Reactivity of Solid Rubrene with Potassium: Competition between Intercalation and Molecular Decomposition.

We present the synthesis and characterization of the K+-intercalated rubrene (C42H28) phase, K2Rubrene (K2R), and identify the coexistence of amorphous and crystalline materials in samples where the crystalline component is phase-pure. We suggest this is characteristic of many intercalated alkali metal-polyaromatic hydrocarbon (PAH) systems, including those for which superconductivity has been claimed. The systematic investigation of K-rubrene solid-state reactions using both K and KH sources reveals a complex competition between K intercalation and the decomposition of rubrene, producing three K-intercalated compounds, namely, K2R, K(RR*), and K xR' (where R* and R' are rubrene decomposition derivatives C42H26 and C30H20, respectively). K2R is obtained as the major phase over a wide composition range and is accompanied by the formation of amorphous byproducts from the decomposition of rubrene. K(RR*) is synthesized as a single phase, and K xR' is obtained only as a secondary phase to the majority K2R phase. The crystal structure of K2R was determined using high-resolution powder X-ray diffraction, revealing that the structural rearrangement from pristine rubrene creates two large voids per rubrene within the molecular layers in which K+ is incorporated. K+ cations accommodated within the large voids interact strongly with the neighboring rubrene via η6, η3, and η2 binding modes to the tetracene cores and the phenyl groups. This contrasts with other intercalated PAHs, where only a single void per PAH is created and the intercalated K+ weakly interacts with the host. The decomposition products of rubrene are also examined using solution NMR, highlighting the role of the breaking of C-Cphenyl bonds. For the crystalline decomposition derivative products K(RR*) and K xR', a lack of definitive structural information with regard to R* and R' prevents the crystal structures from being determined. The study illustrates the complexity in accessing solvent-free alkali metal salts of reduced PAH of the type claimed to afford superconductivity.

Chemical and structural stability of zirconium-based metal-organic frameworks with large three-dimensional pores by linker engineering.

The synthesis of metal-organic frameworks with large three-dimensional channels that are permanently porous and chemically stable offers new opportunities in areas such as catalysis and separation. Two linkers (L1=4,4',4'',4'''-([1,1'-biphenyl]-3,3',5,5'-tetrayltetrakis(ethyne-2,1-diyl)) tetrabenzoic acid, L2=4,4',4'',4'''-(pyrene-1,3,6,8-tetrayltetrakis(ethyne-2,1-diyl))tetrabenzoic acid) were used that have equivalent connectivity and dimensions but quite distinct torsional flexibility. With these, a solid solution material, [Zr6 O4 (OH)4 (L1)2.6 (L2)0.4 ]⋅(solvent)x , was formed that has three-dimensional crystalline permanent porosity with a surface area of over 4000 m(2) g(-1) that persists after immersion in water. These properties are not accessible for the isostructural phases made from the separate single linkers.

New insights in the formation of five- versus seven-membered platinacycles: a kinetico-mechanistic study.

The reaction of Pt(IV) organometallic cyclometalated complexes of type [PtXAr(2)(Ar'CHNCH(2)CH(2)NMe(2))] to produce 5- and 7-membered Pt(II) metalacycles by a formal C-C reductive elimination/C-H oxidative addition/Ar-H reductive elimination sequence has been studied from a preparative and kinetico-mechanistic perspective. The detection and characterization of key intermediates has also been achieved via the careful selection of reaction conditions, including time, extracted from the kinetic studies. From the data collected, it is clear that a fine-tuning of the reactivity is possible with respect to the formation of the alternative 5- and 7-membered cyclometalated complexes (i.e., [PtX(Ar-Ar'CH═NCH(2)CH(2)NMe(2))] and [PtX(Ar-Ar'CH═NCH(2)CH(2)NMe(2))]). In all cases a common reductive elimination reaction occurs to form a non cyclometalated intermediate compound of type [PtX(Ar)(Ar-Ar'CH═NCH(2)CH(2)NMe(2))], which leads to the selective formation of the above-mentioned complexes by the actuation of an unexpected equilibrium between its cis-(X,NMe(2)) and trans-(X,NMe(2)) isomers. While the cis-(X,NMe(2)) isomer produces the 7-membered metallacycle, the trans-(X,NMe(2)) form leads exclusively to the 5-membered analogue. The isomerization process is dominated by the steric hindrance existing between the Ar-Pt and Ar-Ar'CHN-Pt moieties in the cis-(X,NMe(2)) isomer that forces a Z conformation of the imine, thus leading exclusively to the 7-membered ring formation only for the less hindered X = Cl systems.

Kinetico-mechanistic information about alkene hydroamination with aniline in bromide-rich ionic media: importance of solvolysis.

The study of the [PtBr(4)](2-) reactivity with hexene and aniline in highly ionic (Bu(4)P)Br/CH(2)Br(2) media has been studied from a Kinetico-Mechanistic perspective. The results indicate bromide ion association to the square-planar starting material to produce a stable diamagnetic compound that can be described as an ion pair of a [PtBr(5)](3-) square-pyramidal complex stabilized by several phosphonium countercations. While this species reacts rapidly with aniline, producing the known square-planar complex [PtBr(3)(PhNH(2))](-) with release of the apical bromide of the square-pyramidal intermediate, the reaction with hexene, producing the square-planar [PtBr(3)(hexene)](-) complex, is much slower. The thermal and pressure activation parameters determined for these processes fully agree with the proposed reactivity. The gross features of the platinum-catalyzed hydroamination mechanism, occurring via much higher energy transition states, are not necessarily altered by these new findings, given the fact that all ligand exchange reactions occur with relatively low activation barriers. Nevertheless, the nature of the catalyst resting state needs revision as demonstrated. The importance of explicitly considering the solvent for reactions conducted in noninnocent highly organized media is also highlighted.

Diastereoselective room-temperature Pd-catalyzed alpha-arylation and vinylation of arylmandelic acid derivatives.

Palladium-catalyzed alpha-arylation and vinylation of dioxolane (S,S)-I, easily obtained from (S)-mandelic acid, proceeds with high yields and excellent diastereoselectivity at room temperature employing commercially available P(t-Bu)(3).HBF(4) and Pd(OAc)(2) as a catalytic precursor system. This method displays general utility for a large variety of aryl, heteroaryl, and vinyl bromides.

Synthesis, structure, redox properties, and catalytic activity of new ruthenium complexes containing neutral or anionic and facial or meridional ligands: an evaluation of electronic and geometrical effects.

The synthesis of a family of new Ru complexes containing meridional or facial tridentate ligands with the general formula [Ru(II)(T)(D)(X)](n+) [T = 2,2':6',2' '-terpyridine or tripyrazolylmethane; D = 4,4'-dibenzyl-4,4',5,5'-tetrahydro-2,2'-bioxazole (S,S-box-C) or 2-[((1'S)-1'-(hydroxymethyl)-2'-phenyl)ethylcarboxamide]-(4S)-4-benzyl-4,5-dihydrooxazole (S,S-box-O); X = Cl, H(2)O, MeCN or pyridine] has been described. All complexes have been spectroscopically characterized in solution through (1)H NMR and UV-vis techniques. Furthermore, all of the chloro complexes presented here have also been characterized in the solid state through monocrystal X-ray diffraction analysis. The oxazolinic S,S-box-C ligands undergo a Ru-assisted hydrolysis reaction generating the corresponding amidate anionic oxazolinic ligands S,S-box-O, which are also strongly attached to the metal center and produce a strong sigma-donation effect over the Ru metal center. The redox properties of all complexes have also been studied by means of cyclic voltammetry, strongly reflecting the nature of the ligands; both effects, geometrical (facial vs meridional) and electronic (neutral vs anionic), can be unveiled and rationalized. Finally, the reactivity of the Ru-OH(2) complexes has been tested with regard to the epoxidation of trans-stilbene, and it has been shown that, in this particular case, the reactivity is practically not dependent on the redox potentials of the catalyst but, in sharp contrast, it is strongly dependent on the geometry of the tridentate ligands.

Atropisomeric discrimination in new Ru(II) complexes containing the C(2)-symmetric didentate chiral phenyl-1,2-bisoxazolinic ligand.

A new family of Ru(II) complexes containing the tridentate meridional 2,2':6',2''-terpyridine (trpy) ligand, a C(2)-symmetric didentate chiral oxazolinic ligand 1,2-bis[4'-alkyl-4',5'-dihydro-2'-oxazolyl]benzene (Phbox-R, R = Et or iPr), and a monodentate ligand, of general formula [Ru(Y)(trpy)(Phbox-R)](n+) (Y = Cl, H(2)O, py, MeCN, or 2-OH-py (2-hydroxypyridine)) have been prepared and thoroughly characterized. In the solid state the complexes have been characterized by IR spectroscopy and by X-ray diffraction analysis in two cases. In solution, UV/Vis, cyclic voltammetry (CV), and one-dimensional (1D) and two-dimensional (2D) NMR spectroscopy techniques have been used. We have also performed density functional theory (DFT) calculations with these complexes to interpret and complement experimental results. The oxazolinic ligand Phbox-R exhibits free rotation along the phenyloxazoline axes. Upon coordination this rotation is restricted by an energy barrier of 26.0 kcal mol(-1) for the case of [Ru(trpy)(Phbox-iPr)(MeCN)](2+) thus preventing its potential interconversion. Furthermore due to steric effects the two atropisomers differ in energy by 5.7 kcal mol(-1) and as a consequence only one of them is obtained in the synthesis. Subtle but important structural effects occur upon changing the monodentate ligands that are detected by NMR spectroscopy in solution and interpreted by using their calculated DFT structures.

A case for enantioselective allylic alkylation catalyzed by palladium nanoparticles.

Palladium nanoparticles (4 nm, fcc) were prepared through decomposition of [Pd2(dba)3] by H2 in the presence of a chiral xylofuranoside diphosphite. These particles catalyze the allylic alkylation of rac-3-acetoxy-1,3-diphenyl-1-propene with dimethyl malonate leading to an almost total conversion of the (R) enantiomer and almost no reaction with the (S). This gives rise to 97% ee for the alkylation product and a kinetic resolution of the substrate recovered with ca. 90% ee. This behavior was compared to that of a molecular catalyst at various dilutions, and the differences between the two systems are discussed. This is the first colloidal system shown to display such a high enantioselectivity besides the well-known Pt/cinchonidine system.