Raja Mitra

CUO NANOPARTICLES CATALYZED C-N, C-O, AND C-S CROSS-COUPLING REACTIONS: SCOPE AND MECHANISM

CuO nanoparticles have been studied for C-N, C-O, and C-S bond formations via cross-coupling reactions of nitrogen, oxygen, and sulfur nucleophiles with aryl halides. Amides, amines, imidazoles, phenols, alcohols and thiols undergo reactions with aryl iodides in the presence of a base such as KOH, Cs(2)CO(3), and K(2)CO(3) at moderate temperature. The procedure is simple, general, ligand-free, and efficient to afford the cross-coupled products in high yield.

Anticancer Activity of Hydrogen‐Bond‐Stabilized Half‐Sandwich RuII Complexes with Heterocycles

Neutral half-sandwich organometallic ruthenium(II) complexes of the type [(η(6)-cymene)RuCl(2)(L)] (H1-H10), where L represents a heterocyclic ligand, have been synthesized and characterized spectroscopically. The structures of five complexes were also established by single-crystal X-ray diffraction confirming a piano-stool geometry with η(6) coordination of the arene ligand. Hydrogen bonding between the N-H group of the heterocycle and a chlorine atom attached to Ru stabilizes the metal-ligand interaction. Complexes coordinated to a mercaptobenzothiazole framework (H1) or mercaptobenzoxazole (H6) showed high cytotoxicity against several cancer cells but not against normal cells. In vitro studies have shown that the inhibition of cancer cell growth involves primarily G1-phase arrest as well as the generation of reactive oxygen species (ROS). The complexes are found to bind DNA in a non-intercalative fashion and cause unwinding of plasmid DNA in a cell-free medium. Surprisingly, the cytotoxic complexes H1 and H6 differ in their interaction with DNA, as observed by biophysical studies, they either cause a biphasic melting of the DNA or the inhibition of topoisomerase IIα activity, respectively. Substitution of the aromatic ring of the heterocycle or adding a second hydrogen-bond donor on the heterocycle reduces the cytotoxicity.

Functional Mechanically Interlocked Molecules: Asymmetric Organocatalysis with a Catenated Bifunctional Brønsted Acid

Interlocked molecules, such as catenanes, rotaxanes, and molecular knots, have become interesting candidates for the development of sophisticated chemical catalysts. Herein, we report the first application of a catenane-based catalyst in asymmetric organocatalysis, revealing that the catenated catalyst shows dramatically increased stereoselectivities (up to 98 % ee) in comparison to its non-interlocked analogues. A mechanistic rationale for the observed differences was developed by DFT studies, suggesting that the involvement of two catalytically active groups in the stereodetermining reaction step is responsible for the superior selectivity of the interlocked catalyst.

Organonickel(IV) Chemistry: A New Catalyst?

With scorpionate ligands finding their way into organonickel chemistry, the state of the art of present-day nickel(IV) chemistry is highlighted. Will rapid CX coupling reactions emerge as a domain of higher-oxidation-state nickel chemistry?

Dual Brønsted-acid Organocatalysis: Cooperative Asymmetric Catalysis with Combined Phosphoric and Carboxylic Acids

How can an assisting Brønsted‐acid be beneficial in asymmetric Brønsted‐acid catalysis? In this Minireview, we discuss selected examples of chiral organocatalysts that feature two acidic groups working cooperatively by virtue of intra‐ or intermolecular hydrogen‐bonding. In these systems, the assisting Brønsted‐acid can play different roles, ranging from simple hydrogen‐bond donation, to substrate‐binding or even as a nucleophilic reaction partner. By analysis of combined experimental, structural and theoretical data, we aim at developing a better understanding of the reaction mechanisms, which are largely influenced by the underlying intramolecular‐ and intermolecular catalyst‐substrate interactions. This may aid in the future development of more selective dual Brønsted‐acid organocatalysts for specific asymmetric transformations.

Mitigating UVA light induced reactivity of 6-thioguanine through formation of a Ru(II) half-sandwich complex

The organometallic complex of (η6-cymene)Ru(II)Br with 6-thioguanine (6-TG) shows better photostability than the biologically active 6-thioguanine which is used as an immunosuppressant and as an anticancer agent.

9,9-Difluorobispidine Analogues of Cisplatin, Carboplatin, and Oxaliplatin

As part of a comprehensive study of N-unsubstituted bispidines, the novel 9,9-difluorobispidine (D) has been synthesized. The compound crystallizes from pentane below 0 °C in the ordered-crystalline phase D-II and undergoes at 0-30 °C a stepwise endothermic phase transition to a dynamically disordered crystalline phase D-I; melting occurs at 227 °C. Single crystalline D-II has been subjected to X-ray structure analysis, revealing association of the molecules to form chains. Reaction of (1,5-hexadiene)PtCl2 with D affords {C7H10F2(NH)2}PtCl2 (D1), which can be converted by conventional routes to {C7H10F2(NH)2}Pt(cbdca)·5H2O (D2) and {C7H10F2(NH)2}Pt(C2O4) (D3). Compound D1 crystallizes solvent-free from water and is isomorphous to the solvent-free parent bispidine analogue (A1). The pentahydrate D2 is isomorphous to the bispidine and 9-oxabispidine homologues (A2 and C2), as shown by X-ray structure analyses. An increased polarity of the bispidine skeleton as a consequence of the high electronegativity of fluorine is seen as the reason for low cytotoxic potency of D1-D3.