In Silico Acetylene [2+2+2] Cycloadditions Catalyzed by Rh/Cr Indenyl Fragments

Abstract

Metal-catalyzed alkyne [2+2+2] cycloadditions provide a variety of substantial aromatic compounds of interest in the chemical and pharmaceutical industries. Herein, the mechanistic aspects of the acetylene [2+2+2] cycloaddition mediated by bimetallic half-sandwich catalysts [Cr(CO)3IndRh] (Ind = (C9H7)−, indenyl anion) are investigated. A detailed exploration of the potential energy surfaces (PESs) was carried out to identify the intermediates and transition states, using a relativistic density functional theory (DFT) approach. For comparison, monometallic parent systems, i.e., CpRh (Cp = (C5H5)−, cyclopentadienyl anion) and IndRh, were included in the analysis. The active center is the rhodium nucleus, where the [2+2+2] cycloaddition occurs. The coordination of the Cr(CO)3 group, which may be in syn or anti conformation, affects the energetics of the catalytic cycle as well as the mechanism. The reaction and activation energies and the turnover frequency (TOF) of the catalytic cycles are rationalized, and, in agreement with the experimental findings, our computational analysis reveals that the presence of the second metal favors the catalysis.

Designing Rh(I)-Half-Sandwich Catalysts for Alkyne [2+2+2] Cycloadditions

“…Our slippage span model has quantified these observations and has allowed to establish trends of catalyst's performance, which is evaluated computing the TOF. The validity of the slippage span model has been recently extended to more complex cycles, i.e., acetylene [2+2+2] cycloadditions catalyzed by heterobimetallic Rh/Cr indenyl fragments, 91 supporting the idea that this quantitative structure-activity relation is more general and prompting for further testing and application. The metal-Cp′ bonding mode has direct influence on the electron density at the metal, which is the catalytic center.…”

A Density Functional Theory Study on the Cobalt-Mediated Intramolecular Pauson–Khand Reaction of Enynes Containing a Vinyl Fluoride Moiety

“…59,60 This model has been successfully and widely applied to rationalize the reactivity of several cycloaddition reactions, such as strain-promoted azide-alkyne cycloadditions (SPAAC), 61,62 strain-promoted oxidation-controlled cyclooctyne-1,2-quinone cycloadditions (SPOCQ), 63,64 and inverse electron demand Diels-Alder cycloadditions (IEDDA), 65,66 but also in substitution and elimination reactions 67,68 and organometallic chemistry. 69,70 According to this model, the energy along the reaction coordinate can be decomposed into the distortion energy and the interaction energy between the distorted structures of reactants, known as ΔE strain (ζ) and ΔE int (ζ), respectively. Furthermore, the distortion energy can be decomposed into the distortion energies of the individual reactants; in this case, the distortion energy of the enyne and Co 2 (CO) 3 .…”

DFT study on stereoselective Rh-catalyzed intramolecular [2 + 2 + 2] cycloaddition of allene–ene–ynes

“…There are some theoretical works on the mechanisms of transition metal-catalyzed [2 + 2 + 2] cycloaddition reactions, in which the catalysts are Ni(PPh 3 ) 2 Cl 2 , 24 Ni(COD) 2 , 25 [Ir(cod)Cl] 2 [BINAP], 26 [Ir(cod)Cl] 2 [SEGPHOS], 27 [Cp*Ru(CH 3 CN) 3 ]PF 6 [Et 4 NCl], 28 (η 5 -C 5 H 5 )Rh, 29 RhCl(PPh 3 ) 3 , 30 (BINAP/[Rh(cod) 2 ]BF 4 ), 31 CpRh(CH) 4 , 32 and [Cr(CO) 3 IndRh] (Ind = C 9 H 7 − , indenyl anion). 33…”

“…23 There are some theoretical works on the mechanisms of transition metal-catalyzed [2 + 2 + 2] cycloaddition reactions, in which the catalysts are Ni(PPh 3 ) 2 Cl 2 , 24 Ni(COD) 2 , 25 28 (η 5 -C 5 H 5 )Rh, 29 RhCl(PPh 3 ) 3 , 30 (BINAP/[Rh(cod) 2 ] BF 4 ), 31 CpRh(CH) 4 , 32 and [Cr(CO) 3 IndRh] (Ind = C 9 H 7 − , indenyl anion). 33 There was also a theoretical report on the mechanism for transition metal-catalyzed cycloaddition reactions using RhCl (PPh 3 ) 3 and RhCl(CO) 2 (the monomer [RhCl(CO) 2 ] 2 ). 34 For the catalyst RhCl(PPh 3 ) 3 , B3LYP-D3/cc-pVDZ-PP gives an activation free-energy barrier of 30.6 kcal mol −1 , in line with the experimental temperature of 373 K. However, for the catalyst [RhCl (CO) 2 ] 2 , the monomer might not well mimic the real catalyst, since the calculated free-energy barrier is only 15.1 kcal mol −1 , much lower than the best estimation of about 25.0 kcal mol −1 from experimental conditions (333 K and 1 hour).…”