Microkinetic modeling in homogeneous catalysis

Abstract

Computational homogeneous catalysis has focused traditionally on the calculation of free energy barriers, which are ultimately related to rate constants. Experiments do not focus on rate constants, but on reaction rates, which depend also on concentrations. The increasing efficiency of DFT and other electronic structure techniques has led to the development of models that provide quite accurate rate constants, to the extent that improved agreement with experiment requires the introduction of the role of concentration. Microkinetic modeling, consisting in the construction of explicit kinetic reaction networks merging the rate constants provided by calculation and concentration data supplied by experiment, is a simple and elegant way to introduce concentration effects in the computational description of homogeneous catalysis. It has a long history of application in computational heterogeneous catalysis and experimental biochemistry, but its use in computational homogeneous catalysis is still in an early stage. There are a number of situations in homogeneous catalysis where microkinetics have been shown to be critical, such as systems with complex reaction networks and systems where one key species has a concentration orders of magnitude different from the others. Microkinetic modeling, with its low computational cost, is likely to become a standard tool in computational homogeneous catalysis. It is certainly not necessary for all theoretical studies, but the researcher should always be aware of its existence. This article is categorized under: Structure and Mechanism > Reaction Mechanisms and Catalysis

Formic Acid Dehydrogenation by Ruthenium Catalyst – Computational and Kinetic Analysis with the Energy Span Model

“…23 and 39). [46] By comparing Figure 2 and Figure 3 one can appreciate the significant adjustment made on the energy landscape when this correction is considered. This gives the information of which steps are reversible or irreversible, but it erases any information concerning the potential Gibbs energy surface, as all the steps in quasi-equilibrium have, by definition, ΔG = 0 (i.e.…”

Exploring the Role of Coinage Metalates in Trifluoromethylation: A Combined Experimental and Theoretical Study

“…[2d] Gratifyingly,wewereable to in situ generate 1 Cu in quantitative yield using 1equiv of CuI and 1equiv of 1 Ag in THF or DMF at room temperature after one hour( reaction 1). [6] Although 1 Cu is insufficiently stable for isolation, [7] we confirmed its structure by using 19 FNMR spectroscopy,E SI-MS and single-crystal X-ray diffraction. [8] Thisr esult is certainly remarkable in view of the previously described difficulties to access to [Cu(CF 3 ) 2 ] À species in as electivem anner in solution.…”

“…Regardingt he MÀCb onds lengths, the AgÀCi st he longest distance (2.12 ), whereas the CuÀCi st he shortest with 1.94 .T he AuÀCd istances,i nt he range of 2.04-2.07 due to the relativistic gold contraction effect, [10] With ar eliable route in hand for accessing the target 1 M (M = Cu, Au), we next aimed to unravelt he participation of these species, along with 1 Ag ,i nt he activation of aryl halides using as ab enchmark ac ommon model system in trifluoromethylationr eactions, 4-iodobiphenyl (2)( Scheme 1). [11] The reaction of 1 Ag or 1 Au with 2 in DMFa t5 08Cd uring 24 hours did not provide the desired product observing by 19 FNMR the startingm aterials and/or decomposition products. [12] Delightfully,t he reaction of 1 Cu with 1.6 equivalents of 2 under the same reaction conditions led to an excellent yield of 4-trifluoromethylbiphenyl (2 CF3 ,9 3%)a ccording to 19 FNMR spectroscopy,a longw ith the formation of [Cu(CF 3 )I] À (3 Cu )( Scheme 1b).…”

“…[11] The reaction of 1 Ag or 1 Au with 2 in DMFa t5 08Cd uring 24 hours did not provide the desired product observing by 19 FNMR the startingm aterials and/or decomposition products. [12] Delightfully,t he reaction of 1 Cu with 1.6 equivalents of 2 under the same reaction conditions led to an excellent yield of 4-trifluoromethylbiphenyl (2 CF3 ,9 3%)a ccording to 19 FNMR spectroscopy,a longw ith the formation of [Cu(CF 3 )I] À (3 Cu )( Scheme 1b). These preliminary results confirm, for the first time, the involvement of 1 Cu in the activationo f2,i ts capability to transfer the two trifluoromethyl groups,a nd highlightsi ts remarkable performance compared to previously described Cu-mediated systemsu nder analogous reactionconditions.…”

“…[3d,f] Under our standard conditions, we exclusivelyo bserved 7 CF 3 ,d iscarding Scheme1.a) Trifluoromethylation of 2 with 1 Cu , 1 Ag , 1 Au . (i) Yieldc alculated according to 19 FNMR analysis using 4,4'-difluorobiphenyl as an internal standard. b) 19 FNMR spectrumi nthe region of CuCF 3 species after the trifluoromethylationr eaction.…”