Carbonyl displacement

In addition to illustrating the mechanics of translation Figure 28 12 is important m that It shows the mechanism of peptide bond formation as a straightforward nude ophilic acyl substitution Both methionine and alanine are attached to their respective tRNAs as esters The ammo group of alanine attacks the methionine carbonyl displac mg methionine from its tRNA and converting the carbonyl group of methionine from an ester to an amide function... 

The activation of a carboxylate group with CDI proceeds to give an intermediate imide with imidazole as the active leaving group. In the presence of a primary amine-containing compound, the nucleophile attacks the electron-deficient carbonyl, displacing the imidazole and forming a... 

This hypothesis is supported by Chauvin s report (33) on a catalyst derived from (CO)5W=C(OEt)C4H9. This highly stable carbene-W(O) compound does not display catalytic activity for cyclopentene monomer. When mixed in the dark with TiCl4, a slow evolution of 1 equivalent of CO occurs. Subsequent thermal or photochemical activation produces ah extremely efficient catalyst system. Chauvin demonstrated that a high conversion to polypentenamer is obtainable at a W/cyclopentene ratio of 10 li at 5°C. The role of TiCI4 is not well understood nevertheless, it promotes carbonyl displacement which appears to be essential. 

Sulfoxide adducts of chromium, molybdenum, and tungsten carbonyls have been studied as catalysts for the polymerization of monomers such as vinyl chloride (248). Simple adducts of the type [M(CO)5(Me2SO)] may be prepared by carbonyl displacement from the corresponding hexacarbonyl. Photochemical reactions are frequently necessary to cause carbonyl displacement in this manner, many carbonyl complexes of higher sulfoxides have been prepared (255, 256). Infrared (257) and mass spectral studies (154) of these complexes have appeared, and infrared data suggest that S-bonding may occur in Cr(0) sulfoxide complexes, although definitive studies have not been reported. 

The disubstituted methyl isocyanide cations [CpM(CO)2(CNMe)2]+, M = Mo, W, have been obtained by methylation of the corresponding dicyanide anions, [CpM(CO)2(CN)2] (46). Direct interaction between phenyl isocyanide and CpMo(CO)3Cl causes total carbonyl displacement (lM). 

There are many substituted 77-cyclopentadienyliron carbonyl cations, which are often prepared from a 7r-cyclopentadienyliron dicarbonyl halide. The halide may be expelled by a variety of ligands to form a cation in preference to carbonyl displacement. Which actually occurs in practice appears to be a function of the reaction parameters, such as reaction temperature, basicity of the ligand, and halide used. The cations of this type are listed in Table III. 

Thin-layer Chromatography. - Fourteen newly-synthesised organophos-phorus compounds have been separated by TLC, and a study made of their Rf values and structures for the aryloxyphenylthiophosphonyl hydrazides. When electron-donor solvents were used as mobile-phase, there were carbonyl displacement effects and the order of Rf values was reversed. In another study (by HPTLC), a correlation between the molecular structures of sixteen O-ethyl, N-isopropyl phosphoro(thioureido)thioates and their observed Rf values has been checked against a computer-assisted Rf prediction system for these... 

A single P-strand mimic was introduced by Hirschmann, Smith, and their coworkers based on the nitrogen-displaced and carbonyl-displaced pyrrolinone scaffolds (Fig. 14), which mimics both the hydrogen-bonding pattern and the side-chain orientation of the p-strand/p-sheet conformation of peptides (204). 

The iron- olefine complexes Fe(olXCO)4 can be prepared by the thermal reaction of the olefin with FeXCG) in benzene at modest temperatures. The reaction does not formally involve carbonyl displacement it is a bridge splitting reaction in which Fc2(CO)9 is cleared into two moieties Fe(CO)5 and Fe(CO)4 ... 

Ruthenium-olefin complexes have been prepared by photochemical carbonyl displacement reactions ... 

A mechanism, recently modified and discussed further in Section II,1C,6, has been proposed to account for the observation of both CO substitution and one-electron oxidation in the reactions between [Cr(CO)2L(f/-C6Me6)] and [NO]+. Rather than depending simply on the relative ° values, the products arise by the decomposition of the intermediate [Cr(NO)(CO)2-L(f/-C6Me6)]+, in which the NO group functions as a one-electron donor carbonyl displacement gives the cationic nitrosyl but loss of NO yields the radical cation (95). 

Some typical examples of carbonyl displacement reactions are quoted below ... 

The metal center in (i9 -C5H5)M(L)(CO)(allyl) can be considered pseudotetrahedral and characterized by the (R) and (5) nomenclature. Neutral chiral complexes of this type have been prepared previously, e.g., phosphine carbonyl derivatives (21, 75) and nitrosyl halide derivatives prepared by carbonyl displacement from nitrosyl cations by iodide (57, 60). Each of the diastereomers produced by the addition of a prochiral allyl moiety to the chiral metal center exhibit endo-exo isomerism. The endo-exo equilibration depends on charge and the neutral nitrosyl iodides rearrange rapidly compared to the cationic nitrosyls. 

Although ra j-Ru(CO)3(PPh3)2 does not react with C2F4, its phosphite (L) analogue does, by simple carbonyl displacement. Either end-on or sideways-on approach of the fluoro-olefin to the ruthenium is possible the former is nucleophilic attack by Ru° on the olefin. 

The ester carbonyl displaces intramolecularly the mesylate, yielding a carbocation that is happed by edianol. 

Addition of cyclic tin or germanium diamides to 45 results in displacement of the carbonyl, with the generation of new clusters 46 in high yield (Equation (8)) excess germanium reagent results in displacement of the phosphine on the platinum. Similar carbonyl displacements are observed with isocyanide ligands the products of these reactions are discussed in Section 8.07.2.7. ... 

Substitution of nickel, palladium, and platinum complexes forms part of a recent review on the kinetics of reactions of these compounds. A review up to 1971 on the chemistry of Co cyanides contains references relevant to Sections 2 [Mixed-ligand Carbonyls displacement of CO], 3, and 4 of this chapter. ... 

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