Raj K. Chadha

Cationic Cobaltammines as anion receptors: a convenient synthesis, characterization and X-ray structure of [CO(NH3)6]ClSeO4·3H2O

Reddish-orange single crystals of hexaamminecobalt(III) chloride selenate trihydrate, [Co(NH3)6]ClSeO4· 3H2O, have been prepared by reacting aqueous solutions of hexaamminecobalt(III) chloride and potassium selenate in a 1u2009:u20091 molar ratio. The salt was characterized by elemental analyses, thermogravimetry, magnetic moment and spectroscopic studies (IR, electronic). A single crystal X-ray structure determination revealed that the title complex salt crystallizes in the orthorhombic space group Pnma with a = 18.230(2), b = 8.591(2), c = 8.593(2)u2009Å, V = 1345.9(4)u2009Å3, Z = 4, R = 0.0400 and Rw = 0.0980. In the salt the network of hydrogen bonds between the hexaamminecobalt(III) cation, water molecule, chloride and oxygen atoms of the selenate ion represents the second sphere coordination and also suggests that [Co(NH3)6]3+ may be used as an anion receptor for the selenate ion.

Total Synthesis of Combretastatins D

Targeting the wrong isomer, we achieved a synthesis of two natural combretastatins, thanks to an unusual dehydration mechanism and the original incorrect assignment of the natural product. The key step for both syntheses was the application of a Mitsunobu-type macrolactonization of saturated seco acids (below). The synthetic route is effective, simple, and convergent, and may be useful for the synthesis of related derivatives.

SYNTHESIS, CHARACTERISATION AND NONLINEAR OPTICAL PROPERTIES OF TETRAHEDRAL CLUSTERS CP2MO2ME(CO)7, (M = FE, RU, OS; E = S, SE)

Abstract A set of new chalcogen-bridged mixed metal clusters, Cp 2 Mo 2 M( μ 3 -E)(CO) 7 , (M=Fe, Ru, Os; E=S, Se) have been synthesised and characterised by IR and NMR spectroscopy, and structures of Cp 2 Mo 2 Ru( μ 3 -Se)(CO) 7 and Cp 2 Mo 2 Os( μ 3 -Se)(CO) 7 have been established by single crystal X-ray diffraction methods. The nonlinear optical properties of these clusters were investigated through the Z-scan technique, using 35 ps laser pulses at 532 nm. We report large refractive third order nonlinearity for these clusters indicating their promise for optical limiting applications.

Disproportionation reactions of (methoxy/hydroxy)diorganotin(IV) methanesulfonates with carboxylic acids: Synthesis and structure of new diorganotin(IV) carboxylates

Abstract Disproportionation reactions between equimolar quantities of R2Sn(X)OSO2Me [X=OMe or OH] and ethylmalonic/maleic acid in acetonitrile under mild conditions afford new diorganotin dicarboxylates, R2Sn(O2CR′COOH)2 [R′=CHEt, R=n-Pr (3a), n-Bu (3b); R′=CHue605CH, R=n-Pr (3c), n-Bu (3d)] along with R2Sn(OSO2Me)2 [R=n-Pr (4a), n-Bu (4b)]. Similar reactions of the tin precursors with pyridine-2-carboxylic acid provide an access to novel trinuclear tin complexes, R6Sn3(O2CC5H4N-2)3(OSO2Me)3 [R=n-Pr (5a), n-Bu (5b)]. These have been characterized by IR and multinuclear (1H, 13C, 119Sn) NMR spectroscopies. The molecular structures of 3b, 4b and 5b have been determined by X-ray crystallography. Compound 3b is monomeric with bicapped tetrahedron geometry by virtue of anisobidentate coordination of one carboxylate group of each ligand, while the other carboxylic acid group remains free. The polymeric structure of 4b features centrosymmetric eight-membered rings comprising bridging methanesulfonate groups and nearly perfect octahedral geometry around each tin atom. Compound 5b crystallizes as 5b·2H2O·Et2O. Its molecular structure comprises of mixed ligand tin ester, n-Bu2Sn(O2CC5H4N-2)OSO2Me and its disproportionated products, n-Bu2Sn(O2CC5H4N-2)2 and n-Bu2Sn(OSO2Me)2 which are coordinatively associated by varying bonding modes of pyridine-2-carboxylate groups. A possible rationalization of these results are discussed in terms of the intermediacy of mixed ligand tin complexes, R2Sn(L)OSO2Me (L=carboxylate) formed by the selective substitution of Snue5f8OMe group or by the dehydration of Snue5f8OH group in the tin precursors with the carboxylic acid.

Discrete Spirobicyclic Silicate Anions with SiO2N2C, SiN2S2C and SiO4C Frameworks

Bis(2-aminobenzoato)phenylsilicate ( 1 ), bis(2-aminothiophenoxy)phenylsilicate ( 2 ), and bis(2-hydroxybenzoato) phenylsilicate ( 3 ) anions were obtained as their triethylammonium salts from the reactions of phenylsilane with appropriate ligands in the presence of triethylamine. The compounds were characterized by IR, multinuclear ( 1 H, 13 C, and 29 Si) NMR, and FAB mass spectral data. Th X-ray crystal structure of 1 .CH 2 Cl 2 revealed slightly distorted trigonal bipyramidal geometry around silicon. The spirobicyclic silicate anions are the first examples with silicon-heteroatom linkages having six-membered ( 1 ) and five-membered ( 2 ) rings on silicon.