Crystal structures of two Ca(II) complexes with imidazole-4,5-dicarboxylate and water ligands

The structure of compound I: poly-diaqua(μ-imidazole-4,5-dicarboxylato-N,O; -O′; -O′′, -O′′′) calcium(II) monohydrate [Ca(C₅H₂N₂O₄)(H₂O)₂·H₂O] is built of molecular sheets in which imidazole-4,5-dicarboxylate ligands bridge the metal ions using both carboxylate groups, each bidentate. Ca(II) is coordinated by six oxygen atoms and one hetero-ring nitrogen atom distributed at the apices of a capped tetragonal bipyramid. The basal plane of the pyramid is formed by two carboxylate oxygen atoms [d(Ca–O2?=?2.374(1)?Å, d(Ca–O4)?=?2.412(1)?Å] and two water oxygen atoms [d(Ca–O5)?=?2.384(1)?Å, d(Ca–O6)?=?2.455(1)?Å], the capped position is occupied by the carboxylate oxygen atom O3 [d(Ca–O3)?=?2.325(1)?Å], the hetero-ring nitrogen atom [d(Ca–N2)?=?2.523(1)?Å] and the carboxylate oxygen atom O4 [d(Ca–O2)?= 2.412(1)?Å] form the apices of the prism. The solvation water molecule plays a significant role in a framework of hydrogen bonds responsible for the stability of the crystal. The structure of compound II: trans-tetraquadi(H-imidazole-4,5-dicarboxylato-N,O) calcium(II) monohydrate, [Ca(C₅H₃N₂O₄)₂(H₂O)₄·H₂O] consists of monomers in which the Ca(II) ion is located on a centre of symmetry. The coordination around the Ca(II) is a strongly deformed pentagonal bipyramidal with the imidazole-4,5-dicarboxylate (4,5-IDA) ligands in the trans arrangement forming a dihedral angle of 68.3°. An imidazole-ring nitrogen atom [d(Ca–N)?=?2.632(2)?Å] and one carboxylate O atom [d(Ca–O)?=?2.531(2)?Å] from each ligand coordinate to the metal ion. The coordination is completed by four water oxygen atoms [d(Ca–O)?=?2.393(2)?Å] and [d(Ca–O)?=?2.367(2)?Å]. The coordinated water molecules act as hydrogen bond donors and acceptors to the unbonded carboxylate oxygen atoms in adjacent monomers giving rise to a three-dimensional molecular network.     

Tsuji-Trost allylations with palladium recovery by phosphines/Pd(0)-triolefinic macrocyclic catalysts

The allylation of several nitrogen and oxygen based nucleophiles with ethyl cinnamyl carbonate under mild conditions is described. The processes take place in the absence of added base and in the presence of the precatalytic system Pd(0)-triolefinic macrocycle/1,1′-bis(diphenylphosphino)ferrocene. The macrocyclic ligand plays a key role in the recovery of the metal in the form of the initial macrocyclic complex.     

Ring-closing metathesis of fluoroalkenes toward the synthesis of fluorinated heterocycles containing an oxaza bond

This study reports the ring-closing metathesis reaction of bisolefins, including a reluctant fluoroalkenes, linked with oxaza moiety. The resulting heterocycles were produced in high yields under high diluting conditions disfavoring the homodimerization side reaction of nonfluorinated double bond. The use of a mixture of solvents proved to be a good strategy to obtain the fluorinated heterocycles in fair to excellent yields.     

Three-step synthesis of oxylipins from D. loretense

A three-step convergent synthesis of an immunostimulatory oxylipin was developed using an olefin cross metathesis approach. The alkene fragments were prepared in two steps from commercially available starting materials with high stereoselectivity. In particular, an organocatalytic aldehyde α-oxygenation gave high enantioselectivity and yield using as little as 2 mol% catalyst. This synthesis represents the shortest synthesis of any natural product containing the 3-ene-1,2,5-triol moiety and delivers an immunostimulatory oxylipin in 33% overall yield.     

Facile synthesis of [(NHC)(NHCewg)RuCl2(CHPh)] complexes

The utility of [(NHC)(PPh₃)RuCl₂(CHPh)] for the facile and efficient synthesis of ten complexes of the type [(NHC)(NHC_ewg)RuCl₂(CHR)] with saturated and unsaturated NHC ligands in 85-94% isolated yield via a simple one step synthesis utilizing [AgI(NHC_ewg)] as NHC_ewg transfer reagents was demonstrated.     

Olefin bonding mechanism and growth to (1 0 0)(2 × 1):H diamond

The bonding and growth mechanism of photochemically attached olefin molecules to (1 0 0)(2 × 1):H diamond is characterized using atomic force (AFM) and scanning tunneling microscopy (STM) experiments in combination with molecular orbital calculations. To identify growth schemas, diamond surfaces after 10, 40 and 90 min of photo-chemically stimulated growth have been characterized. These data show clearly island formation which is discussed taking into account a growth model from silicon. The island growth shows no directional properties which are attributed to arrangement and geometrical properties of hydrogen terminated carbon bonds at the surface of (1 0 0) oriented (2 × 1) reconstructed diamond.     

Determination of the upper limits, benchmarks, and critical properties for gas separations using stabilized room temperature ionic liquid membranes (SILMs) for the purpose of guiding future research

The literature reports that supported ionic liquid membranes (SILMs) outperform standard polymers for the separations of CO₂/N₂ and CO₂/CH₄, even under continuous flow mixed gas conditions. Before the expenditure of more resources to develop new room temperature ionic liquids (RTILs) and SILMs, it is time to consider what benchmarks for SILM performance exist and if upper limits could be projected based on the physical chemistry of RTILs. At this juncture, we should ask if the current research efforts are properly focused based on the successes and failures in the literature. We summarize literature data, along with adding new data, on the SILM permeabilities and selectivities for the following gas pairs: CO₂/N₂, CO₂/CH₄, O₂/N₂, ethylene/ethane, propylene/propane, 1-butene/butane, and 1,3-butadiene/butane. The analysis predicts a maximum CO₂-permeability for SILMs and an upper bound for permeability selectivity vs. CO₂-permeability with respect to the CO₂/N₂ and CO₂/CH₄ separations. Also summarized are the representative successes and failures for improving the separation performance of SILMs via functionalization and facilitated transport in the context of the CO₂/N₂, CO₂/CH₄, and olefin/paraffin separations. In the context of the CO₂-separations, the analysis recommends a number of future research foci including research into SILMs cast from RTILs with smaller molar volumes. In the context of olefin/paraffin separations, the preliminary data is encouraging when considering the use of facilitated transport via silver carriers. Since RTIL-solvent/solvent interactions dominate in terminating the overall SILM performance, past attempts at enhancing solute/solvent interactions via the addition of functional groups to the RTILs have not produced SILMs with better separation performance compared to the unfunctionalized RTILs. Future research into functionalized RTILs needs to consider the changes to the dominant solvent/solvent interactions and not just the solute/solvent interactions.     

Low energy light-triggered oxidative cleavage of olefins

A series of substituted olefins were tested for their reactivity with singlet oxygen as a singlet oxygen-mediated cleavable linker. Low intensity light of 200 mW/cm² was irradiated to the solution of an olefin and 5,10,15-triphenyl-20-(4-hydroxyphenyl)-21H,23H-porphyrin under atmospheric condition. Among the tested olefins, 1,2-cis-diphenoxyethylene reacted fast with singlet oxygen, >80% within 15 min yielding a stoichiometric conversion to aldehyde product without any side reactions.     

含氮杂茂配体的类茂配合物NpCpTiCl_2催化乙烯聚合研究

茂金属催化烯烃聚合时不仅须大量甲基铝氧烷(MAO)作助催化剂,而且其稳定性较差,结构修饰困难,这都一定程度上限制了茂金属催化剂的发展.近几年来,将非环戊二烯类配体与IVB 族金属作用形成的配合物应用于催化烯烃聚合的研究大量出现[1],其中非环戊二烯配体有脒化物[2,3]、酰胺基[4,5]、NFDA3唑啉[6]、卟啉[7 ]、烷氧基[8]、芳氧基[9～11]、和β-二酮[12,13]、8-羟基喹啉[14～16]等.这些非茂配合物均可催化乙烯或丙烯聚合,但活性都较低.我们曾制备了含配位原子为氧或氮的非环戊二烯基配体的半茂配合物,即茂金属中一个环戊二烯基配体被非环戊二烯基配体取代,使金属中心与一个茂和一个非茂配体配位而形成的桥连或非桥连型的配合物[17,18].这类配合物不仅稳定性好,而且消耗的助催化剂量较少,活性高,对所得聚合物的结构有一定的控制作用.桥连型半茂配合物以“限制几何构型”催化剂为代表[16,19～20 ],非桥连型半茂配合物的报道较少,如CpTi(OiPr)Me2和CpTi(OAr)X2 [21 ,22].我们选择氮杂茂类配体为非环戊二烯阴离子配体,氮杂茂环以一价阴离子的形式与金属中心钛配位,与另一个环戊二烯阴离子形成类茂型配合物.这种类茂配合物易于制备, 稳定性好,而且消耗的助催化剂量较小.