagents with substrates, including alkyl halides, R —X, and unsaturated organic acceptors, A (113)  

Such processes have been recognized when the donor organometallic, R—M, is a radical anion, a dianion, an alkyllithium reagent, or a Grignard reagent (113, 71, 70, 59, 114). In most cases, the anion radical 

Some interesting electron-transfer reactions of sodium naphthalide have recently been reported. Reaction with phenylmercuric chloride or benzylmercuric chloride gives better than 70% yields of the symmetric diphenyl- or dibenzylmercury compounds. Solutions of alkali metals in HMPA lead to the same results (88). Evidence for the reaction of sodium naphthalide with methylene halides to give methylene anion radical, CH2T, has recently appeared (22). 

Sakurai and co-workers (115, 116) have found that trimethylsilylso-dium is an excellent one-electron transfer reagent in HMPA or other highly polar po I vents  

The trimethylsilyl radical produced either rapidly dimerizes or reacts with solvent so that very clean ESR spectra of the radical anion, with minimum interactions with the counterion, can be obtained (116). Further reduction to dianions is very slow, and exhaustive reduction to anion radicals minimizes problems associated with exchange between anion radicals and unreduced substrate (115). It now appears that the solvent HMPA greatly facilitates the one-electron reduction, not only for trimethylsilylsodium, but also for organolithium and magnesium reagents (110). It was found that 0.1F solutions of methyl-, n-butyl-, or f-butyllithium or benzylmagnesium chloride will quantitatively reduce biphenyl to its radical anion in less than 10 minutes (110). 

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Electronic Effects in Metallocenes and Certain Related Systems, 10, 79 Electronic Structure of Alkali Metal Adducts of Aromatic Hydrocarbons, 2, 115 Fast Exchange Reactions of Group I, II, and III Organometallic Compounds, 8,167 Fluorocarbon Derivatives of Metals, 1, 143 Heterocyclic Organoboranes, 2, 257... 

The induced change is decreased by ions of groups I, II and III. The effect of these ions in decreasing F can be ascribed to an increase in the rate of primary reaction (91) . ... 

An outer shell is most stable when it has eight electrons or none at all. The elements of Groups I, II, and III lost electrons when they combined. But the Group IV elements are already halfway to a full eight electrons. Should they lose or gain ... 

Fig. 1. The mGluR family. Amino acid sequence identities between the eight mGluR sub-types and other family C GPCRs are depicted together with prototypic agonists for and G protein coupling preferences of Group I, II, and III mGluRs.

The reviews cited in Section I, A summarize most of the properties of the radical anions of the Group I, II, and III metals. 

ZIEGLER CATALYST. A type of stereospedfre catalyst, usually a chemical complex derived from a transition metal halide and a metal hydride oi a metal alkyl. The transition metal may be any of those in gioups IV to VIII of the periodic table the hydride or alkyl metals are those of groups I, II. and III. Typical, titanium chloride is added to aluminum alkyl in a hydrocarbon solvent to form a dispersion or precipitate of ilie catalyst complex. These catalysts usually operate at atmospheric pressure and are... 

On the basis of the above considerations, a scheme for metal-complexant interactions in aquatic systems can be drawn (Buffle, 1988, Chapter 2) (Fig. 8.9). In this model, discrimination is made between metal ion groups I, II and III (from hard to soft, Fig. 8.8) and between the following groups of complexants ... 

The development of nuclear magnetic resonance spectroscopy for the measurement of the rates of fast reactions (preexchange lifetimes 1-0.001 second) has made it possible to study many alkyl-metal exchange processes which heretofore were experimentally inaccessible. A substantial number of papers dealing with the exchange reactions of Group I, II, and III... 

C-NMR spectra show that the negative charge in the pentadienylmetal derivatives of groups I, II, and III resides preferentially at the terminal and central positions (21). Electrophiles can therefore attack either at the terminal or at the central position Z and E isomers can result from terminal addition. For the reactions to be useful synthetically, high regiospecificity at one or other site is desirable. 

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