Measuring the Relative Reactivity of the Carbon–Hydrogen Bonds of Alkanes as Nucleophiles

Abstract

We report quantitative measurements of the relative reactivities of a series of C-H bonds of gaseous or liquid C H alkanes (n=1-8, 29 different C-H bonds) towards in situ generated electrophiles (copper, silver, and rhodium carbenes), with methane as the reference. This strategy surpasses the drawback of previous model reactions of alkanes with strong electrophiles suffering from C-C cleavage processes, which precluded direct comparison of the relative reactivities of alkane C-H bonds.

Improving Catalyst Activity in Hydrocarbon Functionalization by Remote Pyrene–Graphene Stacking

“…It is well established that N 2 evolution in these transformationsi st he rate-determining step leading to the formation of am etallocarbene intermediate, and that the rate is faster for more electrophilicm etal centers. [10,19] Additionally,i t is also known that the higher the electrophilicity at the metalcarbene intermediate, the highert he yields of the CÀHf unctionalization products. [10] With these two ideas in mind, it seems reasonablet oa ssume that the copper center in 1-rGO is more electrophilic than that in 1,e xplaining the observed behavior in terms of yields and reactionr ates.…”

Gold(I)‐Catalyzed Intramolecular C(sp3)−H Insertion by Decarbenation of Cycloheptatrienes

“…[3a, 4] The group of PØrez reported the first C(sp 3 )ÀHi nsertion of gold(I) carbenes derived from ethyl diazoacetate to functionalize linear alkanes. [5,6] Later,t he groupso fT oste [7a] and Malacria [7b] demonstrated that gold(I) carbenes generatedb ye nyne cyclizationsu ndergo CÀHi nsertions intramolecularly.T he groups of Zhang, [8] Hashmi [9] and Malacria [10] also found that gold(I) vinylidenei ntermediates or a-oxo gold(I) vinylidenes undergo CÀHi nsertion reactions to access complex hydrocarbon skeletons and functionalized cyclopentanones. Other CÀH functionalizations have been reportedu sing gold(I) carbenes generated from diazo compounds [11,12] or by differentp recursors.…”

A Quantitative Model for Alkane Nucleophilicity Based on C−H Bond Structural/Topological Descriptors

“…[24] New descriptors may also be generated by machine-learning techniques. [25][26][27][28][29] Our groups have recently described the first experimental scale of the relative reactivity of carbon-hydrogen bonds in alkanes, [30] with methane as the reference,t owards metal carbene species as organometallic electrophiles (Scheme 1).Herein, we report the statistical treatment of that nucleophilic scale of alkanes,which has led to the development of amodel that replicates the experimental data to avery high degree by using structural characteristics of those CÀHbonds.Our aim is to find ap redictive tool for the challenging,l ow-reactive C À Hb onds of alkanes.Scheme 2s hows the array of 14 alkanes previously evaluated by means of competition experiments using silverbased catalysts to promote the catalytic insertion of the carbene CHCO 2 Et from ethyl diazoacetate (N 2 CHCO 2 Et) into those 29 CÀHb onds.T he relative reactivity (R r )w as Scheme 1. The previously reported first quantitative scale of alkane nucleophilicity has been statisticallys tudied and fitted (radial plot) by using six topologic descriptors of the evaluatedC ÀHbond.…”

“…[24] New descriptors may also be generated by machine-learning techniques. [25][26][27][28][29] Our groups have recently described the first experimental scale of the relative reactivity of carbon-hydrogen bonds in alkanes, [30] with methane as the reference,t owards metal carbene species as organometallic electrophiles (Scheme 1).…”

“…obtained with methane as the reference,a lthough the use of log(R r )s eems more appropriate as it can be correlated with DDG°values.T his is the difference in free energy in the step where the selectivity is decided, that is,the interaction of the electrophilic metallocarbene intermediate with the nucleophilic CÀHb ond (Scheme 2). We first analyzed the previously reported [30] experimental data and explored possible statistical correlations between them with SVD (singular value decomposition), at echnique similar to PCA (principal component analysis) that has been successfully applied in ap revious study to identify hidden descriptors for metal-ligand bond dissociation energies. [24] However,t his approach did not yield significant chemical insight for the current system probably because of the lack of diversity in the available sample.C ÀHbonds behave similarly with all three metal fragments,a nd data for different complexes thus essentially repeat the same information.…”