Barium-Catalysed Dehydrocoupling of Hydrosilanes and Borinic Acids: A Mechanistic Insight

Two very rare cases of barium boryloxides, the homoleptic [Ba(OB{CH(SiMe₃)₂}₂)₂⋅C₇H₈] and the heteroleptic [{LO^NO4}BaOB{CH(SiMe₃)₂}₂] stabilised by the multidentate aminoetherphenolate {LO^NO4}⁻, are presented, and their structural properties are discussed. The electron-deficient [Ba(OB{CH(SiMe₃)₂}₂)₂⋅C₇H₈] shows, in particular, resilient η⁶-coordination of the toluene molecule. Together with its amido parents [Ba{N(SiMe₃)₂}₂⋅thf₂] and [Ba{N(SiMe₃)₂}₂]₂, this complex catalyses the fast and chemoselective dehydrocoupling of borinic acids R₂BOH and hydrosilanes HSiR′₃, yielding borasiloxanes R₂BOSiR′₃ in a controlled fashion. The assessment of substrate scope indicates that, for now, the reaction is limited to bulky borinic acids. Kinetic analysis shows that the rate-limiting step of the catalytic manifold traverses a dinuclear transition state. A detailed mechanistic scenario is proposed on the basis of DFT computations, the results of which are fully consistent with experimental data. It consists of a stepwise process with rate-determining nucleophilic attack of a metal-bound O-atom onto the incoming hydrosilane, involving throughout dinuclear catalytically active species.     

Determination of selected endocrine disrupting compounds in human fetal and newborn tissues by GC-MS

Endocrine disrupting compounds (EDCs) include organochlorine pesticides (OCPs), organophosphate pesticides (OPPs), carbamate pesticides, and plasticizers, such as bisphenol A (BPA). They persist in the environment because of their degradation resistance and bioaccumulate in the body tissues of humans and other mammals. Many studies are focused on the possible correlation between in utero exposure to EDCs and adverse health hazards in fetuses and newborns. In the last decade, environmental pollution has been considered a possible trigger for Sudden Infant Death Syndrome (SIDS) and Sudden Intrauterine Unexplained Death Syndrome (SIUDS), the most important death-causing syndromes in fetuses and newborns in developed countries. In this work, a rapid and sensitive analytical method was developed to determine the level of OCPs and OPPs, carbamates, and phenols in human fetal and newborn tissues (liver and brain) and to unveil the possible presence of non-targeted compounds. The target analytes where selected on the basis of their documented presence in the Trentino-Alto Adige region, an intensive agricultural area in northern Italy. A liquid-solid extraction procedure was applied on human and animal tissues and the extracts, after a solid phase extraction (SPE) clean-up procedure, were analyzed by gas chromatography coupled to a quadrupole mass spectrometric detector (GC-qMS). A GC-TOFMS (time-of-flight) instrument, because of its higher full-scan sensitivity, was used for a parallel detection of non-targeted compounds. Method validation included accuracy, precision, detection, and quantification limits (LODs; LOQs), and linearity response using swine liver and lamb brain spiked at different concentrations in the range of 0.4–8000.0 ng/g. The method gave good repeatability and extraction efficiency. Method LOQs ranged from 0.4–4.0 ng/g in the selected matrices. Good linearity was obtained over four orders of magnitude starting from LOQs. Isotopically labeled internal standards were used for quantitative calculations. The method was then successfully applied to the analysis of liver and brain tissues from SIUDS and SIDS victims coming from the above mentioned region.     

In Silico Olefin Metathesis with Ru‐Based Catalysts Containing N‐Heterocyclic Carbenes Bearing C60 Fullerenes

Density functional theory calculations have been used to explore the potential of Ru‐based complexes with 1,3‐bis(2,4,6‐trimethylphenyl)imidazolin‐2‐ylidene (SIMes) ligand backbone ( A ) being modified in silico by the insertion of a C₆₀ molecule ( B and C ), as olefin metathesis catalysts. To this end, we investigated the olefin metathesis reaction catalyzed by complexes A , B , and C using ethylene as the substrate, focusing mainly on the thermodynamic stability of all possible reaction intermediates. Our results suggest that complex B bearing an electron‐withdrawing N‐heterocyclic carbene improves the performance of unannulated complex A . The efficiency of complex B is only surpassed by complex A when the backbone of the N‐heterocyclic carbene of complex A is substituted by two amino groups. The particular performance of complexes B and C has to be attributed to electronic factors, that is, the electronic‐donating capacity of modified SIMes ligand rather than steric effects, because the latter are predicted to be almost identical for complexes B and C when compared to those of A . Overall, this study indicates that such Ru‐based complexes B and C might have the potential to be effective olefin metathesis catalysts.     

Determination of phthalate esters in vegetable oils using direct immersion solid-phase microextraction and fast gas chromatography coupled with triple quadrupole mass spectrometry

Phthalates are a group of synthetic compounds mainly used as plasticizers, which have been classified as endocrine-disrupting chemicals and potential human-cancer causing agents. They can be found in high amounts in foods, deriving mainly from plastic packaging. The analytical determination of these compounds is very challenging since they are ubiquitous. Therefore, minimization of sample manipulation is highly desirable.     

Transition-metal complexes with bidentate ligands spanning trans-position. Part XVI. X-ray structural and 31P-NMR solution studies of 2,11-Bis(diethylphosphinomethyl)benzo[c]phenanthrenesilver(I) perchlorate

The preparation of complexes {AgX(1c)} (X ? Cl, Br, I, NO₃ and ClO₄; 1c = 2,11-bis(diethylphosphinomethyl)benzo[c]phenanthrene) is reported. The ³¹P-NMR spectra of the above complexes were recorded and the ¹J(¹⁰⁷Ag, ³¹P) values are compared with the corresponding data for related complexes. The X-ray crystal structure of [Ag(1c)](ClO₄) was determined. There are two crystallographically independent molecules in the unit cell each containing two-coordinate silver, the O-atoms of the perchlorate anions being outside bonding range from the central atom. The two molecules, however, show different bonding parameters: Thus for ‘molecule 1’ P(1)? Ag(1)? P(2) = 167.6(1)°, Ag(1)? P(1) = 2.389(3) and Ag(1)? P(2) = 2.393(3) Å, while for ‘molecule 2’ P(3)? Ag(2)? P(4) = 164.8(1)°, Ag(2)? P(3) = 2.377(3), and Ag(2)? P(4) = 2.378(3) Å. These differences are probably due to packing forces in the crystal lattice.