Bond cleavage reaction

Furthermore, Cordes etal995 observed the saturation-type kinetics, strongly suggesting the formation of a complex between the polyelectrolyte and ester preceding bond cleavage reactions, as has been found for micellar catalysis11,1015. 

Saeva, F. D. Photoinduced Electron Transfer (PET) Bond Cleavage Reactions. 156, 59-92... 

FIGURE 2.3. The energetics of a heterolytic bond cleavage reaction in a polar solvent. The specific example shown corresponds to the CH3OCH3— CH3 + CH30 reaction in water. The energy of the covalent state does not include the effect of the solvent on this state, but a more consistent treatment (e.g., eq. (2.21) should account for the polarization of the solvent toward the charges of the ionic state. This would result in destabilization of H31. 

Kaneko C., Katagiri N., Nomura M., Sato H. A New Method for the Stereoselective Synthesis of Nucleosides by Means of Sodium Borohydride Mediated Reductive C-C or C-N Bond Cleavage Reaction Isr. J. Chem. 1991 31 247-259 Keywords carbohydrates... 

Fig. 11. Proposed reaction mechanism for the SbaR bond cleavage reaction...

Takahashi T, Kanno K (2005) Carbon-Carbon Bond Cleavage Reaction Using Metallocenes. 8 217-236... 

Whereas now the bond cleavage reaction is nonsurface dependent, the reverse reaction clearly is. The stronger the NH2 and NH fragments bind, the higher the barrier for the recombination reaction. In the case of methane activation we found the reverse situation. Both situations are consistent with microscopic reversibihty. 

Figure 1.22 Structures of high-barrier and low-barrier transition states of surface bond cleavage reactions.

Scheme 65 The calculated mechanism of H-H bond cleavage reaction of the model complex for [Fe] -hydrogenases...

Shyadehi AZ, DC Lamb, SL Kelly, DE Kelly, W-H Schunck, JN Wright, D Corina, M Akhtar (1996) The mechanism of the acyl-carbon bond cleavage reaction catalyzed by recombinant sterol 14a-demethyl-ase of Candida albicans (other names are lanosterol 14a-demethylase, P-450]4p, and CYP51). J Biol Chem 271 12445-12450. 

It should be noted that the Grob fragmentation reaction and the reductive cyclization (homoallylation) discussed in this section involve the same oxanickellacyclopentane 66 as a common intermediate (Scheme 17). The reversibility of these C - C bond cleavage reaction and C - C bond formation reaction is also supported by the isolation and characterization (by X-ray analysis) of an oxanickellacyclopentane-like 66 (without a tether), which is prepared from a stoichiometric amount of Ni(cod)2, a diene, an aldehyde, and a monodentate phosphine ligand [41]. 

The Hofmann degradation is the most well-known C—N bond cleavage reaction, and its value to structural elucidation of alkaloids has been demonstrated (76). Hofmann degradation of tetrahydroberberine methohy-droxide (1) led to two products base A (2), the C-14—N bond cleavage product, and base B (3), the C-6—N bond cleavage product (Scheme 2) (17,18). The former was the major product when 1 was heated under reduced pressure, but the latter, the thermodynamically controlled product, predominated when the reaction was carried out at atmospheric pressure or in an alkaline medium because base A recyclized back to the starting quaternary base through the transannular reaction. In fact, 2 was heated in aqueous alcohol to afford 1. The mechanism of this recyclization reaction was discussed by Kirby et al. (19). 

Prior et al. (44) found that 13-methylprotoberberine (44) gave the C-14—N bond cleavage product 45, and Hanaoka et al. (45) also detected the C-14—N bond cleavage product 47 as a minor product along with 40b and 46 in the reaction of tetrahydroberberine (26) (Scheme 10). Finally, the C-8—N bond cleavage reaction was applied to synthesis of benzocycloheptaquinoline 23 (46) and 6 -methyl-l-benzylisoquinoline 50 via 49 (Scheme 11) (47). The bond cleavage was found to proceed smoothly in ethanol-free chloroform under reflux (46). 

Although C—O bond cleavage is of little importance for transformations of protoberberines to other types of alkaloids, the selective C—O bond cleavage reaction provides access to naturally unabundant or nonnatural protoberberines from naturally abundant protoberberines such as berberine. 

Basically, the cleavage of the C-O bond takes place through two mechanisms. The first mechanism (the hydrogenolytic cleavage) is a hydrogen-assisted bond-cleavage reaction, whereas the second mechanism is an ionic insertion of the metal into the C-O bond. The characteristic features of the two mechanisms are summarized in Table 4.1. 

The complete elimination of functional groups is often an undesirable side reaction in organic synthesis, but on the other hand it is a possibility for the recycling of environmentally harmful compounds, for example phenols and haloarenes such as polychlorinated dibenzodioxins (PCDDs or dioxins ). For example, aryl chlorides can be effectively dechlorinated with Pd(0) NPs in tetra-butylammonium salts with almost quantitative conversions also after 19 runs (entry H, Table 1.4) [96]. On the other hand, a C-0 bond cleavage reaction also seems suitable for the fragmentation of sugar-based biomass such as cellulose or cello-biose in that way, sugar monomers and bioalcohol can be derived from renewable resources (entry F, Table 1.4) [164]. 

The cause for the high P-P bond reactivity in metathesis and addition reactions of P-phosphino-NHPs was further rationalized when it was established that attack of electrophiles at the PR -substituent facilitates bond cleavage reactions by further boosting the polarization and weakening of the P-P bond and may thus be considered to induce an autocatalytic activating effect [77],... 

The ladder polysilanes can be used as useful probes for obtaining information on the stereochemistry of Si-Si bond cleavage reactions.60 Watanabe and co-workers64 and West and co-workers65 reported that the strained Si-Si bonds of cyclotetrasilanes such as [(z-Pr)2Si]4 and (Et2Si)4 are cleaved by hydrogen chloride, hydrochloric acid, and hydrobromic acid. However, to the best of our knowledge, no report has dealt with the... 

We admit some cowardice. Most of our earlier estimates of entropy invoked symmetry numbers and/or were studies of bond cleavage reactions dominated by translational effects. We hesitate to compare isomers with the same carbon or heavy atom skeleton when effects of a few kJ mol-1 are crucial. 

For the oxidative addition pathway, however, it is not obvious why the C-H bond cleavage reaction should be more facile if the hydrocarbon first binds in the coordination sphere of the metal (Scheme 5, c). One argument could be that the equilibrium between the Pt(II) alkane complex and the five-coordinate Pt(IV) alkyl hydride has an intrinsically low activation barrier. Insight into this question together with detailed information about the mechanisms of these Pt(II) a-complex/Pt(IV) alkyl hydride interconversions has been gained via detailed studies of reductive elimination reactions from Pt(IV), as discussed below. 

Eq. 2.70. Zirconacyclopentadienes which undergo the p,p-C-C bond-cleavage reaction. 

Elimination of an alkoxy group or of a halogen in the case of zirconacyclopentenes has been investigated in combination with the (3, (3-carbon—carbon bond-cleavage reaction. As shown in Eq. 2.73, an OR group or a halogen at a (3-position is eliminated and trapped by the zirconium metal center [53],... 

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