Robert A. Burrow

C-H-π Interactions in 1-n-Butyl-3-methylimidazolium Tetraphenylborate Molten Salt: Solid and Solution Structures

The crystal structure of 1-n-butyl-3-methylimidazolium tetraphenylborate molten salt (1) shows C-H-pi interactions between the hydrogens of the imidazolium cation and the phenyl rings of the tetraphenylborate anion. The imidazolium ring is surrounded by three tetraphenylborate anions that are connected with the same cation by C-H-pi (phenyl rings) interactions. The nearest inter-ion interaction is found between the N-CH-N proton of the cation and the B-phenyl centroid (2.349 A) with a nearly T-shaped geometry. The inter-ionic solution structure of 1 has been investigated by the detection of inter-ionic contacts in 1H NOESY NMR spectra between the protons of the cation and the anion. The 1H-NMR spectra of molten salt 1 is almost independent of its concentration in [D6]DMSO solution, the imidazolium proton chemical shifts are in the expected region and there are no observable NOE effects between the protons of the cation with those of the anion, indicating that 1 behaves in [D6]DMSO as a solvent-separated ion pair. In CDCl3 the 1H-NMR spectra of 1 are concentration dependent and all the imidazolium protons are shielded as compared with those observed in [D6]DMSO. Moreover, the 1H NOESY NMR spectra show all the peaks affected by the interaction between the protons of the imidazolium cation and those of the anion, indicating that in CDCl3 1 possesses a contact ion pair structure. The NCHN proton of the cation exhibits the greatest shielding (up to -4.5 ppm). an indication of the existence of C-H-pi interactions, even in solution. The calculated distance of this proton to the phenyl centroid is 2.3 A for a C-H -pi angle of 180 degrees. The apparent volumes for the cation and anion, calculated from the measured 13C-NMR relaxation times, increase from 38 and 140 A3 in [D6]DMSO to 360 and 600 A3 in CDCl3, respectively; this indicates the formation of floating aggregates of the type (1)(n) in CDCl3 via weak hydrogen bonds, with increasing concentration.

Cyclopeptide alkaloids from Scutia buxifolia Reiss

Scutianene E (1), 3,4,28-tris-epi-scutiaene E (2), 28-epi-scutianene E (3) and scutianene L (4), four neutral cyclopeptide alkaloids, were isolated from Scutia buxifolia Reiss, together with four known cyclopeptide alkaloids, scutianines B, C, D and E. Scutianenes 1-3 are diastereoisomeric compounds, with 3-hydroxyleucine as a β-hydroxy amino acid unit, which is connected to the styryl fragment via an ether bridge, β-phenylserine, as a common ring-bonded amino acid residue. Attached to the amino group of β-hydroxyamino acid is a side chain [trans-CH=CH-Ph]. The structures of the peptides were elucidated by means of spectroscopic analysis, including extensive 2D NMR studies. The stereochemistry for the diastereomeric 3,4,28-tris-epi-scutiaene E and 28-epi-scutianene E was confirmed by X-ray diffraction analysis of their O-acetyl derivatives.

Crystal and molecular structure of (α-naphthyl)TeI3

(α-Naphthyl-Te) 2 reacts with iodine in toluene to give deep brown crystals of (α-naphthyl)TeI 3 . The structure of the new organotellurium trihalide has been studied by means of single crystal X-ray diffractometry. (α-Naphthyl)TeI 3 crystallizes in the monoclinic space group P 2 1 / c . The primary coordination sphere about the Te atom is bisphenoidal. The secondary bonds among the heavy atoms hold the (α-naphthyl)TeI 3 molecules into chains along the lattice; the TeI primary bonds show additionally different lengths. The compound can be considered as a supramolecular array comprised of tectonic charge-transfer complexes.

Reactions of the complexes Pt3(μ-CO)3L3 with SO2. Crystal structure of Pt3(μ-CO)3(PtBu2Ph)3•0.25(C4H8O)

Abstract Reactions of the complexes Pt3(μ-CO)3L3, where LPtBu3 (1a), PtBu2cPr (1b), PtBu2Ph (1c), PCy3 (1d) and PCy2Ph (1e), with SO2 have been examined. The complexes 1 may be divided into two classes: those complexes (1a, 1b and 1c) which fragment to yield a dimer Pt2(μ-SO2)(CO)2L2, where L=PtBu3 (2a), PtBu2CPr (2b), PtBu2Ph (2c), upon brief exposure to SO2 and those complexes (1d and 1e) which substitute CO ligands with SO2 ligands without a change in nuclearity to yield Pt3(μ-SO2)3L3, where L=PCy3 (3d) and PCy2Ph (3e). Traces of the complexes Pt3(μ-SO2)(μ-CO)2L3 (4) were observed after heating the complexes 2 under an SO2 atmosphere for 14 h. As formation of dimeric products appeared to be favoured by larger ligands L, a method of evaluating the non-bonding interactions between the ligands L and the cluster fragment Pt3(μ-CO)3 was used to evaluate the size to the phosphine ligands. The X-ray crystal structure of the complex Pt3(μ-CO)3(PtBu2Ph)3 (1c) is reported.

Bis(1-naphthyl) ditelluride.

The title compound, C(20)H(14)Te(2), shows a transoid conformation, with a C[bond]T[bond]-[bond]Te[bond]C torsion angle of 97.96 (9) degrees. The Te[bond]Te units show approximate eta(6) interactions with neighbouring naphthyl groups, forming chains along the c axis. The molecule lies about a crystallographic twofold axis.

A palladium complex containing a new C2-symmetric bidentate non-racemic oxalamidine ligand: synthesis and catalytic properties

Abstract Non-racemic (S,S,S,S)-(-)-2,2′-bis-(4,5-diphenyl-1, 3-imidazoline) 1 has been prepared in good yields from the reaction of (S,S)-(-)1,2-diphenylethylenediamine with diethyl oxalimidate. The reaction of 1 with sodium tetrachloropalladate yields [ PdCl 2 ( 1 )] complex 2, whose structure has been ascertained by means of X-ray diffraction analysis. Complex 2 catalyzes the hydro-arylation of norbornene in good catalytic activity but with poor enantioselectivity.

SYNTHESIS, CHARACTERIZATION AND REACTIVITY OF BIS(DIPHENYLPHOSPHINO)AMINE NICKEL COMPLEXES

Abstract The binuclear Ni(0) complexes [Ni2(μ-CO)(CO)2(μ-L2)2 (3), where L2 is the bridging diphosphine ligand bis(diphenyl-phosphino)amine (1H) or bis(diphenylphosphino)methylamine (1Me), have been prepared by the reaction of [Ni(CO)4] and L2. The bridging CO ligands in complexes 3 are reversibly displaced by SO2 yielding [Ni2(μ-SO2)(CO)2(μ-L2)2] (4). The single crystal X-ray structure of the binuclear complex. [Ni2(μ-SO2)(CO2)(μ-(PPh2)2NH)2] (4H), is presented. [Ni2(μ-SO2)(CO)2(μ-(Ph2P)2−NH)2]·(C8H10) crystallizes in the monoclinic space group C2 c , Z=4 with lattice parameters a = 27.227(5), b = 9.543(2), c = 22.979(4) A and β = 113.26(3)° . Reaction of the complexes 3 with X2, where X = Cl or I, ultimately gives [NiX2L2] (5), although intermediates in the reactions are observed. 13PNMR and mass spectral data for teh complexes are reported. Attempts to react the binuclear complexes 3 with several other ligands were unseccesful.

Determination of halogens and sulfur in pitch from crude oil by plasma-based techniques after microwave-induced combustion

This work demonstrates the feasibility of halogen and sulfur determination in pitch produced from crude oil residues by inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma optical emission spectrometry (ICP-OES), respectively, after digestion by microwave-induced combustion (MIC). Using the proposed system, it was possible to achieve a very effective digestion of pitch (up to 400 mg) using 20 bar of oxygen and 50 μL of 6 mol L−1 of ammonium nitrate as an ignition aid. Water and NH4OH solutions (10 to 100 mmol L−1) were evaluated for analyte absorption and a reflux step was applied after combustion in order to ensure quantitative analyte absorption. The volume of absorbing solution (6, 8, 10 and 12 mL) was also evaluated and best results were obtained using 6 mL confirming the results of previous studies. Accuracy was evaluated by comparison of results with those obtained using a total Cl and S analyzer, X-ray fluorescence (XRF, for Cl and S determination) and pyrohydrolysis followed by ICP-MS determination (Br and I). By using 50 mmol L−1 NH4OH as the absorbing solution the agreement with reference values ranged from 95 to 103% for all analytes. The results obtained using MIC presented an agreement of 101 and 100% with those obtained using a total Cl and S analyzer, respectively. The results were also compared with XRF analysis (for Cl and S) and agreement was 102 and 92%, respectively. In the same way, the results obtained by MIC were in agreement with those obtained by the pyrohydrolysis method (agreement of 97 and 105% for Br and I, respectively). The residual carbon content of MIC digests was always below 1% showing the high efficiency of pitch digestion. Using 400 mg of sample mass and 6 mL of 50 mmol L-1 NH4OH as the absorbing solution, limits of detection were 3.1 μg g−1 for S by ICP-OES and 3.2, 0.02 and 0.002 μg g−1 for Cl, Br and I by ICP-MS, respectively.

Diterpenoids from Humirianthera ampla.

Two diterpenoids, humirianthol and acrenol, as well as the known annonalide, were isolated from Humirianthera ampla. Humirianthol and acrenol were determined by 1D and 2D NMR spectroscopic techniques to be 3 beta,20:14 beta,16-diepoxy-3 alpha, 15 alpha-dihydroxy-7-pimaren-19,6 beta-olide and 3 beta,20-epoxy-3 alpha,15,16-trihydroxy-7-pimaren-19,6 beta-olide, respectively.

Nickel(II) complexes with methyl(2-pyridyl)ketone oxime: synthesis, crystal structures and DFT calculations.

The synthesis and structural characterization of the three novel nickel(II) complexes [Ni(OOCPh)(2)(mpkoH)(2)] (1), [Ni(NO(3))(2)(mpkoH)(2)] (2) and [Ni(mpkoH)(3)](NO(3))(2)·½H(2)O (3·½H(2)O), with mpkoH=methyl(2-pyridyl)ketone oxime is reported. Geometry optimization and population analyses were performed by means of DFT calculations for the previously mentioned compounds as well as for [NiCl(2)(mpkoH)(2)] (4). Electronic UV-vis spectra were also simulated in the TD-DFT framework to assign the origin of the absorption bands and in doing so, to have a clear picture of the absorptive features of the coordination compounds under investigation.