Reactions Involving CO

CO shows a strong tendency to insert into metal alkyl bonds to give metal acyls. The reaction has been carefully studied for a number of systems. Although the details may differ, most follow the pattern set by the best-known 

By studying the reverse reaction (Eq. 7.8), elimination of CO from Me - COMn(CO)5, where we can easily label the acyl carbon with - C (by reaction of Mn(CO)f with Me COCl), we find that the label ends up in a CO cis to the methyl. This is an example of a general strategy in which we 

This relies on microscopic reversibility, according to which, the forward and reverse reactions of a thermal process will follow the same path. In this case, if the labeled CO ends up cis to Me, the CO to which a methyl group migrates in the forward reaction, must also be cis to methyl. We are fortunate in seeing the kinetic products of these reactions. If a subsequent scrambling of the COs had been fast, we could have deduced nothing. 

It is also possible to use reversibility arguments to show that the acyl ligand in the product is bound at a site cis to the original methyl, rather than anywhere else. To do this we look at CO elimination in cis-(MeCO)Mn(CO)4( CO), in which the label is cis to the acetyl group. If the acetyl CO moves during the elimination, then the methyl in the product will stay where it is and so remain cis to the label. If the methyl moves, then it will end up both cis and trans to the methyl, as is in fact observed  

This observation implies that the methyl also moves when the reaction is carried out in the direction of insertion. The cis-(MeCO)Mn(CO)4( CO) required for this experiment can be prepared by the photolytic method discussed in Section 4.7, and we again use the IR spectrum to tell where the label has gone in the products. This is the only feature of migratory insertion in MeMn(CO)j that does not reliably carry over to other systems, where the product acyl is occasionally found at the site originally occupied by the alkyl.  

The kinetics in this situation are reminisscent of dissociative substitution (Section 4.3) except that the 2e site is formed at the metal in the migraloiy step, not by loss of a ligand, Using the usual steady-state method, the rate is given by 

There are three possible regimes, all of which are found in real cases  

If 4 I is very small relative to fc2lUJ, [L] cancels and the equation reduces to 

Because is small, L always traps the intermediate this means the rate of the overall reaction is governed by and we have a first-order reaction. 2. If k. 1 is very large relative to then the equation becomes 

The vast majority of transition metal clusters contain carbonyl ligands, which have been shown in many cases to be fluxional on the metal skeleton of the cluster (40,41). Therefore, the most obvious reactions to be catalyzed by such clusters should be those involving carbon monoxide. In fact, catalytic carbonylations are frequently encountered with transition metal carbonyl cluster catalysts, but very often the carbonylation step is followed by a consecutive step, e.g., a hydrogenation step, to give an overall hydroformylation. Simple carbonylation reactions have nevertheless been observed for various structures. 

Alcohols are versatile building blocks for the synthesis of basic organic molecules. Thus the carbonylation of a primary alcohol can lead either to the corresponding acid or to the corresponding formyl ester  

The carbonylation of methanol to give acetic acid, according to Eq.(l), based on the catalyst [Rh(CO)2l2] , is a major industrial process (Monsanto acetic acid process). However, ruthenium clusters as catalysts seem to favor the insertion of carbon monoxide into the 0-H and not into the C-O bond, according to Eq.(2). Ru3(CO),2 in basic solution converts methanol to methyl formate with 90% selectivity (400-450 bar CO, 

The regiospecific carbonylation of oxetanes and thietanes, resulting in a ring expansion 

Carbon Monoxide-Mediated Deoxygenation of Oximes and Nitro Corr jounds 

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The coordination chemistry of NO is often compared to that of CO but, whereas carbonyls are frequently prepared by reactions involving CO at high pressures and temperatures, this route is less viable for nitrosyls because of the thermodynamic instability of NO and its propensity to disproportionate or decompose under such conditions (p. 446). Nitrosyl complexes can sometimes be made by transformations involving pre-existing NO complexes, e.g. by ligand replacement, oxidative addition, reductive elimination or condensation reactions (reductive, thermal or photolytic). Typical examples are ... 

The ZwKKER reaction involving Co salts is frequently used for the detection of barbituric acid derivatives [31-35], but some purine, pyridine and piperidine derivatives and heterocyclic sulfonamides also yield colored derivatives. The Zwkker reaction is particularly sensitive when it is possible to form a tetrahedral complex [Co(Barb)2 Xj] (X = donor ligand, e.g. amine) [4]. 

A zeolite catalyst operated at 1 atm and 325-500 K is so active that the reaction approaches equilibrium. Suppose that stack gas having the equilibrium composition calculated in Example 7.17 is cooled to 500 K. Ignore any reactions involving CO and CO2. Assume the power plant burns methane to produce electric power with an overall efficiency of 70%. How much ammonia is required per kilowatt-hour (kWh) in order to reduce NO , emissions by a factor of 10, and how much will the purchased ammonia add to the cost of electricity. Obtain the cost of tank car quantities of anhydrous ammonia from the Chemical Market Reporter or from the web. 

Some interesting differences are found between the reactions of Co(I) and Co—H complexes. For example, [Co (DMG)2py] will react at pH 10-11 with activated olefins to give the -substituted complexes [XCH2CH2Co(DMG)2py)], where X is COOH, COOR, CN, etc. but at pH 7-8, where the complex is present as the hydride, the a-substituted derivatives [CHjCHXCo(DMG)2py] are formed 163, 149). Schrauzer, Weber, and Beckham were able to show that the reactions at higher pH proceeded via the intermediate formation of the 7r-olefin-Co(I) complex 159). The reactions involving Co(I) appear generally to be reversible and the addition of Co—H irreversible (see also Section V,C and VI,B). We can, therefore, write the scheme... 

No insertion of CO into a Co—C bond has been reported, although possible equilibria and reactions involving CO at a pressure of 1 atm have been examined with DMG 163, 80), salen 44), and eorrinoid complexes... 

C15-0102. What happens to the rate of a reaction involving CO if the concentration is doubled and the reaction Is (a) first order in CO (b) half order in CO and (c) inverse first order in CO ... 

It is appropriate to identify our approach to developing the present review in the context of the Co chapter in CCC(1987). The first-edition chapter on Co featured a focused discussion and tabulation of synthetic methods, and many of these basic methods are still employed in synthesis today. Consequently, to avoid repetition, there will be diminished description here where prior appropriate methods have been provided, and only newer developments featured. The last two decades feature the development of many mixed-donor and sophisticated multidentate and macrocyclic ligands, which found limited coverage in the previous edition, and these will be discussed in more detail herein. Reaction kinetics and mechanism were also described thoroughly in the previous edition. We shall not reiterate this material, since the core mechanisms of many reactions involving Co compounds are now adequately defined. 

Figure 3 are reactions involving Co since there is evidence... 

SCHEME 10.1. Formation of silane and SiNW by a series of reactions involving Co nanoparticles, hydrogen, and silicon wafers. 

A plot of the left-hand side of (5.38b) versus InA should be linear with a slope of unity and an intercept = In (k, k 2)-Such a plot for the reactions of Co(phen)3 with Cr(bpy)f, Cr(phen)3 and their substituted derivatives yields a slope of 0.98 and an intercept of approximately —0.55. If k, the self-exchange rate constant for Co(phen)3+ is 30 M s this corresponds to k,2 = 0.13, indicating mild nonadiabaticity for reactions involving Co(phen)3+. Ref. 41. See also Fig. 8.2. 

Ethoxycarbonylation of 4,5-dibromo-2-methylpyridazin-3(2//)-one 202 under a high CO pressure in EtOH yielded diethyl l-methyl-6-oxo-l,6-dihydropyridazine-4,5-dicarboxylate 203 (Equation 46) <2005JHC427>. Surprisingly, aldehyde and ketone formation making use of Pd-catalyzed reactions involving CO insertion has not been studied yet. 

The reactions are thought to proceed by initial formation of a cobalt(III)-oxygen complex 416 from CoX2 and 02 (Fig. 97). The induction period observed in many reactions involving Co(acac)3 can be traced to its initial slow reduction to Co(acac)2. Complex 416 initiates the radical reaction by hydrogen abstraction... 

Mesoionic compounds may undergo 1,3-dipolar cycloaddition reactions. Thus anhydro-1 -hydroxythiazolo[3,2-a]guinolinium hydroxide (396) is a substrate for the reaction with DMAD. The formation of the pyrrolo[l,2-a]quinoline (397) from this reaction involves COS elimination from the initial adduct. Ethyl propiolate also reacts in the same fashion. The orientation in the cycloadduct can be arrived at from the ylide form (396a). With fumaronitrile, however, the fused pyridinone (398) is formed by loss of sulfur from the primary cycloadduct (78JOC2700). 

As noted earlier HCo(CO)4 and H2Fe(CO)4 were the first known hydrides. Carbonyl hydrides and carbonylate anions have been intensively studied in part because they are intermediates in many metal catalyzed reactions involving CO and H2. The structure of HMn(CO)5 is shown in Fig. 2-7. 

Many catalytic reactions involving CO are promoted by halide ions, especially iodide (cf. methanol carbonylation, Section 22-7). For example, in... 

Figure 22-8 Some carbonylation reactions. Reppe reactions involve CO + H20 or CO + ROH. Koch reactions involve CO + H20 in strongly acidic solution. Oxidative carbonylations may involve 02, NO, or ROOR.

These are reactions involving CO, a substrate, and an oxidizing agent. Probably the most important reaction is that used for oxalate ester synthesis the ester can be used as a precursor for ethylene glycol. 

There is yet another biochanical reaction involving CO (apart from its role as a transmitter substance in animals) which should be addressed here CO is activated and linked to some Ni-CH moiety in a [Ni(deprotonated ohgopeptide)(CH3)] complex attached to a Ni or Cu car-bonylpolythiolate complex which affords acetyl-CoA via some Ni acetyl system by CO shift and insertion in a manner very similar to the Monsanto process for production of acetic add from CO and methanol. The latter affords methyl groups attached to the metal (Ni here, Ru in the original Monsanto process). This transformation takes place in a Clostridium, namely Moorella thermoacetica. 

Quite recently, novel cyclization reactions involving CO to give carbocydic and heterocyclic compounds, which are characteristic for mthenium catalysts, have been developed. Ruthenium complexes provide new avenues for cydization reactions. In addition, CO is often used as a reducing agent, and reductive carbonylations of nitro compounds catalyzed by mthenium complexes are very attractive reactions that provide phosgene-free processes [3]. 

Murai s group developed a series of netv Ru3(CO)i2-catalyzed qrcloaddition reactions involving CO. In the intramolecular Pauson-Khand reaction, the olefinic moiety is replaced by a carbonyl [84] or imine group [85] to give either y-lactones or y-lactams (Eqs. 11.40 and 11.41). 

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