Synthesis and reactivity of copper(I) complexes containing a bis(imidazolin-2-imine) pincer ligand

The new pincer ligand 2,6-bis[(1,3-di-tert-butylimidazolin-2-imino)methyl]pyridine (TL(tBu)) has been prepared in high yield from 2,6-bis(hydroxymethyl)pyridine (1) and 1,3-di-tert-butylimidazolin-2-imine (3). Reaction of TL(tBu) with [Cu(MeCN)4]PF6 affords the highly reactive copper(I) complex [(TL(tBu))Cu]PF6, [5]PF6, which forms the stable copper(I) isocyanide complexes [6a]PF6 (nu(CN) = 2179 cm(-1)) and [6b]PF6 (nu(CN) = 2140 cm(-1)) upon addition of tert-butyl or 2,6-dimethylphenyl isocyanide, respectively. For the cations 6a and 6b, DFT calculations reveal ground-state electronic structures of the type [(TL(tBu)-kappaN(1):kappaN(2))Cu(CNR)] with tricoordinate geometries around the copper atoms. Exposure of [5]PF6 to the air readily leads to trapping of atmospheric CO2 to form the square-planar complex [(TL(tBu))Cu(HCO3-kappaO)]PF6, [7]PF6, with the bicarbonate ligand adopting a rarely observed monodentate coordination mode. In chlorinated solvents such as dichloromethane or chloroform, [5]PF(6) rapidly abstracts chloride by reductive dechlorination of the solvent to yield [(TL(tBu))CuCl]PF6, [8]PF6 quantitatively. Reaction of TL(tBu) with copper(I) bromide or chloride affords complexes 9a and 9b, respectively, for which X-ray diffraction analysis, low-temperature NMR experiments and DFT calculations reveal the presence of a kappa(2)-coordinated ligand of the type [(TL(tBu)-kappaN(1):kappaN(2))CuX]. In solution, complex 9b undergoes slow disproportionation forming the mixed-valence copper(II)/copper(I) system [(TL(tBu))CuCl][CuCl2], [8]CuCl2 with a linear dichlorocuprate(I) counterion.     

Homoleptic lanthanide(II)-bis(guanidinate) complexes, [Ln(Giso)(2)] (Giso = [(ArN)(2)CN(C(6)H(11))(2)](-), Ar = C(6)H(3)Pr(i)(2)-2,6): planar 4-coordinate (Ln = Sm or Eu) vs distorted tetrahedral (Ln = Yb) geometries

The first homoleptic lanthanide(II)-guanidinate complexes have been prepared and shown to have differing coordination geometries (including unprecedented examples of planar 4-coordination) that depend on the size of the lanthanide metal.     

Strong resonant intersubband magnetopolaron effect in heavily modulation-doped GaAs/AlGaAs single quantum wells at high magnetic fields

Electron cyclotron resonance (CR) has been studied in magnetic fields up to 32 T in two heavily modulation-δ-doped GaAs/Al_0.3Ga_0.7As single quantum well samples. Little effect on electron CR is observed in either sample in the region of resonance with the GaAs LO phonons. However, above the LO-phonon frequency energy E_LO at B>27 T, electron CR exhibits a strong avoided-level-crossing splitting for both samples at energies close to E_LO+(E₂−E₁), where E₂, and E₁ are the energies of the bottoms of the second and the first subbands, respectively. The energy separation between the two branches is large, reaching a minimum of about 40 cm⁻¹ around 30.5 T for both samples. This splitting is due to a three-level resonance between the second LL of the first electron subband and the lowest LL of the second subband plus an LO phonon. The large splitting in the presence of high electron densities is due to the absence of occupation (Pauli-principle) effects in the final states and weak screening for this three-level process.     

Continuous Reversible Addition‐Fragmentation Chain Transfer Polymerization in Miniemulsion Utilizing a Multi‐Tube Reaction System

Summary: A unique, multi‐tube, continuous reactor has been successfully designed and implemented for the study of reversible addition‐fragmentation chain transfer (RAFT) in miniemulsions. Data collection is greatly enhanced by the ability to simultaneously collect samples at five different residence times. The results of a styrene homopolymerization show that kinetically, the reactor exhibits similar behavior to a batch reaction. Number‐average molecular weights increased linearly with conversion, typical of living polymerizations.

The number‐average molecular weight of the polymers produced in the tubular reactor increased linearly with conversion, indicative of a controlled polymerization.     

Observation and analysis of the Xe−I collisional-pair photoassociation spectrum

The interpretation of the photoassociation spectrum arising in collisions of Xe and I atoms is refined with allowance for new data concerning the interaction potential of Xe and I collisional pairs. Spectroscopic constants for the XeI(B) state are determined:R′ _e =3.264961 Å,D′ _e =33,289.05 cm^?1,w′ _e =113.867826 cm^?1, andw′ _e x′ _e =0.238304 cm^?1.     

Inhibitors of dihydrofolate reductase: Design,synthesis and antimicrobial activities of 2,4-diamino-6-methyl-5-ethynylpyrimidines

Novel 2,4-diamino-6-methyl-5-ethynylpyrimidines were prepared via palladium catalyzed coupling of 2,4-diamino-5-iodo-6-methyl-pyrimidine with terminal acetylenes. The compounds were inhibitors of dihydrofolate reductase and showed in vitro activity against several species of opportunistic fungi and the protozoan Toxoplasma gondii.     

Asymmetric synthesis of α-substituted alkylphosphonates based on symmetrical dialkyl phosphites

Chiral C₂-symmetrical dialkyl phosphites and C₃-symmetrical trialkyl phosphites, derived from (−)-borneol, (−)-menthol, and 1,2∶5,6-di-O-isopropylidene-α-d-glucofuranose, were studied as the starting reagents for the preparation of chiral organophosphorus compounds. The reactions of C₂-symmetrical dialkyl phosphites and C₃-symmetrical trialkyl phosphites with aldehydes and amines or aldehydes are accompanied by asymmetrical induction at the α-carbon atom to yield optically active α-aminoalkylphosphanates or α-hydroxyalkylphosphonates, respectively. The stereoselectivity of the reaction depends on the structure of the starting compounds and the reaction conditions. Translated fromIzvestiya Akademii, Nauk, Seriya Khimicheskaya, No. 8, pp. 1588–1593, August, 1999.     

Optical fibre beam delivery of high-energy laser pulses: beam quality preservation and fibre end-preparation

This paper investigates the extension of optical fibre beam delivery to high-brightness applications, in particular laser percussion drilling, where both a good beam quality and high peak power are required. Beam quality preservation through a number of optical fibres is studied both experimentally and by using a ray propagation model. It is determined that in order to achieve the beam quality required for percussion drilling (M²<30) the largest fibre which can be used is 400 μm diameter. The laser-induced damage threshold is measured for a number of 400 μm fibres, and a CO₂ laser-annealing technique is shown to increase the damage threshold by a factor of 10, allowing 28 J, 1 ms pulses to be transmitted.     

Grenzen für die Bildung lamellarer Metall‐di(arensulfonyl)amide: Drei Lithium‐Komplexe und ein Cadmium‐Komplex

Structures of Ionic Di(arenesulfonyl)amides. 6. Limits to the Formation of Lamellar Metal Di(arenesulfonyl)amides: Three Lithium Complexes and One Cadmium Complex According to low‐temperature X‐ray studies, the new compounds LiN(SO₂C₆H₄‐4‐X)₂ · 2 H₂O, where X = COOH ( 1 ) or COOMe ( 2 ), LiN(SO₂C₆H₄‐4‐CONH₂)₂ · 4 H₂O ( 3 ), and Cd[N(SO₂C₆H₄‐4‐COOH)₂]₂ · 8 H₂O ( 4 ) crystallize in the triclinic space group P1 ( 1 – 3 : Z′ = 1; 4 : Z′ = 1/2, Cd²⁺ on an inversion centre) and display almost perfectly folded anions approximating to mirror symmetry. The lithium ions in 1 – 3 have distorted tetrahedral environments respectively set up by two O=S groups drawn from different anions and two water molecules, two O=S groups of a chelating anion and two water molecules, or one O=C group and three water ligands, whereas the cation of 4 is fully hydrated to form an octahedral [Cd(H₂O)₆]²⁺ complex. The structure refinements for 3 and 4 were marred by positional disorder of the non‐coordinating N(SO₂)₂ moieties. Compounds 1 and 4 extend a previously described series of lamellar metal di(arenesulfonyl)amides where the two‐dimensional inorganic component is comprised of cations, N(SO₂)₂ groups and water molecules and the outer regions are formed by the 4‐substituted phenyl rings. Both crystal packings are governed by self‐assembly of parallel layers through exhaustive hydrogen bonding between carboxylic groups, and there is good evidence that the labile inorganic networks, generated via Li–O and hydrogen bonds in 1 or solely hydrogen bonds in 4 , are efficiently stabilized by the strong cyclic (COOH)₂ motifs within the interlayer regions. In the absence of these, the lamellar architecture is seen to collapse in 2 and 3 , where the carboxyl groups are replaced by methoxycarbonyl or carbamoyl functions and the inorganic components are segregated in parallel tunnels pervading the anion lattices.