Oligomerization of ethylene to branched alkenes using neutral phosphinosulfonamide nickel(ll) complexes

A series of neutral phosphinosulfonamide complexes of nickel(II) were synth esized that catalyzed the oligomerization of ethylene to branched oligomers with average degrees of polymerization between 10 and 35. Branching number s varied from 17 to 80 branches per 1000 carbons, depending on the catalyst structure and reaction conditions. The catalysts were active in a variety of solvents, including toluene, CH2Cl2, tetrahydrofuran, ethyl acetate, and methanol, but showed decreasing activity at temperatures higher than 40 de greesC. Electron-rich phosphinosulfonamides produced the highest catalyst a ctivities in a series of structure-reactivity studies. The mechanism of oli gomer formation was investigated with H-1 NMR spectroscopy, which indicated that branching arose from the isomerization of the nickel alkyl species du ring propagation rather than the reincorporation of alpha -olefin products. (C) 2000 John Wiley & Sons, Inc.