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

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posted on 2018-07-06, 00:00 authored by Rong-Lin Zhong, Masahiro Nagaoka, Yoshiaki Nakao, Shigeyoshi Sakaki
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 PdII 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 tBu-BrettPhos, where NMe2 and 2,6-dimethylphenyl groups are introduced to BrettPhos instead of isopropyl and cyclohexyl groups, respectively.