Sarada Gopinathan

Dioxomolybdenum(VI) and dioxotungsten(VI) complexes of isomeric ONO donor ligands and the X-ray crystal structure of [MoO2(o-OC6H4CHNCH2C6H4O)(MeOH)]2·MeOH

Abstract Dioxomolybdenum(VI) and dioxotungsten(VI) complexes of two isomeric Schiff bases derived from salicylaldehyde, 2-hydroxy-1-naphthaldehyde and o-hydroxybenzylamine or o-aminobenzylalcohol have been prepared and characterized.1H NMR spectral data confirm the formation of [MO2L] (M = Mo or W, LH2 = ligand) types of complexes except the complex of dioxomolybdenum(VI) with the ligand salicylaldehyde-o-hydroxybenzylamine (H2sal-OHYBA) which forms [MoO2(sal-OHYBA)·CH3OH]. An X-ray study of [MoO2(sal-OHYBA)·CH3OH] shows the presence of distorted octahedral geometry around molybdenum in which the tridentate ligand occupies meridional position where two anionic oxygens are mutuallytrans and arecis to thecis dioxo group. Generally the tungsten complex is more stable to decomposition than the molybdenum one within the same ligand.

Reactivity of bis(acetylacetonato)dinitrosylmolybdenum(0) towards schiff bases derived from salicylaldehyde or o-vanillin and benzoylhydrazide, or isonicotinoylhydrazide☆

Abstract The synthesis of dinitrosylmolybdenum(0) complexes of Schiff bases by a single-step ligand-exchange process has been reported for the first time by the reaction of [Mo(NO) 2 (acac) 2 ] with the Schiff bases (LH 2 ) obtained by the condensation of salicylaldehyde or o -vanillin and benzoylhydrazide, or isonicotinoylhydrazide, and are of the type [Mo(NO) 2 (LH) 2 ]. The Schiff behave as monobasic bidentate ligands coordinating through the azomethine nitrogen and enolic oxygen after deprotonation. Two geometric isomers having nitrosyl trans to each other have been observed in solution. Another complex, [MoO 2 (sal-INH) · MeOH], has also been synthesized for comparison.

Insertion reactions of acetylenes with hydridoruthenium(II) carboxylates

Abstract Insertion reactions of acetylene, diphenylacetylene and phenylacetylene into the RuH bond of RuH(CO)(OCOR)(PPh 3 ) 2 (R = CH 3 , C 2 H 5 , C 3 H 7 , C 6 H 5 , p -CH 3 OC 6 H 4 ) have been studied in benzene at ambient and reflux temperatures. The vinylic complex formed results from cis -addition of the RuH bond to the triple bond. An excess of phenylacetylene reacts with RuH(CO)(OCOR))(PPh 3 ) 2 in refluxing benzene to give the σ-vinyl alkynyl complex of formula Ru(CO)(OCOR)(PPh 3 ) 2 {C(CCPh)CHPh) in good yield. The appearance of a single sharp resonance in the 31 P NMR spectra of the complexes suggests that both the phosphorus ligands are equivalent, and trans to each other in these octahedral Ru II complexes.

Beiträge zur chemie des bors: CLXXV. Über den einfluss sterischer faktoren auf die konformation von diborylaminen

The aminoborane Ph 2 BN(CMe 3 SiMe 3 possesses a relatively long BN bond (1.433 A) and a nonplanar C 2 BNCSi (τ(C 2 B/NCSi) 45°) skeleton as shown by X-ray structure analysis. In addition, the structure of five diborylamines have been determined by X-ray methods. The compounds (mes 2 B) 2 NH and (mes 2 BNH) 3 B belong to diborylamines with a coplanar conformation for the C 2 BNHBC 2 (or C 2 BNHBN 2 ) units, while the diborylamines (Ph 2 B) 2 )NH and (Ph 2 B) 2 NMe adopt a twist conformation. Finally, an orthogonal conformation was detected for t-Bu 2 BNMe-9-borafluorene. The T-Bu 2 B group stands almost perpendicular on the BNC-9-borafluorene plane. Consequently, two distinctly different BN bond lengths (1.482 and 1.392 A) are observed. The influence of steric effects on the conformation and bonding parameters is discussed.

Kinetics of oxidation of β-isophorone to keto-isophorone catalyzed by manganese Schiff base complex using molecular oxygen

Abstract Kinetic investigations were carried out on the oxidation of β-isophorone (β-IP) to keto-isophorone (KIP) catalyzed by [LMn(III)(Cl)], (where, L=bis-salicylaldehydeethylenedi-imine, salen) at temperature in the range 10–27°C and partial pressure 0.2–3 atm of molecular oxygen. β-IP gave mainly KIP as the oxidation product under the reaction conditions studied. Initial rate approach was adopted to evaluate kinetic parameters of the reaction. From the kinetic investigations, it was found that the rate of oxidation of β-IP showed a first-order dependence with respect to catalyst and substrate concentrations, and half-order dependence on the partial pressure of oxygen. The effect of temperature on the rates of oxidation was also investigated and from the Arrhenius plot of −ln rate vs. 1/ T , the activation energy estimated is 16.12 kcal mol −1 . Thermodynamic activation parameters such as enthalpy, entropy and free energy of the reaction were calculated from the known thermodynamic equations. Based on the kinetic investigations, a plausible mechanism for manganese salen complex catalyzed oxidation of β-IP to KIP has been proposed.

Novel Ruthenium(II) Schiff Base Complexes

Abstract Schiff bases derived from aromatic aldehydes/ketones and S-benzyldithiocarbazate react with RuHC1 (CO)(PPh3)3 and RuH2(CO)(PPh3)3 to yield [RuX(CO)(PPh3)2(Schiff base] (X = H, C1). The new complexes have been characterised by IR, 1H NMR and UV spectroscopy. The triphenylphosphine ligands in these complexes have been observed to be trans to each other.

Synthesis and characterisation of β-carboalkoxyruthenium(II) complexes

Abstract Methyl, ethyl, and butyl acrylates have been found to insert into the hydridoruthenium complex, HRuClCO(PPh 3 ) 3 under mild conditions to give Ru C σ-bonded mononuclear complexes of the type RuClCO(PPh 3 ) 2 CH 2 CH 2 COOR. The ruthenium atom is six coordinated in these complexes

Dioxomolybdenum(VI) complexes of new binucleating schiff bases derived from methylene- or dithio-bis(salicyclaldehyde) and various amines☆

Abstract The syntheses of binuclear dioxomolybdenum(VI) complexes of the type [(MoO2)2L], where L is a flexibly-bridged hexadentate tetraanionic Schiff base derived from the condensation of methylene- or dithio-bis(salicylaldehyde) with o-aminophenol, 2-aminoethanol, 2-amino-2-methyl propanol or 1-amino-2-propanol, are reported. The IR and NMR spectral data suggest an oligomeric structure in which each molybdenum ion achieves a pseudo-octahedral structure via MoO---Mo bridging. Treatment of [(MoO2)2L] with pyridine leads to the formation of [MoO2)2L(py)2] in which pyridine binds at the sixth labile binding sites in both [MoO2]2+ units. [(MoO2)2L(py)2] is readily convertable inot [(MoO2)2L] at ca 180°C in a single endothermic step, as seen from their DTA analysis. The pyridine adducts show two IR absorption at ca 900 cm−1, attributable to a cis-MoO2 structure, whereas the oligomeric complexes usually show one intense ν(MoO) band at 910–938 cm−1 and a broad but strong band at ca 820 cm−1 due to a weakend ν(MoO) band as a result of MoO → Mo interactions.

Synthesis and Characterisation of Titanium(IV), Tin(IV), and Lead(IV) Complexes of Schiff Bases Derived from S-Benzyldithiocarbazate

Abstract The Schiff bases H2SBVD and H2SBND, derived, respectively, from S-benzyldithiocarbazate and 2-hydroxy-3-methoxybenzaldehyde or 2-hydroxy-1-naphthaldehyde, react with titanium tetrachloride, titanium tetraalkoxides, dicyclopentadienyltitanium dichloride, organotin chlorides/oxides/hydroxides and di-/triphenyllead chlorides in 1:1 molar proportion to yield neutral penta-coordinated complexes of the type X2M(Schiff base) and Ph3M(H-Schiff base) (M - Sn or Pb). The complexes are characterised on the basis of IR, 1H NMR and electronic spectral studies.

Metal Schiff-Base Complex Catalyzed Oxidation of p-Xylene and Methyl 4-Methylbenzoate to Carboxylic Acids

Oxidation of p-xylene and methyl 4-methylbenzoate were catalyzed by transition metal Schiff-base complexes having the general formula LMCl1–2 (where M = manganese or ruthenium and L = salen, salicylaldehydeethylenediimine, saloph, salicylaldehyde-o-phenylenediimine and EDTA, ethylenediaminetetraacetate) at 150°C and 500 psig air and gave p-toluic acid (> 85 %) and monomethyl terephthalate (> 70%) as the major oxidation products, respectively.