M. Nawaz Tahir

Synthesis of a water-soluble carbene complex and its use as catalyst for the synthesis of 2,3-dimethylfuran

Abstract 1,1′,3,3′-Tetrakis(p-dimethylaminobenzyl)-2,2′-biimidazolidinylidene, L2R (R=CH2C6H4NMe2-p) which contains four peripheral NMe2 substituents, was obtained from 4-dimethylaminobenzaldehyde by a three-step reaction sequence, and was used for the preparation of imidazolidin-2-ylidene Ru(II) and Rh(I) complexes 1 and 2. Etherial HCl readily protonates the NMe2 functionality on the carbene ligand of 1 to give the corresponding salt, 1′; whereas the reaction of 2 with HCl gave a hygroscopic and ill-defined rhodium species. In aqueous solution the salt 1′ is an efficient and active catalyst for intramolecular cyclisation of (Z)-3-methylpent-2-en-4-yn-1-ol into 2,3-dimethylfuran. The catalyst 1′ could be recovered by simple phase separation and the catalytic reaction was maintained for five different runs. All of the new compounds were characterised by elemental analyses, IR and NMR spectroscopy and the molecular structure of 1 was determined by X-ray crystallography.

Novel enantioselective synthesis of trans-α-(2-carboxycycloprop-1-yl)glycines: conformationally constrained l-glutamate analogues

Abstract d - and l -α-(2-carboxycycloprop-1-yl)glycines were synthesized from trans -1,3-di(2-furyl)propenone. Conversion of the double bond to a cyclopropane is followed by the formation of an oxime ether. Enantioselective reduction of the oxime ether, separation of diastereomers and oxidation of the furane rings gave enantiomerically pure d - and l -CCG I and CCG II. The structure of oxime 7b was determined by X-ray crystal structure analysis. The key step is the oxazaborolidine catalyzed enantioselective conversion of oxime ethers to amines.

BROMINATION OF NAPHTHALENE AND DERIVATIVES : HIGH TEMPERATURE BROMINATION XI

Abstract Thermal and photobromination of naphthalene and derivatives have been studied. Several hexabromo- (12, 13, 16 and 17), and tetrabromotetralin derivatives (23, 24, and 25) have been obtained as the major products, besides bromonaphthalene derivatives. Base-promoted elimination reactions of 12, 13, 16 and 17 provided di- (8) tri- (10) and tetrabromo-naphthalenes (22). A convenient method was developed for the synthesis of 1,3-dibromonaphthalene (26) starting from (24). The structures of these products were determined by 1H-, 13C-NMR data and X-ray structural analysis.

Synthesis of cis- and trans-dichloro(dimethylphenylphosphine)-(1-methyl-1,4,5,6-tetrahydropyrimidine)platinum(II) and their spectral and structural characterization

Abstract Interaction of [{Pt( μ -Cl)Cl(PMe 2 Ph)} 2 ] with 1-methyl-1,4,5,6-tetrahydropyrimidine, L (R=Me), in boiling toluene produced a mixture of cis- and trans- isomers of [PtCl 2 (PMe 2 Ph){ N=CH(Me)CH 2 CH 2 C H 2 }]; trans -complex 2 isomerizes to give thermodynamically more stable corresponding cis -complex 1 in boiling ethanol. Spectroscopic and X-ray diffraction data permit generalizations about cis- and trans- isomeric pairs to be made. In addition, the trans influence of the ligand L is reliably assessed.

4-(3-Methoxyphenyl)-1-(2-oxoindolin-3-ylidene)thiosemicarbazide

The title compound, C15H11FN4OS, is almost planar, the dihedral angle between the aromatic ring systems being 5.00u2005(13)°. The conformation is stabilized by intramolecular N—H⋯N and N—H⋯O hydrogen bonds, which generate S(5) and S(6) rings, respectively. N—H⋯F and C—H⋯S interactions also occur. In the crystal, inversion dimers linked by pairs of N—H⋯O hydrogen bonds occur, generating R 2 2(8) loops.

5-Chloro-2-hy­droxy­benzoic acid

The asymmetric unit of the title compound, C7H5ClO3, contains two molecules; both feature an intramolecular O—H⋯O hydrogen bond, which generates an S(6) ring. In the crystal, both molecules form inversion dimers linked by pairs of O—H⋯O hydrogen bonds with R 2 2(8) ring motifs. The dimers are interlinked by C—H⋯O interactions.

N-(3-Chlorophenyl)-2-hydroxybenzamide

In the title compound, C13H10ClNO2, the dihedral angle between the aromatic rings is 20.02u2005(6)° and intramolecular N—H⋯O and C—H⋯O hydrogen bonds both generate S(6) rings. In the crystal, molecules are linked by O—H⋯O hydrogen bonds into C(6) chains propagating in [010].

N-{4-[(E)-(4-Methyl-phen-yl)imino-meth-yl]phen-yl}acetamide.

There are two symmetry-independent molecules in the asymmetric unit of the title compound, C16H16N2O, that differ in conformation. The dihedral angles between the benzene rings in the two molecules are 44.35u2005(19) and 48.14u2005(17)°, but the rings twist in opposite directions. The acetamide groups make nearly equal dihedral angles of 25.4u2005(3) and 25.7u2005(3)° with the parent benzene rings. An S(6) ring motif is formed in each molecule by intramolecular C—H⋯O close contacts. In the crystal, strong N—H⋯O hydrogen bonds between acetamide groups generate a C(4) chain motif arranging the molecules into two symmetry-independent polymeric structures extending along [010].

4-(3-Fluorophenyl)-1-(2-oxoindolin-3-ylidene)thiosemicarbazide

In the title compound, C15H11FN4OS, there are three independent molecules, each with a disordered 3-fluorophenyl group [occupancy ratios = 0.547u2005(17):0.453u2005(17), 0.645u2005(5):0.355u2005(5) and 0.626u2005(15):0.374u2005(15)] and displaying dihedral angles of 4.2u2005(3), 25.2u2005(6) and 32.4u2005(5)° between the 2-oxoindoline and fluoro-substituted phenyl rings. Strong intramolecular N—H⋯N and N—H⋯O and weak intramolecular C—H⋯S hydrogen bonds complete S(5) and S(6) ring motifs, while strong intermolecular N—H⋯O hydrogen bonds interconnect the three independent molecules through R 3 3(12) ring motifs. The three-molecule units are in turn linked into polymeric sheets via C—H⋯F and C—H⋯S hydrogen bonds and π–π interactions [centroid–centroid distances in the range 3.520u2005(2)–3.820u2005(9)u2005Å].

Some Complexes of Tin(II) and Tin(IV) with Ono-Type Dihydroxy Schiff Bases

Abstract Coordination compounds of Sn(IV) with four ONO-type Schiff bases, namely, N-(2-hydroxyphenyl)salicylaldimine (I), N-(2-hydroxy-5-metliylphenyl)salicylaldimine (II), N-(2-hydroxy-5-chlorophenyl)salicy1-aldimine (III) and N-(2-hydroxy-4-methylplienyl)salicylaldimine (IV) have been studied. IR spectroscopy in addition to thermogravimetric and elemental analyses have been performed. The molecular structure of the Sn(IV) complex of (IV) as a model structure was solved by X-ray diffraction technique. It is observed that, Sn(II) in the Sn(II) complexes is oxidized in atmospheric oxygen and Sn(IV) complexes are formed in polar solvents such as dioxane, acetonitrile and dimethyl sulphoxide.