Nishibayashis System

In analogy to the Schrock cycle, Nishibayashi et aL postulated a Chatt-like reaction mechanism, where the bimetallic complex breaks into two monometallic fragments in solution, followed by catalytic reduction at a single metal center. However, the proposed intermediates could not be observed, and the reaction mechanism remained unclear. In order to address this problem, DFT calculations on the mechanism of the ammonia synthesis catalyzed by the Nishibayashi system were performed. Importantly, Batista and coworkers found that the bimetallic complex is the effective catalyst instead of the monometallic species that was originally postulated to play this role. Moreover, the dinitrogen-bridged dinuclear structure remains intact throughout... 

Y. Nishibayashi, M. Saito, S. Uemura, S. Takekuma, H. Takekuma, Z. Yoshida, A non-metal system for nitrogen fixation. Nature, 2004, 428, 279-280. 

In 2011, Nishibayashi reported on a new Mo-based catalyst system supported by the tridentate PNP-pincer scaffold (PNP = 2,6-bis(di-tert-butylphosphinomethyl)pyridine) that can readily be modified in its steric and electronic properties (Scheme 34). This Hgand system was expected to provide sufficient steric protection of the Mo atom and being less susceptible to protonation and therefore mitigating the major drawbacks of the Schrock system. 

Nishibayashi Y, Iwai S, Hidai M. Bimetallic system for nitrogen fixation ruthenium-assisted protonation of coordinated N2 on mngsten with H2. Science. 1998 279 540-542. 

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