Insertion reactions of CO

In this chapter we will discuss some aspects of the carbonylation catalysis with the use of palladium catalysts. We will focus on the formation of polyketones consisting of alternating molecules of alkenes and carbon monoxide on the one hand, and esters that may form under the same conditions with the use of similar catalysts from alkenes, CO, and alcohols, on the other hand. As the potential production of polyketone and methyl propanoate obtained from ethene/CO have received a lot of industrial attention we will concentrate on these two products (for a recent monograph on this chemistry see reference [1]). The elementary reactions involved are the same formation of an initiating species, insertion reactions of CO and ethene, and a termination reaction. Multiple alternating (1 1) insertions will lead to polymers or oligomers whereas a stoichiometry of 1 1 1 for CO, ethene, and alcohol leads to an ester. 

CO reacts imder normal conditions of pressure and temperature with some nickel(II) organometallic compounds and an insertion reaction into the original Ni—C a bond results (equations 156-158).1201,1236,1247-1249 A different example of an insertion reaction of CO is reported in equation (159).1250... 

Reviews relevant to Section 61.2.5 and not pertaining to individual metals are collected here. An early review562 and some more recent reviews cover insertion reactions of CO,56 and the water-gas shift.573... 

Flood has recently published an excellent contribution which includes a review of the stereochemistry of insertion reactions of CO and S02 into metal-carbon sigma bonds. 

The insertion reactions of CO, alkenes, and alkynes are particularly important. An early example (Berthelot, 1869) is ... 

The insertion reactions of CO into M—H bonds could be expected to give formyl complexes,... 

Sulfur dioxide reacts generally with transition metal alkyl, aryl, and a-allyl complexes to give sulfinate complexes. The reaction, first described in 1964 by Wojcicki and Bibler, resembles well-known insertion reactions of CO, C2F4, SnCl2, tetracyanoethy-lene, and other unsaturated species into metal-alkyl bonds, but there are important stereochemical and mechanistic differences Sulfur dioxide insertion into metal-alkene and metal-alkyne bonds have not been reported. However, PdCl2 has been used as a catalyst for copolymerization of ethylene and SO2 to polysulfones and insertion into a Pd-ethylene bond is a conceivable reaction step. 

We will illustrate this for the insertion reaction of CO into a CH3 group co-ordinated to Pd ". This reaction can be considered as a prototype for C-C bond formation catalyzed by a metal centre (see Fig. 4.13). 

However, iron complexes may also display a beneficial effect. Thus, a promoting effect on hydroformylation was observed with Si02-supported Rh-Fe " bimetallic carbonyl clusters (Scheme 1.61) [12]. Based on Mossbauer spectroscopy, it was proposed that iron assists during the insertion reaction of CO into the Rh-C bond. Likewise, the hydrogenation of the intermediary alkoxy rhodium species to produce the alcohols may benefit from this bi-site interaction. 

Reaction of CO with the tautomeric mixture of the two aforementioned rhodium complexes (several / flra-substituted imidoaryl groups were tested) afforded a unique bridging isocyanate complex Rh2(CO)2(ii -N,T] -C, x-ArNCO)(p-DPPM)2. The CO insertion is irreversible. Since the two initial tautomers are in equilibrium in solution, insertion of CO may in principle proceed by either of the two (Scheme 20)(next page). However, evidence was given in favour of the amido-path (path b in the Scheme), based on the fact that the cationic complex [Rh2(p-NHPh)(CO)2(DPPM)2] rapidly reacted with CO. No complex could be isolated from this last reaction, but the formation of PhNCO was detected. Two features of this mechanism are worth of note. The first is the contrast between the conclusion reached for this system (amido complex more reactive than imido one in the insertion reaction of CO) and the one reached by Bhaduri et al. [161] for the trinuclear complex Ru3(p-H)(p-NHPh)(CO)io, which, upon deprotonation of the amido group by OH, affords the inserted product [Ru3(p-H)(T] -N,ii -C,p3-PhNCO)(CO)9]. The difference is likely due to the fact that, in this latter case, the complex is trinuclear, so that the inserted CO is already coordinated to the third ruthenium atom and, especially, the formation of the new C-N bond does not require the breaking of any of the pre-existing Ru-N bonds. 

Hartwig JF, Bergman RG, Andersen RA (1991) Insertion reactions of CO and CO2 with ruthenium benzyl, arylamido, and aryloxide complexes a comparison of the reactivity of ruthenium-carbon, ruthenium-nitrogen, and ruthenium-oxygen bonds. J Am Chem Soc 113 6499-6508... 

Cyclic voltammetry, spectroelectrochemistry, and preparative electrolysis have provided evidence for the mechanism of nonmigratory insertion reactions of CO with [Fe(OEP)R] complexes (OEP = octaethylporphyrin)/ > This occurs by the sequence of reactions (30)-(32) when R = alkyl groups... 

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