Robert D. Sanner

Stoichiometric hydrogen reduction of carbon monoxide to methanol promoted by derivatives of bis(pentamethylcyclopentadienyl)zirconium

Reduction of CO in moderate yields was observed when ((eta/sup 5/-C/sub 5/Me/sub 5/)/sub 2/Zr(CO))/sub 2/N/sub 2/ was treated with HCl. Further studies revealed that mononuclear carbonyl and hydride complexes of bis(pentamethylcyclopentadienyl)zirconium were capable of promoting the stoichiometric H/sub 2/ reduction of CO to methoxide under very mild conditions.

The crystal and molecular structure of bis(pentamethylcyclopentadienyl)dichlorotitanium(IV)

Abstract The structure of bis(pentamethylcyclopentadienyl)dichlorotitanium(IV) has been investigated by single-crystal X-ray diffraction techniques. [η-C 5 (CH 3 ) 5 ] 2 TiCl 2 crystallizes in the orthorhombic space group P 2 1 2 1 2 1 with cell dimensions a = 10.816(1), b = 8.132(1), c = 22.259(1) A; Z = 4. Full matrix, least-squares refinement converged to a final R index of 0.032 based on 1429 reflections. The configuration about the titanium atom is a distorted tetrahedron comprised of the two chlorine atoms and the centroids of the two η-cyclopentadienyl rings. Several ring methyl groups are bent considerably out of the cyclopentadienyl plane and away from the titanium atom. These out-of-plane deviations are attributable to chlorine—methyl crowding and methyl—methyl contacts between the two rings.

Photoactivation of cluster catalysis: a comparison of 1-pentene isomerization by tetracarbonyl(triphenylphosphine)ruthenium and 1,1,1,2,2,2,3,3,3-nonacarbonyl-1,2,3-tris(triphenylphosphine)-triangulo-triruthenium

Abstract : The photocatalyzed isomerization of 1-pentene to trans- and cis-2-pentene by Ru(CO)4PPh3 and Ru3(CO)9(PPh3)3 is reported along with data for Ru3(CO)12, Fe3(CO)12, and Fe(CO)5. The primary photoprocess in Ru(CO)4PPh3 is dissociative loss of CO giving a coordinatively unsaturated species having the same empirical formula Ru3(CO)9(PPh3)3; the trinuclear species undergoes Ru-Ru bond rupture and ultimate declusterification subsequent to photo-excitation giving a quantitative yield of Ru(CO)4PPh3 under CO or Ru(CO)3(PPh3)2 in the presence of PPh3. The crucial result is that the cluster yields a different catalytically active species compared to Ru(CO)4PPh3, since the initial ratio of trans- and cis-2-pentene is different for the two photocatalysts. The photocatalysis and primary photoprocesses suggest that the isomerization from the Ru3(CO)9(PPh3)3 results from an active form of the cluster. By way of contrast, Fe(CO)5 and Fe3(CO)12 yields the same initial ratio of photocatalytic products, implicating a common, mononuclear catalytic species. Since the clusters are good visible absorbers compared to the mononuclear species, photoactivation of cluster catalysis can be effected with low energy visible light.

Transparent ceramic scintillators for gamma spectroscopy and radiography

Transparent ceramics combine the scintillation performance of single crystals with the ruggedness and processability of glass. We have developed a versatile, scaleable fabrication method, wherein nanoparticle feedstock is consolidated at temperatures well below melting to form inch-scale phase-pure transparent ceramics with optical scatter of α <0.1 cm-1. We have fabricated Cerium-doped Gadolinium Garnets with light yields of ~50,000 Ph/MeV and energy resolution of <5% at 662 keV. We have also developed methods to form sheets of the high-Z ceramic scintillator, Europium-doped Lutetium Oxide Bixbyite, producing ~75,000 Ph/MeV for radiographic imaging applications.

The preparation of mono(η5-pentamethylcyclopentadienyl) compounds of tantalum(V)

Abstract The synthesis and characterization of (η 5 -C 5 Me 5 )TaCl 4 , (η 5 -C 5 Me 5 )TaCl 4 L (L ue5fb PMe 3 , P(OMe) 3 , Ph 2 PCH 2 CH 2 PPh 2 ), (η 5 -C 5 Me 5 )TaMe 4 , and (η 5 -C 5 Me 5 )Ta(CH 2 Ph) 2 (CHPh) is described. NMR studies of the bis(1,2-diphenylphosphino)ethane (dppe) adduct show exchange of free and ligated dppe, possibly via dissociation of the ligand from a monodentate compound.

Bismuth-loaded plastic scintillators for gamma-ray spectroscopy

Exemplary embodiments of several new metal-loaded plastic scintillators are reported herein, comprising sterically and electronically isolated organotin additive complexes. Distance-dependent quenching relationships have been used as design criteria for the selection and synthesis of these organometallic additives, resulting in increased light yields and improved gamma-ray energy resolution values relative to previously reported PS/PVT examples. Fast scintillation decay properties have also been characterized in the prepared scintillators, rivaling the kinetics of stilbene-doped bibenzyl and BC-422Q-1% while providing higher light yields than these reference materials.

Differential Detection of Enantiomeric Gaseous Analytes Using Carbon Black-Chiral Polymer Composite, Chemically Sensitive Resistors

Carbon black-chiral polymer composites were used to provide diagnostic differential resistance responses in the presence of enantiomers of chiral gaseous analytes. Vapors of (+)-2-butanol and (-)-2-butanol, (+)-α-pinene and (-)-α-pinene, (+)-epichlorohydrin and (-)-epichlorohydrin, and methyl (+)-2-chloropropionate and methyl (-)-2-chloropropionate were generated and passed over a chemically sensitive carbon black-poly((R)-3-hydroxybutyrate-co-(R)-3-hydroxyvalerate) (77% butyrate) composite resistor. Each enantiomer of a pair produced a distinct relative differential resistance change on the chiral detector, whereas both enantiomers of a set produced identical signals on achiral carbon black-poly(ethylene-co-vinyl acetate) (82% ethylene) detectors.

Comparative gamma spectroscopy with SrI 2 (Eu), GYGAG(Ce) and Bi-loaded plastic scintillators

We are developing new scintillator materials that offer potential for high resolution gamma ray spectroscopy at low cost. Single crystal SrI<inf>2</inf>(Eu) offers ∼3% resolution at 662 keV, in sizes of ∼1 in³. We have developed ceramics processing technology allowing us to achieve cubic inch scale transparent ceramic scintillators offering gamma spectroscopy performance superior to NaI(Tl). Our bismuth-loaded plastic scintillator demonstrates energy resolution of ∼8% at 662 keV, for samples of ∼0.5 cm³.

Transparent Ceramic Scintillator Fabrication, Properties and Applications

Transparent ceramics offer an alternative to single crystals for scintillator applications such as gamma ray spectroscopy and radiography. We have developed a versatile, scaleable fabrication method, using Flame Spray Pyrolysis (FSP) to produce feedstock which is readily converted into phase-pure transparent ceramics. We measure integral light yields in excess of 80,000 Ph/MeV with Cerium-doped Garnets, and excellent optical quality. Avalanche photodiode readout of Garnets provides resolution near 6%. For radiography applications, Lutetium Oxide offers a high performance metric and is formable by ceramics processing. Scatter in transparent ceramics due to secondary phases is the principal limitation to optical quality, and afterglow issues that affect the scintillation performance are presently being addressed.

Competitive ligand CH bond activations: ring- and phosphine-metallated forms of (C5Me5)Ta(PMe3)2

Abstract The reduction of (η-C 5 H 5 )TaCl 4 with sodium sand in neat trimethylphosphine gives a mixture of products from which (η-C 5 H 5 ) 2 Ta(H)PMe 3 ( 1 ) may be isolated in low yield and (η-C 5 H 5 )Ta(PMe 3 ) 2 -(H)(η 2 -CH 2 PMe 2 ) ( 2 ) may be identified by NMR spectroscopy. Treatment of (η-C 5 Me 5 )TaCl 4 under similar conditions affords (η-C 5 Me 5 )Ta(PMe 3 )(H) 2 (η 2 -CHPMe 2 ) ( 3 ) which has been characterized spectroscopically and by an X-ray diffraction study. When a more conventional sodium amalgam/tetra-hydrofuran reducing medium is used, (η-C 5 Me 5 )TaCl 4 reacts with excess trimethylphosphine to give (η 7 -C 5 Me 3 (CH 2 ) 2 )Ta(H) 2 (PMe 3 ) 2 ( 4 ) in which two ring methyl Cue5f8bonds have been cleaved. 4 has been characterized spectroscopically and by an X-ray diffraction study. Complexes 3 and 4 do not undergo interconversion readily under thermal conditions, and dynamic NMR studies on 3 provide no evidence for reversible hydrogen migrations. Investigations into use of other reducing media show that the ratio of the isomers obtained is highly dependent upon reducing agent and solvent.