The reactivity of a number of two-coordinate [Pd(L)(L′)] (L = N-heterocyclic carbene (NHC) and L′ = NHC or PR3) complexes with O2 has been examined. Stopped-flow kinetic studies show that O2 binding to [Pd(IPr)(P(p-tolyl)3)] to form cis-[Pd(IPr)(P(p-tolyl)3)(η2-O2)] occurs in a rapid, second-order process. The enthalpy of O2 binding to the Pd(0) center has been determined by solution calorimetry to be -26.2(1.9) kcal/mol. Extension of this work to the bis-NHC complex [Pd(IPr)2], however, did not lead to the formation of the expected diamagnetic complex cis-[Pd(IPr)2(η2-O2)] but to paramagnetic trans-[(Pd(IPr)2(η1-O2)2], which has been fully characterized. Computational studies addressing the energetics of O2 binding have been performed and provide insight into reactivity changes as steric pressure is increased.
ASJC Scopus subject areas
- Colloid and Surface Chemistry