Nitriles reductive coupling

There are a number of ways that nitriles may be converted to alkylimido ligands. Low valent niobium and tantalum complexes have been shown to reductively couple nitriles to give bridging... 

Raman spectroscopy metal in water complexes, 309 Rare earth complexes acetylacetone synthesis, 377 guanidinium, 282 hydroxamic acids, 506 Redox properties bipyridyl metal complexes, 90 Reductive coupling nitrile metal complexes, 265 Resorcinol, 2,4-dinitro-metal complexes, 273 Rhenium complexes acetylacetone, 376 synthesis, 375, 378... 

Due to space limitations, vinylogous reactions of pinacol coupling and reductive coupling using nitriles are not described. Also, reductive coupling reactions between compounds having carbon-carbon multiple bonds and carbonyl compounds are not covered. 

In 1987, Pedersen reported that reductive coupling of A -(trimethylsilyl)imines (or a combination of nitriles and BusSnH) occurred with NbCl4(THF)2 in DME to give 1,2-diamines in 40-73% yields (Equation (67)). ... 

The first tantalum nitrene was obtained in 1959 by thermolysis of [Ta(NEt2)]5-288 This class of compounds is presently accessible by several routes, including hydrogen abstraction from the mono- or di-alkylamides, reaction of metallacarbenes with organic imines, oxidation of low valent species by organic azides, or reductive coupling of nitriles (Table 13). The tantalum derivatives are usually stabler than those of niobium. 

A two metal, two-electron (not two metal, four-electron) reductive coupling of organic nitriles can lead to dimeric methyleneamido complexes (equation 97). 

The above system failed entirely when nonstabilized carbanions such as ketone or ester enolates or Grignard reagents were used as carbon nucleophiles, leading to reductive coupling of the anions rather than alkylation of the alkene. However, the fortuitous observation that the addition of HMPA to the reaction mixture prior to addition of the carbanion prevented this side reaction1 extended the range of useful carbanions substantially to include ketone and ester enolates, oxazoline anions, protected cyanohydrin anions, nitrile-stabilized anions3 and even phenyllithium (Scheme 3).s... 

A mechanistic rationale for the Pd-catalyzed addition of a C-H bond at nitriles to allenes is outlined in Scheme 3. The oxidative insertion of Pd(0) into the C-H bond of nitrile 1 produces the Pd(II) hydride species 16 (or alternatively a tautomeric structure E E2C=C=N PdH Ln may be more suitable, where E = H, alkyl, aryl and/or EWG). Carbopalladation of the allene 2 would afford the alkenylpalladium complex 17 (carbopalladation mechanism), which would undergo reductive coupling to give the addition product 3 and regenerates Pd(0) species. As an alternative mechanism, it may be considered that the hydropalladation of allenes with the Pd(II) intermediate 16 gives the jr-allylpalladium complex 18 which undergoes reductive coupling to afford the adduct 3 and a Pd(0) species (hydropalladation mechanism). 

Carbonylation of [CoH(CN)5]3- in strongly alkaline media results in the formation of [Co(CN)2-(CO)2]2- and the intermediacy of the short-lived tetracyanocobaltate(I) ion [Co(CN)4]3" in this process has been inferred from mechanistic studies (Scheme 9).15 Under very similar conditions [CoH(CN)s]3- catalyzes the cyanation of vinyl halides to form a,j3-unsaturated nitriles with retention of configuration (equation 6). Oxidative addition of vinyl halide to the intermediate [Co(CN)4]3- ion is stereoselective and in the a complex so produced reductive coupling of the vinyl and cyano ligands gives the stereoretentive organic product and regenerates [Co(CN)4]3-.78... 

An important and extensively investigated application of CpCo complex chemistry is the catalyzed synthesis of pyridines from alkynes and nitriles. Dissociation of the L ligands liberates the CpCo fragment to react with alkyne to form a cobaltacyclopentadiene complex. The nitrile coordinates to this intermediate and subsequently undergoes insertion to form a seven-membered cobaltacycle. Reductive coupling gives pyridine and reforms CpCo. Asymmetric alkynes add to the carbon with the bulkier substituent adjacent to the nitrile carbon. 

When coupled with a reductive step, nitriles can be converted directly into alcohols using Ru(P(i-Pr)3)2(CO)(H2)H2 (6) (Scheme 10.10) [14],... 

An intramolecular reductive coupling of ketones with nitriles has been reported for acyclic and monocyclic substrates y9-amino nitriles were isolated from acyclic malononitrile adducts [87]. The Sml2-initiated reductive cyclization of cyclic a-cyanoalkyl-substituted ketones leads to acyloin products in high yields. In this instance further irradiation of the reaction mixtures was performed to afford complete conversion (Scheme 27) [88]. More applications have been collected in several excellent reviews [89-92]. 

This chapter is concerned with the cathodic reduction of carboxylic acids and their derivatives, that is, esters, amides, anhydrides, acyl halides, hydrazides, nitriles, and corresponding thio derivatives. Cyclic derivatives of substituted carboxylic and polycarboxylic acids, such as lactones, lactams, imides, and anhydrides, are also included. Only those transformations in which the functional group itself is involved are discussed. Reductive coupling of carboxylic acids and derivatives is covered in Chapter 22, and there is some overlap with reduction of heterocycles in Chapter 18. 

Related to the intramolecular pinacolic coupling reactions in some respects is a ketone-nitrile reductive coupling process. This process also permits the construction of highly functionalized carbocycles, although the yields are sranewhat reduced owing to the reluctance of nitriles to undergo such radical addition reactions (equation 75). Presumably, simple reduction of the ketone to the alcohol c< npetes with the desired process. 

The dinuclear complex formed from TaCU and CH3CN, of composition Ta2Cl6(CH3CN)4, contains two Ta(V) centers and bridging a ligand formed by reductive coupling of two nitriles no Ta(III) metal-metal-bound species are isolated from these or related reactions . 

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