Palladium(II) benzisothiazolinate (bit) complexes with amino-, acetylamino-, heterocyclic and phosphine co-ligands. Crystal structure of [Pd(bit)2(κ2-dppe)]·2EtOH

Abstract

A series of square-planar palladium(II) benzisothiazolinate (bit) of the general type [Pd(bit)2L2] have been prepared and characterized by analytical and spectroscopic methods. Two synthetic routes have been employed, namely reactions of [Pd(bit)2]·H2O with two equivalents of ligands (L=amine, amide, phosphine) or nucleophile displacement of chloride by benzisothiazolinate starting from trans-[PdCl2L2]. Both routes afford the new complexes in good yields as easily isolated, air and moisture stable, colored solids. The precursor, [Pd(bit)2]·H2O, is itself prepared in high yields upon reaction of Na[bit] with Na2[PdCl4] in methanol and the analogous platinum complex, [Pt(bit)2]·H2O, is similarly prepared from K2[PtCl4]. It is not clear if these species are mono- or dimeric, and formulation as [M2(μ-bit)4(H2O)2] with the four benzisothiazolinate spanning the metal–metal vector and possibly binding through coordination of nitrogen and oxygen is suggested. Diphosphine adducts, cis-[Pd(bit)2{κ2-Ph2P(CH2)nPPh2}] (n=1–4) can be prepared both upon addition of the diphosphine to [Pd(bit)2]·H2O and from reactions of cis-[PdCl2{κ2-Ph2P(CH2)nPPh2}] with two equivalents of Na[bit]. A crystal structure of cis-[Pd(bit)2(κ2-dppe)] reveals that the benzisothiazolinate ligands are bonded in a monodentate fashion through nitrogen and this binding mode is proposed for all [Pd(bit)2L2] and [Pd(bit)2L] complexes. With dppb (n=4) a second product is seen by NMR spectroscopy being proposed to be the part-substituted complex cis-[PdCl(bit)(κ2-dppb)], while with dppm (n=1) two further products are seen spectroscopically, proposed as trans-[Pd(bit)2(κ1-dppm)2] and (more tenuously) [Pd2(bit)4(dppm)2]. The former is also prepared in good yields from reaction of [Pd(κ2-dppm)2]Cl2 with Na[bit]. These studies show that palladium benzisothiazolinate are easily accessed and show good air and moisture stability.