Ring opening polymerization of d,l-lactide and ε-caprolactone catalysed by (pyrazol-1-yl)copper(ii) carboxylate complexes.

1,2-Bis{(3,5-dimethylpyrazol-1-yl)methyl}benzene (L) reacts with [Cu(OAc)] and CHCOOH, 4-OH-CHCOOH, 2-Cl-CHCOOH and (3,5-NO)-CHCOOH to afford the copper complexes [Cu(CHCOO)(L)] (1), [Cu(4-OH-CHCOO)(L)] (2), [Cu(2-Cl-CHCOO)(L)] (3) and [Cu{(3,5-NO)-CHCOO}L] (4) which are characterised by IR, mass spectrometry, elemental analyses, and X-ray crystallography. The structural data revealed two geometries that are adopted by the complexes: (i) paddle wheel in 1, 2·7HO, 3 and (ii) regular chains in 3 and 4. Magnetic studies show strong antiferromagnetic couplings in the paddle wheel complexes and a weak antiferromagnetic coupling in the monometallic chain one.

Intricacies of ligand coordination in tricarbonylchromium(0) complexes with ortho- and para-fluorobiphenyls.

The steric and electronic factors that influence which of the two rings of a substituted biphenyl ligand coordinates to chromium are of interest and it has been suggested that haptotropic rearrangements within these molecules may be limited if the arene-arene dihedral angle is too large. Two tricarbonylchromium(0) complexes and their respective free ligands have been characterized by single-crystal X-ray diffraction. In the solid state, tricarbonyl[(1',2',3',4',5',6'-η)-2-fluoro-1,1'-biphenyl]chromium(0), [Cr(CHF)(CO)], (I), exists as the more stable isomer with the nonhalogenated arene ring ligated to the metal center.

A γ-amino acid that favors 12/10-helical secondary structure in α/γ-peptides.

H-bonded helices in conventional peptides (containing exclusively homochiral α-amino acid residues) feature a uniform H-bonding directionality, N-terminal side C═O to C-terminal side NH. In contrast, heterochiral α-peptides can form helices in which the H-bond directionality alternates along the backbone because neighboring amide groups are oriented in opposite directions. Alternating H-bond directions are seen also in helices formed by unnatural peptidic backbones, e.

Dichlorido{2-[(3,5-diphenyl-1H-pyrazol-1-yl-κN2)methyl]pyridine-κN}palladium(II).

The title compound, [PdCl(2)(C(21)H(17)N(3))], is a member of a sequence of Pd, Pt and Co dichloride complexes bearing polysubstituted (pyrazol-1-ylmethyl)pyridine ligands. It is shown that there is a correlation between the steric bulkiness of the bidentate (pyrazol-1-ylmethyl)pyridine ligands and the Pd-N(pyrazole) distances, i.e.

1,2-Bis[(3,5-diphenyl-1H-pyrazol-1-yl)meth-yl]benzene.

The title compound, C(38)H(30)N(4), a potentially mono- and bidentate ligand, does not seem to form palladium complexes similar to other poly(pyrazol-1-ylmeth-yl)benzenes due to the large steric size of the phenyl substituents on the pyrazole rings. The pyrazole rings have a 21.09 (5)° angle between their mean planes and exhibit a trans-like geometry in which the in-plane lone pairs of electrons on the 2-N nitrogen atoms point in opposite directions.

(3,5-Di-tert-butyl-2-eth-oxy-benzyl-idene)[2-(3,5-di-tert-butyl-1H-pyrazol-1-yl)eth-yl]amine.

The angles within the benzene ring in the title compound, C(30)H(49)N(3)O, ranging from 116.34 (16) to 124.18 (16)°, reflect the presence of electron-donating and electron-withdrawing substituents.

An example of the refinement of positional disorder modeled as compositional disorder in [5-(2-formylphenyl)-10,15,20-triphenylporphyrinato]nickel(II).

The title compound, [Ni(C(45)H(28)N(4)O)], crystallizes in the space group I ̅42d and resides on a crystallographic fourfold rotoinversion axis with only a quarter of the complex in the asymmetric unit. The complex displays positional disorder as the one aldehyde group on the ligand can be located at four different positions. It was necessary to model this as compositional disorder to obtain a correct model and refinement.

New preorganized γ-amino acids as foldamer building blocks.

An asymmetric synthesis of two new diastereomeric γ-amino acids is described. Both molecules contain a cyclohexyl ring to limit conformational flexibility about the Cα-Cβ bond; they differ in having cis vs trans stereochemistry on the ring. Residues derived from the cis γ isomer are shown to support helical secondary structures in α/γ-peptide oligomers.

5',11'-Dihydro-dispiro-[cyclo-hexane-1,6'-indolo[3,2-b]carbazole-12',1''-cyclo-hexa-ne].

The title compound, C(28)H(30)N(2), is a symmetrical 2:2 product from the condensation of indole and cyclo-hexa-none. It is the only reported 5,11-dihydro-indolo[3,2-b]carbazole compound in which the spiro atoms are quaternary C atoms. Crystals were grown by vapor diffusion in a three-zone electric furnace.

Ethyl 3-ferrocenyl-1-(pyridin-2-ylmeth-yl)-1H-pyrazole-5-carboxyl-ate.

The title compound, [Fe(C(5)H(5))(C(17)H(16)N(3)O(2))], crystallizes with an essentially eclipsed conformation of the cyclo-penta-dienyl (Cp) rings. The unsubstituted ring is disordered over two positions with the major component being present 90 (1)% of the time. The substituted Cp ring, the pyrazole ring and three atoms of the eth-oxy-carbonyl group form a conjugated π-system.

Dichlorido[2-(3,5-dimethyl-1H-pyrazol-1-yl-κN)ethanamine-κN]zinc(II).

The amine title complex, [ZnCl(2)(C(7)H(13)N(3))], resulted from imine hydrolysis in a Schiff base compound. The Zn metal atom has a distorted tetra-hedral geometry with the most significant deviation identified in the magnitude of the N-Zn-N angle. This deviation stems from the participation of the Zn and N atoms in a six-membered metallocyclic ring.

(μ-Piperazine-1,4-dicarbodithio-ato-κS,S:S,S)bis-[bis-(triphenyl-phos-phane-κP)gold(I)] chloro-form disolvate.

In the title compound, [Au(2)(C(6)H(8)N(2)S(4))(C(18)H(15)P)(4)]·2CHCl(3), the digold complex resides on a crystallographic inversion center and co-crystallizes with two mol-ecules of chloro-form solvent. The piperazine-1,4-dicarbodithio-ate linker has an almost ideal chair conformation. The geometry about the gold atoms is severely distorted tetra-hedral punctuated by a very acute S-Au-S bite angle.

{1,2-Bis[(3,5-dimethyl-1H-pyrazol-1-yl-κN)meth-yl]benzene}-dichloridozinc(II).

The title zinc complex, [ZnCl(2)(C(18)H(22)N(4))], contains a bidentate 1,2-bis(3,5-dimethyl-1H-pyrazol-1-ylmeth-yl)benz-ene ligand that binds to the zinc atom, forming a nine-membered metallocyclic ring. The geometry about the Zn atom is distorted tetra-hedral, with the largest deviation observed in the magnitude of the Cl-Zn-Cl angle. Similar distortions are observed in the cobalt analogue and related zinc compounds containing metallocyclic rings with more than six members.

Haptotropic rearrangement in tricarbonylchromium complexes of 2-aminobiphenyl and 4-aminobiphenyl.

The para-aminobiphenyl compound [(η(6)-C(6)H(5))(C(6)H(4)-4-NH(2))]Cr(CO)(3) (1) has an arene-phenyl dihedral angle of 38.01(6)°, as determined by single-crystal X-ray crystallography, and 34.7(11)°, as determined by DFT calculations.

Characteristic structural parameters for the γ-peptide 14-helix: importance of subunit preorganization.

[Image: see text] We report crystallographic data for a set of homologous γ-peptides that contain a Boc-protected residue derived from the flexible gabapentin monomer at the N-terminus and cyclically constrained γ-residues at all other positions. The crystallized γ-peptides range in length from 3 to 7 residues. Previously only one atomic-resolution structure had been available for a short γ-peptide 14-helix.

Intramolecular hydrogen bonding in dichloridobis(3,5-di-tert-butyl-1H-pyrazole-κN2)cobalt(II) as a consequence of ligand steric bulk.

The title compound, [CoCl(2)(C(11)H(20)ClN(2))(2)], forms two intramolecular hydrogen bonds [graph set S(5)] between the N atoms of the pyrazole ligands and the chloride ligands. This hydrogen-bonding motif is uncommon among related compounds but occurs here because of the bulk of tert-butyl substituents on the pyrazole ligands which shield the central metal atom to a significantly larger extent than pyrazole ligands with smaller 3,5-substituents.

Crystallographic characterization of 12-helical secondary structure in β-peptides containing side chain groups.

Helices are the most extensively studied secondary structures formed by β-peptide foldamers. Among the five known β-peptide helices, the 12-helix is particularly interesting because the internal hydrogen bond orientation and macrodipole are analogous to those of α-peptide helices (α-helix and 3(10)-helix). The β-peptide 12-helix is defined by i, i+3 C═O···H-N backbone hydrogen bonds and promoted by β-residues with a five-membered ring constraint.

Constructor graph description of the hydrogen-bonding supramolecular assembly in two ionic compounds: 2-(pyrazol-1-yl)ethylammonium chloride and diaquadichloridobis(2-hydroxyethylammonium)cobalt(II) dichloride.

Covalent bond tables are used to generate hydrogen-bond pattern designator symbols for the crystallographically characterized title compounds. 2-(Pyrazol-1-yl)ethylammonium chloride, C(5)H(10)N(3)(+).Cl(-), (I), has three unique, strong, charge-assisted hydrogen bonds of the types N-H.

Synthesis of Pd Complexes Bearing an Enantiomerically-Resolved Seven-Membered N-Heterocyclic Carbene Ligands and Initial Studies of their Use in Asymmetric Wacker-Type Oxidative Cyclization Reactions.

The development of enantiomerically-resolved, axially-chiral seven-membered N-heterocyclic carbene ((7)NHC) ligands for palladium is described. These (7)NHC ligands are derived from enatiomerically pure 2,2'-diamino-6,6'-dimethylbiphenyl, which is transformed via a synthetic sequence consisting of ortho-arylation, N-alkylation, and cyclization to afford seven-membered-ring amidinium salts. Synthesis of the 7-membered amidinium salts benefits from microwave irradiation, and in-situ metalation of the amidinium salts yields (7)NHC-Pd(II) complexes.

Bis(2-hy-droxy-ethanaminium) tetra-chloridopalladate(II).

In the title compound, (C(2)H(8)NO)(2)[PdCl(4)], 2-hy-droxy-ethanaminium cations and tetra-chloridopalladate(II) dianions crystallize in a 2:1 ratio with the anion residing on a crystallographic inversion center. The cations and anions are linked in a complex three-dimensional framework by three types of strong hydrogen bonds (N-H⋯O, N-H⋯Cl, and O-H⋯Cl), which form various ring and chain patterns of up to the ternary graph-set level.

{Bis[2-(3,5-dimethyl-pyrazol-1-yl-κN)eth-yl]amine-κN}chloridopalladium(II) chloride 0.25-hydrate.

The title compound, [PdCl(C(14)H(23)N(5))]Cl·0.25H(2)O, is a pseudopolymorph of the previously reported compound [PdCl(C(14)H(23)N(5))]Cl·2H(2)O [de Mendoza et al. (2006 ▶).

(1,4,7,10-Tetra-oxacyclo-dodeca-ne)(trideuteroacetonitrile)lithium perchlorate.

In the title compound, [Li(C(8)H(16)O(4))(CD(3)CN)]ClO(4), the Li atom is penta-coordinate. The O atoms of the 12-crown-4 ether form the basal plane, whereas the N atom of the trideutero-aceto-nitrile occupies the apical position. The Li(+) atom is displaced by 0.

(μ-1,4,7,10-Tetra-oxacyclo-dodeca-ne)bis-[(1,4,7,10-tetra-oxacyclo-dodeca-ne)lithium] bis-(perchlorate).

12-Crown-4 ether (12C4) and LiClO(4) combine to form the ionic title compound, [Li(2)(C(8)H(16)O(4))(3)](ClO(4))(2), which is com-posed of discrete Li/12C4 cations and perchlorate anions. In the [Li(2)(12C4)(3)](2+) cation there are two peripheral 12C4 ligands, which each form four Li-O bonds with only one Li(+) atom. Additionally there is a central 12C4 in which diagonal O atoms form one Li-O bond each with both Li(+) atoms.

Crystallographic characterization of helical secondary structures in 2:1 and 1:2 alpha/beta-peptides.

Oligomers containing both alpha- and beta-amino acid residues ("alpha/beta-peptides") are intriguing as potential foldamers. A large set of alpha/beta-peptide backbones can be generated by combining alpha- and beta-amino acid residues in different patterns; however, most research to date has focused on the simplest pattern, 1:1 alpha:beta. We have begun to explore the range of variation that can be achieved with alpha-residue/beta-residue combinations by examining the folding behavior of oligomers that contain 2:1 and 1:2 alpha:beta patterns.

N,N'-Dineopentyl-naphthalene-1,8-diamine.

In the title compound, C(20)H(30)N(2), all bond distances and angles fall within the usual ranges but the C(ipso)-N distances [1.391 (5) and 1.398 (4) Å] are slightly shorter than the corresponding typical average distance of 1.