Although the term ‘confinement’ regularly appears in electrochemical literature, up until today the various aspects of confinement in electrochemistry are rather scattered individual contributions outside the established disciplines in this field.

The reactions of the monopentafulvene complexes Ti1a and Ti1b with the general formula [Cp*Ti(Cl)(π-η 5 :σ-η 1 -C 5 H 4 CR 2 )] (R = p-tolyl (Ti1a); CR 2 = adamantylidene (Ti1b)) with the bidentate P,O-ligand precursor L1, featuring a diphenylphosphine and a hydroxyl functional group, are reported, yielding the corresponding complexes Ti2a and Ti2b in good yields as the result of deprotonation. A chloride/methyl exchange reaction and subsequent reaction with B(C 6 F 5 ) 3 was envisaged to yield the corresponding cationic complexes. Instead, the methylation reactions of Ti2a and Ti2b with methyllithium or methylmagnesium bromide selectively yielded the doubly methylated titanium complexes Ti3a and Ti3b with abstraction of LiCl and the lithium salt of the bidentate P,O-ligand. To avoid this reaction, the P,O-ligand precursor L2 was prepared, featuring a carbonyl group instead of the hydroxyl functional group. This change in the general reaction sequence allowed the preparation of a new family of cationic titanium complexes Ti6a and Ti6b and was transferred to the heavier congeners zirconium (Zr4) and hafnium (Hf4). Every step of the reaction pathway was performed under mild reaction conditions and in good to very good yields. The insertion of the carbonyl group into the M−C exo bond of the monopentafulvene complexes Ti1a, Ti1b, Zr1, and Hf1, and consequently the formation of a C−C bond, proved to be mandatory for the methylation and subsequent abstraction of the methyl group by B(C 6 F 5 ) 3 . In effect, a tridentate Cp,O,P-ligand was directly introduced into the coordination spheres of the respective group 4 metals within the cationic complexes. In all cases the phosphorus shows a persistent interaction between the Lewis acidic metal center and the Lewis basic phosphine moiety, as shown by NMR analyses and in the solid state. Every complex was thoroughly characterized, including several X-ray diffraction analyses of each class of compounds reported here.

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To understand corrosion, energy storage, (electro)­catalysis, etc., obtaining chemical information on the solid–liquid interface is crucial but remains extremely challenging. Here, X-ray absorption spectroscopy (XAS) is used to study the solid–liquid interface between TiO2 and H2O. A thin film (6.7 nm) of TiO2 is deposited on an X-ray-transparent SiN x window, acting as the working electrode in a three-electrode flow cell. The spectra are collected based on the electron emission resulting from the decay of the X-ray-induced core-hole-excited atoms, which we show is sensitive to the solid–liquid interface within a few nm. The drain currents measured at the working and counter electrodes are identical but of opposite sign. With this method, we found that the water layer next to anatase is spectroscopically similar to ice. This result highlights the potential of electron-yield XAS to obtain chemical and structural information with a high sensitivity for the species at the electrode–electrolyte interface.

The reactions of monopentafulvene complexes Ti1, Zr1, and Hf1 with bidentate O,P-ligand precursors L1-L3 to form the corresponding cationic complexes employing an established three-step synthetic protocol [insertion, methylation, activation with B(C 6 F 5 ) 3 ] are investigated. Ligands L1-L3 are designed to have different sized spacers between the carbonyl and diphenylphosphine functional groups. The attempts to react Ti1, Zr1, and Hf1 with acetyldiphenylphosphine (L1) proved to yield undesired products at various steps in the synthetic sequence. When Ti1 is used, Ti2 is formed and diphenylphosphine is released at the same time. Compound Ti2, with the exocyclic double bond, is the formal product of insertion of the smallest ketene (H 2 C=C=O) into the Ti-C exo bond. Starting with [a] 5146 Scheme 2. Targeted cationic group 4 metal complexes of this work. 5147 isolation and purification steps before synthesizing the corresponding complexes. In contrast, our approach allows the preparation of densely functionalized Cp,D,P-tridentate ligands directly in the coordination sphere of the respective group 4 metals in good to excellent yields and under mild reaction conditions. [11,12] As a continuation of our efforts, we herein report on limitations and possibilities to expand and modify the tridentate Cp,O,P-ligand framework of this family of cationic complexes with focus on the ring size of the resulting M,O,P-heterocycles (Scheme 2). Results and Discussion Attempts to Synthesize Cationic Group 4 Metal Complexes with Four-Membered M,O,C,P-UnitsScheme 5. Synthesis of complexes Zr2 and Hf2. 5149Scheme 8. Three-step synthesis of cationic group 4 metal complexes Ti6, Zr6, and Hf6 by reacting monopentafulvene complexes Ti1, Zr1, and Hf1 with L2, subsequent methylation and final activation with B(C 6 F 5 ) 3 . Synthesis of Hf5:To a solution of complex Hf4 (0.200 g, 0.232 mmol) in 15 mL of tetrahydrofuran was added a methyllith-