Nucleophilic attacks nitrile complexes

Firstly there is nucleophilic attack of the nitrile carbon atom by hydroxylamine. An amide oxime is produced this then forms an intensely colored complex with the iron(III) chloride. 

Numerous examples of nucleophilic attack on coordinated nitrile ligands are found in the literature, particularly when the transition metal is platinum(II).224 The nucleophilic attack of two equivalents of CIO I2CII20 on the electrophilic nitrile carbon atoms of both nitrile ligands in cis-or /r<7H.v-[PtC12(RCN)2] (R = Et, Prn, Pr1, Bu p-CF3C6H4, p- and o-MeC6H4) affords the corresponding A2-l,3-oxazoline complexes ((76) and (77), respectively), in which the heterocycle acts as a... 

In certain early transition metal complexes and in metal clusters, organic nitriles can insert into metal-hydrogen or metal-carbon bonds (equations 92 and 93). Similarly, nucleophilic attack at coordinated nitrile can yield methyleneamido complexes (equation 94). 

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. 

Figure 4-11. The attack of an external nucleophile upon a complex containing the nitrile ligand 4.1.

The reduction of nitriles by the nucleophilic attack of hydride transfer reagents has also been widely investigated and is a process with considerable synthetic potential. The reduction yields amine complexes, and rates are typically about ten thousand times faster than for reduction of the free ligand (Fig. 4-19). Once again, the principal effect appears to be associated with the build-up of positive charge on the ligand. 

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 ... 

However, when bound to a higher metal oxidation state center, with a limited tt-electron donor ability, the nitriles display v (N C) higher than in the free state and can be activated toward nucleophilic attack, as observed for the reactions of cfr-[ReCLi(NCMe)2] (formed by spontaneous reduction of ReCls in NCMe) with oximes, HON=CRR, amino-alkylated adenines, or alcohols, which behave as protic nucleophiles (reaction 2) to yield, for example, in the flrst case, the imine complexes cA-[ReCl4 NH=C(Me)ON=CRR 2]. 

Cyano-derivatives can be readily obtained by a ruthenium-catalyzed addition of various hydrazines to terminal alkynes [89] in which the cyano carbon atom arises from the terminal alkyne carbon atom. The tris(pyrazolyl)borate (Tp) complex RuCl(Tp)(PPh3)2 (1 mol%) was found to be the most active catalyst, and N,N-dimethylhydrazine (5 equiv.) the best nitrogen source. The proposed mechanism involves the nucleophilic attack of the nitrogen nucleophile on the a-carbon of a vinylidene intermediate (Scheme 8.27). Proton migration in the resulting a-hydrazi-nocarbene, followed by deamination, would give the nitrile derivative and regenerate the catalytic species. 

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-... 

Under neutral conditions Ru(II) complexes catalyze the nucleophilic addition of water to nitriles to yield amides [155], The reaction proceeds via external nucleophilic attack of water to the transition metal-activated nitrile. Under similar conditions <5-ketonitriles are converted into ene-lactams, a reaction that has found elegant application in a short diastereoselective synthesis of (-)-pumiliotoxin C (Sch. 37) [156]. 

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