Dihydrogen Bonding, Proton Transfer and Beyond: What We Can Learn from Kinetics and Thermodynamics

Abstract

Hydrogen bonding to transition metal hydride complexes and its role in the proton transfer process has been a subject of the authors' research interest in recent years. The present microreview analyzes the relationships of kinetic and thermodynamic parameters of dihydrogen bonding, MH···HA, proton transfer, yielding [M(η2‐H2)] species, and subsequent steps such as [M(η2‐H2)] to [M(H)2] isomerization or H2 evolution on the basis of all data acquired so far. It aims at showing the factors that determine the stability of the species involved, the physico‐chemical (thermodynamic and kinetic) origin of the effects observed, and, ideally, allow one to better govern the hydrides reactivity.

Coordinatively Labile 18‐Electron Arene Ruthenium Iminophosphonamide Complexes

“…The dissociation process is exothermic (Δ H d =−5.0±0.2 kcal mol −1 ), with the cationic form dominating at low temperatures. The unexpectedly large negative entropy change (Δ S d =−27.0±0.7 cal mol −1 K −1 ) for the dissociation process is attributed to the need to reorganize the solvent dipoles around the charged species formed on dissociation of 1 c .…”

Acid–Base Interaction between Transition‐Metal Hydrides: Dihydrogen Bonding and Dihydrogen Evolution

“…Despite the stronger NiH interaction with the CH proton, which is most likely caused by the steric hindrance of the bulky tert ‐butyl groups, the most productive interaction in terms of subsequent proton transfer is that with WH. This result is due to the easier polarization and heterolytic splitting of MH bonds in comparison to CH bonds 15. A transition state (TS) was found, at 12.0 kcal mol −1 from the starting geometry (Figure S10).…”

Acid–Base Interaction between Transition‐Metal Hydrides: Dihydrogen Bonding and Dihydrogen Evolution

“…An atoms-in-molecules (AIM) analysis revealed two (3, À1) critical points between the Ni À H and both C À H and W À H bonds of 2 ( Figure S9, Table S6). [15] A transition state (TS) was found, at 12.0 kcal mol À1 from the starting geometry ( Figure S10). Despite the stronger NiÀH interaction with the CÀH proton, which is most likely caused by the steric hindrance of the bulky tert-butyl groups, the most productive interaction in terms of subsequent proton transfer is that with W À H. This result is due to the easier polarization and heterolytic splitting of MÀH bonds in comparison to CÀH bonds.…”