Alkoxy complexes

The diastereomeric a-alkoxy complexes (1 )-15 and (S)-15, separable by chromatography, were each converted to the corresponding aluminum enolates and reacted with 2-methylpropanal (17)49. Enolate (/ )-16 selectively provided a mixture of two diastereomers with the (Fe/ ,2, 3 i )-complex (/ )-18 identified as the major constituent of a 94 6 mixture. The two chiral auxiliaries of complex (S j-lS exerted antagonistic effects and an undefined mixture of all four possible diastereomers was obtained. 

Kwiatek and Seyler were the first to report that many organopenta-cyanides, when treated first with acid and then with alkali, liberate nitriles 110). This reaction occurs with unsubstituted primary and secondary alkyl, benzyl, vinyl, and phenyl complexes, while allyl, 2-oxo-, 2-hydroxy-, and 2-alkoxy complexes simply release the organo-ligand on treatment with acid, and 1-cyanoalkyl and a-pyridyl complexes are stable 105) (see also Table IV). The yield of nitrile is usually far from quantitative and is... 

Figure 4 shows the remarkable structural similarity between the bimetallic carbene (1 2) and alkoxy complexes formed from diverse paths 1,2 addition of Zr-H to a carbonyl bound to tungsten (eq. 1) and 1,1 addition of Re-H to a zirconium-bound acetyl (eq. 2). 

The chlorination of AuCl(vp) apparently proceeds by different paths from the brominations described above the p.m.r. spectrum of the product AuCl3(vp) indicates a 6-membered ring, and the alcoholysis gives 6-membered ring alkoxy-complexes. 

Chelation has been suggested to reinforce the usual preference for the generation of ff-enolates upon deprotonation of the (3-alkoxy complex 10 to generate enolate 11 which is alkylated with excellent stereocontrol67. 

General methods for the preparation of a.jS-unsaturated iron-acyl complexes are deferred to Section D 1.3.4.2.5.1.1. examples of the alkylation of enolates prepared via Michael additions to ii-0 ,/ -unsaturated complexes prepared in situ are included here. Typical reaction conditions for these one-pot processes involve the presence of an excess of alkyllithium or lithium amide which first acts as base to promote elimination of alkoxide from a /f-alkoxy complex to generate the -a,)S-unsaturated complex which then suffers 1,4-nucleophilic addition by another molecule of alkyllithium or lithium amide. The resulting enolate species is then quenched with an electrophile in the usual fashion. The following table details the use of butyllithium and lithium benzylamide for these processes44,46. 

There have been very few reports of alkoxy complexes derived from unsaturated alcohols. A vinoxytitanium derivative can be obtained from the reaction of tetraisopropoxytitanium and acetaldehyde (equation 15).68 More recently, the dimer [Ti(OCH2CHCH2)4]2 has been isolated from reaction (16).69... 

Alkoxy complexes of stoichiometry [Mo(OR)4] can be prepared from the reaction of [Mo(NMe2)4] with alcohols. With bulky groups (R = Bu , CH2Bu ) the complexes are... 

If the study is extended beyond the hydroxy complexes to the alkoxy complexes (77), the following must be mentioned ... 

According to our findings, all soluble metal compounds of an amphoteric nature are effective esterification catalysts. If, when concluding the theoretical considerations, the amphoteric nature of the metals is described as their ability to function as cations in salts, and also to form anionic hydroxy or alkoxy complexes, this offers the possibility of using the reaction mechanism just discussed for all effective metals in a correspondingly modified manner. 

Pathways involving alkyl-acyl rearrangements are proposed to explain the carbonylation of a-bonded alkoxy complexes (17). The stereochemistry of the products indicates that the ester group replaces Pd with retention of configuration at the carbon to which Pd is o-bonded. In all these studies with unconjugated dienes the nature of carbonylation products to be expected is clearly influenced by the geometry of the intermediate Pd complexes. 

Methyl ketones can be catalytically produced when an excess of TBHP is used for regenerating the initial f-butyl peroxide species from the resulting alkoxy complex in Scheme 6- To prevent the formation of a Tr-allylic complex from causing lower selectivities, a large excess of TBHP with respect to the alkene is required (equation 86).260... 

Figure 9-19. In the case of chromium(vi) and other high oxidation state alkoxy complexes, the C-H bond breaking may occur in an intramolecular two-electron process.

The cycle is started with the formation of a Pd-alkoxy complex that reacts with CO to an alkoxycarbonyl intermediate. In the next step, the approach of the olefin and insertion into the carbonyl palladium bond is predicted. In the last step, the starting complex is rebuilt by the addition of an alcohol and the cleavage of the hydroesterification product [59]. 

These tetradentate C -symmetric ligands allow the synthesis of stable alkoxy complexes of the... 

Treatment of the nickel complex 11 with carbon monoxide (5 atm) led to the formation of butadiene 12 and aldehyde 13 with the formation of Ni(GO)3(PCy3) <2006JA7077>. The scission of the nickel-oxygen bond of the alkoxy complex 11 was also achieved with ZnMe2 to afford 14 in very good yield (Scheme 1). 

This reaction differs from that of the analogous triphenylphosphine complex Pt(77-CeHs)(PPh3)a which reacts in refluxing ethanol to give the c-cyclohexenylhydro complex PtH(CeH9)(PPh3)2, presumably via intermediate alkoxy complexes. 

Under neutral or basic conditions with palladium catalysts, another mechanism involving a carbalkoxy complex may operate (Scheme 3) [3]. It is proposed that reaction of an alcohol with a Pd" species forms a labile alkoxy complex. Coordination and insertion of CO into the Pd-0 bond yields the carbalkoxy complex. Insertion of an olefin into the Pd-C02R bond gives an alkyl complex which reacts with HX to yield predominantly the branched carboxylic acid as product, and to regenerate the Pd". 

Organo-substituted 1-acyloxycyclopropanes 2 are obtained by the reaction of acyloxy chromium carbene complexes 1, generated in situ from tetraalkylammonium chromium acylates and acyl bromides, with enol ethers (alkyl or trialkylsilyl). These complexes are much more reactive than the corresponding alkoxy-complexes (see Section 1.2.1.6.3.). 

As we reported in our former works [3,4] alkoxide molecules underwent selective, stoichiometric reactions with surface hydroxyl groups. As a result of this reaction surface alkoxy complex was formed. 

The surface alkoxy complex was then decomposed by calcination of the catalyst in a stream of dry air at 623 K (see eq. 2). During the reaction, the evolution of stoichiometric amount of appropriate alkene was observed. Secondary hydroxyl groups appeared as a result of the reaction (2). Their presence created the possibility of anchoring the subsequent layer of the same or the other transition metal ions. 

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