Synthesis, characterization and coordination properties of bis(alkyl)selenosalen ligands

Abstract

New bis (alkyl) selenosalen podand ligands having Se2N2 donor sites have been synthesized by the condensation of unsymmetrical o-formylphenyl alkyl selenide (1–3) with ethylenediamine. The reaction of bis(alkyl)selenosalen podands with Pd(II) and Pt(II) afforded selenoether-selenolate coordination complexes 7–10via cleavage of one of the two Se–C(alkyl) bonds of bis(alkyl)selenosalen podands upon complexation. DFT calculations revealed that the cleavage of Se–C(alkyl) bonds occurred possibly viaS_N2 mechanism instead of a sequence of oxidative addition and reductive elimination reactions. The spectral data and elemental analyses confirmed the formation of selenoether-selenolate complexes. The structures of the podands N,N′-bis[(2-methylseleno)phenylmethylene]-1,2-ethanediamine (4), N,N′-bis[(2-decylseleno)phenylmethylene]-1,2-ethanediamine (5) and the selenoether-selenolate complex 8 have been determined by single crystal X-ray diffraction analysis. The crystal structure of 5 showed Se⋯H interaction with a ladder like 3D supramolecular arrangement via interdigitation of long alkyl chains. Comparison of crystal packing of podands 4 and 5 indicates that the alkyl chain length has significant impact on the crystal packing. The platinum selenolate complex 8 shows a square planar arrangement around the Pt centre, where the Se atoms in the selenolate and the selenoether have nearly equal Pt–Se bond length.