Organic Chemistry Division

Aflatoxin is a mycotoxin produced by Aspergillus flavus and a common contaminant of food and feed, posing health hazards to humans and animals alike. The aim of this study is to explore the ability of Pseudomonas putida to degrade aflatoxin B 1 (AFB 1 ). The toxigenic strain of A. flavus was isolated from sugarcane and used to produce AFB 1 in yeast extract sucrose medium. Two P. putida strains, MTCC 1274 and 2445, were cultured in mineral salt glucose medium (MSG) containing AFB 1 . The AFB 1 was analyzed qualitatively and quantitatively by TLC and HPLC. It was found that Pseudomonas sp. can tolerate AFB 1 in the medium (0.2 mg ml À1 ), and degrades it very efficiently. Within 24 h of incubation, AFB 1 was reduced to an undetectable level in MSG medium. Analysis with TLC, HPLC, UV spectrophotometer, gas chromatography mass spectrometry (GCeMS), and Fourier transform infra-red spectroscopy (FT-IR) showed that AFB 1 was bio-transformed to structurally different compounds (AFD 1 , AFD 2 , and AFD 3 ), with the modified furan and lactone ring on the AFB 1 molecule. A toxicity study on the HeLa cells showed that the new compounds formed are less toxic when compared with AFB 1 .

Metallacycloalkanes are an important class of compounds which have been known for many years to be key intermediates in useful catalytic reactions. For example, metallacyclobutanes are known to be present in the alkene metathesis reaction. More recently, metallacycloheptanes were first implicated, then proven to be involved in ethylene trimerization. There has been interesting discussion and a belief that the formation of nine-membered and other larger metallacycloalkane rings is unlikely.

and coordination behaviour of several symmetrically and unsymmetrically substituted phosphiniminocyclotrithiazenes have been studied. Polarograms of R 3 (2) reveal nearly the same oxidation peak potential but different reduction potentials. Controlled potential electrolysis of 1 and 2 at +0.6 V indicates exocyclic cleavage and ring degradation. Cathodic reduction behaviour of Ph 3 PN-S 3 N 3 suggests the possibility for the formation of 1,5-(Ph 3 PN) 2 S 4 N 4 under electrochemical conditions. Reaction of nickel chloride hexahydrate with heterocycle 1 in 1:2 molar ratio in acetonitrile affords the complex, [Ni(S 2 N 2 H) 2 ] (A) (90% yield) and [Ph 3 PNH 2 ]Cl salt as products. Analogous reactions with other ligands of this type (two symmetrical (sym.) and three unsymmetrical (unsym.)) except 2 also give A, while ligand 2 reacts with anhyd NiCl 2 in an equimolar ratio to afford a dark green, square-planar complex ((OC 4 H 8 N) 3 PN-S 3 N·NiCl 2 (B)) whose ESCA results assist in providing its coordination details. The study reveals a high tendency of these heterocycles to different types of ring cleavage. Résumé : On a étudié le comportement électrochimique (polarographique, voltampérométrie cyclique et coulométrique) et de coordination de plusieurs phosphiniminocyclotrithiazènes substitués de façon symétrique et asymétrique. Les polarogrammes des R 3 (2) présentent des potentiels d'oxydation maxima qui sont pratiquement les mêmes, mais les potentiels de réduction sont différents. Une électrolyse du composé 1 à potentiel contrôlé, à 0,6 V, indique la présence de clivage exocyclique et de dégradation de cycle. Le comportement du Ph 3 PN-S 3 N 3 lors de la réduction cathodique suggère la possibilité de formation du 1,5-(Ph 3 PN) 2 S 4 N 4 dans les conditions électrochimiques. La réaction du chlorure de nickel hexahydraté avec l'hétérocycle 1, dans un rapport molaire de 2:1 dans l'acétonitrile, conduit à la formation du complexe [Ni(S 2 N 2 H) 2 ] (A) (rendement de 90 %) et du [Ph 3 PNH 2 ]Cl. Des réactions analogues (excepté celles avec le produit 2) avec d'autres ligands de ce type (deux symétriques et trois non symétriques) conduisent aussi au produit à A. Le composé 2 réagit avec le NiCl 2 anhydre, dans un rapport moléculaire de 1:1, pour fournir un complexe plan carré, vert, (OC 4 H 8 N) 3 PN-S 3 N·NiCl 2 (B) dont les résultats de spectroscopie d'électrons pour analyse chimique (« ESCA ») fournissent des détails relatifs à sa coordination. Cette étude révèle la grande tendance de ces hétérocycles à donner lieu à des types différents de clivage de cycle.

Thermal decomposition studies of bis(1-alkenyl)platinum(II) complexes of the type Pt(L 2 )R 2 (where L = PPh 3 or L 2 = dppe or dppp; R = 1-alkenyl) are reported. The results revealed interesting organic product distributions depending on the length of the alkenyl chains, the nature of the supporting ligands and the metal centers. It is believed that the major decomposition pathways for the title complexes involve b-hydride elimination and/or reductive elimination as well as alkene isomerization. Mechanisms for the major and minor decomposition pathways are proposed. The amount of isomeric products obtained, i.e., 2-alkenes and 1,(n À 2)-diene, increases with increasing chain length.

The development of selective, efficient, and direct routes for activation and functionalization of naturally abundant n-alkanes could lead to a new paradigm in materials and energy technologies. In this context, the use of homogeneous catalysts to functionalize C-H bonds of unactivated hydrocarbons is of particular interest from a scientific as well as an economic viewpoint. Despite the large body of work on stoichiometric C-H activation reactions produced over the last three decades, relatively few systems have been developed to allow catalytic functionalization of hydrocarbons. This review deals with homogeneous catalytic processes available in the literature for paraffin activation and functionalization. The key intermediates involved in catalytic systems are highlighted, providing important information in the design of new and efficient catalysts. Also, some of the key challenges and approaches to rational development of the next generation of organometallic catalysts will be highlighted.

The synthesis, characterization and chemistry of novel g 3 -allyl metal complexes (M = Ir, Rh) are described. The structures of compounds (C 5 Me 4 H)Ir(PPh 3 )Cl 2 (1), (C 5 Me 4 H)Ir(PPh 3 )(g 3 -1-methylallyl)Br (3a), (C 5 Me 4 H)Ir(g 4 -1,3,5-hexatriene) (8), and (C 5 Me 5 )Rh-(g 3 -1-ethylallyl)Br (5d) have been determined by X-ray crystallography. Structural comparisons among these complexes are discussed. It is found that the neutral metal allylic complex [Cp * IrCl(g 3 -methylallyl)] (5) ionizes in polar solvents to give [Cp * Ir(g 3 -methylallyl)] + Cl À (6) and reaches equilibrium (5 6) at room temperature. Addition of tertiary phosphine ligands to neutral complexes such as [Cp * Ir(g 3 -methylallyl)Cl], results in the formation of stable ionic phosphine adducts. Factors such as solvent, length of carbon chain, temperature and light are discussed with respect to the formation, stability and structure of the allyl complexes.

A series of new palladacycloalkanes of formula cis-[PdL 2 (CH 2 ) n ] (9. n = 6, L = PPh 3 ; 10. n = 6, L 2 = dppe; 11. n = 8, L = PPh 3 ; 12. n = 8, L 2 = dppe) have been prepared by two routes. In the first route, the precursor bis(1-alkenyl) complexes cis-[PdL 2 ((CH 2 ) n CH@CH 2 ) 2 ] (1. n = 2, L = PPh 3 , 2. n = 2, L 2 = dppe, 3. n = 3, L = PPh 3 , 4. n = 3, L 2 = dppe) were allowed to react with Grubb's 2nd generation catalyst to give the palladacycloalkenes, cis-[PdL 2 (CH 2 ) n CH@CH(CH 2 ) n ] (5. n = 2, L = PPh 3 , 6. n = 2, L 2 = dppe, 7. n = 3, L = PPh 3 , 8. n = 3, L 2 = dppe), which were then hydrogenated to the palladacycloalkanes, 9-12. In the second route, the di-Grignard reagents BrMg(CH 2 ) n MgBr (n = 6, 8) were reacted with the palladium complex [PdCl 2 (COD)] followed by immediate ligand displacement to form the respective palladacycloalkanes 10 and 12. The complexes obtained were characterized by a range of spectroscopic and analytical techniques. Thermal decomposition studies were carried out on the palladacycloalkanes 9-12 and the main organic products shown to be 1-alkenes and 2-alkenes.

The synthesis of the new cyclopentadiene, C 5 Me 4 (hex)H is described and its reaction with Ru 3 (CO) 12 to yield (C 5 Me 4 hex) 2 Ru 2 (CO) 4 (hex = n-hexyl) is reported. The X-ray crystal structure of the dimer confirms the structure with bridging and terminal CO groups. Reactions of the dimer to yield (C 5 Me 4 hex)Ru(CO) 2 X (X = Cl, Br, I) are reported. IR, NMR and mass spectra are reported for all new compounds. The solubility of the dimer is found to be 10 times greater than that for (C 5 Me 5 ) 2 Ru 2 (CO) 4 .

a b s t r a c t H. This latter reaction confirms that it is the methyl group bonded to ruthenium that is involved in the C-H activation process and not the methyl groups on the Cp * ligand system. The compound Cp * Ru(CO) 2 C 6 H 5 (3) has been prepared for the first time in good yield by the reaction of Cp * Ru(CO) 2 Br with NaBPh 4 . X-ray crystal structures of both Cp * Ru(CO) 2 CH 3 (1) and Cp * Ru(CO) 2 C 6 H 5 (3) have been determined and the results are reported and discussed.

Novel large platinacycloalkane compounds containing 19-and 21-membered rings of the type L 2 Pt (CH 2 ) n (L 2 ¼ dppp and n ¼ 18, 20) are synthesized through the ring closing metathesis (RCM) reaction of bis(1-alkenyl)platinum(II) complexes using Grubbs' catalysts. These compounds are characterized by various spectroscopic and analytical techniques. The cross metathesis reactions with different dienes and substituted alkynes yielded interesting inter-and intra-molecular metathesis reaction products. Various factors such as concentration, solvent, phosphine ligand and length of the alkenyl chains affect the RCM reaction significantly to yield different products such as monomeric, dimeric and polymeric species. The novel chemical reactivity aspects of these title compounds with elemental sulfur, carbon monoxide and methyl iodide are discussed.

Heating the 1-alkenyl complexes cis- 2 L 2 ] [alkenyl ) 1-pentenyl, 1-hexenyl, 1-heptenyl, and 1-octenyl; L 2 ) 1,3-bis(diphenylphosphino)propane (dppp) or 1,2-bis(diphenylphosphino)ethane (dppe)] to 100°C caused a quantitative isomerization to the corresponding 2-alkenyl complexes cis-[Pt-(2-alkenyl) 2 L 2 ]. This novel isomerization is strongly dependent on the length of the alkenyl chains as well as the nature of the ligand, L 2 . The new 2-alkenyl complexes were fully characterized by analytical and spectroscopic methods. An X-ray crystal structure of cis-[Pt(2-pentenyl) 2 (dppp)] confirms this isomerization. Possible reaction mechanisms are discussed.

The synthesis and characterization of several new bis(1-alkenyl)platinum(II) complexes have been carried out. The structure of cis-[Pt(dppp)((CH 2 ) 6 CH@CH 2 ) 2 ] has been determined by X-ray crystallography. The stability and reactivity of the compounds, cis-[PtL 2 ((CH 2 ) n CH@CH 2 ) 2 ] (n = 3 or 4 and L 2 = 1,3-bis(diphenylphosphino)propane (dppp), 1,2-bis(diphenylphosphino)ethane (dppe), L = PPh 3 ) is strongly dependent on the nature of ligand systems. It is found that the insertion of carbon monoxide into the metal-carbon bonds of the platinum alkenyl complexes is possible. Other reactions including transmetalation, intermolecular alkenyl migrations, oxidative addition of methyl iodide are described and the thermal decomposition of the bis(alkenyl) complexes are also reported.

A new route for the high yield synthesis of platinum containing mixed bimetallic carbonyl clusters of the type [PtRu 2 (CO) 8 L 2 ] (where L 2 = dppe, 1,2-bis(diphenylphosphino)ethane or dppp, 1,3-bis(diphenylphosphino)propane; L = PPh 3 ) by the reaction of platinum-alkenyl [PtL 2 (1-alkenyl) 2 ] precursors with [Ru 3 (CO) 12 ] is reported. An unexpected multinuclear mixed cluster, [PtRu 4 (CO) 13 (l 4 -PCH 2 CH 2 CH 2 PPh 2 )], obtained under prolonged refluxing conditions was also isolated. All the products were isolated and characterized by various spectroscopic and analytical techniques. In solution, the complex [PtRu 2 (CO) 8 (P Ph 3 ) 2 ] gives [Pt 2 Ru(-CO) 3 (CO) 2 (PPh 3 ) 3 ] and Ru 3 (CO) 11 (PPh 3 ). The structures and relative energies of the intermediates and transition states in the proposed reaction mechanism for the {PtRu 2 } clusters have been investigated using density functional theory.