Appended Lewis Acids Enable Dioxygen Reactivity and Catalytic Oxidations with Ni(II)

We disclose a suite of Ni(II) complexes featuring secondary
sphere
Lewis acids of varied Lewis acidity and tether lengths. Several of
these complexes feature atypical behavior of Ni(II): reactivity with
O2 that occurs only in the presence of a tethered Lewis
acid. In situ UV–vis spectroscopy revealed that, although adducts
are stable at −40 °C, complexes containing 9-borabicyclo[3.3.1]nonane
(9-BBN) Lewis acids underwent irreversible oxidative deborylation
when warmed to room temperature. We computationally and experimentally
identified that oxidative instability of appended 9-BBN moieties can
be mitigated using weaker Lewis acids such as pinacolborane (BPin).
These insights enabled the realization of catalytic reactions: hydrogen
atom abstraction from phenols and room temperature oxygen atom transfer
to PPh3.