Dihydrogen

A better ligand than water? IR and X-ray evidence for aquo coordination in W(CO)3(PR3)2(H2O), thermodynamics of H2O versus η2-H2 binding, and H2O/D2 isotopic exchange. Implications on the biological activation of hydrogen

Gregory J. Kubas, Carol J. Burns, Guru Rattan K Khalsa, Lori Stepan Van Der Sluys, Gabor Kiss, Carl Hoff

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Abstract

Reactions of water with M(CO)3(PR3)2 and M(CO)3(PR3)22-H2) (M = Mo, W; R = Cy (cyclohexyl), i-Pr) have been studied in various organic solvents. The products contained reversibly bound H2O, and infrared studies showed v(OH) modes at widely varying positions. IR of 18O-labeled complexes and 1H NMR gave no evidence for hydride or hydroxide ligands, indicating that oxidative addition of water did not occur. NMR of the aquo complexes showed rapid exchange between free and coordinated water at 298 K. The aquo complex W(CO)3(P-i-Pr3)2(H2O)·THF was isolated from THF and structurally characterized. A long W-O distance of 2.320 (5) Å was observed for the reversibly bound H2O ligand, which also undergoes hydrogen-bonding interactions with both lattice THF and a CO on an adjacent molecule. Water was found to instantaneously displace the dihydrogen ligand in W(CO)3(PR3)22-H2) in THF solution to give aquo complexes, but in hexane H2 remained bound under a H2 atmosphere. Thermodynamic measurements of the equilibrium W(CO)3(PR3)2(H2) + H2O ⇌ W(CO)3(PR3)2(H2O) + H2 in THF showed that the ΔH value for binding was 3-4 kcal/mol higher for H2O. However, a higher entropy change related to hydrogen-bonding interactions between H2O and solvent resulted in ΔG favoring H2 coordination at 25°C by 1-2 kcal/mol. Isotopic exchange of W(CO)3(P-i-Pr3)22-D 2) with H2O under a D2 atmosphere took place in THF, giving W(CO)3(P-i-Pr3)2(D2O). Both the favored binding of H2 versus H2O and the latter exchange are relevant to the function of H2-activating enzymes such as hydrogenase. Crystal data for W(CO)3(P-i-Pr3)2)(H2O)·THF: space group P21/n, a = 13.554 (2) Å, b = 16.417 (5) Å, c = 15.059 (4) Å, β = 116.24 (2)°, Z = 4.

Original languageEnglish
Pages (from-to)3390-3404
Number of pages15
JournalOrganometallics
Volume11
Issue number10
StatePublished - Dec 1 1992

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Carbon Monoxide
Hydrogen
Ion exchange
Chemical activation
Thermodynamics
activation
Ligands
X rays
thermodynamics
ligands
Water
hydrogen
water
x rays
atmospheres
nuclear magnetic resonance
hydroxides
hydrides
enzymes
interactions

ASJC Scopus subject areas

  • Inorganic Chemistry
  • Organic Chemistry

Cite this

Dihydrogen : A better ligand than water? IR and X-ray evidence for aquo coordination in W(CO)3(PR3)2(H2O), thermodynamics of H2O versus η2-H2 binding, and H2O/D2 isotopic exchange. Implications on the biological activation of hydrogen. / Kubas, Gregory J.; Burns, Carol J.; Khalsa, Guru Rattan K; Van Der Sluys, Lori Stepan; Kiss, Gabor; Hoff, Carl.

In: Organometallics, Vol. 11, No. 10, 01.12.1992, p. 3390-3404.

Research output: Contribution to journalArticle

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title = "Dihydrogen: A better ligand than water? IR and X-ray evidence for aquo coordination in W(CO)3(PR3)2(H2O), thermodynamics of H2O versus η2-H2 binding, and H2O/D2 isotopic exchange. Implications on the biological activation of hydrogen",
abstract = "Reactions of water with M(CO)3(PR3)2 and M(CO)3(PR3)2(η2-H2) (M = Mo, W; R = Cy (cyclohexyl), i-Pr) have been studied in various organic solvents. The products contained reversibly bound H2O, and infrared studies showed v(OH) modes at widely varying positions. IR of 18O-labeled complexes and 1H NMR gave no evidence for hydride or hydroxide ligands, indicating that oxidative addition of water did not occur. NMR of the aquo complexes showed rapid exchange between free and coordinated water at 298 K. The aquo complex W(CO)3(P-i-Pr3)2(H2O)·THF was isolated from THF and structurally characterized. A long W-O distance of 2.320 (5) {\AA} was observed for the reversibly bound H2O ligand, which also undergoes hydrogen-bonding interactions with both lattice THF and a CO on an adjacent molecule. Water was found to instantaneously displace the dihydrogen ligand in W(CO)3(PR3)2(η2-H2) in THF solution to give aquo complexes, but in hexane H2 remained bound under a H2 atmosphere. Thermodynamic measurements of the equilibrium W(CO)3(PR3)2(H2) + H2O ⇌ W(CO)3(PR3)2(H2O) + H2 in THF showed that the ΔH value for binding was 3-4 kcal/mol higher for H2O. However, a higher entropy change related to hydrogen-bonding interactions between H2O and solvent resulted in ΔG favoring H2 coordination at 25°C by 1-2 kcal/mol. Isotopic exchange of W(CO)3(P-i-Pr3)2(η2-D 2) with H2O under a D2 atmosphere took place in THF, giving W(CO)3(P-i-Pr3)2(D2O). Both the favored binding of H2 versus H2O and the latter exchange are relevant to the function of H2-activating enzymes such as hydrogenase. Crystal data for W(CO)3(P-i-Pr3)2)(H2O)·THF: space group P21/n, a = 13.554 (2) {\AA}, b = 16.417 (5) {\AA}, c = 15.059 (4) {\AA}, β = 116.24 (2)°, Z = 4.",
author = "Kubas, {Gregory J.} and Burns, {Carol J.} and Khalsa, {Guru Rattan K} and {Van Der Sluys}, {Lori Stepan} and Gabor Kiss and Carl Hoff",
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TY - JOUR

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T2 - A better ligand than water? IR and X-ray evidence for aquo coordination in W(CO)3(PR3)2(H2O), thermodynamics of H2O versus η2-H2 binding, and H2O/D2 isotopic exchange. Implications on the biological activation of hydrogen

AU - Kubas, Gregory J.

AU - Burns, Carol J.

AU - Khalsa, Guru Rattan K

AU - Van Der Sluys, Lori Stepan

AU - Kiss, Gabor

AU - Hoff, Carl

PY - 1992/12/1

Y1 - 1992/12/1

N2 - Reactions of water with M(CO)3(PR3)2 and M(CO)3(PR3)2(η2-H2) (M = Mo, W; R = Cy (cyclohexyl), i-Pr) have been studied in various organic solvents. The products contained reversibly bound H2O, and infrared studies showed v(OH) modes at widely varying positions. IR of 18O-labeled complexes and 1H NMR gave no evidence for hydride or hydroxide ligands, indicating that oxidative addition of water did not occur. NMR of the aquo complexes showed rapid exchange between free and coordinated water at 298 K. The aquo complex W(CO)3(P-i-Pr3)2(H2O)·THF was isolated from THF and structurally characterized. A long W-O distance of 2.320 (5) Å was observed for the reversibly bound H2O ligand, which also undergoes hydrogen-bonding interactions with both lattice THF and a CO on an adjacent molecule. Water was found to instantaneously displace the dihydrogen ligand in W(CO)3(PR3)2(η2-H2) in THF solution to give aquo complexes, but in hexane H2 remained bound under a H2 atmosphere. Thermodynamic measurements of the equilibrium W(CO)3(PR3)2(H2) + H2O ⇌ W(CO)3(PR3)2(H2O) + H2 in THF showed that the ΔH value for binding was 3-4 kcal/mol higher for H2O. However, a higher entropy change related to hydrogen-bonding interactions between H2O and solvent resulted in ΔG favoring H2 coordination at 25°C by 1-2 kcal/mol. Isotopic exchange of W(CO)3(P-i-Pr3)2(η2-D 2) with H2O under a D2 atmosphere took place in THF, giving W(CO)3(P-i-Pr3)2(D2O). Both the favored binding of H2 versus H2O and the latter exchange are relevant to the function of H2-activating enzymes such as hydrogenase. Crystal data for W(CO)3(P-i-Pr3)2)(H2O)·THF: space group P21/n, a = 13.554 (2) Å, b = 16.417 (5) Å, c = 15.059 (4) Å, β = 116.24 (2)°, Z = 4.

AB - Reactions of water with M(CO)3(PR3)2 and M(CO)3(PR3)2(η2-H2) (M = Mo, W; R = Cy (cyclohexyl), i-Pr) have been studied in various organic solvents. The products contained reversibly bound H2O, and infrared studies showed v(OH) modes at widely varying positions. IR of 18O-labeled complexes and 1H NMR gave no evidence for hydride or hydroxide ligands, indicating that oxidative addition of water did not occur. NMR of the aquo complexes showed rapid exchange between free and coordinated water at 298 K. The aquo complex W(CO)3(P-i-Pr3)2(H2O)·THF was isolated from THF and structurally characterized. A long W-O distance of 2.320 (5) Å was observed for the reversibly bound H2O ligand, which also undergoes hydrogen-bonding interactions with both lattice THF and a CO on an adjacent molecule. Water was found to instantaneously displace the dihydrogen ligand in W(CO)3(PR3)2(η2-H2) in THF solution to give aquo complexes, but in hexane H2 remained bound under a H2 atmosphere. Thermodynamic measurements of the equilibrium W(CO)3(PR3)2(H2) + H2O ⇌ W(CO)3(PR3)2(H2O) + H2 in THF showed that the ΔH value for binding was 3-4 kcal/mol higher for H2O. However, a higher entropy change related to hydrogen-bonding interactions between H2O and solvent resulted in ΔG favoring H2 coordination at 25°C by 1-2 kcal/mol. Isotopic exchange of W(CO)3(P-i-Pr3)2(η2-D 2) with H2O under a D2 atmosphere took place in THF, giving W(CO)3(P-i-Pr3)2(D2O). Both the favored binding of H2 versus H2O and the latter exchange are relevant to the function of H2-activating enzymes such as hydrogenase. Crystal data for W(CO)3(P-i-Pr3)2)(H2O)·THF: space group P21/n, a = 13.554 (2) Å, b = 16.417 (5) Å, c = 15.059 (4) Å, β = 116.24 (2)°, Z = 4.

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