Palladium(II) and platinum(II) complexes with aryl selenols and diaryl diselenides: A comparative approach with tellurium and sulfur analogues

Abstract

Sodium aryl selenols, NaSeAr (Ar = phenyl and p-anisyl), react with Na 2PdCl 4/K 2PtCl 4 in aqueous ethanol in 1:1 and 1:2 molar ratios to form polymeric complexes [MCl(SeAr)] n ( I) and [M(SeAr) 2] n ( II) (M = Pd or Pt) at room temperature. Chemical and far IR spectral evidences support alternating chloride and selenol bridges in I and only selenol bridges in II. Reactivity of Pd(II) complexes has been further investigated. While the reaction of I (M = Pd; Ar  Ph) with PPh 3 in stoichiometric amount results in splitting of chloride bridges and formation of a selenol bridged dimeric complex [PdCl(SePh)- (PPh 3)] 2 ( III), with excess of PPh 3 or with a stoichiometric amount of DPPE, simultaneous cleavage of both chloride and selenol bridges leads to the formation of monomeric compounds [PdCl(SeAr)(PPh 3) 2] ( IV) and [PdCl(SePh)(DPPE)] ( V). Complex II (M = Pd) also undergoes bridge splitting reactions with excess of PPh 3 to yield a monomeric compound [Pd(SeAr) 2(PPh 3) 2] ( VI). Complex IV and VI could also be prepared from the reactions between Pd- (PPh 3) 2Cl 2 and NaSeAr in alcohol at room temperature. The reaction of diaryl diselenides, Ar 2Se 2, with Pd(PhCN) 2Cl 2 in benzene or with Na 2PdCl 4 in alcohol affords a dimeric complex [PdCl 2(Se 2Ar 2)] 2 ( VII). No product could, however, be isolated by the reactions of Ar 2Se 2 (or Ph 2S 2) with PtCl 4 2−. The complex VII on refluxing with MeOH/EtOH undergoes cleavage of the SeSe bond to form polymeric complex I. However, the reaction of complex VII with PPh 3 liberated free diselenides. The characterization of all the complexes has been made on the basis of elemental analysis, IR and 1H NMR, conductivity and molecular weight measurements where possible.