Synthesis, characterization, and reactivity of Fe complexes containing cyclic diazadiphosphine ligands: The role of the pendant base in heterolytic cleavage of H 2

Tianbiao Liu, Shentan Chen, Molly J. O'Hagan, Mary Rakowski Dubois, R Morris Bullock, Daniel L DuBois

Research output: Contribution to journalArticle

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Abstract

The iron complexes CpFe(P Ph 2N Bn 2)Cl (1-Cl), CpFe(P Ph 2N Ph 2)Cl (2-Cl), and CpFe(P Ph 2C 5)Cl (3-Cl)(where P Ph 2N Bn 2 is 1,5-dibenzyl-1,5-diaza-3,7-diphenyl-3,7-diphosphacyclooctane, P Ph 2N Ph 2 is 1,3,5,7-tetraphenyl-1,5- diaza-3,7-diphosphacyclooctane, and P Ph 2C 5 is 1,4-diphenyl-1,4-diphosphacycloheptane) have been synthesized and characterized by NMR spectroscopy, electrochemical studies, and X-ray diffraction. These chloride derivatives are readily converted to the corresponding hydride complexes [CpFe(P Ph 2N Bn 2)H (1-H), CpFe(P Ph 2N Ph 2)H (2-H), CpFe(P Ph 2C 5)H (3-H)] and H 2 complexes [CpFe(P Ph 2N Bn 2)(H 2)]BAr F 4, [1-H 2]BAr F 4, (where BAr F 4 is B[(3,5-(CF 3) 2C 6H 3) 4] -), [CpFe(P Ph 2N Ph 2)(H 2)]BAr F 4, [2-H 2]BAr F 4, and [CpFe(P Ph 2C 5)(H 2)]BAr F 4, [3-H 2]BAr F 4, as well as [CpFe(P Ph 2N Bn 2)(CO)]BAr F 4, [1-CO]Cl. Structural studies are reported for [1-H 2]BAr F 4, 1-H, 2-H, and [1-CO]Cl. The conformations adopted by the chelate rings of the P Ph 2N Bn 2 ligand in the different complexes are determined by attractive or repulsive interactions between the sixth ligand of these pseudo-octahedral complexes and the pendant N atom of the ring adjacent to the sixth ligand. An example of an attractive interaction is the observation that the distance between the N atom of the pendant amine and the C atom of the coordinated CO ligand for [1-CO]BAr F 4 is 2.848 Å, considerably shorter than the sum of the van der Waals radii of N and C atoms. Studies of H/D exchange by the complexes [1-H 2] +, [2-H 2] +, and [3-H 2] + carried out using H 2 and D 2 indicate that the relatively rapid H/D exchange observed for [1-H 2] + and [2-H 2] + compared to [3-H 2] + is consistent with intramolecular heterolytic cleavage of H 2 mediated by the pendant amine. Computational studies indicate a low barrier for heterolytic cleavage of H 2. These mononuclear Fe II dihydrogen complexes containing pendant amines in the ligands mimic crucial features of the distal Fe site of the active site of the [FeFe]-hydrogenase required for H-H bond formation and cleavage.

Original languageEnglish
Pages (from-to)6257-6272
Number of pages16
JournalJournal of the American Chemical Society
Volume134
Issue number14
DOIs
Publication statusPublished - Apr 11 2012

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Ligands
Carbon Monoxide
Amines
Atoms
Hydrides
Nuclear magnetic resonance spectroscopy
Conformations
Ion exchange
F 4
Iron
Derivatives
Hydrogenase
X ray diffraction
Hydrogen
Chlorides
X-Ray Diffraction
Catalytic Domain
Magnetic Resonance Spectroscopy

ASJC Scopus subject areas

  • Chemistry(all)
  • Catalysis
  • Biochemistry
  • Colloid and Surface Chemistry

Cite this

Synthesis, characterization, and reactivity of Fe complexes containing cyclic diazadiphosphine ligands : The role of the pendant base in heterolytic cleavage of H 2. / Liu, Tianbiao; Chen, Shentan; O'Hagan, Molly J.; Rakowski Dubois, Mary; Bullock, R Morris; DuBois, Daniel L.

In: Journal of the American Chemical Society, Vol. 134, No. 14, 11.04.2012, p. 6257-6272.

Research output: Contribution to journalArticle

@article{e9351e7f85d24a5cb5dc87c6ce7af93a,
title = "Synthesis, characterization, and reactivity of Fe complexes containing cyclic diazadiphosphine ligands: The role of the pendant base in heterolytic cleavage of H 2",
abstract = "The iron complexes CpFe(P Ph 2N Bn 2)Cl (1-Cl), CpFe(P Ph 2N Ph 2)Cl (2-Cl), and CpFe(P Ph 2C 5)Cl (3-Cl)(where P Ph 2N Bn 2 is 1,5-dibenzyl-1,5-diaza-3,7-diphenyl-3,7-diphosphacyclooctane, P Ph 2N Ph 2 is 1,3,5,7-tetraphenyl-1,5- diaza-3,7-diphosphacyclooctane, and P Ph 2C 5 is 1,4-diphenyl-1,4-diphosphacycloheptane) have been synthesized and characterized by NMR spectroscopy, electrochemical studies, and X-ray diffraction. These chloride derivatives are readily converted to the corresponding hydride complexes [CpFe(P Ph 2N Bn 2)H (1-H), CpFe(P Ph 2N Ph 2)H (2-H), CpFe(P Ph 2C 5)H (3-H)] and H 2 complexes [CpFe(P Ph 2N Bn 2)(H 2)]BAr F 4, [1-H 2]BAr F 4, (where BAr F 4 is B[(3,5-(CF 3) 2C 6H 3) 4] -), [CpFe(P Ph 2N Ph 2)(H 2)]BAr F 4, [2-H 2]BAr F 4, and [CpFe(P Ph 2C 5)(H 2)]BAr F 4, [3-H 2]BAr F 4, as well as [CpFe(P Ph 2N Bn 2)(CO)]BAr F 4, [1-CO]Cl. Structural studies are reported for [1-H 2]BAr F 4, 1-H, 2-H, and [1-CO]Cl. The conformations adopted by the chelate rings of the P Ph 2N Bn 2 ligand in the different complexes are determined by attractive or repulsive interactions between the sixth ligand of these pseudo-octahedral complexes and the pendant N atom of the ring adjacent to the sixth ligand. An example of an attractive interaction is the observation that the distance between the N atom of the pendant amine and the C atom of the coordinated CO ligand for [1-CO]BAr F 4 is 2.848 {\AA}, considerably shorter than the sum of the van der Waals radii of N and C atoms. Studies of H/D exchange by the complexes [1-H 2] +, [2-H 2] +, and [3-H 2] + carried out using H 2 and D 2 indicate that the relatively rapid H/D exchange observed for [1-H 2] + and [2-H 2] + compared to [3-H 2] + is consistent with intramolecular heterolytic cleavage of H 2 mediated by the pendant amine. Computational studies indicate a low barrier for heterolytic cleavage of H 2. These mononuclear Fe II dihydrogen complexes containing pendant amines in the ligands mimic crucial features of the distal Fe site of the active site of the [FeFe]-hydrogenase required for H-H bond formation and cleavage.",
author = "Tianbiao Liu and Shentan Chen and O'Hagan, {Molly J.} and {Rakowski Dubois}, Mary and Bullock, {R Morris} and DuBois, {Daniel L}",
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TY - JOUR

T1 - Synthesis, characterization, and reactivity of Fe complexes containing cyclic diazadiphosphine ligands

T2 - The role of the pendant base in heterolytic cleavage of H 2

AU - Liu, Tianbiao

AU - Chen, Shentan

AU - O'Hagan, Molly J.

AU - Rakowski Dubois, Mary

AU - Bullock, R Morris

AU - DuBois, Daniel L

PY - 2012/4/11

Y1 - 2012/4/11

N2 - The iron complexes CpFe(P Ph 2N Bn 2)Cl (1-Cl), CpFe(P Ph 2N Ph 2)Cl (2-Cl), and CpFe(P Ph 2C 5)Cl (3-Cl)(where P Ph 2N Bn 2 is 1,5-dibenzyl-1,5-diaza-3,7-diphenyl-3,7-diphosphacyclooctane, P Ph 2N Ph 2 is 1,3,5,7-tetraphenyl-1,5- diaza-3,7-diphosphacyclooctane, and P Ph 2C 5 is 1,4-diphenyl-1,4-diphosphacycloheptane) have been synthesized and characterized by NMR spectroscopy, electrochemical studies, and X-ray diffraction. These chloride derivatives are readily converted to the corresponding hydride complexes [CpFe(P Ph 2N Bn 2)H (1-H), CpFe(P Ph 2N Ph 2)H (2-H), CpFe(P Ph 2C 5)H (3-H)] and H 2 complexes [CpFe(P Ph 2N Bn 2)(H 2)]BAr F 4, [1-H 2]BAr F 4, (where BAr F 4 is B[(3,5-(CF 3) 2C 6H 3) 4] -), [CpFe(P Ph 2N Ph 2)(H 2)]BAr F 4, [2-H 2]BAr F 4, and [CpFe(P Ph 2C 5)(H 2)]BAr F 4, [3-H 2]BAr F 4, as well as [CpFe(P Ph 2N Bn 2)(CO)]BAr F 4, [1-CO]Cl. Structural studies are reported for [1-H 2]BAr F 4, 1-H, 2-H, and [1-CO]Cl. The conformations adopted by the chelate rings of the P Ph 2N Bn 2 ligand in the different complexes are determined by attractive or repulsive interactions between the sixth ligand of these pseudo-octahedral complexes and the pendant N atom of the ring adjacent to the sixth ligand. An example of an attractive interaction is the observation that the distance between the N atom of the pendant amine and the C atom of the coordinated CO ligand for [1-CO]BAr F 4 is 2.848 Å, considerably shorter than the sum of the van der Waals radii of N and C atoms. Studies of H/D exchange by the complexes [1-H 2] +, [2-H 2] +, and [3-H 2] + carried out using H 2 and D 2 indicate that the relatively rapid H/D exchange observed for [1-H 2] + and [2-H 2] + compared to [3-H 2] + is consistent with intramolecular heterolytic cleavage of H 2 mediated by the pendant amine. Computational studies indicate a low barrier for heterolytic cleavage of H 2. These mononuclear Fe II dihydrogen complexes containing pendant amines in the ligands mimic crucial features of the distal Fe site of the active site of the [FeFe]-hydrogenase required for H-H bond formation and cleavage.

AB - The iron complexes CpFe(P Ph 2N Bn 2)Cl (1-Cl), CpFe(P Ph 2N Ph 2)Cl (2-Cl), and CpFe(P Ph 2C 5)Cl (3-Cl)(where P Ph 2N Bn 2 is 1,5-dibenzyl-1,5-diaza-3,7-diphenyl-3,7-diphosphacyclooctane, P Ph 2N Ph 2 is 1,3,5,7-tetraphenyl-1,5- diaza-3,7-diphosphacyclooctane, and P Ph 2C 5 is 1,4-diphenyl-1,4-diphosphacycloheptane) have been synthesized and characterized by NMR spectroscopy, electrochemical studies, and X-ray diffraction. These chloride derivatives are readily converted to the corresponding hydride complexes [CpFe(P Ph 2N Bn 2)H (1-H), CpFe(P Ph 2N Ph 2)H (2-H), CpFe(P Ph 2C 5)H (3-H)] and H 2 complexes [CpFe(P Ph 2N Bn 2)(H 2)]BAr F 4, [1-H 2]BAr F 4, (where BAr F 4 is B[(3,5-(CF 3) 2C 6H 3) 4] -), [CpFe(P Ph 2N Ph 2)(H 2)]BAr F 4, [2-H 2]BAr F 4, and [CpFe(P Ph 2C 5)(H 2)]BAr F 4, [3-H 2]BAr F 4, as well as [CpFe(P Ph 2N Bn 2)(CO)]BAr F 4, [1-CO]Cl. Structural studies are reported for [1-H 2]BAr F 4, 1-H, 2-H, and [1-CO]Cl. The conformations adopted by the chelate rings of the P Ph 2N Bn 2 ligand in the different complexes are determined by attractive or repulsive interactions between the sixth ligand of these pseudo-octahedral complexes and the pendant N atom of the ring adjacent to the sixth ligand. An example of an attractive interaction is the observation that the distance between the N atom of the pendant amine and the C atom of the coordinated CO ligand for [1-CO]BAr F 4 is 2.848 Å, considerably shorter than the sum of the van der Waals radii of N and C atoms. Studies of H/D exchange by the complexes [1-H 2] +, [2-H 2] +, and [3-H 2] + carried out using H 2 and D 2 indicate that the relatively rapid H/D exchange observed for [1-H 2] + and [2-H 2] + compared to [3-H 2] + is consistent with intramolecular heterolytic cleavage of H 2 mediated by the pendant amine. Computational studies indicate a low barrier for heterolytic cleavage of H 2. These mononuclear Fe II dihydrogen complexes containing pendant amines in the ligands mimic crucial features of the distal Fe site of the active site of the [FeFe]-hydrogenase required for H-H bond formation and cleavage.

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