Methoxy ligands

Furthermore, the importance of the chelating methoxy ligand in the pyrrolidine side chain was dramatically demonstrated in the alkylation of acyclic hydrazones, c.g., that derived from 3-pentanone8. 

The glycolaldehyde shown in (51) results from a CO insertion reaction followed by reductive elimination, and is presumed to be a precursor of ethylene glycol. Since ethylene glycol is, however, at most a trace product of this catalytic system, step (51) appears to be essentially inoperative. Methyl formate, a major primary product of this system under some conditions, is also presumed to be formed by a CO insertion process, (53). Methanol may be formed by a reductive elimination (hydrogenolysis) of either a hydroxymethyl ligand, (52), or of a methoxy ligand, (54). 

Nb acetyl ligand, 1, 298 Nb methoxy ligand, 1, 300 n-coordinated ligands, 1, 297 Re formyl ligands, 1, 300 M-H bonds... 

Reduction of CO to a methoxy ligand is one of the cleanest examples of metal complex promoted reduction of CO by H2. Equation (c) occurs nearly quantitatively. The starting dicarbonyl forms readily from the dinitrogen complex CP 2ZrN2)2N2 . 

Several derivatives of HUB of type PhI(OR)OTs have been reported. In particular, [methoxy(tosyloxy)iodo]benzene, PhI(OMe)OTs, can be prepared by the treatment of HllB with trimethyl orthoformate [215]. The methoxy ligand in [methoxy(tosyloxy)iodo]benzene (73) can be further substituted with a chiral menthyloxy group by treatment with menthol to give product 74 (Scheme 2.30) [216]. 

Recent studies have illustrated that both borane and silane reductants may be avoided entirely by the use of methanol as the stoichiometric reductant (Scheme 3-50). Deuterium labeling studies illustrated that the hydroxyl proton and a single methyl-derived proton from methanol are transferred to Ae observed reductive coupling product. The likely mechanistic pathway for this transformation involves metallacycle formation, followed by nickel enolate protonation by methanol to afford intermediate 23. p-Hydride elimination of the methoxy ligand extrudes formaldehyde and forms a nickel hydride intermediate that undergoes productforming reductive elimination. 

Attempts to homocouple a-methylstyrene with complex 16a remained unsuccessful. This failure might be attributed to the greater steric congestion imposed to a metal-alkylidene or a metallacyclobutane intermediate by a 1,1-disubstituted double bond compared to its 1,2-disubstituted isomer or a terminal olefin. Another styrene derivative that resisted metathesis under our experimental conditions was 2-methoxystyrene. In this case, the lack of reactivity was most likely due to the formation of a stabilized Ru-benzylidene species possessing a chelated methoxy ligand. 

Analogously, the acyl and methoxy ligands are 3-electron ligands in electron-deficient early transition-metal complexes such as [Ti(OCH3)4]... 

Pettit-type electrophilic alkylidene complexes reaction of an acid with a methoxy ligand, protonation of a vinyl complex, reaction of a diazo or another source of carbene on a complex that has a vacant coordination site or a labile ligand. 

The importance of the metalloporphyrin systems as models for biological sites is clear. The stopped flow kinetics of the reactions of various para-sab-stituted tetraphenylporphinatoiron(III) chlorides with imidazoles in acetone have been reportedReactions where the methoxy ligand in five-coordinate octaethylporphinato-iron(III) methoxide, a model for some of these biological systems, has been substituted by a range of phenols, carboxylic acids, and thiols have been reportedan increase in rate with increasing acidity of the thiol is observed. 

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