Synthesis and characterization of a 2, 5-Bis(trimethylsilyl)-substituted Bis(1, 1′-silolide) dianion

A novel silyl-substituted bis(1, 1′-silolide) dianion has been isolated and characterized by single-crystal X-ray analysis for the first time. The ¹H, ²⁹Si, and ¹³C NMR spectra show significant delocalization of the negative charges to the silole ring. X-ray crystallography revealed equalized C?C distances and DFT calculation also indicates for significant aromaticity. Reaction with trimethylchlorosilane gave the expected bis(1, 2, 5-tris(trimethylsilyl)-3, 4-diphenyl-silacyclopentadienyl).     

Cyclobutadiene dianion derivatives – Planar 4c,6e or three-dimensional 6c,6e aromaticity?

The spatial magnetic properties (Through Space NMR Shieldings – TSNMRS) of two cyclobutadiene derivatives (2 and 5) and of a number of cyclobutadiene dianion derivatives (3, 4 and 6–8) have been calculated by the GIAO perturbation method employing the Nucleus-Independent Chemical Shift (NICS) concept of P. v. Ragué Schleyer, and visualized as Iso-Chemical-Shielding Surfaces (ICSS) of various size and direction. TSNMRS values can be successfully employed to quantify and visualize the (anti)aromaticity of the compounds studied and to discuss the influence of Li⁺ complexation to cyclobutadiene dianion (4a, 7 and 8) on planar 4c,6e or three-dimensional 6c,6e aromaticity.     

Sandwich Complexes of the As42-Aromatic Ring with Some Transition Metals

The equilibrium geometries, energies, harmonic vibrational frequencies, and nuc- leus independent chemical shifts (NICS) of the new type sandwich structures [As4MAs4]n- (M = Fe, Co, Ni, Ru, Rh, Pd, Os, Ir and Pt; n = 0, 1 or 2) are investigated at the B3LYP level.All the [As4MAs4]n- species adopt staggered (D4d) conformations as their stable structures and eclipsed (D4h) conformations as their transition states, and once the sandwich complexes are formed, the As42- square properties remain unchanged.The NICS calculation confirms that the complexes of Fe, Co, and Ni are aromatic with negative NICS values, and those of Ru, Rh, and Ir exhibit slight aromaticity, while those of Pd, Os, and Pt show slight antiaromaticity.     

13C NMR study of 2,3,4,5-tetraphenylsilole dilithium salt

The complete assignment of the signals in the¹³C NMR spectra of 2,3,4,5-tetraphenyl-1-R¹,R²-1-silacyclopenta-2,4-dienes (R¹=R²=H, Me) and of the dianion of lithium salt [(PhC)₄Si]²⁻·2Li⁺ was carried out by 2D NMR spectroscopy. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 216–218, January, 1999.     

Aromatic Metamorphosis of Thiophenes by Means of Desulfurative Dilithiation

A new mode of aromatic metamorphosis has been developed, which allows thiophenes and their benzo-fused derivatives to be converted to a variety of exotic heteroles. This transformation involves 1) the efficient generation of key 1,4-dianions by means of desulfurative dilithiation with lithium powder and 2) the subsequent trapping of the dianions with heteroatom electrophiles in a one-pot manner. Via the desulfurative dilithiation, the sulfur atoms of thiophenes are replaced also with a carbon–carbon double bond or a 1,2-phenylene for the construction of benzene rings.     

Reactivity in the upper limits of the reduction potential in solution: arene dianion intermolecular carbolithiation of alkenes

Lithium salts of dianions derived from arenes of high reduction potential (biphenyl, naphthalene) can carbometallate terminal alkenes (propene, isobutene) in an intermolecular fashion, affording partially dearomatized alkylated aryl anions, which are susceptible to further functionalization by electrophilic capture. This form of reactivity, specific of the arene dianion, deviates from the typical alkali metal-like reactivity displayed by these complexes, affording in most cases regio- and stereocontrolled products. Simple semiempirical calculations (PM3) help predicting the regiochemical outcome of this reaction, where some of the most inexpensive organic starting materials are involved.     

Highly Strained Metallocenophanes: Synthesis and Ring-Opening of Sulfur-, Selenium- and Boron- Bridged [1]Ferrocenophanes

Abstract

The limits of cyclopentadienyl ring-tilting in [l]ferrocenophanes are explored with the incorporation of group 16 elements and a first row element. In this paper the synthesis and ring-opening polymerisation (ROP) behaviour of highly strained chalcogen-and boron- bridged [l]ferrocenophanes will be described.     

Synthesis,characterization and X-ray crystallographic investigation of 2-D hybrid hydrogen bonded and rectangular grid networks in Cu(II) and Co(II) metal complexes

Two copper/cobalt metal complexes, [Cu(l-cys)(2,2′-bpy)(H₂O)] (1) and {[Co(l-cys)(4,4′-bpy)(H₂O)]·H₂O}_n (2), with the N-donor ligands 2,2′-bipyridyl/4,4′-bipyridyl and the l-cysteate dianion (l-cys) have been synthesized by different reaction methods and structurally characterized. Compound 1 exists as a discrete monomeric unit in which the metal ions possess a distorted square-pyramidal coordination environment provided by nitrogen atoms from the 2,2′-bpy ligand and the amino-carboxylate group of l-cys in a chelated coordination, constituting the square base, and with a water molecule occupying the axial coordination site to complete the penta coordination. Packing and hydrogen bonding interactions of 1 reveal that the screw related monomeric units are involved in intermolecular hydrogen bonding with the formation of helical bilayers via O–H?O and N–H?O interactions. These hydrogen bonded bilayered helical nets are involved in stacking and C–H?O interactions which generate a two dimensional hydrogen bonded network in the bc-plane. Complex 2 is a two dimensional coordination polymer which is insoluble in common polar and non-polar solvents. The coordination around the metal center possesses a distorted octahedral geometry. The adjacent metal centers are bridged via the carboxylate group of the l-cys moiety in a syn–anti fashion, generating a one dimensional helical network along the b-axis. Adjacent helical chains are further pillared by the 4,4′-bpy ligand through the terminal nitrogen atoms, generating a two dimensional square grid type coordination network. Both the complexes are characterized well by various physico-chemical techniques such as CHN analysis, IR spectroscopy, PXRD and CD analysis.