Synthesis and characterization of four cubical molybdenum(V) tetramers and their catalytic properties for the epoxidation of cis-cyclooctene using H2O2

Sterically constrained tricyclic phosphine: redox behaviour, reductive and oxidative cleavage of P-C bonds, generation of a dilithium phosphaindole as a promising synthon in phosphine chemistry

The redox behaviour of sterically constrained tricyclic phosphine 3a was investigated by spectroelectrochemistry. The data suggested a highly negative reduction potential with the reversible formation of a dianionic species. Accordingly, 3a reacted with two equivalents of Li/naphthalene by reductive cleavage of a P-C bond of one of the PC4 heterocycles. The resulting dilithium compound 5 represents a phosphaindole derivative with annulated aromatic C6 and PC4 rings. It is an interesting starting material for the synthesis of new heterocyclic molecules, as was shown by treatment with Me2SiCl2 and PhPCl2. The structures of the products (6 and 7) formally reflect ring expansion by insertion of silylen or phosphinidene fragments into a P-C bond of 3a. Treatment of 3a with H2O2 did not result in the usually observed transfer of a single O atom to phosphorus, but oxidative cleavage of a strained PC4 ring afforded a bicyclic phosphinic acid, R2PO2H.

Photo-redox reactivity of titanium-oxo clusters: mechanistic insight into a two-electron intramolecular process, and structural characterisation of mixed-valent Ti(iii)/Ti(iv) products

The photo-reactivity of titanium-oxo clusters is investigated, revealing an intramolecular, solvent assisted, two-electron redox process that generates blue-coloured Ti(iii)/Ti(iv) clusters.

Small titanium-oxo-alkoxide clusters, [TiO(OR)(O₂PR′₂)]₄, synthesised by the stoichiometric reaction of Ti(OⁱPr)₄, phosphinic acid and water, undergo a photo-redox transformation under long-wave UV light. The photo-reaction generates blue coloured, mixed-valence Ti(iii)/Ti(iv)-oxo clusters alongside acetone and isopropanol by-products. This reactivity indicates the ability for photoactivated charge separation to occur in even the smallest of Ti-oxo clusters. EPR and NMR spectroscopic studies support a photo-redox mechanism that occurs via an intramolecular, two-electron pathway, directly relating to current doubling effects observed at TiO₂ photoanodes in the presence of alcohols. The rate of photo-reaction is solvent dependent, with donor solvents supporting the formation of low coordinate Ti(iii) sites. The nature of the electronic transition is identified by DFT and TDDFT calculations as an oxygen to titanium charge transfer and it is possible to finetune the UV absorption onset observed by changing the phosphinate ligand. A two-electron photo-reduced cluster, [Ti₄O₄(O₂PPh₂)₆], forms spontaneously from the photo-reaction and its structure is identified by X-ray crystallography with supporting DFT calculations. These indicate that [Ti₄O₄(O₂PPh₂)₆] is high-spin and contains two ferromagnetically coupled electrons delocalised over the Ti₄ core. [Ti₄O₄(O₂PPh₂)₆] undergoes rapid oxidation in air in the solid-state and performs a remarkable single-crystal to single-crystal transformation, to form a stable cluster-superoxide salt.

Extensive analysis of N-H...O hydrogen bonding in four classes of phosphorus compounds: a combined experimental and database study

The N-H...O hydrogen bond is the characteristic interaction in the crystal structures of N-benzyl-P-phenyl-N'-(p-tolyl)phosphonic diamide, C₂₀H₂₁N₂OP or (C₆H₅)P(O)(NHCH₂C₆H₅)(NHC₆H₄-p-CH₃), (I), diphenylphosphinic 1-methylpropylamide, C₁₆H₂₀NOP or (C₆H₅)₂P(O)[NHCH(CH₃)(C₂H₅)], (II), (S)-1-phenylethylammonium N-[(S)-1-phenylethyl]phenylphosphonamidate, C₈H₁₂N⁺·C₁₄H₁₅NO₂P^- or [S-(C₆H₅)CH(CH₃)NH₃][(C₆H₅)P(O){S-NHCH(CH₃)(C₆H₅)}(O)], (III), and (4-methylbenzyl)ammonium diphenylphosphinate, C₈H₁₂N⁺·C₁₂H₁₀O₂P^- or [4-CH₃-C₆H₄CH₂NH₃][(C₆H₅)₂P(O)(O)], (IV). This article focuses on the N-H...O hydrogen bonds by considering the structures of (I), (II), (III) and (IV), and reviewing their analogous compounds, including 43 (C)P(O)(N)₂, 102 (C)₂P(O)(N), 31 (C)P(O)(N)(O) and 96 (C)₂P(O)(O) structures, deposited in the Cambridge Structural Database (CSD). For the structures with a (C)P(O)(N)₂ segment, only neutral hydrogen bonds were found in the CSD. The other three classes of compounds included both neutral and `charge-assisted' hydrogen bonds, and the (C)₂P(O)(O) structures were particularly noticeable for a high number of cation-anion compounds. The overall tendencies of N...O distances in neutral and cation-anion compounds were compared. The N-H...O hydrogen-bond angles were also analyzed for the four classes of phosphorus compounds.

Expanding molecular transition metal cubane clusters of the form [M4(μ3)-O)4]12+: syntheses, spectroscopic and structural characterizations of molecules M4(μ3-O)4(O2P(Bn)2)4(O4), M = V(V) and W(V)

Oxidizing the trimer V(3)(μ(3)-O)(O(2))(μ(2)-O(2)P(Bn)(2))(6)(H(2)O) in the presence of excess (t)BuOOH results in V(4)(μ(3)-O)(4)(μ(2)-O(2)P(Bn)(2))(4)(O(4)) and heating W(CO)(6) and bis(benzyl)phosphinic acid in 1:1 EtOH/THF at 120 °C produces W(4)(μ(3)-O)(4)(μ(2)-O(2)P(Bn)(2))(4)(O(4)).