Tetradentate selenium ligand as a building block for homodinuclear complexes of Pd(ii) and Ru(ii) having seven membered rings or bis-pincer coordination mode: high catalytic activity of Pd-complexes for Heck reaction

Abstract

1,2,4,5-Tetrakis(phenyselenomethyl)benzene (L) has been synthesized by reaction of in situ generated PhSe(-) with 1,2,4,5-tetrakis(bromomethyl)benzene in N(2) atmosphere. Its first bimetallic complexes and a bis-pincer complex having compositions [(η(3)-C(3)H(5))(2)Pd(2)(L)][ClO(4)](2) (1) [Pd(2)(C(5)H(5)N)(2)(L)][BF(4)](2) (2) and [(η(6)-C(6)H(6))(2)Ru(2)(L)Cl(2)][PF(6)](2) (3) have been synthesized by reacting L with [Pd(η(3)-C(3)H(5))Cl](2), [Pd(CH(3)CN)(4)][BF(4)](2) and [(η(6)-C(6)H(6))(2)RuCl(2)](2) respectively. The structures of ligand L and its all three complexes have been determined by X-ray crystallography. In 1 and 3, ligand L forms with two organometallic species seven membered chelate rings whereas in 2 it ligates in a bis-pincer coordination mode. The geometry around Pd in 1 or 2 is close to square planar whereas in 3, Ru has pseudo-octahedral half sandwich "Piano-Stool" geometry. The Pd-Se bond distances are in the ranges 2.4004(9)-2.4627(14) Å and follow the order 1 > 2, whereas Ru-Se bond lengths are between 2.4945(16) and 2.5157(17) Å. The 1 and 2 have been found efficient catalysts for Heck reaction of aryl halides with styrene and methyl acrylate. The 2 is superior to 1. The TON and TOF values (per Pd) are up to ~47500 and ~2639 h(-1) respectively.

Synthesis of Unsymmetrical Diorganyl Chalcogenides under Greener Conditions: Use of an Iodine/DMSO System, Solvent‐ and Metal‐Free Approach

“…Unsymmetrical organochalcogenides (S, Se, and Te) have become an attractive synthetic target in the past few decades and they have been extensively reported in various research articles,1 reviews2 and books 3. In recent years these compounds have been employed in certain reactions4 as catalysts,5a,b ligands,5c ionic liquids6 and synthetic intermediates in total synthesis2,3,7 besides being applied in asymmetric catalysis 4a. Moreover, synthetic organochalcogen compounds have been found to function as antioxidant, anticancer, antihypertensive and antiviral agents 2d,e,3,8.…”

A cyclodiphosphazane based pincer ligand, [2,6-{μ-(tBuN)2P(tBuHN)PO}2C6H3I]: NiII, PdII, PtII and CuI complexes and catalytic studies

“…[7][8][9] The pincer skeleton generally consists of two mutually trans chelating neutral donor groups and a central aromatic backbone. The neutral donors are typically phosphines (PR 2 ), 7,8,10 arsines, 11 amines (NR 2 ), 8,[12][13][14][15] thioethers (SR), 13,[16][17][18][19][20] selenoethers (SeR) 21 and N-heterocyclic carbenes (NHCs) [22][23][24] or a pair of donor groups among these functionalities. 18,25,26 The pincer complexes of phosphorus donor ligands have been studied extensively.…”

Organochalcogen ligands and their palladium(ii) complexes: Synthesis to catalytic activity for Heck coupling

“…62 The synthesis of symmetric selenium containing pincer ligands viz (Se,C,Se) pincer/bis-pincer and (Se,N,Se) pincer involves the route of selenylation 30 of an appropriate organic halo com-pound with diphenyl diselenide under reductive conditions (Scheme 6). 30,63,64 The ditopic pincer ligand L18, which is also macrocyclic in nature and suitable to design a double ditopic pincer-palladium complex, has been prepared by methodology summarized in Scheme 7. 65 In this case Lawesson's reagent is used to incorporate the sulphur donor into the ligand.…”

“…119 The effect of the palladium precursor on the coordination mode of the ligand and the type of resulting complex has been observed in the case of 1,2,4,5-tetrakis(phenylselenomethyl)-benzene (L17), which forms a non-palladacyclic complex 80 with two seven membered chelate rings on reaction with [Pd(g 3 -C 3 H 5 )(m-Cl)] 2 , and a bis-pincer palladium complex 12 on reaction with [Pd(CH 3 CN) 4 ][BF 4 ] 2 . 64 In the 77 Se{ 1 H} NMR spectrum of L17, a signal appears at 361.2 ppm. It shifts to higher frequency by y33 ppm on the formation of complex 80 and by y35 ppm on the formation of 12.…”