Transition metal chemistry of oxime-containing ligands,VI: magnetic and structural properties of mono (pyridine-2-aldoxime) dithiocyanato iron (II) and mono (6-methylpyridine-2-aldoxime) dithiocyanato iron (II) complexes

The complexes of pyridine-2-aldoxime (HPOX) and 6-methylpyridine-2-aldoxime (HMPX) with iron (II) thiocyanate of the type [Fe(L)(NCS)₂] (L=HPOX and HMPX) have been prepared and characterized. A study of X-ray, magnetic, vibrational spectra (conventional and far-infrared), electronic spectra andMössbauer spectra has indicated that these complexes have polymeric, pseudo octahedral, coordination geometry with linear bridging thiocyanate ligands. The electronic spectra of mono complexes show a larger, low symmetry, ligand field than that present in [Fe(L)₂(NCS)₂] complexes. UnperturbedMössbauer spectra show a large quadrupole splitting, E _Q, and smaller isomer shift values in these iron (II) thiocyanate complexes. The magnetically perturbedMössbauer spectra of these iron(II) thiocyanate complexes at room temperature show that the principal component of the electric field gradient tensor is positive and corresponds to ad _xy (⁵B₂) ground state.With 2 Figures     

Cooperative Effect of Noncovalent Interactions on Tetrel Bonding in Halogenated Silanes

Tetrel bond, a weak noncovalent interaction between the σ-hole of a Group IV element (silicon in our case) and the cloud of an electronegative element (oxygen in our case) is the focus of this work. The percentage strengthening of tetrel bond has been investigated by optimizing 16 binary complexes of halogenated silane and water of general formula SiX_nH_4−n−H₂O and 16 ternary complexes, of general formula NaX−SiX_nH_4−n−H₂O, where X=F, Cl, Br and I and n=1, 2, 3 and 4 at various levels of theory defined within the formalism of density functional theory (DFT). With the addition of NaX, tetrel bond between Si and O in SiX_nH_4−n−H₂O gets strengthened up to 49 %, owing to cooperativity effect exerted by hydrogen bonding between X and H in the ternary complex NaX−SiX_nH_4−n−H₂O. In the series of complexes studied here, overall stabilization due to cooperativity lies between 10 kJ/mol to 170 kJ/mol. This large extent of reinforcement due to cooperativity has never been showcased before. The exceptional stabilization and reinforcement owe its genesis to the transformation of the ternary complex into a cluster orchestrated by the H-bonding in most of the cases and covalent bonding in few of the cases.     

Regioselective Arylation and Alkynylation of 2,3‐Dibromo‐1H‐inden‐1‐one by Suzuki?Miyaura and Sonogashira Cross‐Coupling Reactions

Suzuki? Miyaura reactions of 2,3‐dibromo‐1H‐inden‐1‐one afforded a wide range of arylated 1H‐inden‐1‐ones. Sonogashira cross‐coupling reactions gave alkynylated indenones. The reactions proceeded with very good regioselectivity in the less sterically hindered and more electron‐deficient position 3.     

Reactions of dichloro-bis(cyclopentadienyl)titanium(IV) with bidentate Schiff bases

A series of Cp₂Ti(SB)Cl complexes, whereSB is the anion of bidentate Schiff bases derived from salicylaldehyde and different primary aminesviz o-anisidine,m-anisidine,o-phenetidine,o-chloroaniline,m-chloroaniline,m-nitroaniline, α-naphthylamine and benzylamine, have been synthesised by the reaction of dichloro-bis(cyclopentadienyl) titanium(IV), Cp₂TiCl₂, and bidentate Schiff base (sbh) in a 1:1 molar ratio in refluxingthf in the presence of triethylamine. The new derivatives have been characterised on the basis of their elemental analyses, conductance measurements and spectral (IR,¹Hnmr and electronic) studies     

Synthesis of functionalized triarylmethanes by combination of FeCl3-catalyzed benzylations of acetylacetone with [3+3] cyclocondensations

Functionalized triarylmethanes are prepared in two steps by FeCl₃-catalyzed benzylation of acetylacetone to give 3-(diarylmethyl)pentane-2,4-diones and subsequent formal [3+3] cyclization of the latter with 1,3-bis(trimethylsilyloxy)-1,3-dienes.     

Cyclization vs. Elimination Reactions of 5‐Aryl‐5‐hydroxy 1,3‐Diones: One‐Pot Synthesis of 2‐Aryl‐2,3‐dihydro‐4H‐pyran‐4‐ones

2‐Aryl‐2,3‐dihydro‐4H‐pyran‐4‐ones were prepared in one step by cyclocondensation of 1,3‐diketone dianions with aldehydes. The use of HCl (10%) for the aqueous workup proved to be very important to avoid elimination reactions of the 5‐aryl‐5‐hydroxy 1,3‐diones formed as intermediates. The TiCl₄‐mediated cyclization of a 2‐aryl‐2,3‐dihydro‐4H‐pyran‐4‐one with 1,3‐silyloxybuta‐1,3‐diene resulted in cleavage of the pyranone moiety and formation of a highly functionalized benzene derivative.     

Synthesis of Arylated Benzofurans by Regioselective Suzuki–Miyaura Cross‐Coupling Reactions of 2,3‐Dibromobenzofurans‐ and 2,3,5‐Tribromobenzofurans

Arylated benzofurans were prepared by regioselective Suzuki–Miyaura cross‐coupling reactions of 2,3‐dibromobenzofuran. The reactions proceeded with very good site‐selectivity in favor of the more electron deficient position 2. The Suzuki–Miyaura reactions of 2,3,5‐tribromobenzofuran also proceeded in favor of position 2.     

Synthesis of functionalized arylpyridines and -pyrimidines by domino [4+2]/retro [4+2] cycloadditions of electron-rich dienes with alkynylpyridines and -pyrimidines

Aryl-substituted pyridines and pyrimidines were prepared by [4+2] cycloadditions of alkynyl-substituted pyridines and -pyrimidines with electron-rich dienes. The reactions proceed by formation of a bridged cycloadduct and subsequent thermal extrusion of ethylene. The pyridine moiety plays a crucial role for the success of the reaction.     

DYNGA: a general purpose QM-MM-MD program. I. Application to water

We present a general purpose QM-MM-MD engine (DYNGA) designed to test alternative hybrid Hamiltonians geared towards the treatment of problems of interest in structural biology including the use of experimental data constraints. In this first presentation we use DYNGA to explore the behaviour of a traditional QM-MM approach in the treatment of the water—water interaction. We find the potential energy hypersurface for the water dimer computed with the HF 4–31G*/TIP3P hybrid Hamiltonian tends to be too flat. We also explore the effect of using traditional QM-MM techniques on proton wires and conclude there is a need for improvement, possibly addressed by using polarizable force fields.