Catalytic reduction of dinitrogen to tris(trimethylsilyl)amine using rhodium complexes with a pyrrole-based PNP-type pincer ligand

Abstract

Rhodium complexes bearing an anionic pyrrole-based PNP-type pincer ligand are synthesised and found to work as effective catalysts for the transformation of molecular dinitrogen into tris(trimethylsilyl)amine under mild reaction conditions.

Phosphines and N‐Heterocycles Joining Forces: an Emerging Structural Motif in PNP‐Pincer Chemistry

“…In the presence of potassium graphite and [H(OEt 2 ) 2 ][BAr F 4 ], these complexes were shown to catalyze the reduction of N 2 to NH 3 . Over the course of this catalytic transformation, protonation at the ligand backbone has been proposed to play a role (vide infra),, , , , , but in the syntheses of the catalysts 33‐M , the PNP pincer is thought to serve as a spectator ligand only.…”

“…For iron, cobalt and rhodium, the terminal dinitrogen complexes 39‐M (M = Fe, Co, Rh) have been prepared by reduction of the divalent chloro complexes Pyr ( R PNP)M II Cl ( 38‐M ) in the presence of gaseous N 2 (see Scheme ) , , , …”

“…Once again, the ligand seems to be innocent, at least during the preparation of the iron(II)‐ and cobalt(II)‐chloride and ‐dinitrogen complexes , , . Redox chemistry involving the ligand, however, seems to play a role in the preparation of the rhodium(II)‐chloride derivative Pyr ( t BuPNP)RhCl 38‐Rh , the synthesis of which was achieved by addition of Pyr ( t BuPNP)Li to RhCl 3 (MeCN) 3 in the absence of a reducing agent . The cobalt derivative Pyr ( Cy PNP)Co(N 2 ) 39‐Co was also shown to react with aromatic, vinylic and aliphatic aldehydes, although stoichiometric amounts of the pincer complex have to be employed .…”

“…In addition to their work on azaferrocene‐derived dinuclear N 2 complexes, Nishibayashi and workers have also shown that the reduction of dinitrogen to ammonia and hydrazine is catalyzed by various mononuclear Pyr ( R PNP)M(N 2 ) complexes ( 39‐M with M = Fe, Co, Rh) , , , . Stoichiometric amounts of KC 8 and [H(OEt 2 ) 2 ][BAr F 4 ] are commonly used as reductant and proton source, respectively.…”

Asymmetric bis-PNP pincer complexes of zirconium and hafnium – a measure of hemilability

“…The synthesis of [PNP Ph ]H and its subsequent lithiation has been previously reported and is analogous to the alkylated congeners. 12,17,[20][21][22][23][24][25][26][27][28][29] A variety of lithium bases have been used in the literature but in our hands the conditions outlined in Scheme 1 and the ESI † worked best. The lithium salt could be isolated from an Et 2 O solution in very good yield (86%), but even after prolonged exposure to dynamic vacuum ( Fig.…”