Mechanistic insight into conjugated N–N bond cleavage by Rh(iii)-catalyzed redox-neutral C–H activation of pyrazolones

Abstract

Density functional theory (DFT) calculations have been performed to investigate the detailed mechanism of Rh(III)-catalyzed redox-neutral C-H activation of pyrazolones with PhC≡CPh. It is found that (1) the methylene C-H activation is prior to the phenyl C-H activation, (2) the N-N bond cleavage is realized via Rh(III) → Rh(I) → Rh(III) rather than via Rh(III) → Rh(V) → Rh(III). The zwitterionic Rh(I) complex is identified to be a key intermediate in promoting the N-N bond cleavage. (3) Different from the Rh(III)-catalyzed hydrazine-directed C-H activation for indole synthesis, the rate-determining step of the reaction studied in this work is the Rh(III) → Rh(I) → Rh(III) process resulting in the N-N bond cleavage rather than the alkyne insertion step. The present theoretical study provides new insight into the mechanism of the conjugated N-N bond cleavage.

Theoretical Insight into C(sp3)–F Bond Activations and Origins of Chemo- and Regioselectivities of “Tunable” Nickel-Mediated/-Catalyzed Couplings of 2-Trifluoromethyl-1-alkenes with Alkynes

“…The geometries and energies of the reactants, intermediates, transition states, and products were fully optimized in the framework of density functional theory (DFT) at the B3LYP level, which has been indicated to describe Ni-catalyzed and other transition-metal-catalyzed organometallic systems reasonably well . The SDD basis set was employed for Ni, P, Si, Zn, and Al atoms, whereas the 6-31g­(d,p) basis set was chosen for C, H, O, and F atoms.…”

Mechanistic Insight into the Rh(III)-Catalyzed C—H Activation of 2-Acetyl-1-Arythydrazines in Water

“…By releasing the coordinated HOAc molecule, a more stable intermediate 3 is formed. In the following step, the resting acetate ligand in 3 acts as the base to deprotonate the ortho C2H bond via a concerted metalation–deprotonation (CMD) mechanism. ,− The activation barrier for this step ( 3 → TS3 – 4 → 4 ) is calculated to be 17.3 kcal mol –1 . Subsequently, dissociation of HOAc leads to the 16 e complex I , which lies 5.0 kcal mol –1 above the starting materials ( K + R1 ).…”

“…In the past decade, great progress has been made in transition metal-catalyzed CH functionalizations . In this respect, the Rh­(III) catalyst has been found to be very effective to synthesize indoles. − A metal carbene reaction pattern as a strong tool to functionalize aryl CH bonds has attracted great attention as compared with the traditional mode .…”

Mechanistic Investigation into RhIII‐Catalyzed Intramolecular Redox‐Neutral Annulation of Aryl Hydrazines with a Tethered Alkyne

“…The two N1−N2 bond cleavages that occur through L‐TSII‐V and L‐TSII‐8 clearly involve different reaction modes, the former of which is a proton transfer together with the N1−N2 bond cleavage, and the latter of which is an acylamino migration in which the electron pair of the N1−N2 bond is transferred to the N2 atom, as shown in Figures and in which the N1−N2 bond distance increases from 1.408 Å in L‐II to 1.961 Å in L‐TSII‐8 . The N1−N2 bond cleavage through L‐TSII‐8 clearly demands less energy than that of L‐TSII‐V . In fact, the N2‐electron‐deficient behavior in L‐II reduces the σ‐bonding electron density between the N1 and N2 atoms and increases the electron density on the N2 atom.…”