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Origin of the different reactivity of the high‐valent coinage‐metal complexes [RCu iii Me 3 ] − and [RAg iii Me 3 ] − (R=allyl) **
Author(s) -
Auth Thomas,
Stein Christopher J.,
O'Hair Richard A. J.,
Koszinowski Konrad
Publication year - 2022
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.202103130
Subject(s) - chemistry , dissociation (chemistry) , reactivity (psychology) , density functional theory , metal , transition state , crystallography , reaction mechanism , chemical reaction , computational chemistry , catalysis , organic chemistry , medicine , alternative medicine , pathology
High‐valent tetraalkylcuprates( iii ) and ‐argentates( iii ) are key intermediates of copper‐ and silver‐mediated C−C coupling reactions. Here, we investigate the previously reported contrasting reactivity of [RM iii Me 3 ] − complexes (M=Cu, Ag and R=allyl) with energy‐dependent collision‐induced dissociation experiments, advanced quantum‐chemical calculations and kinetic computations. The gas‐phase fragmentation experiments confirmed the preferred formation of the [RCuMe] − anion upon collisional activation of the cuprate( iii ) species, consistent with a homo‐coupling reaction, whereas the silver analogue primarily yielded [AgMe 2 ] − , consistent with a cross‐coupling reaction. For both complexes, density functional theory calculations identified one mechanism for homo coupling and four different ones for cross coupling. Of these pathways, an unprecedented concerted outer‐sphere cross coupling is of particular interest, because it can explain the formation of [AgMe 2 ] − from the argentate( iii ) species. Remarkably, the different C−C coupling propensities of the two [RM iii Me 3 ] − complexes become only apparent when properly accounting for the multi‐configurational character of the wave function for the key transition state of [RAgMe 3 ] − . Backed by the obtained detailed mechanistic insight for the gas‐phase reactions, we propose that the previously observed cross‐coupling reaction of the silver complex in solution proceeds via the outer‐sphere mechanism.