Direct orthoruthenation of planar prochiral pyridine derivatives by C-H bond activation with [Ru(CO)2Cl2]n and its unexpected stereoselectivity

The treatment of planar prochiral pyridine derivatives with d6 [Ru(CO)2Cl2]n stereoselectively and efficiently produces new dimeric ortho-ruthenated complexes.     

19F/29Si rotational-echo double-resonance and heteronuclear spin counting under fast magic-angle spinning in fluoride-containing octadecasil

19F/29Si rotational-echo double-resonance (REDOR) and theta-REDOR NMR techniques have been applied under fast magic-angle spinning to a powder sample of fluoride-containing octadecasil. Efficient dipolar recoupling was observed and the effect of finite pulse lengths was found to be negligible using standard radiofrequency field strengths. Moreover, the determined internuclear distance of the 19F-29Si spin pairs formed by the silicons in the D4R units (T-1 site) and the fluoride anions is in very good agreement with previous REDOR and Hartmann-Hahn cross-polarization measurements. Numerical simulation of the REDOR dephasing curves at both the T-1 and T-2 sites considering all fluoride anions in the infinite solid lattice clearly confirm the X-ray crystal structure of octadecasil. Heteronuclear spin-counting theta-REDOR experiments are found to be very useful to obtain direct insight into the local network of dipolar interactions. Indeed, while 19F-29Si pair-like behavior is confirmed at the T-1 site, multiple dipolar interactions are clearly evidenced at the T-2 site.     

C2-Symmetric enantiopure ethanotethered bis(alpha,beta-butenolides) as templates for asymmetric synthesis. Application to the synthesis of (+)-grandisol

Starting from D-mannitol, we have prepared several C(2)-symmetric ethanotethered bis(alpha,beta-butenolides) and studied their [2+2] photocycloaddition reaction with ethylene. The protective groups of the central diol unit have a noticeable influence on the facial selectivity of the cycloaddition, the bis(trimethylsilyloxy) derivatives showing the highest diastereoselectivity. A theoretical conformational analysis of the substrates in the ground state is in good agreement with the diastereofacial selectivity experimentally observed. The bis(photocycloadducts) have been converted into the enantiopure cyclobutanes formally derived from the photoreaction of ethylene with gamma-hydroxymethyl-alpha,beta-butenolide, in which only a moderate facial selectivity had been previously found. As an application of these studies, we have developed a highly efficient and stereoselective synthesis of (+)-grandisol.     

Anomalous conversion in the decay of197mHg

The total andK-shell conversion coefficients of the 165 keV transition in the decay of^197mHg are determined from intensity balance considerations and a coincidence technique using a Ge(Li)—NaI (Tl) system respectively. The resultant values area _T =274.8±19.2 anda _K =47±12, whil the corresponding theoretical values are 344 and 77 respectively, indicating anomalous conversion. The gamma ray transition probability however, shows a hindrance of only about 6 and cannot be correlated with the present anomalous conversion data. TheK/L ratio of the 130 keV transition, determined using a summing method with a Ge(Li) detector, yielded 0.090±0.012, while the corresponding theoretical value is 0.048, indicating anomalous conversion. The corresponding gamma transition probability shows a hindrance of about 3000, in correlation with anomalous conversion.     

Preparation, spectrochemical, and computational analysis of L-carnosine (2-[(3-aminopropanoyl)amino]-3-(1H-imidazol-5-yl)propanoic acid) and its ruthenium (II) coordination complexes in aqueous solution

This study reports the synthesis and characterization of novel ruthenium (II) complexes with the polydentate dipeptide, L-carnosine (2-[(3-aminopropanoyl)amino]-3-(1H-imidazol-5-yl)propanoic acid). Mixed-ligand complexes with the general composition [ML(p)(Cl)(q)(H?O)(r)]·xH?O (M = Ru(II); L = L-carnosine; p = 3 - q; r = 0-1; and x = 1-3) were prepared by refluxing aqueous solutions of the ligand with equimolar amounts of ruthenium chloride (black-alpha form) at 60 °C for 36 h. Physical properties of the complexes were characterized by elemental analysis, DSC/TGA, and cyclic voltammetry. The molecular structures of the complexes were elucidated using UV-Vis, ATR-IR, and heteronuclear NMR spectroscopy, then confirmed by density function theory (DFT) calculations at the B3LYP/LANL2DZ level. Two-dimensional NMR experiments (1H COSY, 13C gHMBC, and 1?N gHMBC) were also conducted for the assignment of chemical shifts and calculation of relative coordination-induced shifts (RCIS) by the complex formed. According to our results, the most probable coordination geometries of ruthenium in these compounds involve nitrogen (N1) from the imidazole ring and an oxygen atom from the carboxylic acid group of the ligand as donor atoms. Additional thermogravimetric and electrochemical data suggest that while the tetrahedral-monomer or octahedral-dimer are both possible structures of the formed complexes, the metal in either structure occurs in the 2? oxidation state. Resulting RCIS values indicate that the amide-carbonyl, and the amino-terminus of the dipeptide are not involved in chelation and these observations correlate well with theoretical shift predictions by DFT.