Biaryl Reductive Elimination Is Dramatically Accelerated by Remote Lewis Acid Binding to a 2,2′-Bipyrimidyl–Platinum Complex: Evidence for a Bidentate Ligand Dissociation Mechanism

The silicon and zinc Lewis acids
Si­(cat)2 (cat = catecholato),
Si­(catF)2 (catF = tetrafluorocatecholato),
and Zn­(C6F5)2 bind to the remote
ligand site of a 2,2′-bipyrimidyl–platinum diaryl complex.
This platinum complex provides a platform to systematically evaluate
electronic and reactivity differences triggered by Lewis acid binding.
The electron density of the bipyrimidine ligand is substantially depleted
upon Lewis acid binding, as evidenced by UV–vis spectroscopy
and cyclic voltammetry. Biaryl reductive elimination studies allowed
quantification of the effect of Lewis acid binding on reactivity,
and Lewis acid binding accelerated reductive elimination rates by
up to 8 orders of magnitude. Kinetics experiments in combination with
DFT studies support an unusual mechanism featuring complete dissociation
of the Lewis acid-coordinated bidentate bipyrimidine ligand prior
to reductive elimination.