Carbon monoxide reductive coupling

Building Molecules with Carbon Monoxide Reductive Coupling, B. Wayland, X. Fu, Science 2006,311,790. 

A search for organisms with novel metabolic and bioenergetic pathways, particularly pathways involved in carbon dioxide and carbon monoxide reduction and methane oxidation coupled with electron acceptors other than oxygen ... 

The carbene-carbon monoxide coupling was suggested as a potential elementary C—C coupling step in catalytic carbon monoxide reduction systems based on the observation of the reaction product (r -C5(CH3)5)2ZrH 2(p-OCH=CHO) [31]. The zirconoxycarbene complex 3 was found to react with carbon monoxide at room temperature to afford a zirconium-coordinated ketene complex 4 in 30% isolated yield (reaction 8.18). The X-ray structures of both 3 and 4 were determined [32]. 

Although analogous to the direct coupling reaction, the catalytic cycle for the carbonylative coupling reaction is distinguished by an insertion of carbon monoxide into the C-Pd bond of complex A (see A—>B, Scheme 31). The transmetalation step-then gives trans complex C which isomerizes to the cis complex D. The ketone product E is revealed after reductive elimination. 

The reductive coupling of metal coordinated carbon monoxide is a current research objective,... 

Catalytic processes based on the use of electrogenerated nickel(O) bipyridine complexes have been a prominent theme in the laboratories of Nedelec, Perichon, and Troupel some of the more recent work has involved the following (1) cross-coupling of aryl halides with ethyl chloroacetate [143], with activated olefins [144], and with activated alkyl halides [145], (2) coupling of organic halides with carbon monoxide to form ketones [146], (3) coupling of a-chloroketones with aryl halides to give O -arylated ketones [147], and (4) formation of ketones via reduction of a mixture of a benzyl or alkyl halide with a metal carbonyl [148]. 

Two examples of three-components coupling reaction are shown in Reactions (7.77) and (7.78) [27,87]. These radical chain reactions proceeded by the addition of an alkyl or vinyl radical onto carbon monoxide, generating an acyl radical intermediate, which, in turn, can further react with electron-deficient olefins to lead, after reduction, to a formal double alkylation of carbon monoxide. These three-components coupling reactions require the generation of four highly disciplined radical species, which have specific functions during the chain reaction. 

Electron-transfer chains in plants differ in several striking aspects from their mammalian counterparts. Plant mitochondria are well known to contain alternative oxidase that couples oxidation of hydroquinones (e.g., ubiquinol) directly to reduction of oxygen. Semiquinones (anion-radicals) and superoxide ions are formed in such reactions. The alternative oxidase thus provides a bypass to the conventional cytochrome electron-transfer pathway and allows plants to respire in the presence of compounds such as cyanides and carbon monoxide. There are a number of studies on this problem (e.g., see Affourtit et al. 2000, references therein). 

The increased throughput capahihty of the AutoAnalyzer and electronic balance, coupled with the reduction in staff time, substantially increased productivity. Further benefits accrued because implementation of the automatic techniques also coincided with a need for the LGC to measure the carbon monoxide yields of cigarettes because of the interest in the carbon monoxide dehveries of cigarettes hy epidemiologists working in the field of cardiovascular diseases. A development programme was initiated to find a method... 

Hydroformylation is the process of coupling carbon monoxide to an olefin with a reductive catalyst and hydrogen to produce an aldehyde-functionalized substrate. This coupling is typically followed by hydrogenation to produce a primary hydroxyl group. Several academic and commercial programs have participated in the development of hydroformylated triglycerides and fatty acid derivatives for use in polyurethanes. Two main processes for the hydroformylation of seed oils have been utilized. 

Coupling of organometallic reagents with hahdes in a carbon monoxide atmosphere leads to ketones by incorporation of a carbonylation step.147 148 These reactions involved a migration of one of the organic subsituents to the carbonyl carbon, followed by reductive elimination. These reactions can be carried out with stannanes149 or boronic acids150 151 as the nucleophilic component. 

An acyl-palladium complex might undergo a series of follow up reactions. Subsequent transmetalation and reductive elimination lead to the formation of a carbonyl compound. This process is also coined carbonylative coupling, referring to the cross-coupling reaction, which would take place in the absence of carbon monoxide under similar conditions (for more details see Chapter 2.4.). 

The application of surface-enhanced Raman spectroscopy (SERS) for monitoring redox and other processes at metal-solution interfaces is illustrated by means of some recent results obtained in our laboratory. The detection of adsorbed species present at outer- as well as inner-sphere reaction sites is noted. The influence of surface interaction effects on the SER spectra of adsorbed redox couples is discussed with a view towards utilizing the frequency-potential dependence of oxidation-state sensitive vibrational modes as a criterion of reactant-surface electronic coupling effects. Illustrative data are presented for Ru(NH3)63+/2+ adsorbed electrostatically to chloride-coated silver, and Fe(CN)63 /" bound to gold electrodes the latter couple appears to be valence delocalized under some conditions. The use of coupled SERS-rotating disk voltammetry measurements to examine the kinetics and mechanisms of irreversible and multistep electrochemical reactions is also discussed. Examples given are the outer- and inner-sphere one-electron reductions of Co(III) and Cr(III) complexes at silver, and the oxidation of carbon monoxide and iodide at gold electrodes. 

The reaction sequence in the vinylation of aromatic halides and vinyl halides, i.e. the Heck reaction, is oxidative addition of the alkyl halide to a zerovalent palladium complex, then insertion of an alkene and completed by /3-hydride elimination and HX elimination. Initially though, C-H activation of a C-H alkene bond had also been taken into consideration. Although the Heck reaction reduces the formation of salt by-products by half compared with cross-coupling reactions, salts are still formed in stoichiometric amounts. Further reduction of salt production by a proper choice of aryl precursors has been reported (Chapter III.2.1) [1]. In these examples aromatic carboxylic anhydrides were used instead of halides and the co-produced acid can be recycled and one molecule of carbon monoxide is sacrificed. Catalytic activation of aromatic C-H bonds and subsequent insertion of alkenes leads to new C-C bond formation without production of halide salt byproducts, as shown in Scheme 1. When the hydroarylation reaction is performed with alkynes one obtains arylalkenes, the products of the Heck reaction, which now are synthesized without the co-production of salts. No reoxidation of the metal is required, because palladium(II) is regenerated. 

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