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.
| 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 | |
| Publication status | Published - Mar 8 2006 |
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Pendant bases as proton relays in iron hydride and dihydrogen complexes. / Henry, Renee M.; Shoemaker, Richard K.; DuBois, Daniel L; DuBois, M. Rakowski.
In: Journal of the American Chemical Society, Vol. 128, No. 9, 08.03.2006, p. 3002-3010.Research output: Contribution to journal › Article
}
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 -