Gas-Phase Ion–Molecule Reactions of Copper Hydride Anions [CuH₂]⁻ and [Cu₂H₃]⁻

Abstract

Gas-phase reactivity of the copper hydride anions [CuH] and [CuH] toward a range of neutral reagents has been examined via multistage mass spectrometry experiments in a linear ion trap mass spectrometer in conjunction with isotope labeling studies and Density Functional Theory (DFT) calculations. [CuH] is more reactive than [CuH], consistent with DFT calculations, which show it has a higher energy HOMO. Experimentally, [CuH] was found to react with CS via hydride transfer to give thioformate (HCS) in competition with the formation of the organometallic [CuCS] ion via liberation of hydrogen; CO via insertion to produce [HCuOCH]; methyl iodide and allyl iodide to give I and [CuHI]; and 2,2,2-trifluoroethanol and 1-butanethiol via protonation to give hydrogen and the product anions [CuH(OCHCF)] and [CuH(SBu)]. In contrast, the weaker acid methanol was found to be unreactive. DFT calculations reveal that the differences in reactivity between CS and CO are due to the lower lying π* orbital of the former, which allows it to accept electron density from the Cu center to form the initial three-membered ring complex intermediate, [HCu(η-CS)]. In contrast, CO undergoes the barrierless side-on hydride transfer promoted by the high electronegativity of the oxygen atoms. Side-on S2 mechanisms for reactions of [CuH] with methyl iodide and allyl iodide are favored on the basis of DFT calculations. Finally, the DFT calculated barriers for protonation of [CuH] by methanol, 2,2,2-trifluoroethanol, and 1-butanethiol correlate with their gas-phase acidities, suggesting that reactivity is mainly controlled by the acidity of the substrate.

Decomposition of Copper Formate Clusters: Insight into Elementary Steps of Calcination and Carbon Dioxide Activation

“…Decomposition of Cu(II) 8 (HCO 2 ) 17 À towards Cu(II)(HCO 2 ) 3 À irradiated at 1631 cm À 1 . Our calculations suggest that Cu (II) 8 (HCO 2 ) 17 À features a chain of copper centers bridged by formate ligands. Possible structures for Cu(II) n (HCO 2 ) 2n + 1 À (n = 2,4,6,8) are optimized at the DF-PBE/6-31 + g* level of theory.…”

“…Orbital analysis of the TSs confirms a doubly occupied threecenter σ-bond across the CÀ HÀ Cu moiety and an unoccupied antibonding three-center sigma orbital for all cases. [17] The relatively low rate coefficient for the reverse reaction from copper hydride to copper formate reported by O'Hair and co-workers [17] might be explained by this additional TS2 within the BMK method. [34] Hydride transfer is also confirmed by the negative partial charge of the hydrogen atom ranging from À 0.31 e to À 0.44 e and the absence of excess spin density for all decarboxylation reactions of the Cu(I) species.…”

“…Efficient methanol synthesis was demonstrated on size-selected copper clusters deposited on aluminum oxide films. [17][18][19] Hydrated Cu 2 + clusters Cu 2 + (H 2 O) n undergo the charge separation reaction [20] CuOH + (H 2 O) m + H 3 O + (H 2 O) at a critical size [21] of n = 6, which is higher for copper than for most transition metals. [16] Copper hydride anions show reactivity towards CO 2 , leading to formate formation.…”

Release of Formic Acid from Copper Formate: Hydride, Proton‐Coupled Electron and Hydrogen Atom Transfer All Play their Role

“…Copper formate has been chosen since copper is a versatile carboxylation catalyst, [8] and numerous gas phase studies have addressed various aspects of copper catalysis. [5,6,9] Surfacedeposited size-selected copper clusters have even been shown to catalyze the conversion of methane to methanol. [10] Gas phase models of CO 2 functionalization include studies with CO 2 À (H 2 O) n as well as Grignard-type metal complexes.…”

Selective C−O Coupling Hidden in the Thermal Reaction of [Al2CuO5]+ with Methane

“…Further, upon reaction with NH 3 , the clusters [Cu 4 O 2 ] + , [Cu 5 O 3 ] + , [Cu 6 O 3 ] + , [Cu 7 O 3 ] + , and [Cu 7 O 4 ] + give rise to the release of H 2 O, whereas [Cu 7 O 5 ] + affords the generation of neutral HNO . In addition, the copper complex [(dppm)Cu 2 (H)] + (dppm=1,1‐bis(diphenylphosphino)‐methane) selectively decomposes formic acid into H 2 and CO 2 , and the structurally more simple copper hydrides [CuH 2 ] − and [Cu 2 H 3 ] − also exhibit versatile reactivities towards a series of small neutral molecules; finally, the [LCuO] + (L=1,10‐phenanthroline) complex reacts with fluoromethanes to give H/O atom transfers . In addition to these gas‐phase ion/molecule reactions, there also exist a large number of studies dealing with gas‐phase isomerization of Cu complexes .…”