Transient complexes decomposition

B. Acid Dissociation Constants for Transient a-Hydroxyalkyl Complexes Mechanisms of Decomposition of the Transient Complexes LmM +1-R... 

Bimolecular Decomposition of the Transient Complexes Methyl Transfer Reactions Rearrangement of the Carbon-Skeleton of R (H20)sCrCH02+ as a Hydride Transfer Reducing Agent Alkene Complexes... 

The mechanisms and kinetics of decomposition of the transient complexes LmM + 1-R in aqueous solutions depend on the nature of the central cation, of the ligands, L, of the substituents on the aliphatic residue, R, on the pH and on the presence and nature of various substrates, S, in the medium, e.g., 02. In the following section the major mechanisms observed are discussed. 

In many systems studied the results point out that Eq. (9) is an equilibrium process and that the mechanism of decomposition of the transient complex LmMn + 1-R involves radical processes. 

The homolytic decomposition in the absence of scavengers for the radical R is often followed by the reaction of the radical "R with the transient complex with the metal-carbon bond ... 

This reaction leads in many systems to unexpected products. The detailed mechanism of this reaction was studied only in few systems (27,28). Systems which follow this pathway (Eq. (9) followed by (27)), show an inverse dependence on [M"L, ] of their second order rate constant of decomposition of the transient complex with the metal-carbon bond. This is contrary to an inverse dependence on [M Lm]2, which is observed when reaction (9) is followed by reaction (26) (radical radical reaction). 

The (3-elimination mechanism of decomposition of transient complexes of the type LmMre+1 R occurs when a good leaving group, X, e.g., X= OR, NR2, NHC(0)R, and halides, is bound to the (3-carbon ... 

Comparing rates of decomposition for transient complexes containing different metal centers (Table V) it was observed that the specific rates of (3-hydroxyl elimination for Cu" CR T CR R4 complexes are considerably higher than those observed for (H20)sCrinR, (tspc)CoinR and PPFeinR (136). 

A detailed study of the CO insertion, or methyl migration, observing formation and decomposition of the transients, was performed so far only for one Cu(I) model system (93). It was reported that methyl radicals form transient complexes containing metal carbon -bonds with carbonmonoxide (n = 1, 3, 4) complexes of Cu(I). These complexes decompose yielding Cu(II) and acetaldehyde as final products via an copper acetyl intermediate formed by insertion of /migration of CH3 as described in Scheme 4. 

The final products of this reaction were still not determined. These results thus suggest that the detailed mechanism of reduction of ethylene and maleate by Ni1 / + yields as transients complexes with Ni-carbon bonds. The mechanism of decomposition of the latter depends on the nature of substituents on the alkyl radical. 

The P-elimination mechanism of decomposition of transient complexes of the type occurs when a good leaving group, X,... 

Between processes of adsorption and chemisorption there is a close relationship, since in the process of evolution of adsorbed species one can observe formation of transient complexes that are products of reactions proceeding by the Langmuir-Hinshelwood mechanism. According to the accepted classification of reactions in a surface layer of SiOi they are subdivided into two main classes, namely reactions with substitution of structural hydroxyl protons (SeI processes) and reactions with substitution of OH groups at silicon atoms (SnI processes). Reactions of heterolytic decomposition of siloxane bonds proceeding by the AdN3 mechanism form a separate class. 

Several stable Group 6 metal-ketene complexes are known [14], and photo-driven insertion of CO into a tungsten-carbyne-carbon triple bond has been demonstrated [15]. In addition, thermal decomposition of the nonheteroatom-stabilized carbene complexes (CO)5M=CPh2 (M=Cr, W) produces diphenylke-tene [16]. Thus, the intermediacy of transient metal-ketene complexes in the photodriven reactions of Group 6 Fischer carbenes seems at least possible. 

Since the benzene emission in the thermal decomposition of benzoyl peroxide results from radical transfer by the phenyl component of a benzoyloxy-phenyl radical pair, phenyl benzoate produced by radical combination within the same pair should appear in absorption. A weak transient absorption has been tentatively ascribed to the ester (Lehnig and Fischer, 1970) but the complexity of the spectrum and short relaxation time (Fischer, personal communication) makes unambiguous assignment difficult. Using 4-chlorobenzoyl peroxide in hexachloro-acetone as solvent, however, the simpler spectrum of 4-chlorophenyl 4-chlorobenzoate is clearly seen as enhanced absorption, together with... 

The role of the rhodium is probably two-fold. Initially due to its Lewis acidity it reversibly forms a complex with the nitrile nitriles are known to complex to the free axial coordination sites in rhodium(II) carboxylates as evidenced by the change of colour upon addition of a nitrile to a solution of rhodium(II) acetate, and by X-ray crystallography. Secondly the metal catalyses the decomposition of the diazocarbonyl compound to give a transient metallocarbene which reacts with the nitrile to give a nitrile ylide intermediate. Whether the nitrile ylide is metal bound or not is unclear. 

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