Complexes of TaOCl3 and TaSCl3 with neutral N- and O-donor ligands – Synthesis, properties and comparison with the niobium analogues

Molecular Bis(chalcogenido) Titanates of Te, Se, and S

A series of titanate cisoid bis(chalcogenidos) (Ch = Te, Se, and S) complexes supported by the β-diketiminate ligand BDI- = [ArNC(CH3)]2CH (Ar = 2,6-iPr2C6H3) are readily assembled via treatment of the TiIII precursor (BDI)Ti(CH2SiMe3)2 with 2.5 equiv of elemental "Ch" source and 1 equiv of reductant in the presence of crown-ether. In the absence of the electride, Te or S addition to (BDI)Ti(CH2SiMe3)2 results instead in the isolation of a mononuclear tellurido-tellurolate [(BDI)Ti(=Te)(TeCH2SiMe3)] and the bridging sulfido-thiolate complex [(BDI)Ti(SCH2SiMe3)(μ-S)]2, respectively. In the case of Se, the rare selenido-perselenoate complex [(BDI)Ti(=Se)(η2-SeSeCH2SiMe3)] was isolated. In addition to crystallographically and spectroscopically characterizing all of the complexes, we demonstrate the latter species to be likely intermediates in the formation of [(BDI)Ti(Ch)2]- via the addition of electride.

Tungsten(VI) selenide tetrachloride, WSeCl4 - synthesis, properties, coordination complexes and application of [WSeCl4(SenBu2)] for CVD growth of WSe2 thin films

WSeCl₄ was obtained in good yield by heating WCl₆ and Sb₂Se₃in vacuo. Green crystals grown by sublimation were shown by single crystal X-ray structure analysis to contain square pyramidal monomers with apical WSe, and powder X-ray diffraction (PXRD) analysis confirmed this to be the only form present in the bulk sample. Density functional theory (DFT) calculations using the B3LYP-D3 functional replicated the structure, identified the key bonding orbitals, and were used to aid assignment of the IR spectrum of WSeCl₄. Reaction of WSeCl₄ with ligands L gave [WSeCl₄(L)] (L = MeCN, DMF, thf, py, OPPh₃, 2,2'-bipy, SeMe₂, SeⁿBu₂), whilst the dimers [(WSeCl₄)₂(μ-L-L)] were formed with L-L = Ph₂P(O)CH₂P(O)Ph₂, 1,4-dioxane and 4,4'-bipyridyl. The complexes were characterised by microanalysis, IR and ¹H NMR spectroscopy, and single crystal X-ray structures determined for [WSeCl₄(L)] (L = OPPh₃, MeCN, DMF) and [(WSeCl₄)₂(μ-L-L)] (L-L = 1,4-dioxane, 4,4'-bipyridyl). All except the 2,2'-bipy complex, which is probably seven-coordinate, contain six-coordinate tungsten with the neutral donor trans to WSe. Alkylphosphines, including PMe₃ and PEt₃, decompose WSeCl₄ upon contact, forming phosphine selenides (SePR₃). In contrast, the selenoether complexes [WSeCl₄(SeMe₂)] and [WSeCl₄(SeⁿBu₂)] were isolated and characterised. The crystal structure of the minor W(VI) by-product, [(WSeCl₄)₂(μ-SeMe₂)], was determined and using SMe₂, a few crystals of the W(V) species, [{WCl₃(SMe₂)}₂(μ-Se)(μ-Se₂)], were obtained and structurally characterised. The isolated W(VI) complexes are compared with those of WOCl₄ and WSCl₄ and the combination of experimental and computational data are consistent with WSeCl₄ being a weaker Lewis acid and its complexes significantly less stable than those of the lighter analogues, especially in solution. Low pressure chemical vapour deposition (LPCVD) using [WSeCl₄(SeⁿBu₂)] in the range 660-700 °C (0.1 mmHg) produced highly reflective thin films, which were identified to be WSe₂ by grazing incidence X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. XRD analysis of the thinner films revealed them to be highly oriented in the <00l> direction.

A Diverse Array of C-C Bonds Formed at a Tantalum Metal Center

We demonstrate the formation of a diverse array of organic and organometallic products containing newly formed C-C bonds via successive methyl transfers from di-, tri-, and tetramethyl Ta(V) precursors to unsaturated small molecule substrates under mild conditions. The reactions of Ta(V) methyl complexes 1-X [H₂B(^MesIm)₂]TaMe₃X (X = Me, Cl; Im = imidazole, Mes = 2,4,6-trimethylphenyl) with CO led to oxo enolate Ta(V) products, in which the enolate ligands were constructed from Ta-Me groups and two equivalents of CO. Similarly, the reaction of 1-Me with CNXyl yielded an imido enamine Ta(V) product. Surprisingly, 1-Cl reacted with CNXyl (1 equiv) at the borate backbone of the [H₂B(^MesIm)₂] ligand with concomitant methyl transfer from the metal center to form a new, dianionic scorpionate ligand that supported a Ta(V) dimethyl chloro complex (6). Treatment of 1-Cl with further CNXyl led to an azaallyl scorpionate complex, and an imido isocyanide scorpionate complex, along with propene and xylyl ketenimine. Complex 6 reacted with CO to yield a pinacol scorpionate complex 10-a new reaction pathway in early transition metal chemistry. Mechanistic studies revealed that this proceeded via migratory insertion of CO into a Ta-Me group, followed by methyl transfer to form an η²-acetone intermediate. Elimination of acetone furnished a CO-stabilized Ta(III) intermediate capable of rebinding and subsequently coupling two equivalents of CO-derived acetone to form the pinacol ligand in 10.