Metal amide derivatives, multiple bonding

Besides the activation of the olefinic partner by a metal, the unfavorable thermodynamics associated with the addition of an enolate to a carbon—carbon multiple bond could be overwhelmed by using a strained alkene such as a cyclopropene derivative286. Indeed, Nakamura and workers demonstrated that the butylzinc enolate derived from A-methyl-5-valerolactam (447) smoothly reacted with the cyclopropenone ketal 78 and subsequent deuterolysis led to the -substituted cyclopropanone ketal 448, indicating that the carbometallation involved a syn addition process. Moreover, a high level of diastereoselectivity at the newly formed carbon—carbon bond was observed (de = 97%) (equation 191). The butylzinc enolates derived from other amides, lactams, esters and hydrazones also add successfully to the strained cyclopropenone ketal 78. Moreover, the cyclopropylzincs generated are stable and no rearrangements to the more stable zinc enolates occur after the addition. 

This survey is confined to an overview of group 13 amides containing M-NR2 (R = H, alkyl, aryl, silyl, etc.) groups derivatives where nitrogen is part of a delocalized or polydentate ligand, are not generally covered. However, as in the 1980 book, iminome-tallanes (metal imides) of formula (RMNR ) are treated because of their close relationship to amides and also because of the relevance of the lower derivatives (n= 1, 2 or 3) for possible M N multiple bonding. 

A novel route to synthesize phthahmide derivatives through ruthenium-catalyzed C-H bond functionalization of aromatic amides was developed by Ackermann and coworkers (Eq. (7.57)) [66]. This method is applicable to generate a potent COX-2 enzyme inhibitor in step-economical way. The reaction features by the insertion of a cycloruthenated species into a C—Het multiple bond of isocyanate and cleavage of pyrrolidinyl group. Electron-rich amides were found to favor the reaction, and an initial reversible C-H bond metalation step was also observed. 

The increase in activity in the field of organotin hydrides is mostly due to the facility of addition of the tin-hydrogen bond to unsaturated systems and to the multiple mechanistic investigations of the hydrostannation reaction. Hev is a number of organometallic reactions, i.e., addition to transition metal complexes7 condensation with metal alkyls yielding tin-metal derivatives and with metal amides for synthesis of compounds with longer tin chains. 

Amine activatitMi pathway has been well studied in catalysis by lanthanides, early transition metals, and alkali metals. In metal amide chemistry of late transition metals, there are mainly two pathways to synthesize metal amide complexes applicable under hydroamination conditions [54], One is oxidative addition of amines to produce a metal amide species bearing hydride (Scheme 8a). The other gives a metal amide species by deprotonation of an amine metal intermediate derived from the coordination of amines to metal center, and it often occurs as ammonium salt elimination by the second amine molecule (Scheme 8b). Although the latter type of amido metal species is rather limited in hydroamination by late transition metals, it is often proposed in the mechanism of palladium-catalyzed oxidative amination reaction, which terminates the catalytic cycle by p-hydride elimination [26]. Hydroamination through aminometallation with metal amide species demands at least two coordination sites on metal, one for amine coordination and another for C-C multiple bond coordination. Accordingly, there is a marked difference between the hydroamination via C-C multiple bond activation, which demands one coordination site on metal, and via amine activation. 

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