PSP-coordinated nickel(II) complexes as Kumada coupling catalysts

Phosphine-coordinated nickel complexes are well-known catalysts in Kumada-Tamao-Corriu coupling reactions. In this context, often PCP-type phosphines (R2P(C2H4)PR2 or R2P(C3H6)PR2) have been studied, while sulphur-containing analogues, such as PSP-type ligands (R2PSPR2), have been largely overlooked. In this work we present the synthesis of PSP-based nickel complexes of the form [NiHal2(PSP)], PSP = Ph2PSPh2, Hal = Br (1), I (2) via a facile one-pot reaction of the free ligand and the respective nickel halides. Attempts to synthesise the Cl analogue results in the formation of a multinuclear nickel complex, such as [Ni2(Ph2PSS)2(Ph2PS)(Ph2P)], in which Ph2PSS–, Ph2PS– and Ph2P– ligands coordinate to the Ni-centres, which were found to form via ligand rearrangement processes of the parent PSP ligand. Complexes 1 and 2 were used as catalysts in Kumada coupling reactions and revealed a great potential for the coupling of sterically demanding substrates, whereby no sulphur poisoning induced by the ligand backbone could be identified.