A new access to palladium–phosphine chemistry. Formation of polynuclear palladium compounds via the oxidation of ligands in simple palladium(II) complexes

Abstract

The reactions of [Pd(dppp)(edt)] 1 or [Pd(dppp)(pdt)] 2 (edt²⁻ = ethane-1,2-dithiolate, pdt²⁻ = propane-1,3-dithiolate, dppp = 1,3-bis(diphenylphosphino)propane) with oxygen or elemental Se under different reaction conditions gave rise to a series of polynuclear palladium complexes. The oxidation of 1 by oxygen in alkaline DMF solution yielded a dinuclear complex with sulfinato ligand, [Pd₂(O₂SCH₂CH₂SO₂)(edt)(dppp)] 3, while that of 2 afforded a hexanuclear complex, [Pd₆(pdt)₆] 4. The molecular structure of 3 consists of two fragments [Pd(O₂SCH₂CH₂SO₂)] and [Pd(dppp)]²⁺, which are linked by an edt²⁻ bridging ligand. The structure of 4 is made up of [Pd(pdt)] units forming a cyclic neutral complex, of which the Pd₆S₁₂ core possesses pseudo D_6d symmetry and six Pd atoms form a nearly regular six-membered ring with Pd⋯Pd distances ranging from 3.050 to 3.090 Å. The treatment of 2 with elemental Se in the ratios 2∶1 and 1∶1 generated [Pd₂(dppp)₂(pdt)]Cl₂5 and [Pd₃(dppp)₂(pdt)₂]Cl₂6, respectively. The molecular structure of 5 and 6 can be considered as two fragments [Pd(dppp)]²⁺ linked by pdt²⁻ and [Pd(pdt)₂]²⁻, respectively. The reaction of 1 with 0.5 equivalent Se led to formation of [Pd₂(dppp)₂(edt)]Cl₂7. The molecular structure of 7 is quite similar to that of 5. All palladium atoms in the complexes are four-co-ordinated with distorted square-planar geometry. The complexes 1, 3–7 have been characterized by NMR, IR and electronic spectra.