Hydrides carbon—hydrogen bonds

Hydroboration is a reaction m which a boron hydride a compound of the type R2BH adds to a carbon-carbon bond A carbon-hydrogen bond and a carbon-boron bond result... 

The cleavage of a carbon-hydrogen bond (hydride abstraction) has been reported for 7-alkylaminocydoheptatrienes to yield tropenyliden-iminium salts (10a,10b). This unique class of compounds had been prepared... 

There are also reactions in which hydride is transferred from carbon. The carbon-hydrogen bond has little intrinsic tendency to act as a hydride donor, so especially favorable circumstances are required to promote this reactivity. Frequently these reactions proceed through a cyclic TS in which a new C—H bond is formed simultaneously with the C-H cleavage. Hydride transfer is facilitated by high electron density at the carbon atom. Aluminum alkoxides catalyze transfer of hydride from an alcohol to a ketone. This is generally an equilibrium process and the reaction can be driven to completion if the ketone is removed from the system, by, e.g., distillation, in a process known as the Meerwein-Pondorff-Verley reduction,189 The reverse reaction in which the ketone is used in excess is called the Oppenauer oxidation. 

Organometals and metal hydrides as electron donors in addition reactions 245 Oxidative cleavage of carbon-carbon and carbon-hydrogen bonds 253 Electron-transfer activation in cycloaddition reactions 264 Osmylation of arene donors 270... 

The existence of surface hydride groups of the types known in classic organic chemistry is very probable in most carbons. Direct chemical evidence is very difficult to obtain due to the relative inertness of the carbon-hydrogen bond. However, the fact that hydrogen is strongly chemisorbed on carbons and released at high temperatures only in the form of hydrocarbons is sufficient proof of the existence of true carbon-hydrogen bonds. 

Much effort has been devoted to activate hydrocarbons, particularly saturated compounds, through the formation of organometallic compounds and transformation of the latter to substituted derivatives. A number of transition-metal complexes have been found to insert into carbon-hydrogen bonds leading to stable alkyl metal hydrides ... 

Deuterium isotope effect in the hydride ion transfer from carbon-hydrogen bonds to CS ... 

Fig. 12.4 Two distinct C3v C60H18 hydrides are represented with Schlegel diagrams black circles refer to the six Carbon-Hydrogen common bonds molecules are distinguished by the position of the remaining 12 Carbon-Hydrogen bonds the first one places the Hydrogen atoms along the shaded inner crown (a), whereas the in second isomer Hydrogen atoms follow the outer crown ((3)...

Fig. 12.7 C60H36(D3d)(CK) hydride Schlegel diagram black circles refer to the 36 Carbon-Hydrogen bonds graph has two benzenoid rings it contains C3V C6QH18(a) hydrogen atoms sub-set (see Fig. 12.4)...

Fig. 12.11 C60H36(C3 ) hydride Schlegel diagram black circles refer to the Carbon-Hydrogen bonds including sites labeled 16 and 23 graph has three benzenoid rings. By moving carbon-hydrogen bond from site V16 to V17 and from V23 to one obtains C3 graph...

The last step in Equation 8.131 is a reasonable approximation that associates isotope effects with the breaking/making of the carbon-hydrogen bonds and not with alkane dissociation, that is, k /k° 1. The observed isotope effect is then seen as arising from the equilibrium relating the alkyl hydride and O-alkane complexes in Scheme 8.14. 

Arene ruthenium and osmium complexes play an increasingly important role in organometallic chemistry. They appear to be good starting materials for access to reactive arene metal hydrides or 16-electron metal(O) intermediates that have been used recently for carbon-hydrogen bond activation. Various methods of access to cyclopentadienyl, borane, and carborane arene ruthenium and osmium complexes have been reported. 

AUhough the main alkylation reactions are thought to occur at or close to the Interface between the acid and hydrocarbon phases (7,15,16), the acid boundary layer at the interface seems more probable. This conclusion is based on the fact that other isoparaffins (including LE s, TMP s, OMH s, and HE s) appear to be much less reactive relative to hydride transfer steps as compared to Isobutane yet many of these Isoparaffins contain one or more tertiary carbon-hydrogen bonds. These heavy isoparaffins are, however, even less soluble in the-acid phase than isobutane. 

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