Dimerization nitrile metal complexes

Although ethers have been used less frequently than alcohols, it has recently been reported that tetrahydrofuran (THF) is photocatalytically activated by TBADT, and the alkylation of unsaturated nitriles is obtained in good yield [15]. As an alternative, the C—Br bond in various glycosyl bromides has been homolytically cleaved, and the resulting radical trapped by acrylonitrile to form the corresponding C-glycosides. The halogen abstraction step is initiated by a photolabile iron-based dimeric metal complex [16]. 

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. 

A two metal, two-electron (not two metal, four-electron) reductive coupling of organic nitriles can lead to dimeric methyleneamido complexes (equation 97). 

Transition metal carbonyls such as Co2(CO)8 and CoH(CO)4, formed in the reaction of R3SiH with dimer (but also Fe(CO)5 and M3(CO)i2 (M = Fe, Ru, Os)) have been found to be active catalysts for the hydrosilylation of olefins, dienes, unsaturated nitriles, and esters as well as for hydrosilylation C=0 and C=N bonds [56]. Hydrosilylation of phenylthioacetylenes in the presence of this catalyst is extremely regioselective [57]. Cobalt(I) complexes, e. g., CoH(X)2L3 (X = H, N), could be prospective candidates for investigation of the effectiveness of alkene hydrosilylation by trialkoxysilanes as well as dehydro-genative silylation [58]. Direct evidence for the silyl migration mechanism operative in a catalytic hydrosilylation pathway was presented by Brookhart and Grant [59] using the electrophilic Co cationic complex. 

This use of a dimeric metal carbonyl as a catalyst for a reaction not involving carbon monoxide is not too surprising. The carbonyl supplies the simplest surface, two metal atoms, the olefin forms a bridge across these atoms, and the nitrile is formed by transfer of reactants within the complex. 

Nitrido complexes have also been formed by metathesis and atom transfer processes. The reaction of dinitrogen with a molybdenum(III) species forms a molybdenum-nitrido complex, as shown in Equation 13.103. and described in more detail in the section of Chapter 5 on dinitrogen complexes. In a metathesis process involving related complexes, the reaction of a metal-alkylid)me complex with a nitrile extrudes an alkyne to form a metal nitride fliat adopts a dimeric structure (Equation 13.104). - Related nitrido complexes have been formed from an azabicydic compoimd that eliminates anthracene after forming the M-N bond (Equation 13.105). ... 

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