Experimental and Computational Studies of Steric Factors in the Isomerization of Internal Alkynes within the Coordination Environment of Half-Sandwich Metal Complexes.

The isomerization of internal alkynes ArC≡CAr within the coordination environment of low-valent half-sandwich [Ru(dppe)Cp] complexes via a 1,2-migration process affords vinylidene species [Ru{=C=C(Ar)Ar}(dppe)Cp]. The rearrangement reactions of symmetrically and asymmetrically substituted substrates featuring different electron-donating and -withdrawing groups and of varying steric bulk were modelled using density functional theory (DFT), and the conclusions supported by experimental observations. Examination of the reaction pathway and associated activation barriers reveal a high solvent dependency for the generation of the key intermediate species [Ru(dppe)Cp] from [RuCl(dppe)Cp] by halide dissociation in the presence of Na salts of weakly coordinating anions, with the lattice enthalpy of the NaCl by-product playing a critical role in the overall thermochemical balance of the reaction.

Potential-Modulated Ion Distributions in the Back-to-Back Electrical Double Layers at a Polarised Liquid|Liquid Interface Regulate the Kinetics of Interfacial Electron Transfer.

Biphasic interfacial electron transfer (IET) reactions at polarisable liquid|liquid (L|L) interfaces underpin new approaches to electrosynthesis, redox electrocatalysis, bioelectrochemistry and artificial photosynthesis. Herein, using cyclic and alternating current voltammetry, we demonstrate that under certain experimental conditions, the biphasic 2-electron O reduction reaction can proceed by single-step IET between a reductant in the organic phase, decamethylferrocene, and interfacial protons in the presence of O. Using this biphasic system, we demonstrate that the applied interfacial Galvani potential difference provides no direct driving force to realise a thermodynamically uphill biphasic IET reaction in the mixed solvent region.

Quantum Interference in Mixed-Valence Complexes: Tuning Electronic Coupling Through Substituent Effects.

Whilst 2- or 5-OMe groups on the bridging phenylene ring in [{Cp*(dppe)RuC≡C} (μ-1,3-C H )] have little influence on the electronic structure of this weakly coupled mixed-valence complex, a 4-OMe substituent enhances ground state electron delocalization, and increases the intensity of the IVCT transition. Vibrational frequency and TDDFT calculations (LH20t-D3(BJ), def2-SVP, COSMO (CH Cl )) on ([{Cp*(dppe)RuC≡C} (μ-1,3-C H -n-OMe)] (n=2, 4, 5) models are in excellent agreement with the experimental results. The stronger ground state coupling is attributed to the change in composition of the β-HOSO brought about by the 4-OMe group, which is ortho or para to each of the metal fragments.