The effect of N-aryl bisphosphineamine ligands on the selective ethylene tetramerization

Abstract

Bisphosphineamine (PNP) ligands with various aryl substituents attached to the N atom of the ligand backbone were synthesized and tested together with Cr(acac) 3 as ethylene tetramerization catalysts. Activated by methylaluminoxane, the best ligand with 3,5-dimethylphenyl attached to N atom achieved selectivity as high as 86.13% (1-octene and 1-hexene) and catalytic activity up to 4.98 × 10 6 g/mol Cr h toward 1-octene. It was established that the increase of m-substitution steric bulk in the aryl skeleton led to a dramatic increase of catalytic activity. Interestingly, with the increase of steric bulk in the o-substitution of the aryl ring, the catalytic activity declined and the selectivity of the catalyst changed from predominant tetramerization to trimerization. It was concluded that fine tuning of the N-aryl moiety of the PNP ligand in molecular structure is essential for obtaining efficient catalysis of ethylene tetramerization.