First heterodifunctional ligand derived from a tetradentate phosphine: synthesis and characterization of cis,trans,cis-1,3-bis(diphenylphosphino)-2,4-bis(diphenylphosphinothioyl)cyclobutane and its complex with PdCl2

Cis,trans,cis-1,2,3,4-tetrakis(diphenylphosphino)cyclobutane (dppcb) can be selectively oxidized by S in toluene to the disulfide cis,trans,cis-1,3-bis(diphenylphosphino)-2,4-bis(diphenylphosphinothioyl)cyclobutane (dppcbS2). DppcbS2 is the first heterodifunctional ligand derived from a tetradentate phosphine obtained with good yield and high purity. It reacts with two equivalents of PdCl2 producing [Pd2Cl4(dppcbS2)] (1). Both dppcbS2 and 1 have been fully characterized by X-ray structure analyses, NMR spectroscopy (31P{1H}, 13C{1H}, 1H), FAB mass spectrometry, elemental analyses and melting points. The possible catalytic applications of the versatile heterodifunctional ligand dppcbS2 are discussed in view of the two X-ray structures of dppcbS2 and 1.