Acetonitrile metal catalysis

Hydration of nitriles providing carboxamides is usually carried out m strongly basic or acidic aqueous media - these reactions require rather bars conditions and suffer from incomplete selectivity to the desired amide product. A few papers in the literature deal with the possibihty of transition metal catalysis of this reaction [28-30]. According to a recent report [30], acetonitrile can be hydrated into acetamide with water-soluble rhodium(I) complexes (such as the one obtained from [ RhCl(COD) 2] and TPPTS) under reasonably mild conditions with unprecedently high rate... 

Transition metal cations solvated by weakly coordinating solvents are useful precursors for a variety of nonaqueous synthetic applications. The dissociation of acetonitrile ligands opens up vacant coordination sites for catalysis, and allows transition metals to be introduced into extended arrays formed by condensation reactions with polydentate ligandsAlthough salts of homoleptic acetonitrile metal cations with tetrafluoroborate anions have been known since the 1960s, there has been no detailed description of the syntheses and characterization of these compounds. Likewise, there have been general descriptions of the syntheses of trifluoromethanesulfonate salts, but no specific outline for individual metals has been published. In this report, the syntheses of [M (CH3CN)x][BF4]2 (M = Cr,Mn,Fe,Co,Ni,Cu) and [M CHaCNlJlSOsCFsla (M = Mn,Fe,Co,Ni) are described. Two different methods are used to prepare tetrafluoroborate salts (1) the oxidation of metals with nitrosonium tetrafluoroborate, first described by Hathaway et al. and (2) the dehydration of aqueous tetrafluoroborate salts in a Soxhlet extractor with molecular sieves. The oxidation reaction is rapid, anhydrous, and recommended for smaller-scale preparations because of the relatively... 

Supported iron catalysts are notoriously difficult to reduce [6-8] and thus a substantial fraction of the iron can be expected to remain inactive for the catalysis of hydrogenation. Particular attention has therefore been paid to the preparation of Fe/MgO catalysts by several different methods and examination of their effectiveness in producing metallic iron of adequate specific surface area after reduction in hydrogen. The activity and selectivity for primary amine formation have been determined for the hydrogenation of ethanenitrile (acetonitrile) and propanenitrile. 

The NAD+-dependent alcohol dehydrogenase from horse liver contains one catalytically essential zinc ion at each of its two active sites. An essential feature of the enzymic catalysis appears to involve direct coordination of the enzyme-bound zinc by the carbonyl and hydroxyl groups of the aldehyde and alcohol substrates. Polarization of the carbonyl group by the metal ion should assist nucleophilic attack by hydride ion. A number of studies have confirmed this view. Zinc(II) catalyzes the reduction of l,10-phenanthroline-2-carbaldehyde by lV-propyl-l,4-dihy-dronicotinamide in acetonitrile,526 and provides an interesting model reaction for alcohol dehydrogenase (Scheme 45). The model reaction proceeds by direct hydrogen transfer and is absolutely dependent on the presence of zinc(II). The zinc(II) ion also catalyzes the reduction of 2- and 4-pyridinecarbaldehyde by Et4N BH4-.526 The zinc complex of the 2-aldehyde is reduced at least 7 x 105 times faster than the free aldehyde, whereas the zinc complex of the 4-aldehyde is reduced only 102 times faster than the free aldehyde. A direct interaction of zinc(II) with the carbonyl function is clearly required for marked catalytic effects to be observed. 

By comparison of the vibrational spectra of cationic copper and silver tetra (acetonitrile) complexes, the different bond strengths of the metal nitrogen bonds have been determined and the influence of this bond strength on catalysis has been shown to be strong.45... 

The oxidation is catalyzed by various heavy metal ions such as Cu , Fe (hemin complex), Ni and Co and their complexes,and more importantly, the addition of these ions leads to the selective formation of disulfides without any overoxidized products. The cluster (Bu"4N)2[Fe4S4(SR)4], the analog of the active site of nonheme iron-sulfur proteins, catalyzed extremely smooth oxidation of thiols by oxygen to disulfides in acetonitrile at 0 C (equation 4), while in the case of FeCb or FeCb catalysts oxygen uptake was very slow." The catalysis by AI2O3 for aerobic oxidation is also common. Thus, by stirring thiols in benzene with exposure to air at room temperature for 4-6 h disulfides were obtained almost quantitatively except in the hindered case of Bu SH. 

Catalytic activity of rare earth elements (i.e., lanthanides, symbol Ln) in homogeneous catalysis was mentioned as early as 1922 when CeCls was tested as a true catalyst for the preparation of diethylacetal from ethanol and acetaldehyde [1]. Solutions of inorganic Ln salts were subsequently reported to catalyze the hydrolysis of carbon and phosphorous acid esters [2], the decarboxylation of acids [3], and the formation of 4-substituted 2,6-dimethylpyrimidines from acetonitrile and secondary amines [4]. In the meantime, the efficiency of rare earth metals in heterogeneous catalysis, e. g., as promoters in lanthanide (element mixtures)-... 

Sen, A. Lai, T.-W. Catalysis by solvated transition-metal cations. Novel catalytic transformations of alkenes by tetrakis( acetonitrile )paUadium ditetrallnoroborate. Evidence for the formation of incipient carbonium ions as intermediates. J. Am. Chem. Soc. 1981,103, 4627- 629. 

Nucleophiles used in the seminal papers by Tsuji and co-workers were mostly stabilized carbon nucleophiles, and the method found an early synthetic application in a preparation of steroids." It soon became evident that many other types of nucleophiles could be used. In particular, hydride ion equivalents led to l-olefinsf ° " (see Sect. V.2.3.1), Silyl and stannyl enolates of simple ketones and aldehydes and esters can be aUylated, as well as allyl enol carbonates (see Sect. V.2.1.4), This is an indirect a-aUylation of ketones, aldehydes, and esters. Enol derivatives can take another reaction course under Pd(0) catalysis (Scheme 2). Thus, oxidation to a,/3-unsaturated carbonyl compounds ensues if reactions are performed in acetonitrile under precise sources of catalyst precursor. "" "" A full discussion on the dichotomy of allylation-oxidation has been published, as well as a comparison of the usefulness of several transition metals as catalysts in allylation of nucleophiles. ... 

Interestingly, in acetonitrile at 25°C the presence of Zn(II) was found essential for an efficient catalysis of this reaction. Coordination of the metal ion to the substrate is thus a driving force for the reduction to take place. 

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