Electron pair donation Subject

Many complexes containing alkyne ligands are known. Most commonly, these ligands act as two-electron donors, with a n orbital donating an electron pair in a manner analogous to a sidebound alkene. Bridging alkynes may be considered to donate an electron pair to each of two metals (one pair from each of the alkyne s two occupied n orbitals), acting as a two-electron donor to each. Alkyne complexes have been the subject of immense interest in the study of alkyne meth-athesis reactions, to be discussed in Chapter 11.26... 

The participation of the germanium dimers in nucleophilic/electrophilic or Lewis acid/base reactions has been the subject of several investigations on the Ge(100)-2x1 surface [16,49,255,288,294,313-318]. As for the case of silicon, adsorption of amines has provided an excellent system for probing such reactions. Amines contain nitrogen lone pair electrons that can interact with the electrophilic down atom of a tilted Ge dimer to form a dative bond via a Lewis acid/base interaction (illustrated for trimethylamine at the Si(100)-2 x 1 surface in Ligure 5.17). In the dative bond, the lone pair electrons on nitrogen donate charge to the Ge down atom [49]. 

IG basis for methanol, fluoromethanol, and methanediol. In methanol itself, the t-type lone-pair electrons are subjected to back-donation into antibonding-type orbitals of suitable symmetry on the methyl group. This leads to a decrease of the n-orbital population from the value of 2.00, appropriate to water, 1.97. A comparable electron displacement occurs in fluoromethanol when the C-F bond is in the nodal plane of the oxygen lone-pair orbital. If, however, the C-F bond and lone-pair orbital are in the same plane (in the og orientation), the back-donation lowers the population to... 

In contrast to this behavior, [5]radialenes 33b and 33e exhibit notable redox processes, that is, a four-electron transfer occurring simultaneously. Detailed digital simulation analysis assuming Nernstian response in 33e led to the conclusion that the apparent one-step four-electron redox wave involved two redox couples of 33e/33e and 33 33e estimated at —0.074 and —0.066 V (vs Fc/Fc ), respectively. In fact, the CV of 33a having two electron-donating methyl groups clearly exhibits two pairs of two-electron-reversible redox waves. These results suggest that [5]radialenes are subject to a two-step two-electron transfer and sequentially converted into the dication 33 and subsequently into the tetracation 33. ... 

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