Abstract
The copper(I) triphosphine complex LCu(MeCN)PF6 (L = 1,1,1-tris(diphenylphosphinomethyl)ethane), which we recently demonstrated is an active catalyst precursor for hydrogenation of CO2 to formate, reacts with H2 in the presence of a base to form a cationic dicopper hydride, [(LCu)2H]PF6. [(LCu)2H]+ is also an active precursor for catalytic CO2 hydrogenation, with equivalent activity to that of LCu(MeCN)+, and therefore may be a relevant catalytic intermediate. The thermodynamic hydricity of [(LCu)2H]+ was determined to be 41.0 kcal/mol by measuring the equilibrium constant for this reaction using three different bases. [(LCu)2H]+ and the previously reported dimer (LCuH)2 can be synthesized by the reaction of LCu(MeCN)+ with 0.5 and 1 equiv of KB(OiPr)3H, respectively. The solid-state structure of [(LCu)2H]+ shows threefold symmetry about a linear Cu-H-Cu axis and significant steric strain imposed by bringing two LCu+ units together around the small hydride ligand. [(LCu)2H]+ reacts stoichiometrically with CO2 to generate the formate complex LCuO2CH and the solvento complex LCu(MeCN)+. The rate of the stoichiometric reaction between [(LCu)2H]+ and CO2 is dramatically increased in the presence of bases that coordinate strongly to the copper center, e.g. DBU and TMG. In the absence of CO2, the addition of a large excess of DBU to [(LCu)2H]+ results in an equilibrium that forms LCu(DBU)+ and also presumably the mononuclear hydride LCuH, which is not directly observed. Due to the significantly enhanced CO2 reactivity of [(LCu)2H]+ under these catalytically relevant conditions, LCuH is proposed to be the catalytically active metal hydride.
| Original language | English |
|---|---|
| Pages (from-to) | 9968-9977 |
| Number of pages | 10 |
| Journal | Journal of the American Chemical Society |
| Volume | 138 |
| Issue number | 31 |
| DOIs | |
| Publication status | Published - Aug 10 2016 |
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ASJC Scopus subject areas
- Catalysis
- Biochemistry
- Chemistry(all)
- Colloid and Surface Chemistry
Cite this
Triphosphine-Ligated Copper Hydrides for CO2 Hydrogenation : Structure, Reactivity, and Thermodynamic Studies. / Zall, Christopher M.; Linehan, John; Appel, Aaron.
In: Journal of the American Chemical Society, Vol. 138, No. 31, 10.08.2016, p. 9968-9977.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Triphosphine-Ligated Copper Hydrides for CO2 Hydrogenation
T2 - Structure, Reactivity, and Thermodynamic Studies
AU - Zall, Christopher M.
AU - Linehan, John
AU - Appel, Aaron
PY - 2016/8/10
Y1 - 2016/8/10
N2 - The copper(I) triphosphine complex LCu(MeCN)PF6 (L = 1,1,1-tris(diphenylphosphinomethyl)ethane), which we recently demonstrated is an active catalyst precursor for hydrogenation of CO2 to formate, reacts with H2 in the presence of a base to form a cationic dicopper hydride, [(LCu)2H]PF6. [(LCu)2H]+ is also an active precursor for catalytic CO2 hydrogenation, with equivalent activity to that of LCu(MeCN)+, and therefore may be a relevant catalytic intermediate. The thermodynamic hydricity of [(LCu)2H]+ was determined to be 41.0 kcal/mol by measuring the equilibrium constant for this reaction using three different bases. [(LCu)2H]+ and the previously reported dimer (LCuH)2 can be synthesized by the reaction of LCu(MeCN)+ with 0.5 and 1 equiv of KB(OiPr)3H, respectively. The solid-state structure of [(LCu)2H]+ shows threefold symmetry about a linear Cu-H-Cu axis and significant steric strain imposed by bringing two LCu+ units together around the small hydride ligand. [(LCu)2H]+ reacts stoichiometrically with CO2 to generate the formate complex LCuO2CH and the solvento complex LCu(MeCN)+. The rate of the stoichiometric reaction between [(LCu)2H]+ and CO2 is dramatically increased in the presence of bases that coordinate strongly to the copper center, e.g. DBU and TMG. In the absence of CO2, the addition of a large excess of DBU to [(LCu)2H]+ results in an equilibrium that forms LCu(DBU)+ and also presumably the mononuclear hydride LCuH, which is not directly observed. Due to the significantly enhanced CO2 reactivity of [(LCu)2H]+ under these catalytically relevant conditions, LCuH is proposed to be the catalytically active metal hydride.
AB - The copper(I) triphosphine complex LCu(MeCN)PF6 (L = 1,1,1-tris(diphenylphosphinomethyl)ethane), which we recently demonstrated is an active catalyst precursor for hydrogenation of CO2 to formate, reacts with H2 in the presence of a base to form a cationic dicopper hydride, [(LCu)2H]PF6. [(LCu)2H]+ is also an active precursor for catalytic CO2 hydrogenation, with equivalent activity to that of LCu(MeCN)+, and therefore may be a relevant catalytic intermediate. The thermodynamic hydricity of [(LCu)2H]+ was determined to be 41.0 kcal/mol by measuring the equilibrium constant for this reaction using three different bases. [(LCu)2H]+ and the previously reported dimer (LCuH)2 can be synthesized by the reaction of LCu(MeCN)+ with 0.5 and 1 equiv of KB(OiPr)3H, respectively. The solid-state structure of [(LCu)2H]+ shows threefold symmetry about a linear Cu-H-Cu axis and significant steric strain imposed by bringing two LCu+ units together around the small hydride ligand. [(LCu)2H]+ reacts stoichiometrically with CO2 to generate the formate complex LCuO2CH and the solvento complex LCu(MeCN)+. The rate of the stoichiometric reaction between [(LCu)2H]+ and CO2 is dramatically increased in the presence of bases that coordinate strongly to the copper center, e.g. DBU and TMG. In the absence of CO2, the addition of a large excess of DBU to [(LCu)2H]+ results in an equilibrium that forms LCu(DBU)+ and also presumably the mononuclear hydride LCuH, which is not directly observed. Due to the significantly enhanced CO2 reactivity of [(LCu)2H]+ under these catalytically relevant conditions, LCuH is proposed to be the catalytically active metal hydride.
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U2 - 10.1021/jacs.6b05349
DO - 10.1021/jacs.6b05349
M3 - Article
VL - 138
SP - 9968
EP - 9977
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
SN - 0002-7863
IS - 31
ER -