Insertion-coupling reaction

At this juncture there appear to be some distinct similarities between the early transition metal and actinide carbonylation results. The enediolate products are, with the exception of mole-cularity, the same (cf. J, and I), although the insertion/coupling reaction appears to be much more rapid for thorium and uranium. 

Fig. 6. Coupling of polymer chains via (a) photoinduced hydrogen abstraction free-radical reactions and (b) nitrene insertion/addition reactions.

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. 

As complex 67 outperforms the Fe(0)-ate complexes in rate and yield, shown in the reaction of cyclooctenyl bromide with PhMgBr (full conversion complex 67 <20 min, 81% yield, 38 18 h, 39% yield), it was shown that both Fe(0)-ate and Fe (—2)-ate complexes should be intermediates in cross-coupling reactions, but the major contribution should be made by the route emanating from Fe(—2)-com-plexes. The superiority of Fe(—2)-ate complexes was also shown in the stoichiometric insertion of 67 into allylic halides, which proceeded much faster (<5 min) than with any higher valent iron complex (hours or days). 

The 2,3-substituted indols are formed via a palladium-catalyzed coupling reaction of aryl halide, o-alkenylphenyl isocyanide, and amine (Equation (122)).481 Oxidative addition of an aryl halide, insertion of both the isonitrile and alkene moieties of o-alkenylphenyl isocyanide, and 1,3-hydrogen migration may form a 7r-allylpalladium species, which is then attacked by an amine to afford an indol. 

In their resonance forms, the complexes are considered as acetylenic 7t-complexes (+2 oxidation state) or as metallacyclopropenes (+4 oxidation state), which lead to coupling reactions of the alkyne (insertion into the metallacyclopropene) or to a substitution of the alkyne by the substrate. 

Attempts have been made to prepare polysilanes containing the 8-dimethylaminonaphth-l-yl ligand.863 The coupling reaction of 8-dimethylaminonaphth-l-yl lithium with MeSiClj has given the dichlorosilane 909, whose mild reduction with Mg has surprisingly yielded the disilane 910 rather than the expected polysilane (Scheme 128). The formation of the disilane may be rationalized by the insertion of a transient silylene 904 into an Si-N bond of... 

A Pd(II)-catalyzed sequential cyclization-coupling reaction of allenyl N-tosylcar-bamates and acrolein has been developed (Scheme 16.97) [103]. The proposed mechanism involves intramolecular aminopalladation of an allene, followed by insertion of acrolein and carbon-Pd bond protonolysis. 

Palladium salts will attack C-H bonds in functionalised aromatics such as acetoaniline to form palladium-carbon bonds that subsequently undergo insertion of alkenes [31], (3-Hydride elimination gave styryl derivatives and palladium hydride, which requires re-oxidation of palladium by benzoquinone. The reaction can be regarded as a combined Murai reaction (C-H activation, if electrophilic) and a Heck reaction (arylalkene formation), notably without the production of salts as the cross-coupling reactions do. An example is shown in Figure 19.15. 

When the secondary amine 33 was used instead of a primary amine, a different type of three-component coupling reaction took place with aldehyde 34 and 1-alkynes 35 to afford the corresponding allylamines (36 and 37) [22]. In this reaction, Ir-hydride generated by amine (33) with Ir, would be a key intermediate. The reaction may proceed by addition of the Ir-hydride to the enamine derived from amine 33 and alkyne 34, followed by insertion of aldehyde and dehydration to give the coupling product (36 and 37). 

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