Pincer‐Type Phosphorus Compounds With Boryl‐Pendant And Application In Catalytic H₂ Generation From Ammonia‐Borane: A Theoretical Study

Abstract

Metal-free catalysts composed of heavy main group element(s) have been limited. Herein, a theoretical study unveils that pincer-type phosphorus compound bearing a boryl-pendant is good catalyst for H 2 generation from ammonia borane through phosphorus-boryl (PÀ B) cooperation function. Pincer-type phosphorus compound without boryl-pendant is not active for this reaction, indicating the important role of the PÀ B cooperation function.Catalytic generation of dihydrogen molecule (H 2 ) from ammonia borane (NH 3 BH 3 , AB) is drawing much attention owing to its potential application in chemical storage of H 2 molecule because of its high gravimetric hydrogen capacity and low molecular weight. [1] Conventionally, transition-metal complexes have been used as catalysts for this reaction, however, it is difficult to regenerate AB because transition metals tend to form a stable adduct with BNH x molecule, by-product of the reaction. [2] In this context, developing metal-free catalysts for the catalytic dehydrogenation of AB is vital to making further progress towards broadening the utilization of hydrogen energy. To date, two types of non-metal catalyst have been reported. The first type is based on Lewis acid [3] and Brønsted base. [4] The second type is frustrated Lewis pairs (FLPs), [5] which work as catalysts through cooperative function of the unquenched Lewis acid and Lewis base centers (Scheme 1a).Herein, we wish to propose a new metal-free system for catalytic H 2 generation from AB using a modified pincer-type phosphorus compound as a catalyst through careful theoretical study. This type of phosphorus compound, trivalent phosphorus compound 10-P-3 ADPO [6] 1OP (Scheme 1b) was originally reported by Arduengo and coworker in 1980s. [7] Since then, it has been recognized as a non-metal analogue of pincer metal complexes due to their geometrical similarities. In recent years, pincer-type phosphorus compounds have been attractive as one example of excellent metal-free catalyst. For instance, Radosevich and coworkers reported a milestone work by appling 1OP in transfer hydrogenation of azobenzene by AB; [8] This reaction occurs through a phosphorus-oxygen (PÀ O)[a

Reactivity of a Strictly T‐Shaped Phosphine Ligated by an Acridane Derived NNN Pincer Ligand

“…[46] Although further chemistry was not reported, this system holds immense potential for phosphorus-based reactivity and possible redox activity due to the increased chemical inertness and high rigidity of the ligand backbone. [56][57][58] In addition, extensive computational studies by Zhu, Zeng, Maeda, Sakaki and co-workers have suggested that phosphines ligated by NNN donor sets, in particular acridane derived systems, could be highly active in small molecule activation reactions, for example catalytic CO 2 reduction to formid acid, [59] ammonia-borane dehydrogenation, [60] and even dinitrogen splitting. [61] We recently reported the synthesis of NNN pincer ligand 1 iPr (Scheme 1) and its use in the synthesis of tantalum(V) complexes for the activation of small molecule substrates.…”