Synthesis and reactivity of iron–dinitrogen complexes bearing anionic methyl- and phenyl-substituted pyrrole-based PNP-type pincer ligands toward catalytic nitrogen fixation

Sekiguchi, Yoshiya; Kuriyama, Shogo; Eizawa, Aya; Arashiba, Kazuya; Nakajima, Kazunari; Nishibayashi, Yoshiaki

doi:10.1039/c7cc06987a

Cited by 71 publications

(58 citation statements)

References 38 publications

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“…In addition to these examples, the ubiquitous diarylamido-based PNP pincer is capable of ligand-based oxidation in certain instances, 30 and the pyrrole-based pincer ligands, pyr-ONO (pyr-ONO = trianion of 2,5-bis(3-( tert -butyl)2-phenoxy)pyrrole) and t Bu PNP ( t Bu PNP = anion of 2,5-bis((di- tert -butylphosphino)methyl)pyrrole), have been demonstrated to undergo protonation at the 3- and 4-positions of the pyrrolic ring in the presence of strong acids. 31,32 …”

Section: Introductionmentioning

confidence: 99%

Backbone Dehydrogenation in Pyrrole-Based Pincer Ligands

et al. 2018

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Treatment of both [CoCl(tBuPNP)] and [NiCl(tBuPNP)] (tBuPNP = anion of 2,5-bis((di-tert-butylphosphino)methyl)pyrrole) with one equivalent of benzoquinone affords the corresponding chloride complexes containing a dehydrogenated PNP ligand, tBudPNP (tBudPNP = anion of 2,5-bis((di-tert-butylphosphino)methylene)-2,5-dihydropyrrole). Dehydrogenation of PNP to dPNP results in minimal change to steric profile of the ligand but has important consequences for the resulting redox potentials of the metal complexes resulting in the ability to isolate both [CoH(tBudPNP)] and [CoEt(tBudPNP)], which are more challenging (hydride) or not possible (ethyl) to prepare with the parent PNP ligand. Electrochemical measurements with both the Co and Ni dPNP species demonstrate a substantial shift in redox potentials for both the M(II/III) and M(II/I) couples. In the case of the former, oxidation to trivalent Co was found to be reversible, and subsequent reaction with AgSbF6 afforded a rare example of a square-planar Co(III) species. Corresponding reduction of [CoCl(tBudPNP)] with KC8 produced the diamagnetic Co(I) species, [Co(N2)(tBudPNP)]. Further reduction of the Co(I) complex was found to generate a rare pincer-based π-radical anion that demonstrated well-resolved EPR features to the four hydrogen atoms and lone nitrogen atom of the ligand with minor contributions from cobalt and coordinated N2. Changes in the electronic character of the PNP ligand upon dehydrogenation are proposed to result from loss of aromaticity in the pyrrole ligand resulting in a more reducing central amido donor. DFT calculations on the Co(II) complexes were performed to shed further insight into the electronic structure of the pincer complexes.

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Section: Introductionmentioning

confidence: 99%

Backbone Dehydrogenation in Pyrrole-Based Pincer Ligands

et al. 2018

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“…[8][9][10][11] In 2003, Schrock and ac o-worker reported the first catalytic conversion of dinitrogeni nto ammonia with am ononuclear molybdenum-dinitrogen complex under ambientr eactionc onditions. [12][13][14][15] Since the first report using am olybdenum-dinitrogen complex, other research groups have succeeded in catalytic conversion of dinitrogen into ammonia or hydrazine under mild reactionc onditions such as À78 8Ce mploying iron [16][17][18][19][20][21][22][23][24][25] -, cobalt [26] -, ruthenium [27] -, osmium [27] -, vanadium [28] -, and titanium [29] -dinitrogen complexes.…”

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confidence: 99%

Catalytic Reactivity of Molybdenum–Trihalide Complexes Bearing PCP‐Type Pincer Ligands

Eizawa

Arashiba

Egi

et al. 2019

Chemistry An Asian Journal

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“…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.…”

Section: Pnp Pincers and Their Reactivity Patternsmentioning

confidence: 99%

“…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 ) , , , …”

Section: Pnp Pincers and Their Reactivity Patternsmentioning

confidence: 99%

“…Similar to the Ti, Zr and V complexes 33‐M discussed above all these N 2 ‐derivatives were found to catalyze the direct reduction of N 2 to ammonia and hydrazine. 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 .…”

Section: Pnp Pincers and Their Reactivity Patternsmentioning

confidence: 99%

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

2020

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Aminodiphosphines and their monoanionic amido derivatives are among the most widely used tridentate ligands. A good share of these ligands, in particular the ones that are based on a rigid N‐heterocyclic core, is predisposed to coordinate in a meridional fashion. Negatively charged derivatives of these meridionally coordinating N‐heterocyclic ligands satisfy all the criteria for PNP pincer scaffolds. Herein, these ligands and their coordination chemistry is reviewed from the perspective of coordination chemistry. For our discussion, ligands containing a protonated N‐heterocycle (e.g. pyrrole‐ or carbazole‐based PNP scaffolds) are to be distinguished from their counterparts that do not contain such an NH‐functionality (e.g. pyridine‐ or triazine‐based PNP scaffolds). Different synthetic methodologies for the preparation of PNP pincer complexes are presented and shown to often depend on the presence or absence of the aforementioned NH‐proton. The different reactivity patterns of the resulting complexes are sub‐divided into two categories, namely into metal‐centered reactions and reactions that result in a chemical transformation at the metal and the ligand. The latter represent ligand‐cooperative transformations, which often play a key role in catalysis, and are showcased by discussing selected applications in catalysis. It will become evident in this review that this relatively young research field is still emerging and far from reaching maturity. Finally, a brief overview on ligand/metal combinations that have not been explored to date is provided, to stimulate future research on PNP pincers featuring a central N‐heterocycle.

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Synthesis and reactivity of iron–dinitrogen complexes bearing anionic methyl- and phenyl-substituted pyrrole-based PNP-type pincer ligands toward catalytic nitrogen fixation

Cited by 71 publications

References 38 publications

Backbone Dehydrogenation in Pyrrole-Based Pincer Ligands

Backbone Dehydrogenation in Pyrrole-Based Pincer Ligands

Catalytic Reactivity of Molybdenum–Trihalide Complexes Bearing PCP‐Type Pincer Ligands

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

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