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

Pd⁰(BrettPhos) (1) was experimentally applied to Suzuki–Miyaura reactions of nitroarenes which occur through oxidative addition of nitroarene (ArNO₂) to Pd⁰. On the other hand, Pd⁰(^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 ^tBu groups on ^tBu-BrettPhos destabilize the Pd^II complex Pd^II(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 ^tBu-BrettPhos, where NMe₂ and 2,6-dimethylphenyl groups are introduced to BrettPhos instead of isopropyl and cyclohexyl groups, respectively.