(PXP)Mo pincer complexes for catalytic dinitrogen reduction: Synthesis, characterization and mechanistic studies
(PXP)Mo pincer complexes for catalytic dinitrogen reduction: Synthesis, characterization and mechanistic studies
复制标题
用于催化二氮还原的 (PXP)Mo 钳配合物：合成、表征和机理研究
DOI：
10.1021/scimeetings.0c05415
复制
发表时间：
2020
期刊：
影响因子：
--
通讯作者：
Goldman, Alan S
中科院分区：
文献类型：
--
作者：
Malakar, Santanu;Zhou, Xiaoguang;Gordon, Benjamin;Bruch, Quinton J;Miller, Alexander J.;Krogh-Jespersen, Karsten;Goldman, Alan S
过去十年中，使用钳连接过渡金属配合物还原二氮方面取得了巨大进展。然而，此类配合物需要通过 Na/Hg 或 KC8 等强还原剂进行“预激活”，以实现还原性 N2 分解。在这项研究中，非无害的三卤化钼 (III) 配合物 (PhPN5P)MoCl3 和 (tBuPPHP)MoBr3 在配体外围带有酸性 E-H（E = N 或 P）质子，已被用来研究去质子 N2 分裂。这些复合物可以在 KOtBu 存在的情况下被激活，而不需要强还原剂。通过 E-M 键上 HX 的损失，与 KOtBu 的反应可能分别产生 (PhPN5P*)MoCl2 和 (tBuPPP)MoBr2。 N2 在金属上的空配位点结合，然后 N2 分裂，得到氮化物 (PhPN5P*)MoVI(N)Cl2 和 (tBuPPP)MoV(N)Br。先前的研究表明，在化学物质存在下，氮化钼可还原为氨。还原剂和质子源，但人们对各种氮化物的相对反应性以及导致氨形成和活性物质再生的详细事件顺序知之甚少。因此，我们已经开始研究这种氨形成的催化循环。新配合物 (iPrPSP)Mo 和 Nishibayashi 的 (tBuPNpyP)Mo 体系的机理研究，包括 DFT 和电化学研究，揭示了卤化物在分裂二氮中的特征作用。阐明了导致氨形成和催化剂再生的新途径。
Great progress has been made in the past decade in the use of pincer-ligated transition metal complexes for the reduction of dinitrogen. Such complexes, however, have required 'pre-activation' by a strong reducing agent like Na/Hg or KC8 to achieve reductive N2 splitting. In this study, non-innocent pincer molybdenum(III) trihalide complexes, (PhPN5P)MoCl3 and (tBuPPHP)MoBr3, bearing acidic E-H (E = N or P) protons on the ligand periphery, have been utilized to investigate deprotonative N2 splitting. These complexes can be activated in the presence of KOtBu, without the need for a strong reductant. Reaction with KOtBu presumably affords (PhPN5P*)MoCl2 and (tBuPPP)MoBr2 respectively, through the loss of HX across the E-M bond. N2 binding at the vacant coordination site on the metal is followed by splitting of N2 to afford nitrides (PhPN5P*)MoVI(N)Cl2 and (tBuPPP)MoV(N)Br. Previous studies have demonstrated the reduction of molybdenum nitrides to ammonia in the presence of chem. reductants and proton sources but little is known about the relative reactivity of various nitrides and the detailed sequence of events leading to ammonia formation and regeneration of the active species. We, therefore, have begun an investigation of such catalytic cycles for ammonia formation. Mechanistic studies of the new complex (iPrPSP)Mo and of Nishibayashi's (tBuPNpyP)Mo systems, including DFT and electrochemical studies, revealed characteristic roles of the halides in splitting dinitrogen. A new pathway leading to the formation of ammonia and regeneration of the catalyst was elucidated.