The Low-Energy Unimolecular Reaction Rate Constants for the Gas Phase, Ni⁺-Mediated Dissociation of the C−C σ Bond in Acetone

Abstract

The time dependence of the gaseous unimolecular decomposition of the jet-cooled adduct ion, Ni+-OC(CH3)2, was monitored through selective detection of the Ni+CO fragment ion. Various resolved amounts of energy in the range 15600-18800 cm(-1) were supplied to initiate the dissociation reaction through absorption of laser photons by the title molecular complex. First-order rate constants, k(E), ranged from 113000 to 55000 s(-1) and decreased with decreasing amounts of internal excitation. The energy used to initiate the reaction is well below that required to fragment C-C sigma bonds and indicates the necessity of the Ni+ cation to induce bond activation and fragmentation. These measurements are carried out in a unique apparatus and represent the first direct kinetic study of such catalytic type reactions.

An electrospray ionization mass spectrometry study of azidoacetic acid/transition metal complexes

“…Our accurate mass measurement confirmed the composition of the ions [Ni(I)HCOOH] + ( m/z 104) and [Ni(I)NCH] + ( m/z 85) strongly suggesting that the formation of the ion at m/z 85 implies hydrogen transfer to the metal centre. Additionally, the elimination of HCN implies the initial insertion of the metal into the C–CN bond forming an intermediate followed by hydrogen transfer, as has been suggested by others for similar compounds . The proposed mechanism is also in agreement with the role of transition metal ions on catalysis, in particular when they are catalyzing organic reactions, as well as with our previous studies on transition metal interactions with 3‐azidopropionitrile and azidoacetone …”

“…Additionally, the elimination of HCN implies the initial insertion of the metal into the C-CN bond forming an intermediate followed by hydrogen transfer, as has been suggested by others for similar compounds. [45][46][47][48][49][50][51][52][53][54][55][56][57] The proposed mechanism is also in agreement with the role of transition metal ions on catalysis, in particular when they are catalyzing organic reactions, [45][46][47][48][49][50][51][52][53][54][55][56][57] as well as with our previous studies on transition metal interactions with 3-azidopropionitrile [19] and azidoacetone. [21] Under similar experimental conditions, alkaline-earth metals (Ca(II) and Mg(II)) in the presence of 3azidopropionitrile [20] and azidoacetic acid (unpublished data) were not able to replicate the C-CN metal insertion which has been observed with transition metals.…”

“…A mechanistic rearrangement, which establishes a meaningful relationship among these ions, is proposed in Scheme , based on the unambiguously defined composition of these ions using CID MS/MS and FT‐ICR‐MS . In the proposed mechanism, the fragmentation routes observed may require a hydrogen shift to the carbon atom adjacent to the CN group and a C–CN bond insertion of the metal in order to dissociate into HCN + [Ni(I)HCOOH] + or alternatively into [Ni(I)NCH] + + HCOOH.…”

“…A mechanistic rearrangement, which establishes a meaningful relationship among these ions, is proposed in Scheme 4, based on the unambiguously defined composition of these ions using CID MS/MS and FT-ICR-MS. [45][46][47][48][49][50][51][52][53][54][55][56][57] In the proposed mechanism, the fragmentation routes observed may require a hydrogen shift to the carbon atom adjacent to the CN group and a C-CN bond insertion of the metal in order to dissociate into HCN + [Ni(I)HCOOH] + or alternatively into [Ni(I)NCH] + + HCOOH. Our accurate mass measurement confirmed the composition of the ions [Ni(I)HCOOH] + (m/z 104) and [Ni(I)NCH] + (m/z 85) strongly suggesting that the formation of the ion at m/z 85 implies hydrogen transfer to the metal centre.…”

Theoretical study of Ni+ assisted C C and C H bond activations of propionaldehyde in the gas phase

“…and the corresponding ionic fragment. At low energies, Cr + , Cu + and Mn + are unreactive with acetone, but Fe + , Co + , Ni + react with acetone to produce C 2 H 6 and M + CO [17], [18], [19], [20]. On the contrary, transition metal ions with high oxygen affinities react with acetone to form MO + ions and C 3 H 6 , e.g.…”