Modification of Wilkinson's catalyst with triphenyl phosphite: Synthesis, structure, 31P NMR and DFT study of trans-[RhCl(P(OPh) 3)(PPh 3) 2]

The complex trans-[RhCl(P(OPh) 3)(PPh 3) 2] (1) has been prepared and characterized by 31P NMR spectroscopy and single crystal X-ray crystallography. It was found that in the solid state there are two forms of complex 1 in the unit cell forming a cocrystal. DFT theoretical computations have confirmed the existence of the two forms and have provided evidence for the greater stability of 1 compared with Wilkinson's catalyst, [RhCl(PPh 3) 3] (2), in terms of the dissociation energy of the Rh-P(PPh 3) bonds. On the basis of the phosphorus chemical shifts, δ P(PPh 3), and the results of the theoretical computations, it is suggested that the Rh-P(PPh 3) bonding interactions are slightly enhanced in 1 compared with 2. A distinct difference between complexes 1 and 2, was found to be the catalytic activity of 1 in the alkylation of allyl acetate with sodium diethylmalonate, while 2 is almost catalytically inefficient. © 2012 Elsevier Ltd. All rights reserved

Heterotrimetallic tetrathiomolybdate and tetrathiotungstate complexes of rhodium(I) and copper(I) with Rh-Mo(W)-Cu interactions

The synthesis and characterization of the monoanionic heterotrimetallic (d8···d0···d10) complexes [L2Rh(μ-S)2M(μ-S)2CuCl]− (L = P(OPh)3, P(O-o-Tol)3 (P(O-o-CH3C6H4)3), P(OMe)3, P(OEt)3, P(OiPr)3; L2 = COD (1,5-cyclooctadiene), cis-dppen (cis-Ph2PCH = CHPPh2); M = Mo, W) is presented. The complex (NEt4)[(cis-dppen)Rh(μ-S)2W(μ-S)2CuCl] was characterized by X-ray diffraction analysis. The detailed DFT study of the electronic structure of the complexes with P(OMe)3 and COD ligands has revealed the existence of extended electron delocalization over the atom-sharing (spiro) four-membered rings system Rh(μ-S)2M(μ-S)2Cu and the possibility of electronic communication between the terminal metal centers. The electronic spectra of the complexes with P(OMe)3 ligands were studied with TDDFT calculations and the main absorption band in the visible region was assigned to ν(Rh → Mo/W) electron transfer transition. The ν(Rh → Mo/W) transition was found to correlate linearly with Tolman's electronic parameter of the phosphite ligands, making it an electronic parameter for the ligands studied. Finally, the study of the dependence of Δδ(31P) and 1J(Rh-P) of the phosphite complexes, with respect to the QALE model electronic parameters χd, πp and Ear, has succeeded in the assessment of the σ and π effects on these NMR spectral parameters. © 202

Tetrathiomolybdate Complexes of Rhodium(I) with Molybdenum-Rhodium Interactions

The synthesis and characterization of the tetrathiomolybdatorhodium(I) monoanionic complexes [L2Rh(-S)2MoS2]- (L = CO (3), P(OPh)3 (4), P(O-o-Tol)3 (P(o-CH3C6H4)3; 5), P(OMe)3 (6), P(OEt)3 (7), P(O-i-Pr)3 (8); L2 = COD (1,5-cyclooctadiene; 2), cis-dppen (cis-Ph2PCH - CHPPh2; 9), dppe (Ph2PCH2CH2PPh2; 10), dppb (Ph2P(CH2)4PPh2; 11)) is presented. The complex 2 (NEt4+ salt) was characterized by X-ray diffraction analysis. A detailed DFT study of the electronic structures of 2-4 and 6-8 has revealed the existence of extended electron delocalization over the four-membered Rh(-S)2Mo ring and hence the possibility of electronic communication between the metal centers. The electronic spectra were studied with TDDFT calculations, and the main absorption band in the visible region was assigned to ν(Rh→Mo) electron transfer transition, which is actually a HOMO-LUMO transition. The ν(Rh→Mo) transition was found to correlate linearly both with Tolmans electronic parameter of the phosphite ligands and the calculated HOMO-LUMO gap of the complexes, rendering it a well-defined ligand electronic parameter, which describes the net donating ability of monodentate and bidentate ligands (CO, COD, phosphites, diphosphines). The study of the variation of Δδ(31P) and 1J(Rh-P) of the phosphite complexes with respect to the QALE model electronic parameters χd, πp, and Ear has succeeded in the assessment of the σ and π effects on these NMR spectral parameters. © 2016 American Chemical Society

Short-Range Disorder in TeO₂ Melt and Glass

High-resolution X-ray pair distribution functions for molten and glassy TeO2 reveal coordination numbers nTeO ≈ 4. However, distinct from the known α-, β-, and γ-TeO2 polymorphs, there is considerable short-range disorder such that no clear cutoff distance between bonded and nonbonded interactions exists. We suggest that this is similar to disorder in δ-TeO2 and arises from a broad distribution of asymmetric Te–O–Te bridges, something that we observe becomes increasingly asymmetric with increasing liquid temperature. Such behavior is qualitatively consistent with existing interpretations of Raman scattering spectra, and equivalent to temperature-induced coordination number reduction, for sufficiently large cutoff radii. Therefore, TeO2 contains a distribution of local environments that are, furthermore, temperature dependent, making it distinct from the canonical single-oxide glass formers. Our results are in good agreement with high-level ab initio cluster calculations

Lithium ion conducting boron-oxynitride amorphous thin films : synthesis and molecular structure by infrared spectroscopy and density functional theory modeling

Li ion containing oxynitride amorphous thin films are promising materials for electrochemical applications due to their high ionic conductivity, mechanical stability and chemical durability. Here we report on the preparation of Li boron-oxynitride (LiBON) amorphous thin films by rf sputtering of Li-diborate and Li-pyroborate targets in nitrogen atmosphere. The materials produced were subsequently studied by infrared transmittance spectroscopy assisted by density functional theory calculations using representative Li boron-oxide and boron-oxynitride clusters. The combination of experiments and calculations allows us to propose accurate vibrational assignments and to clarify the complex infrared activity of the LiBON films. Both experimental and calculated spectra show that nitrogen incorporation induces significant structural rearrangements, manifested mainly by a change in boron coordination number from four to three, and by the formation of boron-nitrogen-boron bridges. The nature of boron-nitrogen bonding depends on the composition of the sputtering target, with an exponential relationship adequately describing the dependence of B-N stretching frequency on bond length. Besides bonding to two boron atoms by covalent bonds, the nitrogen atoms interact also with Li ions by participating in their coordination sphere together with oxygen atoms. Likely, boron-nitrogen bonding in LiBON films facilitates Li ion transport due to induced charge delocalization within the boron-nitrogen-boron bridges and reduced electrostatic interaction with the Li ions