<p>The
iridium-catalyzed silylation of aromatic C–H bonds has become a synthetically
valuable reaction because it forms aryl silanes with high sterically derived
regioselectivity with silane reagents that are produced and consumed on large
scales. Many groups, including our own, have reported iridium complexes of
phenanthroline or bipyridine ligands as catalysts for this reaction. Yet,
little is known about the mechanism by which the iridium-catalyzed silylation of
arenes occurs. Indeed, no iridium-silyl complexes have been prepared that react
with C-H bonds to form C-Si bonds in a fashion that is chemically and
kinetically competent to be part of the catalytic cycle. </p><p><br></p>
<p>In this
manuscript, we report the synthesis and reactivity of iridium-silyl compelexes
of the 2,9-Me<sub>2</sub>Phen ligand that generates the most active known
catalyst for the silylation of aromatic C-H bonds. We show by experiment and
computation that the most stable and most reactive silyl complex of this ligand
contains two silyl and one hydride ligands and by kinetic analysis of the
catalytic reaction determine the rate-limiting step for arenes with varying
electronic properties. Computational studies indicate that the steric
encumberance of the phenanthroline ligand controls the number of silyl ligands
bound to iridium and that the difference in the number of silyl ligands leads
to large differences to the rates of the reaction. These studies provide
insight into the origins of the high activity of the catalyst containing the
2,9-Me<sub>2</sub>Phen ligand.</p>
Tungsten imido-catalysed dimerisation of α-olefins: insight into the Lewis acid's function revealed from computational studies
