Tris(1,1,1,5,5,5-hexa­fluoro-2,4-pentane­dionato-κ2 O,O′)molybdenum(III)

In the title compound, [Mo(C5HF6O2)3], the unit cell is built up by three independent MoIII atoms located on two different threefold axes. The three independent mol­ecules are roughly identical and each MoIII atom is surrounded by three chelating hexa­fluoro­acetonate ligands in a three-bladed propeller-like arrangement, as observed in related compounds with acetyl­acetonate-type ligands. The structure of the title compound is very similar to the trigonal form of the CrIII analogue. However, the latter crystallizes in a higher-symmetry space group, P c1. Both crystals are twinned by merohedry with the same twin law ( 0/010/00) in reciprocal space, but the symmetry of the Laue group in which it operates is different, to m for the title complex, and m to 6/mmm for the CrIII complex

Ketone Hydrogenation with Iridium Complexes with “non N–H” Ligands: The Key Role of the Strong Base

Ferrocenyl phosphine thioether ligands (PS), not containing deprotonatable functions, efficiently support the iridium catalyzed ketone hydrogenation in combination with a strong base co-catalyst. Use of an internal base ([Ir(OMe)(COD)]2 in place of [IrCl(COD)]2) is not sufficient to insure activity and a strong base is still necessary, suggesting that the active catalyst is an anionic hydride complex. Computational investigations that include solvent effects demonstrate the thermodynamically accessible generation of the tetrahydrido complex [IrH4(PS)]-and suggest an operating cycle via a [Na+(MeOH)3∙∙∙Ir-H4(PS)] contact ion pair with an energy span of 18.2 kcal/mol. The cycle involves an outer sphere stepwise H-/H+ transfer, the proton originating from H2 after coordination and heterolytic activation. The base plays the dual role of generating the anionic complex and providing the Lewis acid co-catalyst for ketone activation. The best cycle for the neutral system, on the other hand, requires an energy span of 26.3 kcal/mol. This work highlights, for the first time, the possibility of outer sphere hydrogenation in the presence of non deprotonatable ligands and the role of the strong base in the activation of catalytic systems with such type of ligands

1-(Diphenyl­phosphinothio­yl)-2-[(4-methyl­phen­yl)meth­oxy­meth­yl]ferrocene

Following our continuing inter­est in developing new chiral phosphine-containing ferrocenyl ligands, we synthesized the title compound, [Fe(C5H5)(C26H24OPS)], in which there are two nearly identical mol­ecules in the asymmetric unit. The conformation of the cyclo­penta­dienyl (Cp) rings in each ferrocenyl group are inter­mediate between eclipsed and staggered, with twist angles of 16.6 (2) and 8.9 (2)°. The protecting S atom is located endo with respect to the substituted Cp ring. In the crystal, mol­ecules are connected through inter­molecular C—H⋯π inter­actions

A density functional study of open-shell cyclopentadienyl-molybdenum(II) complexes. A comparison of stabilizing factors: Spin-pairing, Mo-X π bonding, and release of steric pressure

The dissociation of PH3 from the 18-electron system CpMoX(PH3)3 to afford the corresponding 16-electron CpMoX(PH3)2 fragment has been investigated theoretically by density functional theory for X = H, CH3, F, Cl, Br, I, OH, and PH2. The product is found to prefer a triplet spin state for all X ligands except PH2, the singlet-triplet gap varying between 1.7 kcal/mol for OH to 8.7 kcal/mol for F. The Mo-PH3 bond dissociation energy to the 16-electron ground state varies dramatically across the series, from 4.5 kcal/mol for OH to 23.5 kcal/mol for H, and correlates with experimental observations on trisubstituted phosphine derivatives. Geometry-optimized spin doublet CpMo(PH3)3, on the other hand, has a Mo-PH3 bond dissociation energy of 24.3 kcal/mol. The modulation of the Mo-PH3 bond dissociation energy by the introduction of X is analyzed in terms of three effects that stabilize the 16-electron product relative to the 18-electron starting complex: (i) adoption of the higher (triplet) spin state by release of pairing energy; (ii) Mo-X π interactions; (iii) release of steric pressure. A computational model for the approximate separation and evaluation of these three stabilizing effects is presented. According to the results of these calculations, the relative importance of the three effects depends on various factors related to the nature of X. For double-sided π-donor X ligands, the larger triplet-singlet gap is provided by the more electronegative atoms (F \u3e CL \u3e Br \u3e I), whereas single-sided π donors favor the singlet state. The π-stabilization ability goes in the order PH2 \u3e OH \u3e F \u3e other halogens \u3e H. Finally, the major steric interaction appears to be associated with the presence of inactive lone pairs and by their orientation/proximity to the PH3 ligands (Cl, Br \u3e I, OH \u3e F, PH2, H, CH3). The 16-electron methyl system establishes a marked α-agostic interaction in the singlet state, which nevertheless remains unfavored relative to an undistorted triplet configuration

Spectroscopic characterisation of hydroxyapatite and nanocrystalline apatite with grafted aminopropyltriethoxysilane: nature of silane–surface interaction

Heterogenised homogeneous catalysis is commonly performed with molecular catalysts grafted on solids via adsorption or via a covalent molecular link. Covalent grafting of organic groups on solid supports is usually carried out by silylation, using functionalised trialkoxysilanes. Among these solids supports, very few studies have been published on apatites. In the present work,aminopropyltriethoxysilane (APTES) grafting was performed in toluene on different apatitic supports: crystallised stoichiometric hydroxyapatites differing by the drying method, freeze-dried (HAP) and dried at 100 °C (HAPD), and a nanocrystalline apatite. All materials were fully characterised, before and after grafting, for better understanding of the nature of the alkoxysilane/surface interaction. The data show a clear competition between the covalent grafting of APTES and its polycondensation reaction, depending on the nature of the solid support surface. Silylation is accompanied by APTES covalent grafting to oxygen atom of the hydroxyl groups of the apatitic structure and/or of the OH− species that are present on the surface hydrated layer. This work clarifies the nature of silane grafting onto selected apatitic surfaces and especially the influence of the composition and properties of the apatitic surfaces on the process of silylation