English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

The electron transfer occurring between subvalent metals and organic compounds often plays a pivotal role in the syntheses and the reaction mechanisms of organometallic compounds. This presentation examines the factors that promote such electron transfer, namely the metal's oxida— tion potential, the organic substrate's electron affinity, the auto— association of RN units and the coordination on the metal of ligands or donor solvent. Examples of such electron—transfer processes with main— group and transition metal complexes are offered for: a) the formation of carbon—carbon and carbon—element bonds; b) the cleavage of carbon—hetero— atom bonds; c) the oligomerization of unsaturated hydrocarbons; and d) the action of RNgX and RLi on olefins or acetylenes bearing electronegative substituents. INTRODUCTION The interaction of zerovalent metals with various organic substrates, such as unsaturated hydrocarbons, halides, ethers or even other orgamometallics constitutes a versatile method for the preparation of main—group and transition—metal organometallic compounds (1,2). In a formal sense, such reactions may be viewed as oxidative additions, whereby the metal transfers electron density to the organic substrate and thereby gains in oxidation number (eq. 1): k1 M + R-E R-M-E or R-EM (1) In organometallic synthesis (3) and in the study of reaction mechanisms (4) it is of cardinal importance to understand the factors determining the rate (k1) and the equilibrium constant (K1) of equation 1. This view of metal reactions as electron—transfer processes can be carried over to the reactions of organometallics themselves, in which view both the rate (k2) and the equilibrium constant (K2) are ascribed to the ease of electron transfer from the carbon—metal bond (eq. 2): k2 +  R'—M + R—E R'. M + (R-E) Products (2) The suggestion that organometallic reactions might proceed via such single—electron transfer (SET) is at least 50 years old, for it was invoked by Blicke and Powers to explain the reduction products encountered in the reactions of ketones with Grignard reagents (5). In recent years, Ashby has adduced impressive experimental evidence for the occurrence of just such SET processes with ortho—substituted benzophenones and branched alkylmagnesium halides (6). Furthermore, by application of appropriate chemical trapping or instrumental detection, free— radical transients now have been shown to be intermediates in a large number of organometal— lic processes. This presentation wishes to explore the utility of treating the reactions of both metals and organometallic compounds as electron—transfer processes. Offered for consideration are selected studies carried out in the author's laboratory that involve alkali metals, magnesium, nickel, cobalt and titanium. In defense of drawing this parallel in behavior between metals and organometallics, the author refers with approval to the fruitful suggestion of Rundle that metallic character arises from metals having insufficient valence electrons to fill the available, low—energy bonding orbitals. The resulting "electron—deficient" systems would therefore display greater delocalization. Rundle recognized that metals represented only an extreme stage in such delocalization and that alloys (M—M'), interstitial compounds (M—E),

Mechanistic and synthetic aspects of organometallic oxidative additions