Nitrile, coordinated

The functional form of this rate expression is consistent with the behavior of the iridium system observed throughout the kinetic investigations. The coordination of nitrile to iridium is anticipated to produce more than a simple inhibitory effect. Being the dominant equilibrium in the mechanism, nitrile coordination may produce the observed first order dependence of the reaction rate with respect to hydrogen. Given Kcn[RCN] is the predominant term in the denominator, the rate expression may be reduced to the form of (8) which is first order with respect to both olefin and [H2]. 

The reacting species is a rather weak electrophile and, therefore, only particularly reactive aromatics are suitable substrates. Consequently, the reaction is restricted for polyhydric phenols and their ethers, and reactive heterocycles. With strong acidic systems, such as AICI3 in halogenated benzene solvents, alkylben-zenes can react at more elevated temperatures (>50°C). Trichloroacetonitrile works also well with nonactivated aromatics. The 12 chloroimine, the protonated nitrile (13), or the nitrile coordinated with the Lewis acid are possible involved electrophiles. 

The positions of the three principal bands (A, B, and C) are listed in Table IX for several complexes. B and C appeared when Ni[P-(C6H5)3]3 was added to a solution of the nitrile (band B). Therefore it is reasonable to assign band B and C> respectively, to the free nitrile and to the nitrile coordinated on the nickel(0). A shift of v (CN) to lower frequency on complexation of benzonitrile to Ni[P(0-o-C6H4CH3)3]3 has been reported recently (20). A further proof that nickel(0) complex is responsible for band C is its disappearance on addition of an aromatic halide. 

Studies of equilibria in which cyanoolefins are allowed to react with Ni[P(0-o-tolyl)3]3 have shown (36) that olefin coordination of 4PN is preferred over 3PN by a factor of 200, while olefin coordination of 2PN is preferred over 3PN by a factor of 1000. (Note the decreasing K for olefin complex formation in Table II in the series CH2=CH(CH2)BCN as n increases from 0 to 3 4 x 104,10,3.6, and 2.2. A value of 0.5 can be estimated for n - oo, based on the K for 1-hexene.) The relative amount of nitrile-coordinated nickel in solutions of cyanoolefins increases with added free phosphorus ligand, because of the different stoichiometries in Eqs. (14) and (15). 

The interaction (3.194) of oximes and nitriles, coordinated to RhCl3, takes place differently in comparison with the described reactions (3.192) and (3.193) [416a] ... 

Another impressive example of the transition metal-catalyzed Michael reaction was reported by Sawamura and Ito in 1992 (Scheme 6) [7]. a-Methylcyanoacetate was treated with enones using 1 mol% Rh-TRAP (12) complex, and the corresponding adduct 13 was formed in up to 93 % ee. For this reaction, the trans-coordination mode of the chiral diphosphine 12 was essential for high asymmetric induction. It was proposed that coordination of the nitrile group to Rh, then oxidative addition of the active methine C-H bond gave not the a-C-bound enolate, but the nitrile-coordinating enolate 14, which was considered to be a reactive intermediate. The unique structure of this enolate was supported by X-ray analysis of a similar achiral Ru-cyanoacetate complex [8]. 

Most metals form complexes with nitriles. Coordinated nitriles are electrophilic at the a-carbon atom and many nucleophilic attacks have been demonstrated, some of the more important being the following125 ... 

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. 

An electron transfer-sensitive oln coordination alternative of substituted olefins to metal centers has been demonstrated [81] in the system [(NC)2C=C(CN)2W(CO)5]" (20) where the n complex with n = 0 (olefin coordination) changes reversibly to an ESR detectable a complex (nitrile coordination) after one-electron reduction ( = -1). Even in the absence of a detailed spin population analysis the low symmetry of the anionic complex is evident from at least three distinctly different N coupling constants in the ESR spectrum [81]. 

Bulky Nitrile Coordination-Induced Skeleton Rearrangement of Zr-/Si-Containing Metallacycles and Selective Synthesis of 5-Azaindoles... 

Bulky Nitrile Coordination-Induced Skeleton Rearrangement. .. 

Scheme 3.2 Bulky nitrile coordination-induced skeleton rearrangement of Zr-/Si-containing metallacycles and selective synthesis of S-azaindoles...

IPr)Ni(NCR)]2 complexes, obtained in high yields from [Ni(COD)2], IPr and nitrile, are also competent in the formation of pyridines from cycloaddition of diynes and nitrile (Scheme 10.7). The mechanism pathway could involve a partial dissociation of a dimer in which nitriles are Tj - and T -coordinated, allowing exogenous nitrile coordination before cycloaddition. 

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