Innocent and Less‐Innocent Solvent Ligands: A Systematic Investigation of Cationic Iron Chloride/Alcohol Complexes by Electrospray Ionization Mass Spectrometry Complemented by DFT Calculations

Abstract

The influence of anionic and neutral ligands on the reactivity of cationic iron complexes towards methanol, ethanol, and iso- and n-propanol has been investigated by means of electrospray ionization (ESI) mass spectrometry, and in key questions the experimental results are supported by DFT calculations. The chemical processes taking place when FeCl2+ is coordinated to a variable number of alcohol molecules were investigated by collision experiments, as well as reactivity and labeling studies. The most abundant cations formed upon ESI of FeCl3/ROH mixtures can be described as consisting of a covalently bound FeCl2+ core, which is stabilized by neutral ROH ligands, for example, FeCl2(CH3OH)n+. Indications for a hydrogen-bonding mechanism of ligands in the second coordination sphere are given by the observation of the formally hypercoordinated ion FeCl2(CH3OH)5+ and interpretation of kinetic data for n=4. Further, deuterium labeling experiments disclose a number of hidden hydrogen transfers and imply that complexes with n=1 and 2 can exist in two tautomeric forms. Upon change of the alcohol ligand from methanol to ethanol and propanol, additional reaction pathways become accessible, among which metal-assisted dehydration of the respective alcohols by means of an ion/dipole mechanism is the most important.

Preferential Activation of Primary CH Bonds in the Reactions of Small Alkanes with the Diatomic MgO+. Cation

“…Qualitative inspection of the energy behavior of the two competing processes (Figure 1) suggests that Reaction (2) begins to occur at lower collision energies, but is entropically disfavored over the reaction in Reaction (1), as the latter predominates at elevated collision energies. Such a behavior indicates the occurrence of a structural rearrangement [19] (or a spin inversion) [20] in the course of Reaction (2), which imposes an entropic bottleneck to its occurrence. In contrast, Reaction (1) can be considered to occur as a direct, continuously endothermic, cleavage of the N À O bond without a barrier in excess of the reaction endothermicity.…”

Fragmentation of the (Cyclam‐acetato)iron Azide Cation in the Gas Phase

“…Qualitatively, however, it can be noted that the fragments associated with ∆m = -17, -30, -44, and -99 already appear at lower collision energies (Figure 2, a), whereas those with ∆m = -16, -61, and -142 are more pronounced at elevated collision energies ( Figure 2, b); the comparison indicates that the latter are either due to consecutive fragmentations or correspond to entropically favored, but energy-demanding, direct bond cleavages. [19] In general, isotopic labeling would appear to be an ideal strategy for the identification of the various neutral losses. Selective isotope labeling of the ligand is, however, not easily applicable here because the precursor synthesis is not trivial and our major interest concerns the nature of the putative nitridoiron species rather than the degradation of the ligand backbone.…”

Solvent and Ligand Effects on the Structures of Iron Halide Cations in the Gas Phase

“…[6][7][8][9] The unique features of electrospray ionization (ESI) [10,11] mass spectrometry allow the straightforward generation of a large number of solvated ions. [3,4,[12][13][14][15] Here, we report a systematic study of the cationic complexes formed upon ESI of methanolic solutions of FeX 2 (X = F, Cl, Br, I) and FeX 3 (X = F, Cl, Br). Iron was investigated because of its growing impor- [ tance in the field of catalysis [16] and biochemistry.…”

“…and, moreover, also has a potential for bond activation processes. [15] Results and Discussion FeX 2 (X = F, Cl, Br, I): In general, two different types of mononuclear ions are formed upon ESI of methanolic FeX 2 solutions: XFe(CH 3 OH) n + with n Յ 5 and Fe(OCH 3 )-(CH 3 OH) n + with n Յ 3. In addition, iron clusters of the formal composition (Fe m X 2m-1 )(CH 3 OH) n + are formed, in which m can reach numbers of up to six and n up to eight.…”