Four (2,2'-bipyridyl)(ferrocenyl)boronium derivatives.

Crystal structures are reported for four (2,2'-bipyridyl)(ferrocenyl)boronium derivatives, namely (2,2'-bipyridyl)(ethenyl)(ferrocenyl)boronium hexafluoridophosphate, [Fe(C5H5)(C17H15BN2)]PF6, (Ib), (2,2'-bipyridyl)(tert-butylamino)(ferrocenyl)boronium bromide, [Fe(C5H5)(C19H22BN3)]Br, (IIa), (2,2'-bipyridyl)(ferrocenyl)(4-methoxyphenylamino)boronium hexafluoridophosphate acetonitrile hemisolvate, [Fe(C5H5)(C22H20BN3O)]PF6·0.5CH3CN, (IIIb), and 1,1'-bis[(2,2'-bipyridyl)(cyanomethyl)boronium]ferrocene bis(hexafluoridophosphate), [Fe(C17H14BN3)2](PF6)2, (IVb). The asymmetric unit of (IIIb) contains two independent cations with very similar conformations. The B atom has a distorted tetrahedral coordination in all four structures. The cyclopentadienyl rings of (Ib), (IIa) and (IIIb) are approximately eclipsed, while a bisecting conformation is found for (IVb). The N-H groups of (IIa) and (IIIb) are shielded by the ferrocenyl and tert-butyl or phenyl groups and are therefore not involved in hydrogen bonding. The B-N(amine) bond lengths are shortened by delocalization of π-electrons. In the cations with an amine substituent at boron, the B-N(bipyridyl) bonds are 0.035 (3) Šlonger than in the cations with a methylene C atom bonded to boron. A similar lengthening of the B-N(bipyridyl) bonds is found in a survey of related cations with an oxy group attached to the B atom.

A new weakly coordinating aluminate anion incorporating a chelating perfluoro-bis-anilido ligand.

The synthesis of the fully fluorinated bis-anilido ligand N,N'-bis-pentafluorophenyl-3,4,5,6-tetrafluorophenylene-1,2-diamine, 1 is described. Reaction of one or two equivalents of 1 with AlMe(3) gives aluminium compounds incorporating one or two ligands, the latter being the protonated form of a new weakly coordinating anion (WCA), 3-H. Alternatively, reaction of 1 with LiAlH(4) yields the lithium salt of this anion, 3-Li, which may be employed as a reagent for preparing the trityl and N,N-dimethylanilinium salts of the aluminate anion. All ion pairs are fully characterized and the use of 3-Ph(3)C to generate titanium-based alkyl cations is also described.

The silicate-mediated formose reaction: bottom-up synthesis of sugar silicates.

Understanding the mechanism of sugar formation and stabilization is important for constraining theories on the abiotic origin of complex biomolecules. Although previous studies have produced sugars from small molecules through the formose and related reactions, the product mixtures are complex and unstable. We have demonstrated that simple two- and three-carbon molecules (glycolaldehyde and glyceraldehyde), in the presence of aqueous sodium silicate, spontaneously form silicate complexes of four- and six-carbon sugars, respectively. Silicate selects for sugars with a specific stereochemistry and sequesters them from rapid decomposition. Given the abundance of silicate minerals, these observations suggest that formose-like reactions may provide a feasible pathway for the abiotic formation of biologically important sugars, such as ribose.

[Simultaneous determination of platinum (IV) and palladium (II) using spectrophotometry method].

The N-(m-methylphenyl)-N'-(sodium p-aminobenzenesulfonate)-thiourea (MMPT) was good reagent of water solubility. In the medium of an HAc-NaAc buffer solution and hexadecyltrimethylammonium bromide (CTMAB), MMPT can react with platinum (IV) and palladium (II) to form green and brown soluble complex. The maximum absorbance of the complex was at lambdaPt(max) = 754.4 nm and lambdaPD(max) = 304.6 nm. Beer's law was obeyed with the concentration in the range of 0-32.0 microg Pt(IV)/25 mL and 0-25.0 microg Pd(II)/25 mL for platinum (IV) and palladium(II) respectively. The correlated coefficient was r754.4 = 0.999 5 for platinum (IV); and r304.6 = 0.999 9 for palladium (II). Their molar absorption coefficients were epsilonPT(754.4 = 8.6 x 10(4) L x mol(-1) x cm(-1) and epsilonPd(304.6) = 7.4 x 10(4) L x mol(-1) x cm(-1) respectively. The contents of platinum (IV) and palladium (II) were converted by determination of the absorbency of mix solution of platinum (IV) and palladium (II) at 754.4 and 304.6 nm. Only Cu2+ and Co2+ interfered with the determination of palladium (II) among 50 coexistent ions, so the selectivity was good. It can be used for the determination of content of synthesis samples. The relative standard deviation (RSD) was less than 2.0%, and the recovery (%) was in the range of 96%-104%. The results are satisfactory. Because the reagent reacts with platinum (IV) and palladium (II) to form water soluble complex and does not require pre-separation for simultaneous determination of platinum (IV) and palladium (II), the method is easy to operate, rapid and environment-friendly.

Synthesis of calixarene-capped carbosilane dendrimers.

A new class of polycalix[4]arene hosts has been constructed based on a carbosilane dendrimer architecture, in which each dendritic branch terminates with a calix[4]arene entity. This study reports the synthesis and characterization of the zeroth generation example with four calix[4]arenes and of the first generation example with 12 calix[4]arenes.

Competitive ArC-H and ArC-X (X = Cl, Br) activation in halobenzenes at cationic titanium centers.

The titanium methyl cation [Cp*((tBu3P=N)TiCH3]+ [B(C6F5)4]- reacts rapidly with H2 to give the analogous cationic hydride [Cp*((tBu3P=N)TiH(THF)n]+ [B(C6F5)4]- (n = 0, 1), which can be trapped and isolated as its THF adduct 1 x THF (n = 1). When generated in the presence of chloro or bromobenzene, 1 undergoes C-X activation or ortho-C-H activation, depending on the amount of dihydrogen present in the reaction medium. At approximately 4 atm of H2, C-X activation is preferred, giving the halocations [Cp*((tBu3P= N)TiX]+ [B(C6F5)4]- (2X) and C6H6/biphenyl mixtures. At lower pressures of H2 (>1 atm), the beta-halophenyl cations [Cp*((tBu3P=N)Ti(2-X-C6H4)]+ [B(C6F5)4]- (3X) are the products isolated. In the absence of H2, these compounds are quite thermally stable, but undergo beta-halogen elimination upon moderate heating, to give 2X (approximately 20%) and compounds 4X which are the result of reaction between 2X and benzyne via addition of the benzyne C-C triple bond across the Ti-N bond of the phosphinimide ligand. Thus, three separate bond activation processes are operative in this system: direct C-X activation, ortho-C-H activation, and indirect C-X activation via beta-halogen elimination. Mechanistic studies on all three processes have been done and support a radical pathway for direct C-X cleavage, sigma-bond metathesis of the ortho-C-H bond of eta(1)-coordinated C6H5X, and beta-halogen elimination from base-free compound 3X.

Isolation and characterization of a monomeric cationic titanium hydride.

Methyl cations 1-Cp and 1-Cp*, stabilized by the tri-tert-butylphophinimine ligand and either C5H5 or C5Me5, were generated from the neutral dimethyl precursors and [Ph3C]+[B(C6F5)4]-. Reaction of these compounds with H2 resulted in contrasting reactions. For 1-Cp, hydrogenolysis of the Ti-CH3 group led to rapid reduction to Ti(III) and production of a cationic Ti(III) dimer, 2, presumably formed upon loss of H2 from a transiently generated Ti(IV) hydride. Compound 2 was characterized crystallographically and via its cleavage with donor solvents such as THF to form the monomeric [Cp(L)Ti(THF)2]+[B(C6F5)4]-, 3. In contrast, 1-Cp* reacted rapidly with H2 to form a cationic Ti(IV) hydride species, 4, which was resistant to reduction. While only moderately stable in solution under H2, a stable, isolable THF adduct preciptitated upon addition of THF, giving 4.THF, which was fully characterized, including via X-ray crystallography. Naked hydride 4 was very reactive toward haloarene solvents such as bromobenzene, giving the cationic bromide [Cp*(L)TiBr]+[B(C6F5)4]-, 5, which was fully characterized as its THF adduct 5.THF. The contrasting behavior of 1-Cp and 1-Cp* is a result of the greater steric protection and electron donation provided by the Cp* ligand relative to the Cp donor.

Isomorphism and phase transition in triferrocenylboroxine and triferrocenylborazine.

The crystal structures of triferrocenylboroxine, [Fe(3)(C(5)H(5))(3)(C(15)H(12)B(3)O(3))], (I), and triferrocenylborazine, [Fe(3)(C(5)H(5))(3)(C(15)H(15)B(3)N(3))], (II), are isomorphous. At room temperature, the space group is Cmc2(1) and the molecules have crystallographic m symmetry. A reversible phase transition occurs at 283(2)K for (I) and at 263(5)K for (II). In the low-temperature phase, the space group of both compounds is P2(1) and the molecules no longer have internal symmetry. Intermolecular C-H...pi interactions are enhanced in the low-temperature phase.