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Zwitterionic nickel(II) compounds with a borate-containing anionic bidentate phosphine ligand (PBP − ) have been synthesized and some of them crystallographically characterized. The methyl complex, (PBP − )Ni + CH 3 (NCCH 3 ), reacts with H 2 to form an 12-membered macrocycle containing three Ni nuclei and reacts with carbon monoxide (CO) to afford the acetyl complex (PBP − )Ni + COCH 3 (CO). The square planar acetyl complex is stable in solution under 1 atm of CO but undergoes irreversible decomposition under high CO pressure at room temperature. X-Ray crystallographic characterization of a decomposition product revealed fragmentation of the anionic borate under high pressure. (PBP − )Ni + COCH 3 (CO) is an active catalyst for ethylene-CO copolymerization, but its productivity is low likely due to its instability under high CO pressure. [ABSTRACT FROM AUTHOR]

In this work, we report the synthesis, spectroscopic characterization, and theoretical analysis of a linearly conjugated pentacene-fused porphyrin dimer and cross-conjugated quinone-fused dinaphtho[2,3]porphyrins. These multichromophoric systems display non-typical UVvisible absorptions of either porphyrins or pentacenes/quinones. UV-visible, emission and magnetic circular dichroism (MCD) spectroscopy suggest strong electronic interactions among the multichromophores in the system. DFT calculations revealed the delocalization of the HOMOs and LUMOs spanning the entire dimer and linker assembly. The pentacene-fused porphyrin dimer is significantly more stable than both the corresponding pentacene and the heptacene derivatives. The availability of these huge π-extended and electronically highly interactive multichromophoric systems promises unprecedented electronic and photophysical properties. [ABSTRACT FROM AUTHOR]

The crystal structures of six cobalt sandwich complexes—four in the η5-cyclopentadienyl/η4-cyclobutadiene family, two from the related η5-cyclopentadienyl/η4-cyclopentadienone family—are presented and discussed alongside related structural precedents. In each of the complexes an undecorated cyclopentadienyl ligand is present whereas the partner cyclobutadiene or cyclopentadienone ligand bears four identical aromatic substituents (phenyl, p-tolyl, p-fluorophenyl, 2-thienyl or 2,2′-bithienyl). This range of substituents allows for detailed structural comparison between members of the families of sandwich complexes presented here, and with previously reported structures. Crystal structures of members of the η5-cyclopentadienyl/η4-tetraarylcyclobutadiene (left) and η5-cyclopentadienyl/η5-cyclopentadienone (right) families of sandwich complexes are presented. [ABSTRACT FROM AUTHOR]

We present the synthesis of several azadipyrromethenes with four peripheral arene units which can be readily generated via the well-established chalcone synthetic method. The stability and yields of these azadipyrromethenes is highly dependent on the nature of the arene substituent, with the bis-pyridine systems exhibiting the highest degree of instability. The structures of several of the compounds and their BF 2 adducts are presented; intramolecular hydrogen bonding is observed in the free base ADPMs. We also present a study into the absorption and emission properties of the ADPMs and their BF 2 adducts and observe that they are also highly dependent on the identity of the substituents. [ABSTRACT FROM AUTHOR]

Irradiation of [Ru(bpy)2(bpSOp)](PF6)2 (where bpy is 2,2'-bipyridine and bpSOp is 1,3-bis(phenylsulfinyl)-propane) results in the formation of two new isomers, namely the S,O- and O,O-bonded species. The crystal structure of the bis-thioether and bis-sulfoxide complexes are reported. NMR spectroscopy of the bis-thioether complex in solution is consistent with the molecular structure determined by diffraction methods. Further, NMR spectroscopy of the bis-sulfoxide complex reveals two conformers in solution, one that is consistent with the solid state structure and a second conformer showing distortion in the aliphatic portion of the chelate ring. Time-resolved visible absorption spectroscopy reveals isomerization time constants of 91 ps in dichloroethane (DCE) and 229 ps in propylene carbonate (PC). Aggregate isomerization quantum yields of 0.57 and 0.42 have been determined in DCE and in PC, respectively. The kinetics of the thermal reversion from the O,O- to S,O-bonded isomer are strongly solvent dependent, occurring with rates of 2.41 × 10-3 and 4.39 × 10-5 s-1 in DCE, and 4.68 × 10-4 and 9.79 × 10-6 s-1 in PC. The two kinetic components are assigned to the two isomers identified in solution. [ABSTRACT FROM AUTHOR]

Diiminoisoindoline (DII) can be modified with primary amines to afford bis-substituted heterocycles. Although the metal binding chemistry of isoindoline-based macrocycles and chelates has been explored, the corresponding chemistry of hydrocarbon substituted diiminoisoindolines remains open. The reaction of the bis(benzylimino)isoindoline with AgNO 3 affords a Ag 6 cluster complexed by four equivalents of ligand. The cluster exhibits a previously unknown argentophilic geometry. The Ag 6 unit forms a compressed hexagon, comprised of two Ag 3 triangles that are linked together to form a parallelogram. The argentophilic interactions range from ~ 2.76 to ~ 3.17 Å. [ABSTRACT FROM AUTHOR]

A new zwitterionic nickel(II) catalyst that comprises a partially fluorinated tetrakis(aryl)borate center in a bidentate phosphine ligand and a cationic Ni center has been developed and studied for CO-ethylene copolymerization in the context of comparison with a previously reported zwitterionic catalyst that carries a nonfluorinated borate anion. The crystal structures of several zwitterionic and related nickel compounds are characterized. Partial fluorination of the tetrakis(aryl)borate only brings a modest increase in productivity (2700 vs 1600 g of polyketone per gram of Ni, g (g of Ni)-1). Like the nonfluorinated catalyst, the fluorinated zwitterionic catalyst is extremely active at the beginning of the polymerization but deactivates rapidly. Deactivation of the two catalysts apparently follows different mechanisms. Stoichometric decomposition studies show that the partially fluorinated tetrakis(aryl)borate in the Ni compounds is stable under acidic conditions either directly introduced by addition of an acid or created by a CO atmosphere. In contrast, the nonfluorinated tetrakis(aryl)borate is readily decomposed by an acid or under acidic conditions created by CO. For the new catalyst system with the partially fluorinated tetrakis(aryl)borate anion, the deactivation likely involves initially redox processes and eventually ligand redistribution around Ni, as inferred from the stoichiometric decomposition studies. It turns out that such a process allows the deactivated catalyst to be reactivated by H2. When the polymerization is carried out in the presence of H2, the productivity of the new zwitterionic catalyst can reach 6400 g (g of Ni)-1. The zwitterionic catalyst with the nonfluorinated tetrakis(aryl)borate anion cannot be reactivated by H2. A cationic analogue of the zwitterionic catalysts is also studied for comparison. Its productivity for CO-ethylene copolymerization (230 g (g of Ni)-1) is about 1 order of magnitude lower than that of the zwitterionic catalysts, demonstrating the critical role of the zwitterionic character in attaining the aforementioned high productivity. At the productivity level of the zwitterionic catalysts, which to our knowledge is among the highest observed for Ni catalysts, an unacceptable amount of residual Ni(II) species is left in the product, causing the alternating CO-ethylene copolymer to begin to decompose near its melting temperature and hence making melt processing difficult. [ABSTRACT FROM AUTHOR]

To improve understanding of copper at the active site of Type 1 copper proteins, CuI and CuII complexes of 1,8-dithia-4,11-diazacyclotetradecane, shown in FIGREFFig. 1/FIGREF, have been successfully isolated and structurally characterized by X-ray crystallography. In these compounds, both CuI and CuII are centered in the plane of the macrocycle containing two sulphur and two nitrogen heteroatoms comprising the distorted tetrahedral/square planar coordination geometry. The UV/VIS spectra, electrochemistry and EPR properties have been obtained for the CuII complex 2. Three absorption bands at 295 nm, 354 nm, and 545 nm are observed in aqueous solution at a pH of 5. These bands have been assigned to the N → CuII and S → CuII charge transfer bands and the d–d transitions respectively. The CuI/II redox midpoint potential of complex 2 in CH3CN is +403 mV versus NHE. [ABSTRACT FROM AUTHOR]