The modulating possibilities of dicarbollide clusters: optimizing the Kharasch catalysts

exo-Cluster dicarbollides substitution has allowed tuning of the E degrees (Ru(II)/Ru(III)) potential to obtain the best-performing Kharasch catalyst. We postulate that this is possible through the to-and-fro electron movement between the boron cluster and the sulfonium moieties.     

Ag(I) complexes with alkylidene-bis(2-aminopyrimidines) as building units for discrete metallomacrocyclic frames. A structural and solution study

Alkylidene-bis(2-aminopyrimidines) (pyr2Cx, x = 2-5) are useful ligands to interact with Ag(I) yielding discrete metallocycles. Crystal structures of the [(pyr2C2)Ag(NO3)]2 and [(H-pyr2C4)Ag(NO3)2]2 have been isolated where each macrocyclic moiety interacts with their surroundings through weak interactions, yielding 3D discrete structures, On the other hand, the solution study shows that the equilibrium constants for the formation of Ag(pyr2Cx)+ complexes are higher than the literature values for Ag(I) complexes with single pyrimidines, although the differences could be explained by invoking the solid-state structures of the Ag(I)-pyr2Cx complexes.     

Synthesis of S,N-chelating heterocyclic thionates of palladium(II). Crystal structure of cis-[Pd(pym2S)(PPh3)2] (pym2S = pyrimidine-2-thionate)

The synthesis of mononuclear palladium(II) complexes containing chelating heterocyclic thionates is described. The new compounds of general formula cis-[Pd(RS-N)(L) _x ](ClO₄) [x = 2, L = PPh₃, RS-N = pyridine-2-thionate (py2S) (1), pyrimidine-2-thionate (pym2S) (2), imidazolidine-2-thionate (imzdS) (3), 1-methylimidazoline-2 thionate (mimzS) (4), 1,3-thiazoline-2-thionate (tzdS) (5); x = 1, L = dppe, RS-N = pyridine-2-thionate (py2S) (6), pyrimidine-2-thionate (pym2S) (7), imidazolidine-2-thionate (imzdS) (8), 1-methylimidazole-2 thionate (mimzS) (9) and 1,3-thiazoline-2-thionate (tzdS) (10)] were prepared by directly reacting the hydroxo-complexes [{Pd(PPh₃)₂(-OH) }₂](ClO₄)₂ and [ {Pd(dppe)(-OH) }₂](ClO₄)₂ with the corresponding heterocyclic thiones (RS-N)H. The complexes have been characterized by partial elemental analyses, conductance measurements and spectroscopic methods (I.r., FAB, ¹H- and ³¹P-n.m.r.). No evidence for monomer-dimer equilibrium was found in solution. The crystal structure of (2) has been determined by X-ray diffraction analysis.     

Crystal and Molecular Structure of (BzlMe3N) 2 + [Fe2OCl6]2-

The crystal and molecular structure of (BzlMe₃N) ₂ ⁺ [Fe₂OCl₆]^2- has been determined. The asymmetric unit contains two benzyltrimethylammonium cations and two half -oxo-bis(trichloro-iron(III)) anions. The bridging -oxygen atoms of these anions are located over crystallographic symmetry elements. Therefore, the two anions resulting from the symmetry operations correspond to two different conformers presenting angular and linear dispositions of the Fe-O-Fe bond angle. Mössbauer spectrum consists of two asymmetric lines that are adequately simulated by two equally populated quadrupole doublets associated with the two iron sites.     

Biogenetically inspired enantioselective approach to Indolo[2,3-a]- and benzo[a]quinolizidine alkaloids from a synthetic equivalent of secologanin

[reaction: see text] Racemic oxodiester 1 undergoes stereoselective cyclocondensation with (S)-tryptophanol, (S)-(3,4-dimethoxyphenyl)alaninol, or the corresponding amino acids, in a process involving a tandem dynamic kinetic resolution/desymmetrization of diastereotopic groups, to give bicyclic lactams, which are cyclized to substituted indolo[2,3-a]- and benzo[a]quinolizidines.     

Synthesis,X‐ray characterization and density functional theory studies of N6‐benzyl‐N6‐methyladenine–M(II) complexes (M = Zn,Cd): The prominent role of π–π, C–H···π and anion–π interactions

We report the synthesis and X‐ray characterization of the N⁶‐benzyl‐N⁶‐methyladenine ligand (L) and three metal complexes, namely [Zn(HL)Cl₃]·H₂O ( 1 ), [Cd(HL)₂Cl₄] ( 2 ) and [H₂L]₂[Cd₃(μ‐L)₂(μ‐Cl)₄Cl₆]·3H₂O ( 3 ). Complex 1 consists of the 7H‐adenine tautomer protonated at N3 and coordinated to a tetrahedral Zn(II) metal centre through N9. The octahedral Cd(II) in complex 2 is N⁹‐coordinated to two N⁶‐benzyl‐N⁶‐methyladeninium ligands (7H‐tautomer protonated at N3) that occupy apical positions and four chlorido ligands form the basal plane. Compound 3 corresponds to a trinuclear Cd(II) complex, where the central Cd atom is six‐coordinated to two bridging μ‐L and four bridging μ‐Cl ligands. The other two Cd atoms are six‐coordinated to three terminal chlorido ligands, to two bridging μ‐Cl ligands and to the bridging μ‐L through N3. Essentially, the coordination patterns, degree of protonation and tautomeric forms of the nucleobase dominate the solid‐state architectures of 1 – 3 . Additionally, the hydrogen‐bonding interactions produced by the endocyclic N atoms and NH groups stabilize high‐dimensional‐order supramolecular assemblies. Moreover, energetically strong anion–π and lone pair (lp)–π interactions are important in constructing the final solid‐state architectures in 1 – 3 . We have studied the non‐covalent interactions energetically using density functional theory calculations and rationalized the interactions using molecular electrostatic potential surfaces and Bader's theory of atoms in molecules. We have particularly analysed cooperative lp–π and anion–π interactions in 1 and π⁺–π⁺ interactions in 3 .     

1,1',3,3',6,6',8,8'-Octachloro-9,9'-bifluorenylidene and perchloro-9,9'-bifluorenylidene,two exceedingly twisted ethylenes

The syntheses of 1,1',3,3',6,6',8,8'-octachloro-9,9'-bifluorenylidene (1), its precursors, and the byproduct 3,3',5,5'-tetrachloro-4-(trichloromethyl)biphenyl (5) are described. Accurate structural X-ray data on 1 and on perchloro-9,9'-bifluorenylidene (2) are reported and discussed. Because of chlorine overcrowding, the dihedral angles between their two identical fluorenylidene moieties are abnormally large, the central-ethylene twist angles being 55 and 66 degrees, respectively. Significant out-of-plane carbon-chlorine bond bending is likewise exhibited. Their ESR spectra and magnetic measurements prove that they are singlet species. The exceptionally large bathochromic displacements of their UV-vis absorption spectrum with respect to that of their parent hydrocarbon are mainly attributed to bond bending and molecular warping.     

Oxidation of the perchlorotriphenylmethyl radical to the carbocation,and its unique abrupt reversion

A solution of AlCl(3) in CH(2)Cl(2) reacts slowly, at room temperature, with perchlorotriphenylmethyl radical (PTM(*)), an inert carbon free radical, to give perchlorotriphenylmethyl cation (PTM(+)) quantitatively. However, by gradual addition of CH(2)Cl(2) into the resulting solution a point is reached where the PTM(+) reverts to PTM(*) instantaneously and quantitatively. A mechanism for this exceptional phenomenon is suggested. Some PTM(+) reactions, namely hydrolysis yielding quinonoid species and single-electron transfers with hydride ion donors, are reported and discussed.     

Highly stereoselective double (R)-phenylglycinol-induced cyclocondensation reactions of symmetric aryl bis(oxoacids)

The double cyclocondensation of symmetric pyridyl bis(oxoacids) 2b and 3b with (R)-phenylglycinol stereoselectively gave access to bis-phenylglycinol-derived oxazolopyrrolidine 9 and oxazolopiperidone 10, respectively. Application of the stereocontrolled cyclocondensation reaction to phenyl bis-γ-oxoacid 4b provided 11, which was converted to the corresponding enantiopure di(pyrrolidinyl)benzene 22. The absolute configuration of the new stereogenic centers generated in the key cyclocondenstion step was unambiguously established by X-ray crystallographic analysis.