How To Perform Suzuki-Miyaura Reactions of Nitroarene or Nitrations of Bromoarene Using a Pd0 Phosphine Complex: Theoretical Insight and Prediction

Pd-0(BrettPhos) (1) was experimentally applied to Suzuki-Miyaura reactions of nitroarenes which occur through oxidative addition of nitroarene (ArNO2) to Pd-0. On the other hand, Pd-0(tBu-BrettPhos) (2) was experimentally applied to nitrations of bromoarenes which occur through reductive elimination of nitroarene. DFT calculations disclosed that oxidative addition of 4-nitroanisole to 1 was exergonic but that to 2 was endergonic, indicating that 1 is useful for oxidative addition of an Ar-NO2 bond but 2 is useful for reductive elimination of an Ar-NO2 bond. This difference in reactivity between 1 and 2 is explained in that bulky Bu-t groups on tBu-BrettPhos destabilize the Pd-II complex PdII(Ar)(NO2)(tBu-BrettPhos) due to large steric repulsion between Ar and tBu-BrettPhos but less bulky cyclohexyl groups on BrettPhos do not. It is theoretically predicted here that NMe2-substituted BrettPhos is better for Ar-NO2 bond cleavage than BrettPhos but xyl-BrettPhos is good for Ar-NO2 formation, as is Bu-t-BrettPhos, where NMe2 and 2,6-dimethylphenyl groups are introduced to BrettPhos instead of isopropyl and cyclohexyl groups, respectively.