Theoretical Study on the Formation of Ni(PR 3 )(Aryl)F Complexes Observed in Ni-Catalyzed Decarbonylative C–CCoupling of Acyl Fluorides
2020
Recently a promising,
conceptually new base-free, nickel-catalyzed
decarbonylative Suzuki–Miyaura coupling method was reported
which employs acyl fluorides to produce transmetalation-active catalytic
intermediates. In the present study we have performed computations
to identify the reaction mechanism of the formation of these intermediates
and to address important reactivity issues. We have contrasted the
effect of two typical phosphine ligands (P = PCy3, PPh2Me), which show different behaviors according to two recent
but separate experimental reports. We have also considered different
experimental (stoichiometric and catalytic) conditions to elucidate
the corresponding experimental observations. The free energy profiles
of the most likely mechanisms supported the more facile formation
of the transmetalation-active catalytic intermediate with PPh2Me and also justified why the intermediate of the oxidative
addition cannot be observed for this ligand. A crucial ingredient
of the mechanisms is the cis–trans rearrangement
in the square-planar ligand structure around the Ni(II) center to
stabilize the complexes and to facilitate the Ni insertion preceding
the decarbonylation. We obtained two distinct pathways for this rearrangement:
either a square-planar–tetrahedral conformational transition
or a route through five-coordinated, more fluxional configurations,
depending on the phosphines. In fact, molecular dynamics simulations
revealed that the mobile trigonal-bipyramidal structures can remarkably
simplify the decarbonylation mechanism predicted by optimization calculations,
implying an even faster decarbonylation.
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