Electronic Unsaturation of Organometallic Complexes Imparted by Sterically Demanding Ligands

The reactivity of bulky ligands with various transition metal complexes was studied to better understand the nature of organometallic electronic unsaturation and the role this plays in small molecule activation. A bulky stannyl hydride, tBu3SnH, was synthesized by a revised procedure that is far more facile and reproducible. This sterically encumbered ligand was shown to oxidatively add to a broad range of transition metal complexes, particularly those displaying carbonyl ligands, in greatly differing manners. Reaction of tBu3SnH with Ni(COD)2 and tBuNC was found to yield the mononuclear complex Ni(SntBu3)2(tBuNC)3. This compound possesses photochemical reactivity, most likely attributable to the massive steric bulk surrounding the Ni center, and generates electronically unsaturated metal centered radicals upon photolysis. This complex and its photochemical products were studied from both experimental and spectroscopic aspects. The stable organic radical TEMPO was also reacted with Ni(COD)2 to afford the unsaturated square planar complex Ni(TEMPO)2 which was studied both experimentally and spectroscopically. This deceivingly simple compound displays a wide spectrum of complicated reactivity and small molecule activation which may be utilized in future catalysis

Synthesis and reactivity of a transition metal complex containing exclusively TEMPO ligands: Ni(η2-TEMPO)2

The reaction of Ni(COD)(2) with two equivalents of the TEMPO radical at 68 °C affords the 16 e(-) "bow-tie" complex Ni(η(2)-TEMPO)(2), 1, in 78% yield. Compound 1 reacts with tert-butyl isocyanide and phenylacetylene at room temperature to yield the 16 e(-) distorted square planar nickel complexes Ni(η(2)-TEMPO)(η(1)-TEMPO)(CN(t)Bu), 2, and Ni(η(2)-TEMPO)(η(1)-TEMPOH)(CCPh), 4, respectively. The facile reactivity of 1 is aided by the transition of the TEMPO ligand from an η(2) to η(1) binding mode. Complex 4 is an unusual example of hydrogen atom transfer from phenylacetylene to a coordinated TEMPO ligand

Build-up of a Ru6 octahedral cluster core stabilized by tert-butyl germyl ligands

In heptane solvent, Ru3(CO)12 reacts with tertiary butyl germane at reflux, to afford six new bimetallic ruthenium–germanium carbonyl cluster complexes Ru3(CO)9(μ3-GetBu)2, 1, Ru2(CO)6(μ-GetBuH)3, 2, Ru4(CO)10(μ4-Ge2tBu2)(μ-GetBuH)2, 3, Ru4(CO)8(μ4-Ge2tBu2)(μ-GetBuH)2(μ3-GetBu)(H), 4, Ru5(CO)12(μ3-GetBu)2(μ4-GetBu)(H), 5, Ru6(CO)12(μ3-GetBu)4(H)2, 6. Complex 2 was obtained as a result of cluster fragmentation while cluster condensation provided higher nuclearity ruthenium–germanium complexes 3–6 with varying Ru–Ge ratios. All six compounds were structurally characterized by a combination of IR, 1H NMR, mass spectrometry and single-crystal X-ray diffraction analyses. The reaction of Ru3(CO)12 with tertiary butyl germane has yielded six new ruthenium–germanium carbonyl cluster complexes with a variety of Ru–Ge ratios. All six compounds were structurally characterized by single-crystal X-ray diffraction analyses. [Display omitted] •Six new bimetallic ruthenium–germanium carbonyl cluster complexes are reported.•Compound 1, shows the addition of GetBu groups to the intact starting Ru3 cluster.•Compound 2 provides evidence for cluster fragmentation in the reaction system.•Higher nuclearity ruthenium–germanium complexes 3–6 with varying Ru–Ge ratios are obtained as a result of cluster condensation

Photochemical synthesis and radical generation of the nickel-tin dimer [Ni(SnBut3)(CNBut)2(CO)]2

•Unusual reactivity of a Ni-Sn2 complex with sunlight.•Photochemical generation of Ni and Sn radicals.•New Ni-Sn dimeric complex of Ni(I). Ni(COD)2 reacts with But3SnH and CNBut at room temperature to afford the trigonal bipyramidal complex Ni(SnBut3)2(CNBut)3, 3. Exposing a solution of 3 to CO gas results in ligand exchange generating the pale yellow complex, Ni(SnBut3)2(CNBut)2(CO), 4. In the presence of light, a Ni-Sn bond in 4 is cleaved converting two equivalents of compound 4 into the deep purple nickel-tin dimer, [Ni(SnBut3)(CNBut)2(CO)]2, 5. The reaction is believed to proceed through radical mechanisms. [Display omitted

Theranostic applications of pair-production for enhancing radiation therapy.

Purpose/Objective(s): To enhance radiotherapy by utilizing pair-production, the probability of which increases with X-ray energy and atomic Z number. Introducing high Z metals during 18MV irradiation should result in increased cell killing compared to 18MV irradiation without metal or 6MV with/without metal. This effect will be due to increased pair-production near high Z nuclei which increases locally absorbed radiation dose. This effect requires metal, preferably nontoxic, to be present during irradiation and will be measured in vitro with clonogenic survival assays. Purpose/Objective(s): Clonogenic survival assays were carried out using A549 human lung cancer cells. Tissue culture plates were irradiated with 2Gy of either 6MV or 18MV photons with or without metal drugs (100 uM sodium phosphotungstate hydrate, 4ug/ml cisplain, and 12ug/ml carboplatin) present during radiotherapy. Metal drugs were introduced to culture media 2 hours prior to irradiation and left in place during irradiation. The media was replaced immediately after irradiation with metal-free media. Calibrated output factors were used to ensure the same absorbed dose between the two beam energies under identical experimental setup conditions. Results: Mean plating efficiency was determined to be 41% on average for A549. Incubating cells in 100uM tungsten for 4 hours without irradiation produced no significant toxicity (\u3e95% survival). In the absence of metal drug, the 2Gy 6MV and 18MV plates showed similar survival (64% vs 67%). When tungsten compound was introduced, the 6MV plate again showed 66% survival, however the 18MV plate showed 34% survival, approximately double cell killing. These experiments were repeated at 4, 6, and 8Gy to generate cell survival curves and the radiation sensitization enhancement ratio (SER) was found to be approximately 1.5. The tungsten 18MV survival curve shows a minimal shoulder region compared to the 6MV with/without tungsten and 18MV without tungsten curves, suggesting inhibition of sublethal damage repair. The 2Gy 6MV vs 18MV clonogenic survival studies were carried out for 4ug/ml cisplatin and 12ug/ml carboplatin which similarly showed approximately 40% enhancement of cell killing for both drugs at 18MV compared to 6MV. Conclusion: Cells treated with 18MV irradiation in the presence of 100uM sodium phosphotungstate hydrate showed approximately 50% less cell survival at 2, 4, 6, and 8Gy compared to 6MV with/without metal and 18MV without metal. Cisplatin and carboplatin show similar radiosensitization at 18MV yielding 40% more cell killing than 6MV. This effect is due to pair-production leading to increased photon-matter interaction and requires metal to be present at time of irradiation. The survival curves at 2, 4, 6, and 8Gy show loss of initial shoulder region suggesting impaired sublethal damage repair or increased effective LET. The generation of 511keV annihilation photons in situ may allow tumor imaging and dose measurement via PET technology. Confirmatory in vivo studies are planned

Radical Exchanges and Structural Transformations on the Iron Carbonyl-Bulky Tin Cluster Complex, Fe2(μ-SnBu 2 t )2(CO)8 by Solvents Toluene, Xylenes and Ethylbenzene

The reaction of Fe2(CO)9 and Bu 3 t SnH yielded the bimetallic cluster complexes Fe2(μ-SnBu 2 t )2(CO)8, 1, and Fe4(μ4-Sn)(μ-SnBu 2 t )2(CO)16, 3. Compound 3 contains two Fe2(CO)8(μ-SnBu 2 t ) groups held together by a central quadruply bridging tin atom, giving an overall bow-tie structure for the one tin and four iron atoms. Refluxing compound 1 in toluene solvent affords the complex Fe2[μ-SnBut(CH2Ph)]2(CO)8, 4, where two of the But groups in 1 have been replaced with benzyl groups, as a result of selective benzylic C–H bond activation of solvent toluene. Similarly refluxing compound 1 in ortho-, meta- and para-xylene solvents gives the complexes where two, three and four of the But groups in 1 have been replaced by the respective xylyl groups. Compound 1 also reacts with ethylbenzene to furnish the complex Fe2[μ-SnBut(MeCHPh)]2(CO)8, 14, where two of the But groups in 1 have been replaced as a result of the benzylic C–H activation of ethylbenzene. A mechanism based on a radical pathway is proposed for the selective C–H bond activation by 1

Thlaspi montanum L. (BR0000010535356)

Belgium Herbarium image of Meise Botanic Garden

Solitary ovarian plasmacytoma. A case report and review of literature

• A patient with rare solitary ovarian plasmacytoma is reported; • Diagnostic work-up is mandatory to rule out ovarian involvement as part of multiple myeloma. • After complete surgical resection, the prognosis appears to be very favorable