Some diels—alder reactions of η1-bonded cyclopentadienylmetal compounds

Bis(cyclopentadienyl)mercury readily undergoes Diels—Alder reactions with RCCR (R = CO₂Me or CF₃), CF₃CFCFCF₃, CF₃CFCF₂, (CF₃)₂CC(CN)₂, C₂(CN)₄ and Ph$\text{NCONNC}$O to give stable adducts characterised by¹H, ¹⁹F and ¹³C NMR, spectroscopy. Similar reactions of CF₃CCCF₃ and CF₃CFCFCF₃ with the cyclopentadiene derivatives Me₃MC₅H₅ and (Me₃M)₂C₅H₄ (M = Si, Sn) are also described.     

Nuclear Fréchet spaces without bases III. Every nuclear Fréchet space not isomorphic to ω admits a subspace and a quotient space without a strong finite dimensional decomposition

The result stated in the title is proved.Research of the second author partially supported by the National Science Foundation. He would also like to thank the Banach Institute, Polish Academy of Sciences and Universität Kaiserslautern for their hospitality.     

Unprecedented cage-carbon to cage-boron NMe(3) transfer in a monocarbon Molybdenacarborane

The reagent Li(2)[7-NMe(3)-nido-7-CB(10)H(10)] reacts with [Mo(CO)(3)(NCMe)(3)] in THF-NCMe (THF = tetrahydrofuran) to give a molybdenacarborane intermediate which, upon oxidation by CH(2)[double bond]CHCH(2)Br or I(2) and then addition of [N(PPh(3))(2)]Cl, gives the salts [N(PPh(3))(2)][2,2,2-(CO)(3)-2-X-3-NMe(3)-closo-2,1-MoCB(10)H(10)] (X = Br (1) or I (2)). During the reaction, the cage-bound NMe(3) substituent is transferred from the cage-carbon atom to an adjacent cage-boron atom, a feature established spectroscopically in 1 and 2, and by X-ray diffraction studies on several of their derivatives. When [Rh(NCMe)(3)(eta(5)-C(5)Me(5))][BF(4)](2) is used as the oxidizing agent, the trimetallic compound [2,2,2-(CO)(3)-7-mu-H-2,7,11-[Rh(2)(mu-CO)(eta(5)-C(5)Me(5))(2)]-closo-2,1-MoCB(10)H(9)] (10) is formed, the NMe(3) group being lost. Reaction of 1 in CH(2)Cl(2) with Tl[PF(6)] in the presence of donor ligands L affords neutral zwitterionic compounds [2,2,2-(CO)(3)-2-L-3-NMe(3)-closo-2,1-MoCB(10)H(10)] for L = PPh(3) (4) or CNBu(t) (5), and [2-Bu(t)C[triple bond]CH-2,2-(CO)(2)-3-NMe(3)-closo-2,1-MoCB(10)H(10)] (6) when L = Bu(t)C[triple bond]CH. When 1 is treated with CNBu(t) and X(2), the metal center is oxidized, and in the products obtained, [2,2,2,2-(CNBu(t))(4)-2-Br-3-X-closo-2,1-MoCB(10)H(10)] (X = Br (7), I (8)), the B-NMe(3) bond is replaced by B-X. In contrast, treatment of 2 with I(2) and cyclo-1,4-S(2)(CH(2))(4) in CH(2)Cl(2) results in oxidative substitution of the cluster and retention of the NMe(3) group, giving [2,2,2-(CO)(3)-2-I-3-NMe(3)-6-[cyclo-1,4-S(2)(CH(2))(4)]-closo-2,1-MoCB(10)H(9)] (9). The unique structural features of the new compounds were confirmed by single-crystal X-ray diffraction studies upon 6, 7, 9 and 10.     

The magnetic moment of103Ru

The nuclear magnetic moment of¹⁰³Ru has been determined using the technique of low-temperature nuclear orientation on¹⁰³Ru as a dilute impurity in Fe. The Fe lattice was cooled to 1.7 mK using a PrNi₅ enhanced nuclear demagnetisation stage precooled with a³He–⁴He dilution refrigerator. The¹⁰³RuFe system was observed to have a long nuclear spin-lattice relaxation time, but analysis of the relaxation indicates that the¹⁰³Ru nuclei are close to thermal equilibrium with the Fe lattice at times>200 min after demagnetising. From the near thermal equilibrium anisotropy of the 497 keV -ray in¹⁰³Rh we have deduced the nuclear magnetic moment as |(¹⁰³Ru)|=0.18(2)_N. This value is almost independent of the choice of spinI=3/2 or 5/2 for the nucleus, but is only consistent with systematics ifI(¹⁰³Ru)=3/2 and <0. UsingI=3/2 we obtain the E2/M1 mixing ratio of the 497 keV -ray as =–0.42(4). The sign of the anisotropy of the 610 keV -ray from the 650 keV level in¹⁰³Rh is only consistent with an allowed -decay to the state ifI(650 keV,¹⁰³Rh)=5/2. The E2/M1 mixing ratio of the 610 keV -ray is then =+0.15(3) or +60( _–40 ⁺ ), <–80. From the initial rise in -ray anisotropy following demagnetisation we determine the Korringa constant for¹⁰³RuFe to beC=5.7(5) K·s.     

Synthesis, structure, and dynamics of nickelacarboranes incorporating the [nido-7,9-C(2)B(9)H(11)](2)(-) ligand

The nickelacarboranes [NEt(4)][2-(eta(3)-C(3)H(4)R)-closo-2,1,7-NiC(2)B(9)H(11)] (R = H (1a), Ph (1b)) have been synthesized via reaction between [Na](2)[nido-7,9-C(2)B(9)H(11)] and [Ni(2)(micro-Br)(2)(eta(3)-C(3)H(4)R)(2)] in THF (THF = tetrahydrofuran), followed by addition of [NEt(4)]Cl. Protonation of 1a in the presence of a donor ligand L affords the complexes [2,2-L(2)-closo-2,1,7-NiC(2)B(9)H(11)] (L = CO (2), CNBu(t) (3)). Addition of PEt(3) (1 equiv) to 2 produces quantitative conversion to [2-CO-2-PEt(3)-closo-2,1,7-NiC(2)B(9)H(11)], 4. Species 2-4 exhibit in solution hindered rotation of the NiL(2) fragment with respect to the eta(5)-C(2)B(9) cage unit. Protonation of 1a in the presence of a diene affords the neutral complexes [2-(eta(2):eta(2)-diene)-closo-2,1,7-NiC(2)B(9)H(11)] (diene = C(5)Me(5)H (5), dcp (6), cod (7), nbd (8), chd (9), and cot (10a); dcp = dicyclopentadiene, cod = 1,5-cyclooctadiene, nbd = norbornadiene, chd = 1,3-cyclohexadiene, and cot = cyclooctatetraene). Variable temperature (1)H NMR experiments show that the [Ni(diene)] fragments are freely rotating even at 193 K. A small quantity of the di-cage species [2,2'-micro-(1,2:5,6-eta-3,4:7,8-eta-cot)-(closo-2,1,7-NiC(2)B(9)H(11))(2)] (10b) is formed as a coproduct in the synthesis of 10a. This species can be rationally synthesized by protonation of 1a and subsequent addition of 10a.     

Hydrogels of poly(hydroxyethyl methacrylate) and hydroxyethyl methacrylate—glycerol monomethacry-late copolymers

Hydrophilic three-dimensional polymer networks (hydrogels) were prepared from hydroxyethyl methacrylate (HEMA) and the copolymer HEMA and glycerol monomethacrylate (GMMA). The equilibrium water content of the hydrogels in water was investigated as a function of the initial dilution of the polymerization mixture, the type of solvent, and the hydrophilicity of the polymer. The initial dilution was found to have a decisive effect on the swelling or deswelling of hydrogels after the completion of the gel formation. With relatively less hydrophilic hydrogels, there is a critical initial dilution to produce the gel which does not swell or deswell in water after the gel formation. This “isovolumic” initial dilution shifts toward a higher dilution as the hydrophilicity of the hydrogels increases; however, when hydrophilicity of the polymer rises above a certain point, gels always swell in water. Permeability of oxygen through hydrogels was also studied.     

Hyperfine fields in the 5sp series studied by the low temperature nuclear orientation of83Rb,83Sr,85Sr and85Ym in iron

The hyperfine fields B_hf (RbFe), B_hf (SrFe) and B_hf (YFe) have been determined by the low temperature nuclear orientation of dilute samples of⁸³Rb,^83,85Sr and⁸⁵Y^m in an iron lattice to be B_hf (RbFe)=+54 (10) kG, B_hf (SrFe)=(?)100 (30) kG and B_hf (YFe)=?226 (10) kG. These results are compared with recent calculations for these fields (1), (2).     

EFFECT OF SINGLET OXYGEN QUENCHERS ON OXIDATIVE DAMAGE TO LIPOSOMES INITIATED BY PHOTOSENSITIZATION OR BY RADIOFREQUENCY DISCHARGE

Abstract —Lipid model membrane systems, liposomes, may be oxidized by both toluidine blue Osensitized photo-oxidation and radiofrequency-discharge-generated singiet oxygen. Oxidation can be followed by the appearance of lipid peroxides, malondialdehyde formation, and ultimately by the lysis of the liposomes. Inhibition of oxidation is observed in both systems using either β-carotene or DABCO. These observations are consistent with the view that type II (singlet oxygen) reactions are involved in this photodynamic system.     

Neutron captue prompt gamma-ray activation analysis at the NIST Cold Neutron Research Facility

An instrument for neutron capture prompt gamma-ray activation analysis (PGAA) has been constructed as part of the Cold Neutron Research Facility at the 20 MW National Institute of Standards and Technology Research Reactor. The neutron fluence rate (thermal equivalent) is 1.5·10⁸ n ·cm^–2·s^–1, with negligible fast neutrons and gamma-rays. With compact geometry and hydrogen-free construction, the sensitivity is sevenfold better than an existing thermal instrument. Hydrogen background is thirtyfold lower.