Hydration of Propargyl Esters Catalyzed by Gold(I) Complexes with Phosphoramidite Calix[4]pyrrole Cavitands as Ligands.

We report the synthesis and characterization of two diastereomeric phosphoramidite calix[4]pyrrole cavitands and their corresponding gold(I) complexes, 2in•Au(I)•Cl and 2out•Au(I)•Cl, featuring the metal center directed inward and outward with respect to their aromatic cavity. We studied the catalytic activity of the complexes in the hydration of a series of propargyl esters as the benchmarking reaction. All substrates were equipped with a six-membered ring substituent either lacking or including a polar group featuring different hydrogen bond acceptor (HBA) capabilities. We designed the substrates with the polar group to form 1:1 inclusion complexes of different stabilities with the catalysts. In the case of 2in•Au(I)•OTf, the 1:1 complex placed the alkynyl group of the bound substrate close to the metal center. We compared the obtained results with those of a model phosphoramidite gold(I) complex lacking a calix[4]pyrrole cavity. We found that for all catalysts, the presence of an increasingly polar HBA group in the substrate provoked a decrease in the hydration rate constants. We attributed this result to the competing coordination of the HBA group of the substrate for the Au(I) metal center of the catalysts.

Anion binding and transport with meso-alkyl substituted two-armed calix[4]pyrroles bearing urea and hydroxyl groups.

Calix[4]pyrroles bearing hydroxyl (1) or urea (3) groups attached to the meso-positions with propyl linkers were synthesized as cis- and trans-isomers. The anion binding properties of cis-1 and cis-3 were screened with ion-mobility mass spectrometry, where cis-1 formed complexes with Cl-, Br- and H2PO4-, whereas cis-3 formed complexes with most of the investigated anions, including Cl-, Br-, I-, NO3-, ClO4-, OTf-, SCN- and PF6-. The structures of the chloride complexes were further elucidated with density functional theory calculations and a crystal structure obtained for cis-1. In solution, chloride and dihydrogenphosphate anion binding with cis-1 and cis-3 were compared using 1H NMR titrations. To assess the suitability of two-armed calix[4]pyrroles as anion transporters, chloride transport studies of cis-1, cis-3 and trans-3 were performed using large unilamellar vesicles. The results revealed that cis-3 had the highest activity among the investigated calix[4]pyrroles, which was related to the improved affinity and isolation of chloride inside the binding cavity of cis-3 in comparison to cis-1. The results indicate that appending calix[4]pyrroles with two hydrogen bonding arms is a feasible strategy to obtain anion transporters and receptors with high anion affinity.

Phenanthrenequinone-Sensitized Photocatalytic Synthesis of Polysubstituted Quinolines from 2-Vinylarylimines.

Visible-light-excited 9,10-phenanthrenequinone (PQ*) was used as a photocatalyst for the synthesis of polysubstituted quinolines via the electrocyclization of 2-vinylarylimines. Up to quantitative yields of 2,4-disubstituted quinolines were received after 1 h of excitation with blue LEDs at room temperature when MgCO3 was used as an additive in DCM. On the basis of experimental and DFT studies, we propose that PQ* induces one-electron oxidation of the imine substrate that triggers the electrocyclization mechanism.

Noncovalent Axial I⋠⋠⋠Pt⋠⋠⋠I Interactions in Platinum(II) Complexes Strengthen in the Excited State.

Coordination compounds of platinum(II) participate in various noncovalent axial interactions involving metal center. Weakly bound axial ligands can be electrophilic or nucleophilic; however, interactions with nucleophiles are compromised by electron density clashing. Consequently, simultaneous axial interaction of platinum(II) with two nucleophilic ligands is almost unprecedented. Herein, we report structural and computational study of a platinum(II) complex possessing such intramolecular noncovalent I⋅⋅⋅Pt⋅⋅⋅I interactions. Structural analysis indicates that the two iodine atoms approach the platinum(II) center in a "side-on" fashion and act as nucleophilic ligands. According to computational studies, the interactions are dispersive, weak and anti-cooperative in the ground electronic state, but strengthen substantially and become partially covalent and cooperative in the lowest excited state. Strengthening of I⋅⋅⋅Pt⋅⋅⋅I contacts in the excited state is also predicted for the sole previously reported complex with analogous axial interactions.

Self-healing, luminescent metallogelation driven by synergistic metallophilic and fluorine-fluorine interactions.

Square planar platinum(ii) complexes are attractive building blocks for multifunctional soft materials due to their unique optoelectronic properties. However, for soft materials derived from synthetically simple discrete metal complexes, achieving a combination of optical properties, thermoresponsiveness and excellent mechanical properties is a major challenge. Here, we report the rapid self-recovery of luminescent metallogels derived from platinum(ii) complexes of perfluoroalkyl and alkyl derivatives of terpyridine ligands. Using single crystal X-ray diffraction studies, we show that the presence of synergistic platinum-platinum (PtPt) metallopolymerization and fluorine-fluorine (FF) interactions are the major driving forces in achieving hierarchical superstructures. The resulting bright red gels showed the presence of highly entangled three-dimensional networks and helical nanofibres with both (P and M) handedness. The gels recover up to 87% of their original storage modulus even after several cycles under oscillatory step-strain rheological measurements showing rapid self-healing. The luminescence properties, along with thermo- and mechanoresponsive gelation, provide the potential to utilize synthetically simple discrete complexes in advanced optical materials.

Non-conventional synthesis and photophysical studies of platinum(ii) complexes with methylene bridged 2,2'-dipyridylamine derivatives.

Methylene bridged 2,2'-dipyridylamine (dpa) derivatives and their metal complexes possess outstanding properties due to their inherent structural flexibility. Synthesis of such complexes typically involves derivatization of dpa followed by coordination on metals, and may not always be very efficient. In this work, an alternative synthetic approach, involving the derivatization step after - rather than prior to - coordination of dpa on metal center, is proposed and applied to synthesis of a number of platinum(ii) complexes with substituted benzyldi(2-pyridyl)amines. Comparison with the more conventional synthetic route reveals greater efficiency and versatility of the proposed approach. The obtained complexes are not luminescent in solution at room temperature, but display blue phosphorescence emission (ca. 415 nm) with the lifetimes of µs order in glassy matrix at 77 K, with additional green (ca. 485 nm) and relatively long living (τ = 3.7 ms) emission in the case of iodine substituted derivative.

Infinite coordination polymer networks: metallogelation of aminopyridine conjugates and in situ silver nanoparticle formation.

Herein we report silver(i) directed infinite coordination polymer network (ICPN) induced self-assembly of low molecular weight organic ligands leading to metallogelation. Structurally simple ligands are derived from 3-aminopyridine and 4-aminopyridine conjugates which are composed of either pyridine or 2,2'-bipyridine cores. The cation specific gelation was found to be independent of the counter anion, leading to highly entangled fibrillar networks facilitating the immobilization of solvent molecules. Rheological studies revealed that the elastic storage modulus (G') of a given gelator molecule is counter anion dependent. The metallogels derived from ligands containing a bipyridine core displayed higher G' values than those with a pyridine core. Furthermore, using single crystal X-ray diffraction studies and 1H-15N two-dimensional (2D) correlation NMR spectroscopy, we show that the tetracoordination of silver ions enables simultaneous coordination polymerization and metallosupramolecular cross-linking. The resulting metallogels show spontaneous, in situ nanoparticle (d < 2-3 nm) formation without any additional reducing agents. The silver nanoparticle formation was followed using spectroscopic studies, and the self-assembled fibrillar networks were imaged using transmission electron microscopy (TEM) imaging.

5-Imino-3,4-diphenyl-1H-pyrrol-2-one.

The title compound, C16H12N2O, exists in the crystalline state as the 5-imino-3,4-di-phenyl--1H-pyrrol-2-one tautomer. The dihedral angles between the pyrrole and phenyl rings are 35.3 (2) and 55.3 (2)°. In the crystal, inversion dimers linked by pairs of N-H⋯N hydrogen bonds generate a graph-set motif of R 2 (2)(8) via N-H⋯N hydrogen bonds.

2,3-Di-phenyl-male-imide 1-methyl-pyrrol-idin-2-one monosolvate.

In the title compound, C16H11NO2·C5H9NO, the dihedral angles between the male-imide and phenyl rings are 34.7 (2) and 64.8 (2)°. In the crystal, the 2,3-di-phenyl-male-imide and 1-methyl-pyrrolidin-2-one mol-ecules form centrosymmetrical dimers via pairs of strong N-H⋯O hydrogen bonds and π-π stacking inter-actions between the two neighboring male-imide rings [centroid-centroid distance = 3.495 (2) Å]. The dimers are further linked by weak C-H⋯O and C-H⋯π hydrogen bonds into a three-dimensional framework.

Bis(hy-droxy-ammonium) hexa-chlorido-platinate(IV)-18-crown-6 (1/2).

In the title complex, (NH3OH)2[PtCl6]·2C12H24O6, the Pt(IV) atom is coordinated by six chloride anions in a slightly distorted octa-hedral geometry. The Pt-Cl bond lengths are comparable to those reported for other hexa-chlorido-platinate(IV) species. The hy-droxy-ammonium groups act as linkers between the [PtCl6](2-) anion and the crown ether mol-ecules. The anion is linked to two hy-droxy-ammonium cations via O-H⋯Cl hydrogen bonds and each hy-droxy-ammonium moiety is linked to a crown ether mol-ecule by hydrogen bonds between ammonium H atoms and 18-crown-6 O atoms. The crown ether mol-ecules have the classic crown shape in which all O atoms are located in the inner part of the crown ether ring and all -CH2- groups are turned to the outside.