Nitriles metal carbonyl complexes

AT-heterocyclic carbenes show a pure donor nature. Comparing them to other monodentate ligands such as phosphines and amines on several metal-carbonyl complexes showed the significantly increased donor capacity relative to phosphines, even to trialkylphosphines, while the 7r-acceptor capability of the NHCs is in the order of those of nitriles and pyridine [29]. This was used to synthesize the metathesis catalysts discussed in the next section. Experimental evidence comes from the fact that it has been shown for several metals that an exchange of phosphines versus NHCs proceeds rapidly and without the need of an excess quantity of the NHC. X-ray structures of the NHC complexes show exceptionally long metal-carbon bonds indicating a different type of bond compared to the Schrock-type carbene double bond. As a result, the reactivity of these NHC complexes is also unique. They are relatively resistant towards an attack by nucleophiles and electrophiles at the divalent carbon atom. 

Nitrile derivatives of the metal carbonyls have been discussed together with other nitrogen donor molecules in a number of contexts. Much of the early work has been reviewed by Manuel 337) in his article on Lewis base-metal carbonyl complexes in Volume 3 of this series, and by Stroh-meier 436) in his review of photochemical substitution reactions. In general, nitriles are weaker Lewis donors than phosphorus and nitrogen bases 436), but compared to carbon monoxide, better electron donors but poorer acceptors 427). Force constants and assignments for a series of complexes [(MeCN)jjM(CO)g J (M = Cr, Mo, W) were studied 165, 228, 296) and... 

Nitrile complexes are obtained by dissolving a metal halide in the nitrile or by replacing CO from carbonyl complexes. A kinetic investigation of the reaction of acetonitrile on Group VI hexa-carbonyls22 showed that substitution by the first acetonitrile leads to increased replacement rates for the next two molecules. The second MeCN is built in cis to the first one, and replacement of the third CO gives /ac-Mo(CO)3(MeCN)3. Further substitution does not occur. The rate law comprises two terms and is of the form22 of equation (1). 

Recently the unprecedented example of stereoselective C—Si bond activation in cu-silyl-substituted alkane nitriles by bare CQ+ cations has been reported by Hornung and coworkers72b. Very little is known of the gas-phase reactions of anionic metal complexes with silanes. In fact there seems to be only one such study which has been carried out by McDonald and coworkers73. In this work the reaction of the metal-carbonyl anions Fe(CO) (n = 2, 3) and Mn(CO) (n = 3, 4) with trimethylsilane and SiH have been examined. The reactions of Fe(CO)3 and Mn(CO)4 anions exclusively formed the corresponding adduct ions via an oxidative insertion into the Si—H bonds of the silanes. The 13- and 14-electron ions Fc(CO)2 and Mn(CO)3 were observed to form dehydrogenation products (CO) M(jj2 — CH2 = SiMe2) besides simple adduct formation with trimethylsilane. The reaction of these metal carbonyl anions with SiFLj afforded the dehydrogenation products (CO)2Fe(H)(SiII) and (CO)3Mn(II)(SiII). ... 

T he free radical initiated polymerization of polar monomers containing pendant nitrile and carbonyl groups—e.g., acrylonitrile and methyl methacrylate—in the presence of metal halides such as zinc chloride and aluminum chloride, is characterized by increased rates of polymerization (2, 3, 4, 5,10, 30, 31, 32, 33, 34, 53, 55, 65, 66, 75, 76, 77, 87). Imoto and Otsu (30, 33, 34) have attributed this effect to the formation of a complex between the polar group and the metal halide. The enhanced reactivity of the complexed monomer extends to copolymerization with uncomplexed monomers, such as vinylidene chloride, which are readily responsive to... 

Nitrile complexes may be synthesized by the thermal reaction of the parent carbonyl with the appropriate nitrile, but elevated temperatures are required, and this often leads to complications of thermal decomposition and/or further reaction. A more controlled route widely used is the irradiation of the metal carbonyl in a solution of the nitrile, or in a donor solvent capable of forming a labile complex such as Cr(CO),THF. Addition of the nitrile displaces the weakly bound solvent molecule 172, 248). 

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. 

Some metal carbonyl hydrides dissolved in polar solvents such as water, alcohols, nitriles, ketones, etc., are acids. The acidic character of these complexes is due not only to the polarity of the metal-hydrogen bond, but to solvation of the proton and the carbonylate anion. Acidic metal carbonyl hydrides dissolved in nonpolar solvents do not dissociate, and their chemical properties are like those of nonacidic metal hydrides. [HCo(CO)4] and [HV(CO)6] are strong acids (Table 2.28). 

The metal-benzyne complexes, that can also be represented as metallacyclopro-penes, can insert a variety of unsaturated substrates (alkenes, alkynes, carbonylated derivatives, nitriles, etc.), if their NVE is lower or equal to 16, to give 5-membered metallocycle precursors of organic heterocycles ... 

The CP3UCHPR3 complexes also undergo insertion into the CsN bonds of nitriles and the C s O bonds of metal carbonyls. Thus, Cramer et al. [39] reported that insertion reactions with acetonitrile yield uranium imido complexes ... 

Metal-Cyano and Nitrile Complexes Ammine, Amido, Urea and Related Complexes Metal Carbonyl Compounds Metal-Acetylacetonato Compounds, Carboxylate Complexes and Complexes Involving the Carbonyl Group... 

Octacarbonyldicobalt shares with many other metal carbonyls and other organometallics the ability to catalyze the cyclotrimer-ization of alkynes and related condensations, e.g. of two alkyne and one nitrile molecule to give pyridines. Derived compounds including Hg[Co(CO)4]2, Co(CO)3NO (obtained from Co2(CO)g with NO or other nitrosating agents) and the alkyne complexes (RC2R )Co2(CO)6 (see below) all share this activity, but none of these compare in efficiency with the preferred CpCoL2 catalysts. 

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