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

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 [(eta(3)-C3H5)(2)Pd-2(L)][ClO4](2) (1) [Pd-2(C5H5N)(2)(L)][BF4](2) (2) and [(eta(6)-C6H6)(2)Ru-2(L)Cl-2][PF6](2) (3) have been synthesized by reacting L with [Pd(eta(3)-C3H5)Cl](2), [Pd(CH3CN)(4)][BF4](2) and [(eta(6)-C6H6)(2)RuCl2](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) angstrom and follow the order 1 > 2, whereas Ru-Se bond lengths are between 2.4945(16) and 2.5157(17) angstrom. 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 similar to 47500 and similar to 2639 h(-1) respectively.