Dillip Kumar Chand

New multinuclear discrete heteroleptic complexes have been synthesized by mixing Pd(II), 2,2′-bipyridine and N,N′-(1,2-phenylene) diisonicotinamide in a single pot as a new approach. A dimeric molecular rhombus and a trimer in equilibrium are obtained where the dimer is the major product. Similar equilibrium is also observed when classical method is employed for the synthesis. The equilibrium is shifted exclusively in favour of the dimer upon addition of benzene. The complexes are characterized by NMR and ESI-MS methods. Crystal structure of the benzene encapsulated rhombus is presented. © 2010 Elsevier Ltd.

This work reports a facile synthesis of palladium nanoclusters (PdNCs) in MeCN/MeOH mixture without any stabilizer. The PdNCs were found to be effective catalysts for copper-free, amine-free and ligand-free Songashira coupling reactions under ambient conditions. © 2008 Elsevier Ltd. All rights reserved.

A series of self-assembled "double saddle"-type trinuclear complexes of [Pd3L′3L3] formulation have been synthesized by complexation of a series of cis-protected palladium(II) components with a slightly divergent "Eshaped" non-chelating tridentate ligand, 1,1′-(pyridine-3,5-diyl)bis(3-(pyridin-3-yl)urea (L). The cis-protecting agents L′ employed in the study are ethylenediamine (en), tetramethylethylenediamine (tmeda), 2,2′-bipyridine (bpy), and 1,10-phenanthroline (phen), for 1, 2, 3, and 4, respectively. The crystal structures of [Pd3(tmeda)3(L)2](NO3)6 (2), [Pd3(bpy)3(L)3](NO3)3 (3), and [Pd3(phen)3(L)2](NO3 )6 (4) unequivocally support the new architecture. Two of the "double saddle"-type complexes (3 and 4) are suitably crafted with p surfaces at the strategically located cis-protecting sites to facilitate intermolecular p-p interactions in the solid state. As a consequence, six units of the 3 (or 4 ) are assembled, by means of six-pairs of p-p stacking interactions, in a circular geometry to form an octadecanuclear molecular ring of [(Pd3L′3L3)3] composition. The overall arrangement of the rings in the crystal packing is equated with the traditional Indian art form rangoli.

Bis(pyridin-3-ylmethyl) pyridine-3,5-dicarboxylate (L) possessing one internal and two terminal pyridine moieties displayed differential coordination ability when combined with suitable PdIIcomponents. The compound L acted as a bidentate chelating ligand to form mononuclear complexes when combined with cis-[Pd(tmeda)(NO3)2] or Pd(NO3)2in calculated ratios. The combination of Pd(NO3)2with L in a ratio of 3:4, however, afforded the trinuclear “double-decker” cage [(NO3)2⊂Pd3(L)4](NO3)4, in which L acts as a nonchelating tridentate ligand and the counter anion (i.e., NO3–) acts as template. The encapsulated NO3–can be replaced by F–, Cl–, or Br–but not by I–. The F–-encapsulated cage could not be isolated due to its reactivity, whereas the Cl–or Br–encapsulated cages could be isolated. Although anionic guests such as NO3–, Cl–, or Br–stabilized the cages, the presence of excess Cl–or Br–(not NO3–) facilitated decomplexation reactions releasing the ligand. The complexation of Pd(Y)2(Y = BF4–, PF6–, CF3SO3–, or ClO4–) with L afforded the corresponding mononuclear complexes under appropriate conditions. However, these counter anions could not act as templates for the construction of double-decker cages.

An interesting phenomenon of ligand exchange is observed in the DMSO solution of certain self-assembled molecules generated from cis-protected PdII and organic ligands. Upon heating, assemblies such as [{Pd(en)}x(ligand)y](NO3)2x change to [Pdm(ligand)n](NO3)2m and [Pd(en)2](NO3)2. The change is also possible at room temperature when 0.5 equiv. Pd(en)(NO3)2 is added in excess to the system. The transformation is incomplete when the ligand moiety is monodentate in nature, for example in the case of 4-phenylpyridine. However, multinuclear assemblies containing nonchelating, polydentate ligands used in this study entirely favor the transformation. This process is not possible with some related PtII compounds. © Wiley-VCH Verlag GmbH & Co. KGaA, 2005.

A different approach developed for the preparation of palladium(II) based complexes [(Pd(bpy))x(L)y](NO3) 2x is modelled by using 4-phenylpyridine as ligand (L = 1). Various solvent systems are inspected to optimize the reaction condition for the preparation of the model complex [Pd(bpy)(4-phenylpyridine) 2](NO3)2. The model complex is obtained quantitatively as a single product from a 1:1:2 mixture of Pd(NO 3)2, 2,2′-bipyridine and 4-phenylpyridine when stirred at room temperature in CH3CN:H2O (1:1). The same reaction is performed in CD3CN:D2O (1:1) to monitor the progress of the reaction by recording 1H NMR. The kinetic products that formed initially got self-healed to give the desired product with in 6 h. However, in DMSO-d6 spontaneous arrangement leading to the targeted complex was observed and no kinetic product could be detected. When a similar reaction is performed with ethylenediamine instead of 2,2′-bipyridine a mixture of compounds are observed. Theoretical calculation throws some light on the principle behind the success of this method for the bpy based systems. The assembly, [Pd(bpy)(4-phenylpyridine)2](NO3)2 has been characterised by NMR, ESI-MS and single-crystal X-ray diffraction methods. © 2011 Elsevier B.V. All rights reserved.

The pyridine-appended non-chelating bidentate ligands 1,4-bis(3-pyridyl) benzene (1) and 4,4′-bis(3-pyridyl) biphenyl (2) were complexed with a naked PdII ion for the construction of molecular cage compounds. Prior to these experiments, the complexation of the ligands with cis-[Pd(en)(NO3)2] was also examined, because self-assemblies from the cis-protected PdII ion were expected to be simple motifs that constitute the assemblies from naked PdII ion. The structures of the self-assembled compounds resulting from 1 and [Pd(en)(NO 3)2] depended on the solvent employed. In aqueous solution, an M2L2 trenchlike compound was obtained. In dimethyl sulfoxide, however, a mixture of the M2L2 trench and an M3L3 macrocycle was found in equilibrium, the dynamic nature of which was confirmed by the concentration-dependent nature of the species. At higher concentration, an M4L4 macrocycle was mostly observed. The complexation of 1 with naked PdII ions was expected to produce novel structures that are combinations of the M nLn type frameworks. A peculiar tetrahedral M 4L8 assembly was obtained quantitatively from 1 and Pd(NO3)2, rather than the smallest possible M 3L6 double-walled triangle. Interestingly, the use of Pd(CF3SO3)2 resulted in the sole formation of the latter structure. Thus, the anion is important as a template in the formation of these assemblies. Ligand 2, which contains an extra p-phenylene unit compared to 1, behaved in a similar manner when treated with [Pd(en)(NO3)2], but showed subtle differences with naked PdII ions. With Pd(NO3)2, 2 gave mostly a tetrahedron along with a double-walled triangle. With Pd(CF3SO 3)2, this longer ligand formed a double-walled triangle with a negligible amount of tetrahedra. A single discrete assembly of a perfect tetrahedron was obtained from 2 and PdII ions by choosing p-tosylate as a counterion. © 2006 Wiley-VCH Verlag GmbH & Co. KGaA.

The complexation study of cis-protected and bare palladium(II) components with a new tridentate ligand, i.e., pyridine-3,5-diylbis(methylene) dinicotinate (L1) is the focus of this work. Complexation of cis-Pd(tmeda)(NO3)2 with L1 at a 1:1 or 3:2 ratio produced [Pd(tmeda)(L1)](NO3)2 (1a). The reaction mixture obtained at 3:2 ratio upon prolonged heating, produced a small amount of [Pd3(tmeda)3(L1)2](NO3)6 (2a). Complexation of Pd(NO3)2 with L1 at a 1:2 or 3:4 ratios afforded [Pd(L1)2](NO3)2 (3a) and [(NO3)2@Pd3(L1)4](NO3)4 (4a), respectively. The encapsulated NO3- ions of 4a undergo anion exchange with halides (F-, Cl- and Br- but not with I-) to form [(X)2@Pd3(L1)4](NO3)4 5a-7a. The coordination behaviour of ligand L1 and some dynamic properties of these complexes are compared with a set of known complexes prepared using the regioisomeric ligand bis(pyridin-3-ylmethyl)pyridine-3,5-dicarboxylate (L2). Importantly, a ligand isomerism phenomenon is claimed by considering complexes prepared from L1 and L2.

The meta-pyridine appended bidentate ligands L1, L2 and L3, crafted with flexible polyether spacer, are prepared by condensation of nicotinoyl chloride hydrochloride with di, tri-, and tetra-ethylene glycol, respectively. Self-assembled palladium(II) based mononuclear molecular loops of general formula cis-[Pd(N-N)(L)](NO 3)2 are obtained exclusively by combining 1 equiv. of a ligand L with 1 equiv. of a cis-protected palladium(II) component, cis-[Pd(N-N)(NO3)2]. Complexation of 2 equiv. of L with 1 equiv. of palladium(II) nitrate also resulted mononuclear complexes, i.e. [Pd(L)2](NO3)2. The ligands used in the complexation reactions are L1, L2 and L3 where as the cis-protecting units N-N employed are ethylenediamine (en), 2,2′-bipyridine (bpy), and 1,10-phenanthroline (phen). Thus 12 number of mononuclear complexes are prepared using all possible combination of above mentioned three number of ligands and four variety of palladium(II) components. Large chelate rings are realized irrespective of the spacer length or type of palladium(II) component used. All the resulted compounds are characterized by NMR and ESI-MS techniques and the structure of cis-[Pd(en)(L1)] (NO3)2, cis-[Pd(bpy)(L1)](NO3) 2 and [Pd(L3)2](NO3)2 are confirmed by single crystal X-ray diffraction. The binding abilities of cis-[Pd(phen)(L1)](NO3)2, cis-[Pd(phen)(L 2)](NO3)2 and cis-[Pd(phen)(L 3)](NO3)2 with DNA has been investigated by ethidium bromide displacement assay and gel electrophoresis. © 2013 Elsevier B.V. All rights reserved.