C−C Bond Cleavage of Acetonitrile by a Carbonyl Iron Complex with a Silyl Ligand

Rhodium-catalyzed alkenylation of nitriles via silicon-assisted C-CN bond cleavage

Rhodium-catalyzed Mizoroki-Heck type reaction of nitriles via the cleavage of C-C bonds is described. Orthogonal and iterative functionalizations of arenes were also demonstrated by combining the present and conventional halide-based cross-coupling reactions.

Nickel-catalyzed carbocyanation of alkynes

Nickel-catalyzed carbocyanation reaction of alkynes is described. Alkynes undergo aryl- and allylcyanation reaction in the presence of nickel-phosphine catalysts to give a wide range of substituted acrylonitriles in highly stereo-, regio-, and chemoselective manners. Lewis acid cocatalysts, such as AlMe3, AlMe2Cl, and BPh3, are found to promote the arylcyanation significantly. The cooperative catalysis of nickel and Lewis acid also allows the carbocyanation reaction using alkenyl and alkyl cyanides.

Theoretical Study of Oxidative Additions of H2 and MeCN to a Nickel(0) Complex: Significantly Large Correlation Effects and Characteristic Features of the Reaction

Oxidative addition of H2 to Ni(PH3)2 was theoretically studied as a prototype of nickel-catalyzed sigma-bond activation reaction, where CASSCF, CASPT2, CCSD(T), broken symmetry (Bs) MP2 to MP4(SDTQ), and DFT methods were employed. The CASPT2 method yields a reliable potential energy curve (PEC) when the active space consists of 10 electrons and 10 orbitals including five outer 3d' orbitals. The CCSD(T) method presents almost the same PEC as the CASPT2-calculated one, when either the ANO or the cc-pVTZ basis set is used for Ni. Bs-MP4(SDTQ)-calculated PEC is similar to those calculated by the CASPT2/ANO method, while the PEC is not smooth around the transition state. In the DFT calculation, ANO, cc-pVTZ, and triple-zeta quality basis sets (SDB) with Stuttgart-Dresden-Bonn effective core potentials (ECPs) must be used for Ni. The DFT-calculated reaction energy is somewhat smaller than the CASPT2- and CCSD(T)-calculated values, while B3PW91 and mPW1PW91 present moderately better energy changes than BLYP, B1LYP, and B3LYP. Oxidative addition of MeCN to Ni(PH3)2 was investigated by the DFT(B3PW91) and CCSD(T) methods. Almost the same activation barrier was calculated by these methods, when cc-pVTZ was employed for Ni. However, the DFT method moderately underestimates the binding energy of the reactant complex and the reaction energy compared to the CCSD(T) method. This oxidative addition exhibits interesting characteristic features, as follows: The barrier height relative to infinite separation is lower, and the product is more stable than those of the oxidative addition of C2H6. These differences are discussed in detail in terms of Ni-Me and Ni-CN bond energies and the participation of the CN pi* orbital to stabilization interaction in the transition state.

Iron-Complex-Catalyzed CC Bond Cleavage of Organonitriles: Catalytic Metathesis Reaction between HSi and RCN Bonds to Afford RH and SiCN Bonds

The first example of the catalytic C-CN bond cleavage of acetonitrile as well as Si-CN bond formation have been achieved in the photoreaction of MeCN with Et3SiH promoted by [Cp(CO)2FeMe]. This catalytic system is applicable to other organonitriles. Several iron complexes [(eta(5)-C5R5)(CO)2FeR'] (R5 = H5, H4Me, Me5, H4SiMe3, H4I, H4P(O)(OMe)2; R' = SiMe3, CH2Ph, Me, Cl, I) were examined as catalyst, and [Cp(CO)2FeMe] was found to be the best precursor. A catalytic reaction cycle was proposed, which involves oxidative addition of Et3SiH to [Cp(CO)FeMe], reductive elimination of CH4 from [Cp(CO)FeMe(H)(SiEt3)], coordination of RCN to [Cp(CO)Fe(SiEt3)], silyl migration from Fe to N in the coordinated RCN, and dissociation of Et3SiNC from Fe. The reaction with MeCN of [Cp(CO)Fe(py)(SiEt3)], which was newly prepared and determined by X-ray analysis, and the reaction of Et3SiH with MeCN in the presence of a catalytic amount of [Cp(CO)Fe(py)(SiEt3)] showed that the 16-electron species [Cp(CO)Fe(SiEt3)] is the active species in the catalytic cycle (TON up to 251).

Experimental and Theoretical Examination of C−CN and C−H Bond Activations of Acetonitrile Using Zerovalent Nickel

Experimental and density functional theory show that the reaction of acetonitrile with a zerovalent nickel bis(dialkylphosphino)ethane fragment (alkyl = methyl, isopropyl) proceeds via initial exothermic formation of an eta(2)-nitrile complex. Three well-defined transition states have been found on the potential energy surface between the eta(2)-nitrile complex and the activation products. The lowest energy transition state is an eta(3)-acetonitrile complex, which connects the eta(2)-nitrile to a higher energy eta(3)-acetonitrile intermediate with an agostic C-H bond, while the other two lead to cleavage of either the C-H or the C-CN bonds. Gas-phase calculations show C-CN bond activation to be endothermic, which contradicts the observation of thermal C-CN activation in THF. Therefore, the effect of solvent was taken into consideration by using the polarizable continuum model (PCM), whereupon the activation of the C-CN bond was found to be exothermic. Furthermore the C-CN bond activation was found to be favored exclusively over C-H bond activation due to the strong thermodynamic driving force and slightly lower kinetic barrier.

The activation of alkyl cyanides using a rhodiumtrispyrazolylborate complex

The photochemical reaction of Tp'Rh(L)(eta2-PhN=L) [Tp' = tris-(3,5-dimethyl pyrazolyl)borate, L = CNCH(2)CMe(3)] to form the coordinatively unsaturated reactive fragment, [Tp'Rh(L)], in the presence of alkylnitriles has been studied. The [Tp'Rh(L)] complex has been shown to selectively activate the primary C H terminus of acetonitrile, propionitrile, butyronitrile, and valeronitrile. The resulting hydrides showed uncharacteristic stability in the presence of C(6)D(6) and their rates of reductive elimination were monitored by (1)H NMR spectroscopy. Competition reactions permit the establishment of the relative stabilities of the activation products.

Rh(I)-Catalyzed Silylation of Aryl and Alkenyl Cyanides Involving the Cleavage of C−C and Si−Si Bonds

The Rh(I)-catalyzed silylation of nitriles with disilanes is described. The cleavage of inert carbon-cyano and silicon-silicon bonds occurs in this catalysis.