Palladium(II) complexes of bis(phosphine)monooxide and bis(phosphine)monosulphide ligands bearing o-N,N-dimethylanilinyl substituents

Abstract

Palladium(II) complexes of bis(phosphine)monooxide and bis(phosphine)monosulphide ligands with the general formula Ar2P(CH2)nP(E)Ar2 are described (n = 1 (dmapmE), E = O, S; n = 2 (dmapeE), E = O; Ar = o-N,N-dimethylanilinyl). The precursor, PdCl2(dmapm), which exists in solution as an equilibrium mixture of the P,P- and P,N-ligated isomers, reacts with peroxides to form PdCl2(P,N-dmapmO) and with sulphur to give [PdCl(P,N,S-dmapmS)]Cl, probably by direct oxidation of the "dangling" P atom of the P,N-isomer. PdCl2(dmape), which exists in solution as a mixture of PdCl2(P,P-dmape) and [PdCl(P,P,N-dmape)]Cl, reacts with hydroxide in H2O–CH2Cl2 under argon to give the face-to-face Pd(II)2 complex containing the cation [Pd2Cl2(µ-P,N:O-dmapeO)2]2+, which was isolated and crystallographically characterized as the PF6 salt. The remarkable structure, consisting of two face-to-face Pd(II) square planes in a head-to-tail orientation, reveals a 12-membered ring containing the two non-bonded metal centres (Pd—Pd = 4.873(2) Å). The dmapmS complex shows marginal activity as a catalyst for the hydration of maleic to malic acid.Key words: phosphine, phosphine oxide, phosphine sulphide, palladium.