Iminobisphosphines to (Non-)Symmetrical Diphosphinoamine Ligands: Metal-Induced Synthesis of Diphosphorus Nickel Complexes and Application in Ethylene Oligomerisation Reactions

We describe the synthesis of a range of novel iminobisphosphine ligands based on a sulfonamido moiety [R1SO2N=P(R2)2‐P(R3)2]. These molecules rearrange in the presence of nickel by metal‐induced breakage of the P–P bond to yield symmetrical and nonsymmetrical diphosphinoamine nickel complexes of general formula Ni{[P(R2)2]N(SO2R1)P(R3)2}Br2. The complexes can be isolated and are very stable. Upon activation by MAO, these complexes oligomerise ethylene to small chain oligomers (mainly C4–C8) with high productivity. Surprisingly fast codimerisation reactions of ethylene with butenes is observed, leading to a high content of branched C6 products. Alkyl‐substituted symmetrical and nonsymmetrical diphosphinoamine nickel complexes have been prepared by using sulfonamido‐based iminobisphosphines as ligand promoters. The complexes with basic substituents, activated by methylaluminoxane, oligomerise ethylene to short oligomers (C4–C8) with high activity. Fast codimerisation is observed, leading to highly branched C6 product distribution.