DFT Investigation of Suzuki–Miyaura Reactions with Aryl Sulfamates Using a Dialkylbiarylphosphine-Ligated Palladium Catalyst

Aryl
sulfamates are valuable electrophiles for cross-coupling reactions
because they can easily be synthesized from phenols and can act as
directing groups for C–H bond functionalization prior to cross-coupling.
Recently, it was demonstrated that (1-tBu-Indenyl)­Pd­(XPhos)­Cl
(XPhos = 2-dicyclohexylphosphino-2′,4′,6′-triisopropylbiphenyl)
is a highly active precatalyst for room-temperature Suzuki–Miyaura
couplings of a variety of aryl sulfamates. Herein, we report an in-depth
computational investigation into the mechanism of Suzuki–Miyaura
reactions with aryl sulfamates using an XPhos-ligated palladium catalyst.
Particular emphasis is placed on the turnover-limiting oxidative addition
of the aryl sulfamate C–O bond, which has not been studied
in detail previously. We show that bidentate coordination of the XPhos
ligand via an additional interaction between the biaryl ring and palladium
plays a key role in lowering the barrier to oxidative addition. This
result is supported by NBO and NCI-Plot analysis on the transition
states for oxidative addition. After oxidative addition, the catalytic
cycle is completed by transmetalation and reductive elimination, which
are both calculated to be facile processes. Our computational findings
explain a number of experimental results, including why elevated temperatures
are required for the coupling of phenyl sulfamates without electron-withdrawing
groups and why aryl carbamate electrophiles are not reactive with
this catalyst.