Theoretical Insights into [NHC]Au(I) Catalyzed Hydroalkoxylation of Allenes: A Unified Reaction Valley Approach Study

Hydroxylation
is an effective approach for the synthesis of carbon–oxygen
bonds and allylic ethers. The [NHC]­Au­(I) catalyzed intermolecular
hydroalkoxylation of allene was studied at the DFT and Coupled Cluster
level of theory. Using the Unified Reaction Valley Approach (URVA),
we carry out a comprehensive mechanistic analysis of [NHC]­Au­(I)-catalyzed
and noncatalyzed reactions. The URVA study of several possible reaction
pathways reveal that the [NHC]­Au­(I) catalyst enables the hydroalkoxylation
reaction to occur via a two step mechanism based upon the Au ability
to switch between π- and σ-complexation. The first step
of the mechanism involves the formation of a CO bond after the transition
state with no energy penalty. Following the CO bond breakage, the
OH bond breaks and CH bond forms during the second step of the mechanism,
as the catalyst transforms into the more stable π–Au
complex. The URVA results were complemented with local vibrational
mode analysis to provide measures of intrinsic bond strength for Au­(I)-allene
interactions of all stationary points, and NBO analysis was applied
in order to observe charge transfer events along the reaction pathway.
Overall, the π–Au CC interactions of the products
are stronger than those of the reactants adding to their exothermicity.
Our work on the hydroxylation of allene provides new insights for
the design of effective reaction pathways to produce allylic ethers
and also unravels new strategies to form C–O bonds by activation
of CC bonds.