Nitriles, coordinated Reaction with nucleophiles

The presence of the electron-withdrawing nitrile group in acrylonitrile leads to polarization (6+CH2=CH-C=N6-) that promotes nucleophilic attack at the methylene carbon atom. The coordination of acrylonitrile to a metal center through the nitrile group results in enhanced polarization and further promotes reactions with nucleophilic reagents. For example, acetylacetonate ion reacts with the acrylonitrile complex, [Co(NH3)5NsCCH=CH2] , in aqueous solution at pH = 9, Eq. 1.28 62... 

New chelate rings have been formed by the nucleophilic attack of carbanions and nitriles, with both groups being coordinated throughout the reaction to either iron(II) or cobalt(III) (Scheme 61188189 and equation 56).190... 

Cationic methylplatinum(II)-nitrile complexes of the type m is-PtMeL2(NCR)+X have been isolated by the reaction of //vms-PtMeClL2, where L = dimethylphenylphosphine or trimethyl-arsine, with an aryl nitrile and AgX, where X = BF4, PF. Use of pentafluorobenzonitrile and 2,3,5,6-tetrafluorotetraphthalonitrile in alcohol has led to the synthesis of a series of imino ether complexes. A mechanism for imino ether formation, involving nucleophilic attack by an alcohol at a coordinated nitrile, is suggested and the course of the reaction is shown to be dependent not only on the alcohol but also on the size of the anion used.110... 

The metal-bound RCN group is also activated on coordination towards nucleophilic attack by alcohols, thiols or amines to give stable N-bonded iminoether, iminothioether and amidine complexes respectively.332 Several cationic cyanobenzylpalladium(II) complexes have been prepared, and the reactivity of the CN group towards nucleophiles has been studied.333,334 The palladium complex (97) reacts with aromatic amines to give chelated amidino complexes (98) and the reaction has been studied kinetically.333 In this case intermediates with the nitrile group bonded side-on are considered to be involved. 

Mechanistically, two scenarios have been advanced. The first involves coordination of the nitrile to the Ru center which is followed by nucleophilic attack at the nitrile, while the second entails a sequence of events starting with oxidative addition of water, an alcohol or an amine to the metal center, followed by insertion of the nitrile into the Ru-OH bond. A recent report describes the conjugate addition of alcohols to acrylonitrile compounds catalyzed by a mthenium-acetamido complex [Ru(PCy3)2(CO)(CH3CONH)-(i-PrOH)H] (7) (Scheme 10.13) [17]. The mechanistic investigation of this reaction supports the proposal that the N-coordination of acrylo-... 

Another example is found in the various platinum (II) ammines which contain acetonitrile. One such is formed by reaction of [Pt(CH3CN)2Cl2] with ammonia. This gives a product with a formal composition corresponding to [Pt(CH3CN)2(Cl)2(NH3)2]. For many years this was considered to be an unusual complex in which platinum (II) was 6-coordinated. There are very few instances (if any) in which platinum (II) exhibits a coordination number other than 4. It has been shown by x-ray studies (67) that the product of this reaction is [Pt(acetamidine)2Cl2] and that the reaction may be written as shown at the top of the next page. Here, the coordination act accentuates the electron drift from the nitrile carbon atom and makes it more susceptible to attack by nucleophiles—in this case, ammonia. This kind of process had been essentially substantiated by chemical studies carried out previously, and the formation of... 

Condensation reactions. Nitriles activated through coordination to Rh become nucleophilic toward aldehydes in DMSO such that p-hydroxy alkanitriles are formed at room temperature. The Rh complex also promotes transfer reaction of an organoborane to conjugated esters, and those with additional bonding opportunities cyclic structures may be erected. ... 

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