Homoatomic cations: From [P5]+ to [P9].

Recent synthetic approaches to a series of [P9]X salts (X = [F{Al(ORF)3}2], [Al(ORF)4], and (RF = C(CF3)3); Ga2Cl7) overcome limitations in classical synthesis methods that proved unsuitable for phosphorus cations. These salts contain the homopolyatomic cation [P9]+ via (I) oxidation of P4 with NO[F{Al(ORF)3}2], (II) the arene-stabilized Co(I) sandwich complex [Co(arene)2][Al(ORF)4] [arene = ortho-difluorobenzene (o-DFB) and fluorobenzene (FB)], or (III) the reduction of [P5Cl2][Ga2Cl7] with Ga[Ga2Cl7] as Ga(I) source in the presence of P4. Quantum chemical CCSD(T) calculations suggest that [P9]+ formation from [Co(arene)2]+ occurs via the nido-type cluster [(o-DFB)CoP4]+, which resembles the isoelectronic, elusive [P5]+. Apparently, the nido-cation [P5]+ forms intermediately in all reactions, particularly during the Ga(I)-induced reduction of [P5Cl2]+ and the subsequent pick up of P4 to yield the final salt [P9][Ga2Cl7]. The solid-state structure of [P9][Ga2Cl7] reveals the anticipated D2d-symmetric Zintl-type cage for the [P9]+ cation. Our approaches show great potential to bring other [Pn]+ cations from the gas to the condensed phase.

Towards clustered carbonyl cations [M3(CO)14]2+ (M = Ru, Os): the need for innocent deelectronation.

To access the hitherto almost unknown class of clustered transition metal carbonyl cations, the trimetal dodecacarbonyls M3(CO)12 (M = Ru, Os) were reacted with the oxidant Ag+[WCA]-, but yielded the silver complexes [Ag{M3(CO)12}2]+[WCA]- (WCA = [Al(ORF)4]-, [F{Al(ORF)3}2]-; RF = -OC(CF3)3). Addition of further diiodine I2 to increase the redox potential led for M = Ru non-specifically to divalent mixed iodo-RuII-carbonyl cations. With [NO]+, even the N-O bond was cleaved and led to the butterfly carbonyl complex cation [Ru4N(CO)13]+ in low yield. Obviously, ionization of M3(CO)12 with retention of its pseudo-binary composition including only M and CO is difficult and the inorganic reagents did react non-innocently. Yet, the radical cation of the commercially available perhalogenated anthracene derivative 9,10-dichlorooctafluoroanthracene (anthraceneHal) is a straightforward accessible innocent deelectronator with a half-wave potential E 1/2 of 1.42 V vs. Fc0/+. It deelectronates M3(CO)12 under a CO atmosphere and leads to the structurally characterized cluster salts [M3(CO)14]2+([WCA]-)2 including a linear M3 chain. The structural characterization as well as vibrational and NMR spectroscopies indicate the presence of three electronically independent sets of carbonyl ligands, which almost mimic M(CO)5, free CO and even [M(CO)6]2+ in one and the same cation.

Synthesis and Characterization of Stable Iron Pentacarbonyl Radical Cation Salts.

The open-shell iron pentacarbonyl cation [Fe(CO)5 ].+ was isolated by deelectronation, i.e., the single-electron oxidation of the parent neutral Fe(CO)5 using [phenazineF ].+ as the [Al(ORF )4 ]- and [F-{Al(ORF )3 }2 ]- salt (RF =C(CF3 )3 ; phenazineF =perfluoro-5,10-bis(perfluorophenyl)-5,10-dihydrophenazine). [Fe(CO)5 ].+ [Al(ORF )4 ]- was fully characterized (scXRD analysis, IR, NMR, EPR, 57 Fe spectroscopy, CV and SQUID magnetization study) and, apart from being a compound of fundamental interest, may serve as a precursor for low-valent iron coordination chemistry.

Experimental and quantum chemical studies of anionic analogues of N-heterocyclic carbenes.

A combination of quantum chemical and synthetic/crystallographic methods have been employed to probe electronic structure in two series of anionic ligands related to the well known N-heterocyclic carbene (NHC) class of donor. Analyses of (i) the respective frontier orbital energies/compositions for the 'free' ligands and the results of ETS-NOCV studies of the bonding in model group 11 complexes; and (ii) the structural metrics for (new) linear gold(i) compounds, have been used to probe the bonding in complexes of NHC ligands which incorporate a backbone-appended weakly-coordinating anion component (WCA-NHCs) and in systems featuring the isoelectronic (formally anionic) diazaborolyl ligand family. Key findings are that WCA-NHC ligands - in which the anionic component is attached to the ligand heterocycle via a methylene (CH2) spacer - offer electronic (and steric) properties which are largely unperturbed from their 'simple' NHC counterparts, while diazaborolyl donors (in which the negative charge is formally located at the boron donor atom) offer significantly stronger σ-donation and a very high trans influence.

Backbone-Degradable Polymers Prepared by Chemical Vapor Deposition.

Polymers prepared by chemical vapor deposition (CVD) polymerization have found broad acceptance in research and industrial applications. However, their intrinsic lack of degradability has limited wider applicability in many areas, such as biomedical devices or regenerative medicine. Herein, we demonstrate, for the first time, a backbone-degradable polymer directly synthesized via CVD. The CVD co-polymerization of [2.2]para-cyclophanes with cyclic ketene acetals, specifically 5,6-benzo-2-methylene-1,3-dioxepane (BMDO), results in well-defined, hydrolytically degradable polymers, as confirmed by FTIR spectroscopy and ellipsometry. The degradation kinetics are dependent on the ratio of ketene acetals to [2.2]para-cyclophanes as well as the hydrophobicity of the films. These coatings address an unmet need in the biomedical polymer field, as they provide access to a wide range of reactive polymer coatings that combine interfacial multifunctionality with degradability.

Homoleptic Gold Acetonitrile Complexes with Medium to Very Weakly Coordinating Counterions: Effect on Aurophilicity?

A series of gold acetonitrile complexes [Au(NCMe)2 ]+ [WCA]- with weakly coordinating counterions (WCAs) was synthesized by the reaction of elemental gold and nitrosyl salts [NO]+ [WCA]- in acetonitrile ([WCA]- =[GaCl4 ]- , [B(CF3 )4 ]- , [Al(ORF )4 ]- ; RF =C(CF3 )3 ). In the crystal structures, the [Au(NCMe)2 ]+ units appeared as monomers, dimers, or chains. A clear correlation between the aurophilicity and the coordinating ability of counterions was observed, with more strongly coordinating WCAs leading to stronger aurophilic contacts (distances, C-N stretching frequencies of [Au(NCMe)2 ]+ units). An attempt to prepare [Au(L)2 ]+ units, even with less weakly basic solvents like CH2 Cl2 , led to decomposition of the [Al(ORF )4 ]- anion and formation of [NO(CH2 Cl2 )2 ]+ [F(Al(ORF )3 )2 ]- . All nitrosyl reagents [NO]+ [WCA]- were generated according to an optimized procedure and were thoroughly characterized by Raman and NMR spectroscopy. Moreover, the to date unknown species [NO]+ [B(CF3 )3 CN]- was prepared. Its reaction with gold unexpectedly produced [Au(NCMe)2 ]+ [Au(NCB(CF3 )3 )2 ]- , in which the cyanoborate counterion acts as an anionic ligand itself. Interestingly, the auroborate anion [Au(NCB(CF3 )3 )2 ]- behaves as a weakly coordinating counterion, which becomes evident from the crystallographic data and the vibrational spectral characteristics of the [Au(NCMe)2 ]+ cation in this complex. Ligand exchange in the only room temperature stable salt of this series, [Au(NCMe)2 ]+ [Al(ORF )4 ]- , is facile and, for example, [Au(PPh3 )(NCMe)]+ [Al(ORF )4 ]- can be selectively generated. This reactivity opens the possibility to generate various [AuL1 L2 ]+ [Al(ORF )4 ]- salts through consecutive ligand-exchange reactions that offer access to a huge variety of AuI complexes for gold catalysis.

Ultrasensitive In Situ Fluorescence Analysis using Modulated Fluorescence Interference Contrast at Nanostructured Polymer Surfaces.

The precise modulation of fluorescence interference contrast is achieved by introducing a nanoscopically engineered spacer layer prepared by chemical vapor deposition (CVD) of functional polymers. These novel imaging substrates are chemically identical throughout their entire detection area, yet present patterns of nanoscale thickness. A protein binding cascade is studied in real time and in the presence of high background noise.

Unprecedented pseudo-ortho and ortho metallation of [2.2]paracyclophanes--a methyl group matters.

The first example of a pseudo-ortho metallation on [2.2]paracyclophane is presented, giving easy access to enantiopure compounds of this type. By slight modification of the directing group, metallation of the ortho- and C2-positions is possible. The mechanism was further investigated by means of density functional theory (DFT) calculations.

Free-standing nanomembranes based on selective CVD deposition of functional poly-p-xylylenes.

The precise engineering of ultrathin nanofilms with variable functionality remains an unmet challenge in nanotechnology. We report a strategy for generating free-standing nanomembranes based on the selective chemical vapor deposition polymerization of functional [2.2]paracyclophanes on micropatterned self-assembled monolayers of alkanethiolates on gold. This fabrication strategy can yield microstructured nanofilms that are between 2 and 5 nm thick. Subsequent release from the substrate results in free-standing nanoscale membranes with controlled pore size and geometry. The process allows for modification of important functional parameters, such as ultrasmall membrane thickness, membrane pore geometry, and chemical functionality.

Improved synthesis of enantiopure 4-hydroxy[2.2]paracyclophane.

4-Hydroxy[2.2]paracyclophane is readily prepared via an improved synthetic protocol from unsubstituted [2.2]paracyclophane. The key step is a Dakin oxidation of 4-formyl[2.2]paracyclophane. This allows a rapid access to large quantities of the product and an easy synthesis of the enantiopure form.

Diastereoselective Hartwig-Buchwald reaction of chiral amines with rac-[2.2]paracyclophane derivatives.

A Hartwig-Buchwald addition of a variety of chiral amines to rac-4-bromo-[2.2]paracyclophane and rac-trifluoromethanesulfonic acid (4-[2.2]paracyclophane) ester was performed with high diastereoselectivities. Kinetic racemic resolution of the starting materials was achieved, providing a rapid access to enantiomerically enriched 4-bromo-[2.2]paracyclophane and the corresponding enantiomerically pure [2.2]paracyclophane amines. Additionally, the first reaction of a secondary amine with a [2.2]paracyclophane halide was achieved.