Lanthanide borohydride complexes supported by diaminobis(phenoxide) ligands for the polymerization of epsilon-caprolactone and L- and rac-lactide

Reaction of Na2O2NN' [H2O2NN' = (2-C5H4N)CH2N[2-HO-3,5-C6H2(t)Bu2]2] with M(BH4)3(THF)3 afforded the dimeric, rare-earth borohydride compounds [M(O2NN')(mu-BH4)(THF)n]2 [M = Y(III), n = 0.5 (1-Y); M = NdIII, n = 1 (1-Nd); M = SmIII, n = 0 (1-Sm)]. For comparison the chloride analogues [M(O2NN')(mu-Cl)(THF)n]2 (2-M; M = La(III) or Sm(III), n = 0; M = Nd(III), n = 1) and the corresponding pyridine adducts [M(O2NN')(mu-X)(py)]2 [X = BH4 (3-M) or Cl (4-M); M = La(III), Nd(III), or Sm(III)] were prepared and structurally characterized for 4-La. Compounds 1-M initiated the ring-opening polymerization of epsilon-caprolactone. The best molecular weight control (suppression of chain transfer) for all three monomers was found for the samarium system 1-Sm. The most effective heterotactic enrichment (Pr) in the polymerization of rac-lactide was found for 1-Y (P(r) = 87%). Compound 1-Nd catalyzed the block copolymerization of epsilon-caprolactone and L- and rac-lactide provided that epsilon-caprolactone was added first. Attempted block polymerization by the addition of L-lactide first, or random copolymerization of a ca. 1:1 mixture of epsilon-caprolactone and L-lactide, gave only a poly(L-lactide) homopolymer.     

Rhodium(II,II) dimer as an efficient catalyst for aziridination of sulfonamides and amidation of steroids

[reaction: see text] Unsaturated sulfonamides underwent direct intramolecular aziridination catalyzed by Rh(2)(OAc)(4) with PhI(OAc)(2) and Al(2)O(3) to give the corresponding aziridine products in excellent yields (up to 98%) and with good to excellent conversions. High turnovers (up to 1375) were achieved. The intermolecular rhodium-catalyzed amidation of cholesteryl acetate with PhI=NTs or PhI(OAc)(2)/NH(2)R as the nitrogen source exhibited both excellent regio- and alpha-selectivity (alpha/beta ratio up to 9:1).     

Synthesis of a μ4-PPh mixed metal cluster: the x-ray structures of [Ru3Rh2(CO)13(PEt3)(μ4-PPh)] and [Ru3Au(μ2-H)(CO)9(PMe2Ph)(μ3-PPh)]

The synthesis of a (μ₄-PPh) and some related (μ₃-PPh) mixed metal clusters containing ruthenium is described together with the X-ray structures of [Ru₃Rh₂(CO)₁₃(PEt₃)(μ₄-PPh)] and [Ru₃Au(μ₂-H)(CO)₉(PMe₂Ph)(μ₃-PPh)].     

Microanalysis of polymers using a windowless energy-dispersive X-ray detector

The surface compositions of various polymeric films, grown electrochemically on platinum foils, have been investigated by energy-dispersive x-ray analysis in conjunction with scanning electron microscopy (SEM/EDS). Comparison of the relative area ratios of peaks for the C and N K_emission lines show that the EDS may be used to study the surface composition of polymers. The evidence presented strongly suggests that there is limited structural degradation and the elemental composition is not changed under the electron beam at relatively low accelerating voltages. This technique statistically samples the repeat units of the polymer. For samples grown in both aqueous and nonaqueous solutions. SEM/EDS provides evidence for extensive contamination with oxygen.     

The synthesis of 1-methyl-1-germaadamantane

The syntheses of 1-methyl-1-germaadamantane and 1-chloro-1-germaadamantane are described. Attempts to prepare the 1-methyl-1-stannaadamantane and the novel cage systems, 1-silatris-nor- and 1-silatris-homo-adamantanes are also described as well as the syntheses of a variety of Group IV 1,3,5-trisubstituted cyclohexanes.     

S-(2-Pyrimidinyl)- and S-(2-(4,6-dimethylpyrimidinyl))-1,1,3,3-tetramethylthiouronium hexafluorophosphates: novel reagents for in situ peptide coupling

Two new reagents for in situ peptide coupling based on the 2-mercaptopyrimidine core have been developed. The readily prepared thiouronium salts were found to promote both peptide and segment coupling efficiently with low racemization/epimerization levels.     

An ab initio study of the geometry,energy, and selected force constants for the three planar conformers of carbonic acid,and the bicarbonate ion; and of the energy for the reaction H2O + CO2 → H2CO3

Ab initio calculations using the unscaled 4-31G basis set have been carried out on the cc, tc, and tt conformers of carbonic acid and the bicarbonate ion, with full geometry optimization assuming the structures to be planar. The complete harmonic force field is reported for the (most stable) tt conformer and for the bicarbonate ion, also selected quadratic force constants for the cc and tc conformers. The changes in certain bond lengths and stretching force constants in the cc → tc, tc → tt, and cc → tt conformer conversion reactions are indicative of intramolecular hydrogen bonding, C?O…H? O and H? O…H? O, which is examined in greater detail by partitioning the overall conformer conversion energy into distortion and bonding energy components. The fundamental vibration frequencies for the tt conformer and the bicarbonate ion are calculated from the force constant matrices, and hence, using a scaling factor based on a comparison of calculated and experimental values for the bicarbonate ion and trans-formic acid, a value is predicted for the zero-point energy of the tt conformer. A new estimate of ΔH? for the hydration reaction, H₂O + CO₂ → H₂CO₃, at 298 K in the gas phase; is made from thermochemical data, +20.2 ± 3.4 kJ mol^?1, which, together with estimates of (H₂₉₈? – H₀?) and the zero-point energy for H₂CO₃, gives +8.1 ± 7.0 kJ mol^?1 for ΔE_T(expt). ΔE_T calculated from the 4-31G basis set data is -29.1 kJ mol^?1. Comparison of the experimental value, the Hartree–Fock limit value, and values calculated with a variety of basis sets for the bond separation reaction, CO₂ + CH₄ → 2H₂CO, suggests that the differences, ΔE_T(expt) minus ΔE_T(SCF ), are due mainly to basis set limitations and not substantial correlation energy contributions.     

Selective chemical treatment of cellular microdomains using multiple laminar streams

There are many experiments in which it would be useful to treat a part of the surface or interior of a cell with a biochemical reagent. It is difficult, however, to achieve subcellular specificity, because small molecules diffuse distances equal to the extent of the cell in seconds. This paper demonstrates experimentally, and analyzes theoretically, the use of multiple laminar fluid streams in microfluidic channels to deliver reagents to, and remove them from, cells with subcellular spatial selectivity. The technique made it possible to label different subpopulations of mitochondria fluorescently, to disrupt selected regions of the cytoskeleton chemically, to dislodge limited areas of cell-substrate adhesions enzymatically, and to observe microcompartmental endocytosis within individual cells. This technique does not require microinjection or immobilization of reagents onto nondiffusive objects; it opens a new window into cell biology.     

Synthesis and Characterization of Sterically Encumbered Derivatives of Aluminum Hydrides and Halides: Assessment of Steric Properties of Bulky Terphenyl Ligands

The synthesis and characterization of several sterically encumbered monoterphenyl derivatives of aluminum halides and aluminum hydrides are described. These compounds are [2,6-Mes(2)C(6)H(3)AlH(3)LiOEt(2)](n)() (1), (Mes = 2,4,6-Me(3)C(6)H(2)-), 2,6-Mes(2)C(6)H(3)AlH(2)OEt(2) (2), [2,6-Mes(2)C(6)H(3)AlH(2)](2) (3), 2,6-Mes(2)C(6)H(3)AlCl(2)OEt(2) (4), [2,6-Mes(2)C(6)H(3)AlCl(3)LiOEt(2)](n)() (5), [2,6-Mes(2)C(6)H(3)AlCl(2)](2) (6), TriphAlBr(2)OEt(2) (7), (Triph = 2,4,6-Ph(3)C(6)H(2)-), [2,6-Trip(2)C(6)H(3)AlH(3)LiOEt(2)](2) (8) (Trip = 2,4,6-i-Pr(3)C(6)H(2)-), 2,6-Trip(2)C(6)H(3)AlH(2)OEt(2) (9), [2,6-Trip(2)C(6)H(3)AlH(2)](2) (10), 2,6-Trip(2)C(6)H(3)AlCl(2)OEt(2) (11), and the partially hydrolyzed derivative [2,6-Trip(2)C(6)H(3)Al(Cl)(0.68)(H)(0.32)(&mgr;-OH)](2).2C(6)H(6) (12). The structures of 2, 3a, 4, 6, 7, 9a, 10a, 10b, 11, and 12 were determined by X-ray crystallography. The structures of 3a, 9a, 10a, and 10b, are related to 3, 9, and 10, respectively, by partial occupation of chloride or hydride by hydroxide. The compounds were also characterized by (1)H, (13)C, (7)Li, and (27)Al NMR and IR spectroscopy. The major conclusions from the experimental data are that a single ortho terphenyl substituent of the kind reported here are not as effective as the ligand Mes (Mes = 2,4,6-t-Bu(3)C(6)H(2)-) in preventing further coordination and/or aggregation involving the aluminum centers. In effect, one terphenyl ligand is not as successful as a Mes substituent in masking the metal through agostic and/or steric effects.     

1-Ethyl-1,4-dihydro-4-oxo-7-(pyridinyl)-3-quinolinecarboxylic acids. I. Synthesis of 3- and 4-(3-aminophenyl)pyridine intermediates

A series of substituted 3- and 4-(3-aminophenyl)pyridines has been prepared as intermediates for the synthesis of some 1-alkyl-1,4-dihydro-4-oxo-7-pyridinyl-3-quinolinecarboxylic acids. The Hantzsch, Hauser and other pyridine syntheses were used. 4-(3-Aminophenyl)pyridine was prepared via 3-(4-pyridinyl)-2-cyclohexen-1-one using the Semmler-Wolff reaction.