Louis Messerle

A new class of reactive, transition metal–metal doubly-bonded organodimetallic complexes: synthesis, structure, and reactivity of (η-C5Me4R)2Ta2(µ-X)4(R = Me, Et; X = Cl, Br)

Reduction of (η-C5Me4R)TaX4(R = Me, Et; X = Cl, Br) with two equivalents of sodium amalgam in toluene affords the reactive tantalum–tantalum doubly-bonded species (η-C5Me4R)2Ta2(µ-X)4 in 70% yield; the solid-state structure of (C5Me5)2Ta2(µ-Br)4 consists of a TaTa double bond, 2.748(2)A in length, bridged symmetrically by four bromide ligands.

Low-temperature, high yield synthesis, and convenient isolation of the high-electron-density cluster compound Ta6Br14·8H2O for use in biomacromolecular crystallographic phase determination

Reduction of TaBr(5) with Ga in the presence of KBr in a sealed borosilicate ampule at 400 degrees, followed by aqueous Soxhlet extraction and addition of stannous bromide and hydrobromic acid to the extract, yielded Ta(6)Br(14).8H(2)O in 80-84% yield. The new procedure provides a convenient, low temperature, high yield route to the synthesis of the title compound from inexpensive precursors.

X-ray attenuation coefficients of high-atomic-number, hexanuclear transition metal cluster compounds: a new paradigm for radiographic contrast agents.

RATIONALE AND OBJECTIVES The purpose of this study was to examine the radiologic attenuation properties of the parent cluster compounds, particularly attenuation as a function of discrete photon energy, before investigating ligand substitutions, which are necessary to improve cluster biocompatibility and to impart desirable physicochemical properties. MATERIALS AND METHODS The linear attenuation coefficients for solutions of the cluster compounds Ta6Br14, K8Ta6O19, and (H3O)2W6Cl14 were determined at 60, 80, 103, 122, and 140 keV from gamma-ray transmission measurements with americium-241, xenon-133, gadolinium-153, cobalt-57, and technetium-99m radioactive sources. Transmission measurements were obtained for a fixed time interval that ensured a statistically accurate count distribution exceeding 20,000 counts through the sample for each trial. RESULTS On a strictly mole per liter basis, a 0.075 mol/L aqueous solution of K8Ta6O19 showed 1.08 times the attenuation of 0.063 mol/L aqueous iohexol at 60 keV and 3.30 times the attenuation at 80 keV. Similarly, a 0.05 mol/L methanolic solution of (H3O)2W6Cl4 showed 0.96 times (96%) the attenuation of 0.063 mol/L aqueous iohexol at 60 keV but 3.09 times the attenuation of the iohexol solution at 80 keV. Attenuations of 0.063 mol/L aqueous iohexol and 0.0125 mol/L Ta6Br14 (ie, at approximately one-fifth the iohexol concentration) were comparable at greater than 60 keV. CONCLUSION These results confirm the theoretic potential for use of early transition metal cluster compounds as radiographic contrast agents. At higher x-ray energies, cluster compounds demonstrate multiplied x-ray attenuation relative to iodinated contrast agents.

An alkylidene-tethered tantallanorbornadiene from reduction of a tantalum(phenylalkenyl)alkylidene derived from 3,3-diphenylcyclopropene ring opening by (η-C5Me4R)2Ta2(μ-X)4 (TaTa)

The terminal (diphenylalkenyl)alkylidene complexes (C 5 Me 4 R)Ta(CHCHCPh 2 )X 2 (R = Me, Et; X = Cl, Br) are formed in moderate yields from the ring-opening reaction of 3,3-diphenylcyclopropene with the organoditantalum(III) halides (η-C 5 Me 4 R) 2 Ta 2 (μ-X) 4 . Potassium amalgam reduction of these alkenylalkylidene complexes afforded the alkylidene-tethered tantallanorbornadienes (C 5 Me 4 R)Ta[CHCHCPh(σ 2 -C 6 H 5 )], which possess a bent, boat conformation σ 2 -arene ligand with a fold angle of 19.24(46)° (R = Me) in the solid state. 1 3 C and 1 H NMR spectroscopies are consistent with a rapid flip-flop motion that averages the resonances of the σ 2 -phenyl group to fewer resonances than expected from the solid-state structure.

Solvolytic routes to new nonabismuth hydroxy- and alkoxy-oxo complexes: synthesis, characterization and solid-state structures of novel nonabismuth polyoxo cations Bi9(μ3-O)8(μ3-OR)65+(R = H, Et)

Base hydrolysis of BiO(ClO4) yields ClO4- salts of the novel nonabismuth polyoxo cation Bi9(mu3-O)8(mu3-OH)6(5+); ethanolysis converts to the ethoxide Bi9(mu3-O)8(mu3-OEt)6(5+).

Utility of hydridotributyltin as both reductant and hydride transfer reagent in organotransition metal chemistry: I. A convenient synthesis of the organoditantalum(IV) hydrides (η-C5Me4R)2Ta2(μ-H)2Cl4 (R=Me, Et) from (η-C5Me4R)TaCl4, and probes of the possible reaction pathways

Abstract The reaction of (η-C5Me4R)TaCl4 (R=Me, Cp*; Et) with two equivalents of Bu3SnH in toluene at 25°C yields (η-C5Me4R)2Ta2(μ-H)2Cl4 in 92% yield (R=Me) or 63% (R=Et) along with Bu3SnCl and H2. The μ-H group is derived from the tin reagent, as shown by a deuterium labelling study. UV/vis spectra of the reaction mixture exhibit several isosbestic points during the reaction which are consistent with the absence of significant concentrations of intermediate(s). The ditantalum(IV) halide (η-C5Me4R)2Ta2Cl6 is not a major species on the pathway from (η-C5Me4R)TaCl4 to (η-C5Me4R)2Ta2(μ-H)2Cl4, since the reaction of (η-C5Me4R)2Ta2Cl6 with two equivalents of Bu3SnH to form (η-C5Me4R)2Ta2(μ-H)2Cl4 is significantly slower. Possible pathways for the formation of (η-C5Me4R)2Ta2(μ-H)2Cl4 from (η-C5Me4R)TaCl4 are discussed.

[Bi5(dpd)6⊂CH3CN](ClO4)3·3CH3CN: a supramolecular, tetrahedral pentabismuth cluster derived from a nonabismuth oxo/hydroxide

The novel tetrahedral [Bi(5)(dpd)(6) within CH(3)CN](ClO(4))(3).3CH(3)CN (dpd = di-2-pyridyl-gem-diolate) has been synthesized from [Bi(9)(mu(3)-O)(8)(mu(3)-OH)(6)](ClO(4))(5) and di-2-pyridyl ketone. The Bi(5) complex incorporates CH(3)CN via C-HO hydrogen bonding.

Syntheses and structures of W2(µ-Cl)3Cl6– and W2(µ-Cl)2Cl82–, new d2–d2 confacial and edge-sharing bioctahedral ditungsten compounds, and a convenient synthesis of W2(µ-Cl)3Cl62–

(NR4)W2Cl9 and (NR4)2W2Cl10, prepared by addition of NR4Cl (R = alkyl) to (WCl4)x powder in CH2Cl2, have confacial [WW, 2.689(1) A] and edge-sharing bioctahedral [WW, 2.792(1) A] structures, respectively, as NBnEt3+ salts, and convert with added NR4Cl to (NR4)2W2Cl9 and (NR4)WCl6 and eventually (NR4)2WCl6; (NR4)W2Cl9 can be converted to (NR4)2W2Cl10 by NR4Cl at –30 °C.