Theoretical Study of N–H σ-Bond Activation by Nickel(0) Complex: Reaction Mechanism, Electronic Processes, and Prediction of Better Ligand

Abstract

N−H σ-bond activation of alkylamine by Ni(PCy 3 ) was investigated using density functional theory (DFT) calculations. When simple alkylamine NHMe 2 is a reactant, both concerted oxidative addition in Ni(PCy 3 )(NHMe 2 ) and ligand-to-ligand H transfer reaction in Ni(PCy 3 )(C 2 H 4 )(NHMe 2 ) are endergonic and need a high activation energy. When NH(Me)(Bs) (Bs = SO 2 Ph, a model of tosyl group used in experiments) is a reactant, both reactions are exergonic and occur easily with a much smaller activation energy. The much larger reactivity of NH(Me)(Bs) than that of NHMe 2 results from the stronger Ni− N(Me)(Bs) bond than the Ni−NMe 2 bond and the presence of the Ni−O bonding interaction between the Bs group and the Ni atom in the product. N-Heterocyclic carbene, 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr), is computationally predicted to be better than PCy 3 because the Ni−NMe 2 and Ni−N(Me)(Bs) bonds in the IPr complex are stronger, respectively, than those of the PCy 3 complex. The introduction of the electronwithdrawing Bs group to the N atom of amine and the use of IPr as a ligand are recommended for the N−H σ-bond activation. The C−H σ-bond activations of benzene via the oxidative addition and the ligand-toligand H transfer reaction were also investigated here for comparison with the N−H σ-bond activation. The differences between the C−H σ-bond activation of benzene and the N−H σ-bond activation of these amines are discussed in terms of the N−H, C−H, Ni− Ph, and Ni−NMe 2 , and Ni−N(Me)(Bs) bond energies and back-donation to benzene from the Ni atom.

Comprehensive Theoretical Study of Cp*IrIII-Catalyzed Intermolecular Enantioselective Allylic C–H Amidation: Reaction Mechanism, Electronic Processes, and Regioselectivity

“…The covalent bond energy BDE cov was approximately represented by eq based on the simple Hückel MO theory − BDE cov = false{ false( ε normalA − ε normalB false) 2 + 4 β 2 false} 1 / 2 where an A–B covalent bond is generated between the valence orbitals of A and B species, ε A and ε B are their valence orbital energies, and β is a resonance integral. Equation was successfully employed to discuss M–X, M–N, M–H, etc. − The β value was similar between the iridium and nitrogen atoms because the Ir valence orbital overlapped with the N valence orbital. Consequently, the difference among the Ir–N bond energies in 12 , 22 , 16 , and 17 resulted from the difference in the valence orbital energy.…”

“…The next question was the reason why the Ir–N bond energy decreased following the order alkene > allyl > OAc – . The covalent bond energy BDE cov was approximately represented by eq based on the simple Hückel MO theory − where an A–B covalent bond is generated between the valence orbitals of A and B species, ε A and ε B are their valence orbital energies, and β is a resonance integral. Equation was successfully employed to discuss M–X, M–N, M–H, etc. − The β value was similar between the iridium and nitrogen atoms because the Ir valence orbital overlapped with the N valence orbital.…”

DFT calculations in solution systems: solvation energy, dispersion energy and entropy

“…Sakaki et al employed this method to calculate the free-energy profiles of a series of transition metal catalytic reactions, e.g., the migratory insertion reactions CO 2 , 185,186 borylation, 187,188 [2 + 2] and [4+2] oxidative cyclization reactions, 189,190 and oxidative addition/reductive elimination reactions. [191][192][193][194][195] In addition, Guan,196,197 Bao, [198][199][200] Huang, 201 and Lei 202 applied this model to investigate the reaEction mechanisms and free-energy profiles of catalytic reactions.…”