Chlorides, oxochlorides, and oxoacids of 1,8-diphosphanaphthalene: a system with imposed close p...p interaction

Several new 1,8-diphosphanaphthalene oxochloro compounds and oxoacids were prepared and fully characterized. The new compounds are discussed in the broader context with other known congeners to demonstrate the variability of the diphosphanaphthalene scaffolding's bonding patterns. Three principal modes of interaction of the phosphorus moieties were observed in the series: bonding, bridging, and repulsive, resulting respectively in none, moderate, and substantial crowding and distortions. The unexpected dimeric diphosphaacenaphthene anion has been obtained from disproportionative hydrolysis of Nap(PCl(2))(2) (Nap = naphthalene-1,8-diyl).     

Mechanically linked polycarbonate

The synthesis, by solid-state copolymerization, and characterization of the first polycatenanes based on a commercial polymer are reported. Various amounts of a benzylic amide [2]catenane, the corresponding macrocycle, and a rigid bisphenol fluorene derivative have been quantitatively and homogeneously incorporated into bisphenol A polycarbonate. The resulting copolymers were characterized by size exclusion chromatography coupled with viscosimetry, (1)H NMR, differential scanning calorimetry, and dynamic mechanical analysis. The unexpectedly small influence of [2]catenane incorporation on the glass transition temperature of the copolymers points to remarkable internal mobility of the catenane comonomer rings. A new relaxation linked to the flexible catenane units is also observed. The studies represent a detailed structural characterization of a polymer containing small amounts of mechanical linkages in its backbone and demonstrate that significant effects can be induced by doping conventional polymers with small percentages (2-6% of repeat units) of flexible catenanes.     

Synthesis and full characterisation of 6-chloro-2-iodopurine, a template for the functionalisation of purines

A simple and efficient synthesis of 6-chloro-2-iodopurine from hypoxanthine has been achieved. This strategy relied on a regiospecific lithiation/quenching sequence of 6-chloro-9-(tetrahydropyran-2-yl)purine using Harpoon's base and tributyltin chloride. HMBC NMR studies on the product and intermediates confirmed the regioselectivity of this methodology. The molecular structures of the final dihalogenopurine and its 9-protected precursor were determined by single crystal X-ray diffraction.     

New mode of sterically imposed phosphorus hyperco-ordination

The sterically imposed electronic interaction in Nap (POCl2)(PCl4) (Nap = naphthalene-1,8-diyl) results in hyperco-ordination of the P atom by the O donor in the bridging position between the two peri-substituents.     

Novel small organo-P-S/Se heterocycles

Oxidative addition of elemental sulfur and selenium to cyclomonocarbatetraphosphines (PhP)4CR2 (R = H, Me) afforded novel five- and four-membered heterocycles PhP(E)CH2PhP(E)E2(E = S, Se) and PhP(Se)CMe2-PhP(Se)Se.     

A new class of ferromagnetically-coupled mixed valence vanadium(IV/V) polyoxometalates

Reaction of [V(VI)OCl(2)(thf)(2)] with a bidentate nitrogen-donor ligand (L: phen=1,10-phenanthroline, 5-mephen=5-methyl-1,10-phenanthroline, bipy=2,2'-bipyridine, 5,5'-me(2)bipy=5,5'-dimethyl-2,2'-bipy) in methyl alcohol, in the presence of triethylamine, leads to the formation of hexameric [V(2) (IV)V(4) (V)] oxo-alkoxo-vanadates of the general formula [V(6)O(12)(mu(2)-OCH(3))(4)(L)(4)].x H(2)O [L=phen (1.4 H(2)O), 5-mephen (2.6 H(2)O), bipy (3.4 H(2)O), 5,5'-me(2)bipy (4.H(2)O)]. X-ray structure analysis of 1.2 H(2)O and 4.8 CH(3)OH revealed a pair of V(3)O(13)N(4) trimeric units sharing two corners, with a centrosymmetric planar V(6)-core. In addition, a fully oxidized V(V) species [V(V) (4)O(8)(OCH(3))(2)(mu(3)-OCH(3))(2)(5,5'-me(2)bipy)(2)].3 CH(3)OH (5.3 CH(3)OH) was isolated from the reaction mixture used for the synthesis of 4.H(2)O. The crystal structure of 5.3 CH(3)OH revealed a dicubane-like framework with two missing vertices. Electron paramagnetic resonance (EPR) and variable temperature magnetic susceptibility studies for the hexamers 1.4 H(2)O and 3.4 H(2)O showed the complete localization of the single 3d electrons on the V(IV) ions and unusual ferromagnetic interaction between the two paramagnetic vanadium(IV) ions separated by a distance of about 5.1 A. Furthermore, intermolecular antiferromagnetic interactions through pi-contacts of phenyl rings were observed for these species below 8 K. The ferromagnetic exchange coupling observed in the hexanuclear compounds 1.4 H(2)O and 3.4 H(2)O is also discussed using ab initio UHF calculations on a model compound. The value of the exchange coupling constant (3.7 cm(-1)) for this model compound, calculated using the broken symmetry approach, is in good agreement, both in sign and magnitude, with the experimental J values (6.00 cm(-1) for 1.4 H(2)O and 8.54 cm(-1) for 3.4 H(2)O).     

Titanium mediated asymmetric aldol reaction with α-fluoropropionimide enolates

Aldol reaction utilising Evans N-(α-fluoropropyl)-2-oxazolidinones with TiCl₄ have been explored. Reactions of N-(α-fluoropropyl)-2-oxazolidinones with aliphatic aldehydes generated α-fluoro-β-hydroxy-aldol products with high diastereoselectivities. When (αR)- and (αS)-N-(α-fluoropropyl)-2-(4S)-oxazolidinones were explored as substrates they gave rise to identical aldol diastereoisomer products. Examination of the enolates formed in each case by ¹⁹F NMR, after treatment with TiCl₄, indicated that both preparations gave the same predominant enolate. This was assumed to be the E-enolate. The α-fluoro-β-hydroxy-aldol products were removed from the auxiliary either by alcoholysis or reduction and converted to the corresponding α,β-difluoro products by treatment with Deoxofluor™.