Nitriles insertion

Cyclopentadienylamine)scandium(2,3-dimethyl-l,3-butadiene) 7 was synthesized in good yield, as shown in Scheme 2. Complex 7 reacted with benzonitrile to form a /rz-imido complex 8, the structure of which was characterized by single crystal X-ray diffraction. This product 8 was proposed to be formed by nitrile insertion followed by an attack of another diene methylene group on the carbon atom of the imido intermediate.3 An unsaturated metal imido species was formed, which easily dimerized to produce 8. However, the yield of 8 was not reported. 

In marked contrast to the above results, double nitrile insertion into both the titanium-alkyl and titanium—vinyl bonds occurs to form the diazatitanacycles 74. Treatment of these titanacycles with dry hydrogen chloride affords the tetrasubstituted pyridine derivatives 75 (Scheme 14.32) [74], On the other hand, 2,3-diphenyltitanacyclobutene reacts with various nitriles to afford the products of mono-insertion, which afford the corresponding unsaturated ketones upon hydrolysis [73,74]. 

Irradiation of (38) with nitriles induces dimerization of the silirene with nitrile insertion to give the azadisilabicyclo[3.2.1]octa-3,6-diene (39), except with acrylonitrile, when the isoskeletal bicyclo[3.3.0]octa-3,6-diene (40) also results. It seems reasonable to suppose they form through [2+2] and [4 + 2] addition (Scheme 44) (78CC80). By way of contrast,... 

More recently, a novel metal-substituted methylenecyclopropene (triafulvene) derivative was obtained when bis(propyne)zirconocene was treated with one equivalent of tris(pentafluorophenyl)borane, followed by excess of benzonitrile (equation 367)430. The first step involves alkynyl ligand coupling to give the isolable Cp2Zr(//-2,4-hexadiyne)B(C6F5)3 betaine. This undergoes a formal intramolecular nitrile insertion into the Zr—C(sp2) c-bond of the adjacent alkenyl zirconocene unit, leading to the zirconium-boron triafulvene-betaine. X-ray analysis of the triafulvene confirmed the planar... 

Isolation of the air-sensitive silacyclopropene was avoided by development of a two-step, one-flask procedure, which transformed alkynes into the desired azasilacyclopentadienes (Scheme 7.29)." For terminal alkynes, silver phosphate was employed for di-terf-butylsilylene transfer and copper(I) triflate was used to promote nitrile insertion. These conditions successfully transformed phenylacetylene into azasilacyclopentadiene 106b. For internal alkynes, copper(I) triflate catalyzed both silylene transfer to 3-hexyne as well as nitrile insertion to produce enamine 106k. 

Nitriles can also undergo [2 + 2] cycloadditions with metal unsaturated bonds, e.g., at metallocenes with Zr=E (with E = 0 or s)180,181 or Ti=CH2182-187 moieties, giving unstable 4-membered metallacycles which are intermediates for other products. Other formal cyclo-additions involving nitrile insertions into metal carbon bonds are also known. Examples of cycloadditions of nitriles with C N bond formation to produce metallacycles were presented above ((11), Table 1 (7) and (8), Table 3). 

The scandium diene complex reacts with PhCN via initial nitrile insertion into the Sc-diene bond to give a dimeric r/2-imido species, but with a 2,2 -bipyridine under elimination of the free diene (Scheme 71). The latter reaction... 

As with the aryl compounds the reaction scheme is simplified for the sake of clarity. The reactions observed are various and include reductive coupling (ketones, nitriles), insertion (diphenylacetylene, isocyanate, isonitrile, CO2 and CO), and disproportionation (diphenylacetylene, CS2). The course of the reactions and the complexity of the product mixtures strongly depend on the nature of the alkyl groups and the substituents on the substrate molecule. As examples we will discuss reactions with ketones, acetylenes and CO. The reaction with ketones strongly resembles the coupling of nitriles R C=N on Cp2TiR (R = aryl). The coupling proceeds more slowly when R, R and R" increase in size. 

Ugolotti J, Kehr G, Frohlich R et al (2009) Nitrile insertion into a boryl-substituted five-membered zirconacycloallenoid unexpected formation of a zwitterionic boratirane noduct Chem Commun, 6572-6573... 

---