Catalytic Dibenzocyclooctene Synthesis via Cobalt(III)–Carbene Radical and ortho‐Quinodimethane Intermediates

The metalloradical activation of ortho‐benzallylaryl N‐tosyl hydrazones with [Co(TPP)] (TPP=tetraphenylporphyrin) as the catalyst enabled the controlled exploitation of the single‐electron reactivity of the redox non‐innocent carbene intermediate. This method offers a novel route to prepare eight‐membered rings, using base metal catalysis to construct a series of unique dibenzocyclooctenes through selective C_carbene?C_aryl cyclization. The desired eight‐membered‐ring products were obtained in good to excellent yields. A large variety of aromatic substituents are tolerated. The proposed reaction mechanism involves intramolecular hydrogen atom transfer (HAT) to Co^III–carbene radical intermediates followed by dissociation of an ortho‐quinodimethane that undergoes 8π cyclization. The mechanism is supported by DFT calculations, and the presence of radical‐type intermediates was confirmed by trapping experiments.     

Observations of tetrel bonding between sp3-carbon and THF

We report the direct observation of tetrel bonding interactions between sp³-carbons of the supramolecular synthon 3,3-dimethyl-tetracyanocyclopropane (1) and tetrahydrofuran in the gas and crystalline phase. The intermolecular contact is established via σ-holes and is driven mainly by electrostatic forces. The complex manifests distinct binding geometries when captured in the crystalline phase and in the gas phase. We elucidate these binding trends using complementary gas phase quantum chemical calculations and find a total binding energy of −11.2 kcal mol⁻¹ for the adduct. Our observations pave the way for novel strategies to engineer sp³-C centred non-covalent bonding schemes for supramolecular chemistry.

sp³-C⋯THF tetrel bonding was observed in the crystalline state and in the gas phase. Density functional calculations revealed interaction energies up to −11.2 kcal mol⁻¹ and showed that these adducts are held together mainly by electrostatics.     

Multiinstrument study of the electrophoretic mobility of quartz

The electrophoretic mobility of quartz in 0.01 mol dm(-3) NaCl and NaNO3 over the pH range 2-8 was studied using five different commercial instruments. The mobilities over the pH range 4-8 were relatively consistent, but the mobilities over the pH range 2-4 and the position of the isoelectric point IEP varied from one instrument to another. This result suggests that the discrepancies in the apparent IEP of quartz (and other silicas) reported in the literature are due to the instrument artifacts.     

Diferrous cyanides as models for the Fe-only hydrogenases

The first systematic study of diferrous dicyano dithiolates is described. Oxidation of [Fe2(S2C2H4)(CN)2(CO)4](2-) in the presence of cyanide and tertiary phosphines and of Fe2(S2C2H4)(CO)4(PMe3)2 in the presence of cyanide affords a series of diferrous cyanide derivatives that bear a stoichiometric, structural, and electronic relationship to the H(ox)(air) state of the Fe-only hydrogenases. With PPh3 as the trapping ligand, we obtained an unsymmetrical isomer of Fe2(S2C2H4)(mu-CO)(CN)2(PPh3)2(CO)2, as confirmed crystallographically. This diferrous cyanide features the semibridging CO-ligand, with Fe-muC bond lengths of 2.15 and 1.85 A. Four isomers of Fe2(S2C2H4)(mu-CO)(CN)2(PMe3)2(CO)2 were observed, the initial product again being unsymmetrical but more stable isomers being symmetrical. DFT calculations confirm that the most stable isomers of Fe2(S2C2H4)(mu-CO)(CN)2(PMe3)2(CO)2 have cyanide trans to mu-CO. Oxidative decarbonylation also afforded the new tetracyanide [Fe2(S2C2H4)(mu-CO)(CN)4(CO)2]2-. Insights into the oxidative decarbonylation mechanism of these syntheses come from the spectroscopic characterization of the tetracarbonyl [Fe2(S2C2H4)(mu-CO)(CN)3(CO)3](-). This species reacts with PEt3 to produce the stable adduct [Fe2(S2C2H4)(mu-CO)(CN)3(CO)2(PEt3)](-).     

Aqueous Amino Silane Modification of E-glass Surfaces

The majority of work available in the literature examines the effect of epoxy silane, gamma-aminopropyltrimethoxy silane, and methacrylate silane on E-glass surfaces. As alternatives to the most commonly used silanes, we investigated two novel silanes: gamma-ureidopropyltriethoxy silane and Nbeta(aminoethyl) gamma-aminotrimethoxy silane and additionally an amino-functional polysiloxane. The ureido silane-treated E-glass fibers demonstrated a zeta potential similar to that of the untreated E-glass fibers, which was independent of deposition solution pH over the pH range investigated. A moderately hydrophobic E-glass surface, which was silane concentration dependent, was noted as being due to condensed Si-O-Si bonds at the surface. The diamino silane demonstrated an extremely basic surface at the higher silane concentrations investigated. These outer surface layers were modified by changing the pH and the concentration of the deposition solution. The polysiloxane produced an increase in the hydrophobicity of the E-glass fiber, especially when deposited from extremely basic solutions. At the higher solution concentrations investigated, the silanes and the siloxane was initially deposited in patches and an outer surface or "skin" was formed over these patches, giving the appearance of fully coated fibers. Copyright 2001 Academic Press.     

Oligomerization of indole derivatives with incorporation of thiols

Two molecules of indole derivative, e.g. indole-5-carboxylic acid, reacted with one molecule of thiol, e.g. 1,2-ethanedithiol, in the presence of trifluoroacetic acid to yield adducts such as 3-[2-(2-amino-5-carboxyphenyl)-1-(2-mercaptoethylthio)ethyl]-1Hindole-5-carboxylic acid. Parallel formation of dimers, such as 2,3-dihydro-1H,1'H-2,3'-biindole-5,5'-dicarboxylic acid and trimers, such as 3,3'-[2-(2-amino-5-carboxyphenyl) ethane-1,1-diyl]bis(1H-indole-5-carboxylic acid) of the indole derivatives was also observed. Reaction of a mixture of indole and indole-5-carboxylic acid with 2-phenylethanethiol proceeded in a regioselective way, affording 3-[2-(2-aminophenyl)-1-(phenethylthio)ethyl]-1H-indole-5-carboxylic acid. An additional product of this reaction was 3-[2-(2-aminophenyl)-1-(phenethylthio)ethyl]-2,3-dihydro-1H,1'H-2,3'-biindole-5'-carboxylic acid, which upon standing in DMSO-d6 solution gave 3-[2-(2-aminophenyl)-1-(phenethylthio)ethyl]-1H,1'H-2,3'-biindole-5'-carboxylic acid. Structures of all compounds were elucidated by NMR, and a mechanism for their formation was suggested.     

Mixed electrolytes producing very weak electroacoustic signal

The electrokinetic potential of powders dispersed in concentrated solutions of salts can be determined by electroacoustic methods when the ESA (electrokinetic sonic amplitude) signal of electrolyte is properly corrected for. We propose an alternative solution to the problem of electroacoustic measurements at high ionic strengths; that is, the composition of mixed electrolytes with common ions can be adjusted to minimize the ESA signal of the electrolyte. The measurement of electrokinetic potential of powders dispersed in such mixed electrolytes does not require electrolyte background correction. Mixed electrolytes, which produce very weak ESA signals, were prepared from the following salts with common ions: Li+ (LiNO3 + LiCl), Na+ (NaNO3 + NaBr), K+ (KBr + KNO3), and NO(-)3 (LiNO3 + KNO3). Proportions of the components in these mixed electrolytes are concentration dependent. The electrokinetic potentials of alumina in these mixed electrolytes determined with and without background correction were only marginally different.     

Platinum-catalyzed hydroformylation of terminal and internal octenes

A brief historic overview of Pt/Sn-catalyzed hydroformylation as well as recent advances in the hydroformylation of internal alkenes is provided. This serves as background for the results obtained with the [Pt(Sixantphos)Cl(2)] system, for which the molecular structure and the spectroscopic data are described. Insitu UV/Vis-spectroscopic studies have revealed rapid formation of the corresponding Pt-stannate complex upon reaction with SnCl(2), whereas high-pressure insitu IR-spectroscopy showed formation of a Pt-CO species and a short-lived Pt-H species under syngas, as well as rapid evolution of aldehyde product upon addition of 1-octene to the preformed catalyst in the IR autoclave. The hydroformylation of 1-octene and the i-octenes has been performed. For the internal alkenes, selective tandem isomerization/hydroformylation towards n-nonanal is observed with this catalyst system.     

T-shaped cationic CuI complexes with hemilabile PNP-type ligands

The versatile coordination behavior of the PNP ligands 1A (2,6-bis[(di-tert-butylphosphino)methyl]pyridine) and 1B (2,6-bis[(diphenylphosphino)methyl]pyridine) to CuI is described, whereby a hemilabile interaction of the pyridine N-donor atom to the copper center resulted in a rare T-shaped complex with 1A, while with 1B also a tetracoordinated species could be isolated. Theoretical calculations support the weak interaction of the pyridine N donor in 1A with the Cu center.