Alkoxides carbon monoxide

Early in the twentieth century, the first attempts to manufacture formamide directiy from ammonia and carbon monoxide under high temperature and pressure encountered difficult technical problems and low yields (23). Only the introduction of alkaU alkoxides in alcohoHc solution, ie, the presence of alcoholate as a catalyst, led to the development of satisfactory large-scale formamide processes (24). 

Reactions of the Side Chain. Benzyl chloride is hydrolyzed slowly by boiling water and more rapidly at elevated temperature and pressure in the presence of alkaHes (11). Reaction with aqueous sodium cyanide, preferably in the presence of a quaternary ammonium chloride, produces phenylacetonitrile [140-29-4] in high yield (12). The presence of a lower molecular-weight alcohol gives faster rates and higher yields. In the presence of suitable catalysts benzyl chloride reacts with carbon monoxide to produce phenylacetic acid [103-82-2] (13—15). With different catalyst systems in the presence of calcium hydroxide, double carbonylation to phenylpymvic acid [156-06-9] occurs (16). Benzyl esters are formed by heating benzyl chloride with the sodium salts of acids benzyl ethers by reaction with sodium alkoxides. The ease of ether formation is improved by the use of phase-transfer catalysts (17) (see Catalysis, phase-thansfer). 

If hydrogen gas is added to the reaction mixture of J, and 11 the hydrogenolysis reaction of thorium-to-carbon sigma bonds (J-1 22) allows interception of species 13 and thus, catalytic hydrogenation of the inserted carbon monoxide functionality. At 35 C under 0.75 atm initial H2 pressure with [JJ =9.0 x 10" M and [ 1JJ = 6.5 x 10" M, hydrogenation and isomerization are competitive and both the enolate and the alkoxide reduction product 14 are produced (eq.(13)). Under these conditions, turnover fre-... 

Hence, lithium salt 343a is trapped by aldehydes, and subsequent intramolecular attack of the intermediate alkoxide on the lactam moiety leads to pyridinophanes 405a and b. Ethanolysis of lactam 288 under acidic or basic conditions, even at —78°C, affords ester 406, whereas the reactions of lactams 288 and 290 with 4-methyl-l,2,4-triazoledione (MXAD) give mixtures of cycloadducts 407a and b or the respective isoquinolines. Tricyclic 290 when irradiated suffers loss of carbon monoxide to form butadiene 408. 

Treatment of the /J-hydroxy complex 15 with two equivalents of strong base followed by alkylation produces a mixture of the diastereomers 20 and 21 with an anomalously low d.r.27. The low degree of diastereofacial discrimination has been rationalized by invoking the formation of both rotamers of the initially formed alkoxide, 16 and 17. Rotamer 16 undergoes a-proton abstraction by a second equivalent of base to form the chelated dianionic Tf-enolate 18 which upon alkylation affords the usual diastereomer 20. Rotamer 17 is thought to rapidly transform to a metallo-lactone species by intramolecular attack of the alkoxide upon the proximate carbon monoxide ligand, which must occur faster than conversion to the less sterically encumbered conformer 16. Subsequent deprotonation to generate dianion 19, which is constrained to exist as the unusual Z-enolate, followed by alkylation provides the other diastereomer 21, which is formed in an amount nearly equal to 20. 

The formation of formate esters in the hydroformylation reaction (90, 64) may be explained by a CO-alkoxide insertion reaction as well as by the CO-hydride insertion mechanism mentioned above. Aldehydes formed in the hydroformylation reaction can be reduced by cobalt hydrocarbonyl (27) presumably by way of an addition of the hydride to the carbonyl group (90, 2). If the intermediate in the reduction is an alkoxycobalt carbonyl, carbon monoxide insertion followed by hydrogenation would give formate esters (90, 64). 

Two alkoxide derivatives also seem to insert carbon monoxide. The products obtained when these alkoxides are formed in the presence of carbon monoxide have CO inserted between the oxygen and the metal. These two products can also be... 

Lanthanide hydrides of type CpfSmH are capable of both reducing and coupling carbon monoxide (Scheme 38) [282]. The initially formed cis enediolate isomerizes to trans-[Cp Sm(Ph3pO)]2(jt-OCH=CHO) at ambient temperature in hours to days depending on sample concentration. The Sm-O bond of the bridging enediolate moiety is in the range of terminal Sm-0(alkoxide, enolate) bonds (Table 18). 

The formation of free carbon monoxide, and consequent degradation reactions can be avoided using alkali hydroxides or alkoxides as reducing... 

Z-Eburnamonine (XXXVI) has been produced by other reactions of vincamine. Oxidation of vincaminic acid (XL R = H) by means of ammoniacal silver nitrate was one way, and periodic acid fission of vincaminol was another (16). A different group of workers, who had probably attempted to prepare vincaminol by lithium aluminum hydride reduction of vincamine, obtained instead Z-ebumamonine in excellent yield (18). This has been rationalized as illustrated (partial formulas) by analogy with the base-induced decomposition of formic esters to carbon monoxide and alkoxide ion ... 

Carbon monoxide is also known to insert into metal alkoxides (M—OR), di-alkylamides (M—NR2), and some hydroxymethyls (M—CH2OH). For the reaction of the alkoxide (PPh3)2Ir(CO)(OMe) with CO the intermediate [Ir(CO)3(PPh3)2]+ OMe has been identified, and the insertion therefore proceeds via external nucleophilic attack of OMe" on Ir—CO rather than intramolecular OMe migration. True intramolecular transfer is, however, evident for (dppe)PtMe(OMe) where the rate of OMe migration is much faster than for Me migration, to give (dppe)PtMe(COOMe). 

In addition to catalyzing hydroformylation, the platinum SPO complexes are excellent hydrogenation catalysts for aldehydes (as already demonstrated by the side products of hydroformylation), in particular, in the absence of carbon monoxide. Further, in ibis process, the facile heterolytic splitting of dihydrogen may play a role. The hydrogenation of aldehydes requires the presence of carboxylic acids, and perhaps the release of alkoxides from platinum requires a more reactive proton donor than that available on the nearby SPO. For example, 4 hydrogenates 2-methylpropanal at 95 °C and 40 bar of H2 to give the alcohol, with a TOF of 9000 mol moN h (71). 

Insertion reactions involving metal alkoxides are also known. For example, carbon dioxide is known to react with some metal alkoxides as shown in equation (12). The formation of a bidentate ligand is a significant thermodynamic driving force for some of these reactions. The isoelectronic aryl and alkyl isocyanates and carbodiimides can react similarly. Insertion reactions involving alkenes and carbon monoxide are known for platinum alkoxides. 

Figure 8 Phospha-alkoxide complex generated by insertion of carbon monoxide into a homoleptic thorium dialkylphosphide complex (Edwards, Hursthouse et al. J. Chem. Soc., Chem. Commun. 1994, 1249).

Here, hydrogen and carbon dioxide react to form water vapor (and carbon monoxide via water-gas shift), which hydrolyzes the aluminum trichloride. If the deposition surface is temperature sensitive, a metal-organic precursor is preferred. Again, an alkoxide is generally used ... 

Despite the presence of a formally divalent carbon atom, CO is not in fact a particularly reactive molecule and much of its chemistry depends on the use of either extreme conditions, energetic reagents or some form of catalysis. Perhaps the simplest examples of such catalysis are found in the reactions of carbon monoxide with protic reagents such as alcohols or secondary amines, affording esters or amides of formic acid. These reactions are catalyzed by alkoxide or amide anions, respectively, and, as shown in Scheme 1, the key step is nucleophilic attack on CO by the catalyst to give a strongly basic alkoxyacyl or aminoacyl anion which is immediately trapped by proton transfer from the alcohol or amine, so generating the catalytic species. 

Dimethoxyethane is preferred to dimethyl sulfoxide as solvent for the formyl-ation of ketones with carbon monoxide in the presence of an alkali metal alkoxide. This is due to the fact that DMSO is slightly protic in the presence of a strong base (potassium t-butoxide) and hence not inert. 

The C-0 bond can be more easily activated when the CO molecule interacts with more than two metal atoms. Recently, the dissociative adsorption of carbon monoxide by polynuclear metal complexes, such as [(silox)2TaH2]2 (Eq. 57) [126, 127] and [(silox)2WCl]2 (Eq. 58) [126-129], and tetratungsten alkoxides [129] has been achieved. Hydrogenation of CO to give hydrocarbons promoted by metal clusters has been reviewed [130]. 

Reduction of Ta(silox)3Cl2 with Na/Hg leads to a three-coordinate alkoxide complex Ta(silox)3. The coordinatively unsaturated tantalum complex is capable of cleaving H2 and O2 bonds resulting in the hydride and 0x0 complexes as illustrated in Scheme 7.14. Carbon monoxide is also split upon carbonylation of Ta(silox)3 generating the 0x0 and p-dicarbide complexes. This reaction models the C—O bond cleavage and C—C bond formation believed to occur in the Fischer-Tropsch reaction, and the ketenylidene complex Ta(silox)3(=C=C=0) was postulated as the key intermediate. On the other hand, when Ta(silox)3 was treated with pyridine and benzene, remarkable T -coordinated complexes were formed. 

A related group of compounds is that of the gold(III) dimethyl(alkoxycarbonyl) complexes, accessible by the reaction of carbon monoxide with dimethyl(alkoxy)(triphenyl-phosphine)gold(III), which is prepared in situ from cw-[AuIMe2(PPli3)] and sodium alkoxide in methanol (equation 80)353,359. Thermolysis of the methoxycarbonyl complex in benzene leads to the reductive elimination of methyl acetate and ethane, indicating competition between the two modes of decomposition illustrated in Scheme 27. The reaction of the same complex with electrophiles such as hydrogen chloride proceeds with liberation of carbon monoxide and methanol, as illustrated in equation 81. 

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