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 [(R1SON)-N-2=P(R-2)(2)-P(R-3)(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(R-2)(2)]N(SO2R1)P(R-3)(2)}Br-2. The complexes can be isolated and are very stable. Upon activation by MAO, these complexes oligomerise ethylene to small chain oligomers (mainly C-4-C-8) with high productivity. Surprisingly fast codimerisation reactions of ethylene with butenes is observed, leading to a high content of branched C-6 products.