Piyali Paul

Unusual chemical transformations of acetone thiosemicarbazone mediated by ruthenium: C–H bond activation, thiolation, and C–N bond cleavage

Upon reaction with Ru(PPh3)3Cl2 in ethanol in the presence of triethylamine, acetone thiosemicarbazone undergoes several interesting chemical transformations, such as thiolation via methyl C–H bond activation, C–N bond cleavage, and conversion of the CS fragment to CO. Two complexes (1 and 2) were obtained from this reaction, both of which contained a modified thiosemicarbazone coordinated in SNS- or SNO-mode, two triphenylphosphines and a N-bound thiocyanate. The crystal structures of both the complexes have been determined. Theoretical and mass spectral studies have been carried out to probe the transformations. These complexes show intense absorptions in the visible and ultraviolet regions. Cyclic voltammetry on both the complexes show a reversible oxidation near 0.6 V vs. SCE, followed by an irreversible oxidation near 1.2 V vs. SCE. DFT calculations have been carried out to explain the electronic spectra, as well as the electrochemical observations.

Organometallic complexes of the platinum metals: Synthesis, structure, and catalytic applications

AbstractReaction of a group of N-(aryl)picolinamides (pic-R) with [Ru(PPh3)2(CO)2Cl2] in refluxing 2-methoxyethanol in the presence of a base affords hydrido complexes of two types (1-R and 2-R), which are geometric isomers. Similar reaction with N-(naphthyl)picolinamide (pic-nap) yields an organoruthenium complex (3) via formation of a hydrido intermediate. Reaction of 2-(arylazo)phenols (ap-R) with [Ir(PPh3)3Cl] in refluxing ethanol affords a mono-hydrido intermediate (4-R), a di-hydrido intermediate (5-R) and an organoiridium complex (6-R) as the final product, where the azo-ligand is coordinated as CNO-donor. Reaction of ap-R ligands with [Rh(PPh3)3Cl] yields organorhodium complexes (7-R) analogous to 6-R, but without any hydrido intermediate. N-(2′-hydroxyphenyl)benzaldimines (hpbz-R) react with [Rh(PPh3)3Cl] to yield a group of organorhodium complexes (8-R), where the hpbz-R ligands are coordinated in CNO-fashion. Upon interaction with [Ir(PPh3)3Cl] 2-(2′,6′-dimethylphenylazo)-4-methylphenol (dmap) undergoes a methyl C–H activation and affords organoiridium complex 9, while 2-(2′-methylphenylazo)-4-methylphenol (mmap) undergoes a phenyl C–H activation and gives organoiridium complex 10. Reaction of benzaldehyde thiosemicarbazones (bztsc-R) with [Pd(PPh3)2Cl2], carried out with the expectation of inducing CNS-mode of coordination, actually has yielded complexes (11-R) where the bztsc-R is coordinated in an uncommon NS-mode forming a five-membered chelate ring associated with a restricted rotation around the imine (C=N) bond. These palladium complexes are found to catalyse C–C cross coupling reactions very efficiently. Crystal structures of selected complexes of each type have been determined by X-ray crystallography. Graphical AbstractIf an alkyl or aryl C–H bond of a judiciously chosen ligand is brought in close proximity to a platinum metal-bound hydride or chloride by coordination through regular donor atoms (as in I), then facile activation of that C–H bond takes place leading to the formation of cyclometallated species (II).

Palladium complexes of pyrrole-2-aldehyde thiosemicarbazone: Synthesis, structure and spectral properties

AbstractReaction of pyrrole-2-aldehyde thiosemicarbazone (abbreviated as H2L, where H2 stands for the two potentially dissociable protons) with [Pd(PPh3)2Cl2] in ethanol in the presence of NEt3 afforded two complexes, [Pd(PPh3)(HLNS)Cl] and [Pd(PPh3)(LNNS)], where the thiosemicarbazone ligand is coordinated to the metal centre respectively as monoanionic N,S-donor (depicted by HLNS) and dianionic N,N,S-donor (depicted by LNNS). Similar reaction with Na2[PdCl4] afforded a bis-complex, [Pd(HLNS)2]. Crystal structures of all the three complexes have been determined. With reference to the structure of the uncoordinated thiosemicarbazone (H2L), the N,S-coordination mode observed in [Pd(PPh3)(HLNS)Cl] and [Pd(HLNS)2] is associated with a geometrical change around the imine bond. While the N,N,S-mode of binding observed in [Pd(PPh3)(LNNS)] takes place without any such geometrical change. All three complexes display intense absorptions in the visible and ultraviolet regions, which have been analyzed by TDDFT method. Graphical AbstractReaction of pyrrole-2-aldehyde thiosemicarbazone (H2L) with [Pd(PPh3)2Cl2] in ethanol afforded the [Pd(PPh3)(HLNS)Cl] and [Pd(PPh3)(LNNS)] complexes, and similar reaction with Na2[PdCl4] afforded the [Pd(HLNS)2] complex.