Pendant bases as proton relays in iron hydride and dihydrogen complexes

Renee M. Henry; Richard K. Shoemaker; Daniel L. DuBois; M. Rakowski DuBois

doi:10.1021/ja057242p

Pendant bases as proton relays in iron hydride and dihydrogen complexes

Renee M. Henry, Richard K. Shoemaker, Daniel L. DuBois, M. Rakowski DuBois

Pacific Northwest National Laboratory

Research output: Contribution to journal › Article › peer-review

104 Citations (Scopus)

Abstract

The complex trans-[HFe(PNP)(dmpm)(CH₃CN)]BPh₄, 3, (where PNP is Et₂PCH₂N(CH₃)CH ₂PEt₂ and dmpm is Me₂PCH₂PMe ₂) can be successively protonated in two steps using increasingly strong acids. Protonation with 1 equiv of p-cyanoanilinium tetrafluoroborate in acetone-d₆ at -80 °C results in ligand protonation and the formation of endo (4a) and exo (4b) isomers of frans-[HFe(PNHP)(dmpm)(CH ₃CN)]-(BPFu)₂. The endo isomer undergoes rapid intramolecular proton/hydride exchange with an activation barrier of 12 kcal/mol. The exo isomer does not exchange. Studies of the reaction of 3 with a weaker acid (anisidinium tetrafluoroborate) in acetonitrile indicate that a rapid intermolecular proton exchange interconverts isomers 4a and 4b, and a pK_a value of 12 was determined for these two isomers. Protonation of 3 with 2 equiv of triflic acid results in the protonation of both the PNP ligand and the metal hydride to form the dihydrogen complex [(H₂)Fe(PNHP) (dmpm)(CH₃CN)]³⁺, 11. Studies of related complexes [HFe(PNP)(dmpm)(CO)]⁺ (12) and [HFe(depp)(dmpm)(CH ₃CN)]⁺ (10) (where depp is bis(diethylphosphino)propane) confirm the important roles of the pendant base and the ligand trans to the hydride ligand in the rapid intra- and intermolecular hydride/proton exchange reactions observed for 4. Features required for an effective proton relay and their potential relevance to the iron-only hydrogenase enzymes are discussed.

Original language	English
Pages (from-to)	3002-3010
Number of pages	9
Journal	Journal of the American Chemical Society
Volume	128
Issue number	9
DOIs	https://doi.org/10.1021/ja057242p
Publication status	Published - Mar 8 2006

ASJC Scopus subject areas

Catalysis
Chemistry(all)
Biochemistry
Colloid and Surface Chemistry

Access to Document

10.1021/ja057242p

Fingerprint Dive into the research topics of 'Pendant bases as proton relays in iron hydride and dihydrogen complexes'. Together they form a unique fingerprint.

Cite this

@article{aa1746fbc03d494d9cd8874e77eb5a77,

title = "Pendant bases as proton relays in iron hydride and dihydrogen complexes",

abstract = "The complex trans-[HFe(PNP)(dmpm)(CH3CN)]BPh4, 3, (where PNP is Et2PCH2N(CH3)CH 2PEt2 and dmpm is Me2PCH2PMe 2) can be successively protonated in two steps using increasingly strong acids. Protonation with 1 equiv of p-cyanoanilinium tetrafluoroborate in acetone-d6 at -80 °C results in ligand protonation and the formation of endo (4a) and exo (4b) isomers of frans-[HFe(PNHP)(dmpm)(CH 3CN)]-(BPFu)2. The endo isomer undergoes rapid intramolecular proton/hydride exchange with an activation barrier of 12 kcal/mol. The exo isomer does not exchange. Studies of the reaction of 3 with a weaker acid (anisidinium tetrafluoroborate) in acetonitrile indicate that a rapid intermolecular proton exchange interconverts isomers 4a and 4b, and a pKa value of 12 was determined for these two isomers. Protonation of 3 with 2 equiv of triflic acid results in the protonation of both the PNP ligand and the metal hydride to form the dihydrogen complex [(H2)Fe(PNHP) (dmpm)(CH3CN)]3+, 11. Studies of related complexes [HFe(PNP)(dmpm)(CO)]+ (12) and [HFe(depp)(dmpm)(CH 3CN)]+ (10) (where depp is bis(diethylphosphino)propane) confirm the important roles of the pendant base and the ligand trans to the hydride ligand in the rapid intra- and intermolecular hydride/proton exchange reactions observed for 4. Features required for an effective proton relay and their potential relevance to the iron-only hydrogenase enzymes are discussed.",

author = "Henry, {Renee M.} and Shoemaker, {Richard K.} and DuBois, {Daniel L.} and DuBois, {M. Rakowski}",

year = "2006",

month = mar,

day = "8",

doi = "10.1021/ja057242p",

language = "English",

volume = "128",

pages = "3002--3010",

journal = "Journal of the American Chemical Society",

issn = "0002-7863",

publisher = "American Chemical Society",

number = "9",

}

TY - JOUR

T1 - Pendant bases as proton relays in iron hydride and dihydrogen complexes

AU - Henry, Renee M.

AU - Shoemaker, Richard K.

AU - DuBois, Daniel L.

AU - DuBois, M. Rakowski

PY - 2006/3/8

Y1 - 2006/3/8

N2 - The complex trans-[HFe(PNP)(dmpm)(CH3CN)]BPh4, 3, (where PNP is Et2PCH2N(CH3)CH 2PEt2 and dmpm is Me2PCH2PMe 2) can be successively protonated in two steps using increasingly strong acids. Protonation with 1 equiv of p-cyanoanilinium tetrafluoroborate in acetone-d6 at -80 °C results in ligand protonation and the formation of endo (4a) and exo (4b) isomers of frans-[HFe(PNHP)(dmpm)(CH 3CN)]-(BPFu)2. The endo isomer undergoes rapid intramolecular proton/hydride exchange with an activation barrier of 12 kcal/mol. The exo isomer does not exchange. Studies of the reaction of 3 with a weaker acid (anisidinium tetrafluoroborate) in acetonitrile indicate that a rapid intermolecular proton exchange interconverts isomers 4a and 4b, and a pKa value of 12 was determined for these two isomers. Protonation of 3 with 2 equiv of triflic acid results in the protonation of both the PNP ligand and the metal hydride to form the dihydrogen complex [(H2)Fe(PNHP) (dmpm)(CH3CN)]3+, 11. Studies of related complexes [HFe(PNP)(dmpm)(CO)]+ (12) and [HFe(depp)(dmpm)(CH 3CN)]+ (10) (where depp is bis(diethylphosphino)propane) confirm the important roles of the pendant base and the ligand trans to the hydride ligand in the rapid intra- and intermolecular hydride/proton exchange reactions observed for 4. Features required for an effective proton relay and their potential relevance to the iron-only hydrogenase enzymes are discussed.

AB - The complex trans-[HFe(PNP)(dmpm)(CH3CN)]BPh4, 3, (where PNP is Et2PCH2N(CH3)CH 2PEt2 and dmpm is Me2PCH2PMe 2) can be successively protonated in two steps using increasingly strong acids. Protonation with 1 equiv of p-cyanoanilinium tetrafluoroborate in acetone-d6 at -80 °C results in ligand protonation and the formation of endo (4a) and exo (4b) isomers of frans-[HFe(PNHP)(dmpm)(CH 3CN)]-(BPFu)2. The endo isomer undergoes rapid intramolecular proton/hydride exchange with an activation barrier of 12 kcal/mol. The exo isomer does not exchange. Studies of the reaction of 3 with a weaker acid (anisidinium tetrafluoroborate) in acetonitrile indicate that a rapid intermolecular proton exchange interconverts isomers 4a and 4b, and a pKa value of 12 was determined for these two isomers. Protonation of 3 with 2 equiv of triflic acid results in the protonation of both the PNP ligand and the metal hydride to form the dihydrogen complex [(H2)Fe(PNHP) (dmpm)(CH3CN)]3+, 11. Studies of related complexes [HFe(PNP)(dmpm)(CO)]+ (12) and [HFe(depp)(dmpm)(CH 3CN)]+ (10) (where depp is bis(diethylphosphino)propane) confirm the important roles of the pendant base and the ligand trans to the hydride ligand in the rapid intra- and intermolecular hydride/proton exchange reactions observed for 4. Features required for an effective proton relay and their potential relevance to the iron-only hydrogenase enzymes are discussed.

UR - http://www.scopus.com/inward/record.url?scp=33644950893&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=33644950893&partnerID=8YFLogxK

U2 - 10.1021/ja057242p

DO - 10.1021/ja057242p

M3 - Article

C2 - 16506781

AN - SCOPUS:33644950893

VL - 128

SP - 3002

EP - 3010

JO - Journal of the American Chemical Society

JF - Journal of the American Chemical Society

SN - 0002-7863

IS - 9

ER -

Pendant bases as proton relays in iron hydride and dihydrogen complexes

Abstract

ASJC Scopus subject areas

Access to Document

Other files and links

Cite this