Transition metal complexes with nitriles

The first two transition-metal complexes of 2-naphthalyne78 have been prepared79 to be used as intermediates in the synthesis of polysubstituted naphthalenes. The naphthalyne intermediate 206, prepared from 205 [Eq. (31)], couples with a wide array of nitriles to give zirconocycles (207) that have been converted into substituted naphthalenes (208) by reaction with HC1 and iodonaphthalenes (209) by reaction with I2 followed by HC1. The... 

Organic nitriles, in particular acetonitrile, form stable electron-donor-acceptor (EDA) complexes with a number of Lewis acids such as BX3(X = Cl, Br, 1), SnC, AICI3, and with many transition metal halides, the nitrile group acting as the electron donor ... 

Although the C-Zn bond is rather unreactive toward electrophiles such as aldehydes, ketones, esters, and nitriles, it undergoes transmetalations with many transition metal complexes to furnish new organometallics capable of reacting with a variety of electrophilic substrates (see Section 7.10). 

Treatment of alkylating agents with metal cyanides should in principle be the method of choice for preparing isocyanides (equation 25). But as the cyanide ion again represents an ambident nucleophile, the well-known problems already discussed will arise (Section 1.8.2.1.i). It remains to be stated that simple alkylation of alkali metal cyanides with halogen compounds or dialkyl sulfates is not useful for the preparation of isonitriles. The formation of nitriles always prevails and isocyanides are at best obtained in yields of up to 25%. " The prospects are much tetter in the alkylation of heavy metal cyanides, if the reaction is done under conditions which initially give rise to isocyanide-transition metal complexes (equation 26). These will then be transformed into isonitriles by treatment with KCN. Under optimized conditions this technique yielded 55% of ethyl isocyanide. ... 

So it became very surprising to see that the middle transition metal complexes 21-24 with Re(l) centers bearing chelate cw-diphosphine ligands were efficient catalysts in homogeneous hydrogenations of nitriles [75]. For instance, the hydrogenation of benzonitrile furnished the products dibenzylimine (PI), dibenzylamine (P2), and tribenzylamine (P3) with P2 as the major product (Scheme 27). Formation of benzylimine or benzylamine was not observed. Dibenzylimine was formed by the hydrogenation of dibenzylimine, while the... 

Although less studied, the hydrocyanation of alkynes in the presence of soluble transition metal complexes has also been reported. - The reactions conducted with nickel(O) catalysts occur with cis stereochemistry, high regioselectivity, and moderate-to-high yields. Again, both steric and electronic effects control the regioselectivity. These points are illustrated by the data in Equation 16.11. Terminal, straight-chain alkynes such as l-hex)me react to form predominantly the branched nitrile, whereas tert-butyl acetylene reacts to form mostly the terminal nitrile. Reactions conducted with DCN have shown that the addition occurs in a syn fashion. ... 

Among transition-metal complex catalyzed reactions of alkynes with carbon-heteroatom unsaturated compounds the most studied is co-cyclotrimer-ization of alkynes with nitriles to pyridines. For this process the same complexes can be used as for the cyclotrimerization of alkynes. The first report of a cyclopentadienylcobalt complex catalyzed co-cyclotrimerization of alkynes with nitriles appeared in 1973 [92] and was soon followed by other papers [93]. Co-cyclotrimerization of alkynes and nitriles with all its aspects has been recently reviewed [94] and because of that we will focus only on recent developments in this area. In this regard, advances have been made in simple co-cy-clotrimerization of ethyne with various nitriles [95], combinatorial synthesis of substituted pyridines [96], and co-cyclotrimerization of hydroxyalkynes with nitriles in aqueous media catalyzed by cobalt complex with hydrophobic chain attached to the cyclopentadienyl ring [97]. 

Finally, the coordination and reactivity of nitriles with low-valent late transition-metal complexes is of interest because catalytic hydration of nitriles to amides remains a challenging goal. The development of catalytic reactions that employ transition-metal complexes as catalysts under neutral and mild conditions has been proposed as a particularly important alternative for the nitrile hydration process and considerable efforts have been spent in this direction. 

---