Cobalt carbonyls 11 hydroxide

The catalyst is a cobalt carbonyl that is prepared in situ from cobaltous hydroxide, and nonylpyridine is the promotor. Oxidation of the aldehyde produces 3-hydroxypropionic acid. 1,3-Propanediol and 3-hydroxypropi-onic acid could also be produced from acrolein (Chaper 8). ... 

Although the acylcobalt tetracarbonyls react with hydroxide ion under phase-transfer conditions, in the presence of alkenes and alkynes they form o-adducts rapidly via an initial interaction with the ir-electron system. Subsequent extrusion of the organometallic group as the cobalt tetracarbonyl anion leads to a,(J-unsaturated ketones (see Section 8.4). In contrast, the cobalt carbonyl catalysed reaction of phenylethyne in the presence of iodomethane forms the hydroxybut-2-enolide (5) in... 

Acetylation occurs at the 2-position of allene systems (Scheme 8.14). The intermediate 7t-allyl complex breaks down via the nucleophilic displacement of the cobalt carbonyl group by the hydroxide ion to produce the hydroxyketone (7) [ 11 ]. An alternative oxygen-initiated radical decomposition of the complex cannot, however, be totally precluded. The formation of a second major product, the divinyl ketone (8), probably arises from direct interaction of the dicobalt octacarbonyl with the allene and does not require the basic conditions. 

As the supported glycol catalysts worked better in promoting reactions in a single solvent system, we explored the direct carbonylation of benzyl halides using an alcohol solvent, base, and cobalt carbonyl. Our initial experiments concentrated on the reaction of benzyl bromide at room temperature and one atmosphere carbon monoxide. We chose sodium hydroxide as the base, methanol as the solvent, and looked at the product distribution. We were interested in the selectivity to ester and the reactivity of this system. The results are given in Table III. 

We further investigated the formation of Ni(CO)4 and cobalt carbonyls by the action of carbon monoxide on a suspension of the appropriate metal hydroxide [Blanchard and Gilmont (82)] by using potassium cyanide (83) (see Section VIII). 

It is reported that the two-phase carbonylation methodology has been used on a pilot plant scale by Montedison [31 ] for the conversion of benzyl chloride to phenylacetic acid for use in perfume constituents and pesticides (eq. (8)). The carbonylation is run in a biphasic medium employing diphenyl ether and aqueous 40 % sodium hydroxide as solvents. The catalyst system consists of a cobalt carbonyl complex and a benzyltrialkylammonium surfactant. The reaction takes place at low temperature and CO pressure, while benzyl chloride is added continuously to the reaction mixture. 

The carbonylation of a benzyl halide in the presence of iron pentacarbonyl to give a phenylacetic acid may serve to exemplify the interaction of a metal carbonyl, carbon monoxide, PT catalyst, aqueous sodium hydroxide, and the substrate [79]. Fe(CO)5 is attacked by QOH at the interphase, and the species formed is extracted into the depths of the oganic phase, where it reacts with CO and benzyl halide (Eqs. 13 and 14). This new anion 3 is the actual catalyst. It reacts with a second benzyl halide to give a non-ionic intermediate 4 (Eq. 15). By insertion of CO and attack of QOH, 4 is decomposed to the reaction product under regeneration of 3 (Eq. 16). Thus, the action of the PT catalyst is twofold. Firstly it transports the metal carbonyl anion. More important seems to be its involvement in the (rate-determining) decomposition step. A basically similar mechanism was proposed for cobalt carbonyl reactions [80], which have been modified somewhat quite recently (see below). 

Alper et al. have shown that cobalt carbonyl can catalyze the carbonylation of thi-iranes to 3-mercapto acids. This was accomplished by using methyl iodide or a benzylic bromide, 3 N potassium hydroxide, benzene as the organic phase, and polyethylene glycol as the phase-transfer agent [30]. 

Cobalt carbonyl I potassium hydroxide jpolyethylene glycol-400 a-Acylaminoketones from azomethines Phase transfer catalyzed carbonylation... 

Cobalt carbonyl j calcium hydroxide jmethyl iodide 2(5L0-Furanones from 2-ethylene-3,l-chlorhydrins Carbonylation... 

Carbonyl Nitric Oxides. Another group of metal-carbonyl complexes, worthy of investigation as CVD precursors, consists of the carbonyl nitric oxides. In these complexes, one (or more) CO group is replaced by NO. An example is cobalt nitrosyl tricarbonyl, CoNO(CO)3, which is a preferred precursor for the CVD of cobalt. It is a liquid with a boiling point of 78.6°C which decomposes at 66°C. It is prepared by passing NO through an aqueous solution of cobalt nitrate and potassium cyanide and potassium hydroxide. ... 

Carbonvlation of Benzyl Halides. Several organometallic reactions involving anionic species in an aqueous-organic two-phase reaction system have been effectively promoted by phase transfer catalysts(34). These include reactions of cobalt and iron complexes. A favorite model reaction is the carbonylation of benzyl halides using the cobalt tetracarbonyl anion catalyst. Numerous examples have appeared in the literature(35) on the preparation of phenylacetic acid using aqueous sodium hydroxide as the base and trialkylammonium salts (Equation 1). These reactions occur at low pressures of carbon monoxide and mild reaction temperatures. Early work on the carbonylation of alkyl halides required the use of sodium amalgam to generate the cobalt tetracarbonyl anion from the cobalt dimer(36). 

In this study a cobalt(I) carbonyl complex serves as the catalyst. The complex [Co(CO)(CN)2(PEt3)2r is oxidized stepwise by two equivalents of Fe(CN)g" leading to formation of the Co(III) carbonyl species (19) which is readily attacked by water or hydroxide in the pH range 6-12.5. This attack produces the hydroxycarbonyl intermediate (20) which is identified as the main species in solution. 

Reductive decarboxylation of (20) yields C02, H+, and a Co(I) species at a measurable rate (94). In the presence of CO, the starting cobalt complex is regenerated, and a catalytic system for the oxidation of CO by ferricyanide is established. It is significant that in this system the metal-carbonyl bond is formed when the cobalt is in a reduced state. It is the subsequent oxidation of the cobalt by electron transfer that activated the carbonyl to attack by water or hydroxide. That this activation results in a weaker metal-carbonyl bond is evident since the Co(III)-carbonyl may be hydrolyzed in acidic solution with loss of the carbon monoxide ligand (94). 

The rate enhancements in the copper(II)-glycine ester systems are large (ca. 103-106-fold These rate accelerations are similar to the rate accelerations of ca. 106 observed in the ine cobalt(III) systems where direct metal-ester carbonyl bonding occurs. It is thus likely that sue hydrolyses occur by the reactions outlined in Scheme 1. However, attack by coordinated hydroxid (equation 10) cannot be excluded and hydrolysis could occur by a combination of both reactio pathways. 

A variety of N-O-chelated glycine amide and peptide complexes of the type [CoN4(GlyNR R2)]3+ have been prepared and their rates of base hydrolysis studied.169 The kinetics are consistent with Scheme 8. Attack of solvent hydroxide occurs at the carbonyl carbon of the chelated amide or peptide. Amide deprotonation gives an unreactive complex. Rate constants kOH are summarized in Table 16. Direct activation of the carbonyl group by cobalt(III) leads to rate accelerations of ca. 104-106-fold. More recent investigations160-161 have dealt with... 

Carbonic anhydrase is a zinc(II) metalloenzyme which catalyzes the hydration and dehydration of carbon dioxide, C02+H20 H+ + HC03. 25 As a result there has been considerable interest in the metal ion-promoted hydration of carbonyl substrates as potential model systems for the enzyme. For example, Pocker and Meany519 studied the reversible hydration of 2- and 4-pyridinecarbaldehyde by carbonic anhydrase, zinc(II), cobalt(II), H20 and OH. The catalytic efficiency of bovine carbonic anhydrase is ca. 108 times greater than that of water for hydration of both 2- and 4-pyridinecarbaldehydes. Zinc(II) and cobalt(II) are ca. 107 times more effective than water for the hydration of 2-pyridinecarbaldehyde, but are much less effective with 4-pyridinecarbaldehyde. Presumably in the case of 2-pyridinecarbaldehyde complexes of type (166) are formed in solution. Polarization of the carbonyl group by the metal ion assists nucleophilic attack by water or hydroxide ion. Further studies of this reaction have been made,520,521 but the mechanistic details of the catalysis are unclear. Metal-bound nucleophiles (M—OH or M—OH2) could, for example, be involved in the catalysis. 

With cobalt complex catalysts, in polar, aprotic solvents like DME it is often possible to get a-keto acids by controlled double carbonylation874-877. Alternatively, a-hydroxy acids are formed when benzyl halides are carbonylated in the presence of calcium hydroxide, in aqueous media878. Presumably the initially formed a-keto acid is reduced in the Meerwein-Ponndorf fashion to give the a-hydroxy group878. 

A more favorable synthesis of salts of the iron, cobalt and nickel carbonyl anions, which were initially prepared by disproportionation reactions of Fe(CO)5, Co2(CO)8, and Ni(CO)4 with pyridine and other amines, was found by treatment of the neutral carbonyls with alkali in aqueous or alcoholic solutions. Careful studies by Hieber revealed that Fe(CO)5 as well as Fe3(CO)12 reacted with exactly four equivalents of hydroxide ions to give the corresponding dianionic iron carbonylates (Scheme 4.4). These dianions are relatively strong bases and readily accept a proton from a water molecule to give the monoanionic hydrido carbonylates [I IFe(CO)4] and [HFe3(CO)n], respectively [36]. The related carbonylates of cobalt and manganese, [Co(CO)4] and [Mn(CO)5], were obtained by a similar way as [Fe(CO)4]2 [25]. With regard to the mechanism of Hieber s Basenreaktion , the most plausible explanation is based on an initial nucleophilic attack by the hydroxide ion at the carbon atom of a CO... 

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 rate of hydrolysis of esters is dependent upon whether the ester is activated (bound to the metal) or unactivated. For esters that are coordinated to cobalt(III) in a monodentate fashion (Figure 12), the rate of hydrolysis is only accelerated by about 100 times over that of an uncoordinated ester. However, when the ester is coordinated in a bidentate fashion through the amino nitrogen and carbonyl oxygen (Figure 13), the rate of hydrolysis is accelerated by 10 times. " Compared to hydroxide, water does not cause a large increase in the rate of hydrolysis, and it is lO" times slower. ... 

The linear CO stretching frequency for the carbonylated platinum colloid while lower than that found for surface bound CO, is in the range reported for the platinum carbonyl clusters [Pt 3 (CO) 6 ] n / sind we find that the carbonylated colloid is easily transformed into the molecular cluster [Pt 12 (CO) 24 ] (10) reaction with water. The cluster was isolated in 50 yield based on platinum content of the precipitate by extraction with tetraethylammonium bromide in methanol from the aluminum hydroxide precipitated when water is added to the aluminoxane solution. The isolation of the platinum carbonyl cluster reveals nothing about the size or structure of the colloidal platinum particles, but merely emphasizes the high reactivity of metals in this highly dispersed state. The cluster isolated is presumably more a reflection of the stability of the [Pt3(CO)6]n family of clusters than a clue to the nuclearity of the colloidal metal particles - in a similar series of experiments with colloidal cobalt with a mean particle size of 20A carbonylation results in the direct formation of Co2(CO)8. 

The lack of reactivity at C-3 of the a-D anomer as compared with that of the /8-D anomer of methyl 4,6-O-benzylidene-D-glucoside has been noted by other workers. Presumably, the bulky cobalt tetra-carbonyl anion is hindered from approaching C-3 by the methoxyl group on C-1, whereas the less bulky methoxide ion, or hydroxide ion, can open the epoxide ring in the normal, frans-diaxial way. 

Another way of bringing reactants into close proximity, which is encountered commonly in transition metal chemistry, is through metal ion complexation. The coordination of a reactant to a metal ion complex often activates its reactivity and can bring the reactant into close proximity with a second reactant or with a catalytic group. One example, shown in Fig. 6, is a zinc (11) complex of 1,5,9-triazacyclononane, as a model for the enzyme carbonic anhydrase, which contains a zinc (11) cofactor in its active site (4). In the aqua complex, the bound water molecule has a dramatically reduced pKa value of 7.3, which is similar to the pKa of the active site nucleophihc water. The corresponding cobalt (111) complex catalyzed ester hydrolysis at twice the rate because Co(lll) can coordinate both the hydroxide nucleophile and the ester carbonyl via a... 

Co(in) complexes promote similar reactions. When four of the six octahedral positions are occupied by amine ligands and two cis positions are available for further reactions, it is possible to study not only the hydrolysis itself, but the steric preferences of the complexes. In general, these compounds catalyze the hydrolysis of N-terminal amino acids from peptides, and the amino acid that is removed remains as part of the complex. The reactions apparently proceed by coordination of the free amine to cobalt, followed either by coordination of the carbonyl to cobalt and subsequent reaction with OH or H2O from the solution (path A in Figure 12-15) or reaction of the carbonyl carbon with coordinated hydroxide (path B). As a result, the N-terminal amino acid is removed from the peptide and left as part of the cobalt complex in which the a-amino nitrogen and the carbonyl oxygen are bonded to the cobalt. Esters and amides are also hydrolyzed by the same mechanism, with the relative importance of the two pathways dependent on the specific compoimds used. 

---