Cobalt alkoxides

A special role in the chemistry of nickel and cobalt alkoxide derivatives is played by the poorly soluble methoxide halids studied in detail by the group of Winter [964, 865]. According to the diffuse reflectance spectra, the coordina-... 

With weak catalysts such as aluminium alkoxides with C0C13, cobalt acetyl acetonate, etc. polymerization was exceedingly slow. 

Palladium complexes also catalyze the carbonylation of halides. Aryl (see 13-13), vinylic, benzylic, and allylic halides (especially iodides) can be converted to carboxylic esters with CO, an alcohol or alkoxide, and a palladium complex. Similar reactivity was reported with vinyl triflates. Use of an amine instead of the alcohol or alkoxide leads to an amide. Reaction with an amine, AJBN, CO, and a tetraalkyltin catalyst also leads to an amide. Similar reaction with an alcohol, under Xe irradiation, leads to the ester. Benzylic and allylic halides were converted to carboxylic acids electrocatalytically, with CO and a cobalt imine complex. Vinylic halides were similarly converted with CO and nickel cyanide, under phase-transfer conditions. ... 

The mechanism of [3 + 2] reductive cycloadditions clearly is more complex than other aldehyde/alkyne couplings since additional bonds are formed in the process. The catalytic reductive [3 + 2] cycloaddition process likely proceeds via the intermediacy of metallacycle 29, followed by enolate protonation to afford vinyl nickel species 30, alkenyl addition to the aldehyde to afford nickel alkoxide 31, and reduction of the Ni(II) alkoxide 31 back to the catalytically active Ni(0) species by Et3B (Scheme 23). In an intramolecular case, metallacycle 29 was isolated, fully characterized, and illustrated to undergo [3 + 2] reductive cycloaddition upon exposure to methanol [45]. Related pathways have recently been described involving cobalt-catalyzed reductive cyclo additions of enones and allenes [46], suggesting that this novel mechanism may be general for a variety of metals and substrate combinations. 

Cobalt(II) alkoxides are known and monomeric forms are part of a wider review.413 The interest in these compounds pertains to a potential role in catalysis. For example, a discrete cobalt(II) alkoxide is believed to form in situ from a chloro precursor during reaction and performs the catalytic role in the decomposition of dialkyl pyrocarbonates to dialkyl carbonates and carbon dioxide.414 A number of mononuclear alkoxide complexes of cobalt(II) have been characterized by crystal structures, as exemplified by [CoCl(OC(t-Bu)3)2 Li(THF)].415 The Co ion in this structure and close relatives has a rare distorted trigonal-planar coordination geometry due to the extreme steric crowding around the metal. 

Srivastava DN, Perkas N, Seisen Bueva GA, Koltypin Y, Kessler VP, Gedanken A (2003) Preparation of porous cobalt and nickel oxides from corresponding alkoxides using a sonochemical technique and its application as a catalyst in the oxidation of hydrocarbons. Ultrason Sonochem 10(1) 1-9... 

The reaction conditions were mild (room temperature, 1 atm CO) and a two-fold excess of base was used along with a catalytic amount of cobalt carbonyl. The product distribution was quantified by VPC. The mixtures contained starting material, ester product, and various amounts of methyl benzyl ether. No detectable amounts of benzyl alcohol, ketones, or hydrocarbons were seen. Potassium methoxide alone afforded mostly the ether. A mixture of potassium methoxide and alumina gave a slight improvement in ester yield but the predominant product was again the ether. In contrast, when potassium methoxide on alumina was used, the carboxyalkylated product, methyl phenylacetate, was prepared in 70 yield with little ether detected. Benzyl chloride reacted in a similar fashion under these mild reaction conditions. Other alkoxide and carbonate bases could be used as... 

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). 

Again several alkyls add—molybdenum, chromium, iron, cobalt, nickel, the alkali metal alkyls and aluminum alkyls react. A tin alkoxide has recently been studied by Russian workers and found to add to acetylenes. Mercury chloride, of course, adds and two cobalt—cobalt bonded compounds add to acetylene. The second is questionable because it dissociates in solution and the reaction may be a radical reaction, one cobalt adding to each end of the triple bond. 

Cobalt hydrocarbonyl, diborane, and aluminum hydrides add, I think, to all of these carbonyl compounds. Of course, there is the well known Grignard reagent and the alkyllithium additions to carbonyl compounds. Aluminum alkyls add, and we could have listed all the other alkali metal alkyls. Recent work has shown that the tin alkoxides add readily to all these derivatives, and similarly, a tin amide adds to most of these carbonyl compounds. 

All known C02 insertions into a metal-carbon bond result in carbon-carbon bond formation, except in one instance. The insertion of C02 with formation of a metallocarboxylate ester is claimed in the reaction of C02 with a cobalt complex (108, 139). Two species were isolated from the reaction of C02 with a mixture of acrolein and the complex CoH(N2)(PPh3)3, which was assumed to form Co(CO)(C2H5)(PPh3)2 before the C02 was introduced. The two reaction products were characterized by their ir spectra and chemical reactions, and formulated as Co(02CEt)2(PPh3)2 and the metallocarboxylate ester Co(C03) (COOEt)(PPh3), n = 0.5-1.0. Metallocarboxylate esters are well-known products from the attack of alkoxides on metal carbonyls. 

Co(OAc)2 in the presence of sodium hydride and a sodium alkoxide has been used to catalyze the carbonylation of aryl bromides, giving mixtures of carboxylic acids and esters, again at normal pressure. When amines were present, amides were formed. Unfortunately, nothing is known about the nature of the cobalt complexes involved. 

This problem has been partially overcome by elimination of the phosphorus-oxygen bonds, as, for example, in the poly(phosphinoisocyanates), which have the structure shown in 6.47.42 It is also possible to form poly(metal phosphinates) with repeat unit -M(0PR20)2- by allowing a metal alkoxide to react with a phosphinic acid.43 Typical metal atoms are aluminum, cobalt, chromium, nickel, titanium, and zinc.43 Polymeric phosphine oxides can be prepared by the reactions... 

By polymerizing the trans isomer of 1,3-pentadiene two different types of crystalline cis-1,4 polymers have been obtained, one with an isotactic, the other with a syndiotactic structure. The isotactic polymer was obtained by homogeneous systems from an aluminum alkyl chloride and a cobalt compound, the syndiotactic one by homogeneous systems from an aluminum trialkyl and a titanium alkoxide. Some features of the polymerization by Ti and Co catalysts are examined. IR and x-ray spectra, and some physical properties of the crystalline cis-1,4 polymers are presented. The mode of coordination of the monomer to the catalyst, and possible mechanisms for the stereospecific polymerization of pentadiene to cis-1,4 stereoisomers are discussed. 

One of the main questions in the cobalt(III)-promoted hydrolysis of activated amino acid esters is whether the ratedetermining step is addition of hydroxide to the carbonyl carbon, or loss of the alkoxide from the intermediate. Work with /3-alanine ester showed that below pH 8.5 the ratedetermining step was the elimination of alkoxide. At pH 10 and above, the rate-determining step changes and the addition of hydroxide to the activated ester becomes the rate-controlling step. This is due to the fact that above pH 10 the hydroxyl group of the intermediate becomes deprotonated (equation 7). The deprotonation of the hydroxyl group accelerates the loss of alkoxide by 10 times. ... 

The red rhenium(I) complex [Re(CO)4(phen)]Co(CO)4(compound A) on warming to 90°C affords the compound (phen)(CO)sRe-Co(CO)4 which contains a rhenium to cobalt bond. The irradiation of a THF solution of the latter material gives the yellow binuclear compound [Re(CO)3(phen)]2 (443, 444). Compound A (above) undergoes the followuag reversible reaction with various alkoxide species RO (446) ... 

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