Link between Isostructurality, Polymorphism, and Weak Interactions in Palladacycle Crystals: Chemical Insight

Abstract

The chemistry of organopalladium compounds is significant owing to the presence of the PdÀC bond and its utility in the organic synthesis. 1,2 The Pd(II)/Pd(0) oxidation state interchange is a well-known event in the catalytic studies of such compounds during organic synthesis. 3 Palladium(II) salts are known to form PdÀC bonds with bidentating azobenzenes (C, N) and tridentating thioazobenzenes (C, N, S), which are commonly referred to as palladacycles. 4,5 Such palladium complexes have been extensively studied for CÀH bond activation and ArÀPd f ArÀOÀPd transformations. 6,7 Organopalladium compounds are also known to act as effective diagnostic probes in metalloporphyrin catalyzed oxidation reactions. 7,8 In these studies it has been frequently observed that the substitution at the phenyl ring drastically alters the diagnostic properties of the palladacycles. In a few cases, the solvent also plays a significant role in the regioselective reactions on PdÀC bonds. 9,10 In order to ascertain the nature of these catalytically active molecules, we have attempted crystallization to isolate them as solids and subject them to unambiguous structural elucidation. We have reported the presence of two polymorphs in the case of chlorido-{4-chloro-1-[2-(methylsulfanyl)-phenyldiazenyl]phenyl-k 3 C,N, S}-palladium(II). 11,12 Crystal structure analysis of these two polymorphs suggests that competing CÀH 3 3 3 Cl synthons are probably responsible for its occurrence. It remains an interesting point to address how the substituent on the ligand affects the solution and solid state properties of the palladacycles. Hence, we have judiciously designed a synthetic protocol to crystallize several palladacycle based salts, [X{4-R-1-[2-(R 0 -sulfanyl)-phenyldiazenyl]phenyl-k 3 C,N,S}-palladium(II)] where R = H, Cl and Me, R 0 = Me and Et, and X = Cl, Br, I, NO 3 , and ClO 4 . The paper reports the synthesis, characterization and crystal packing analysis of all solids. We also investigate the directional characteristics of CÀH 3 3 3 X interactions in dictating isostructures and polymorphs in the reported series.' EXPERIMENTAL SECTION Synthesis. The chloride salts 1a, 2a, 3a, and 4a were synthesized according to reported methods. 5,13À15 In a typical synthesis, a 15 mL warm ethanolic solution (45 °C) of Na 2 PdCl 4 (∼250 mg, 0.85 mmol) was added dropwise to a 15 mL warm ethanolic solution of phenyl azothioether based tridentate ligand (∼185 mg, 0.81 mmol). After continuously stirring for one hour over a steam bath (∼90 °C), a residual powder and well separated shiny crystals appeared. The solid was filtered, washed with 25% ethanol in water, and dried in air. The total yields of the solids were in the range of 90À95% with respect to the initial ligand.A modified methodology was adopted for the synthesis of the bromide salts (1b, 2b, 3b, and 4b) and the iodide salts (1c, 2c, 3c, and 4c). In a typical synthesis, the chloride salt (∼100 mg, 0.27 mmol) was dissolved in 60À70 mL CH 3 CN and a slight excess of solid

Halogen bonds in some dihalogenated phenols: applications to crystal engineering

“…Although Cl/CH 3 isostructurality has been thoroughly studied over the years (Jones et al, 1983;, and more recently with the CSD (Jones et al, 1983;Edwards et al, 2001Edwards et al, , 2006Polito et al, 2008;Braga et al, 2009;Singh et al, 2011;Nath & Nangia, 2012), Cl/Br isostructurality has not been well studied. It has been noted that Cl/Br isostructurality could arise when the ClÁ Á ÁCl (or BrÁ Á ÁBr) contact is important in the respective structures (Pedireddi et al, 1992).…”

Isomeric and Isostructural Oligothienylsilanes–Structurally Similar, Physicochemically Different: The Effect of Interplay between C–H···C(π), S···C(π), and Chalcogen S···S Interactions

“…While polymorphism implies the ability of the compound to self-assemble into multiple crystal structures, the isostructurality refers to the similarity of the molecular arrangement in the crystal of different compounds. Much research in these areas focuses on systems that involve strong interactions such as metal–ligand coordination bonds and hydrogen-bond interactions; − however, in the past two decades a significant body of work was undertaken to study more subtle effects resulting from weak solid-state interactions such as π···π stacking and weak hydrogen bonds. − A lot of attention also has been paid to halogen interactions. − For instance, structurally equivalent halogen-bonded iodine and bromine atoms have been explored as a tool to construct isostructural co-crystals. − The formation of halogen bonds has been rationalized using a σ-hole concept consistent with the anisotropical charge density distribution within the halogen atomic basin. − As a consequence, electrophilic and nucleophilic regions can simultaneously be involved in highly directional halogen bond interactions. More recently, this concept has been expanded to the Main Group VI elements in order to rationalize frequently occurring chalcogen Chal1···Chal2 interactions. − Their role in crystal engineering, − molecular recognition, , biological systems, − and materials scien...…”

Dual Catalysis with an IrIII–AuI Heterodimetallic Complex: Reduction of Nitroarenes by Transfer Hydrogenation using Primary Alcohols

“…Two molecules in an anti disposition show hydrogen‐bonding interactions between one chloride and one methyl group of the ligand (Figure 5). In general, these types of chloride–hydrogen interactions are not very strong, but in this case the distance ClC methyl of 3.52 Å is significantly shorter 21. We did not find any Au I –Au I interaction contact as observed for compound 7 .…”

“…In general, these types of chloride-hydrogen interactions are not very strong, but in this case the distance ClÀC methyl of 3.52 is significantly shorter. [21] We did not find any Au I -Au I interaction contact as observed for compound 7.…”