Ethylene dimerization and oligomerization is catalyzed in homogenous processes using bis(phosphino)boryl ligated Ni(II) complexes as catalyst precursors. Using Lewis acid additives, Ni(II) complexes of the type (RPBP)NiBr (R = tBu or Ph) show activity for the production of butenes and higher olefins. Catalyst activity and selectivity varies as a function of the RPBP ligand. Optimized turnover frequencies of 640 molethylene-molNi−1-s−1 for the formation of butenes, using (PhPBP)NiBr, and 68 molethylene-molNi−1-s−1 for butenes production, using (tBuPBP)NiBr, have been demonstrated. With methylaluminoxane as co-catalyst and (tBuPBP)NiBr as the precatalyst, ethylene oligomerization to form C4 through C20 products was achieved. In contrast, using (PhPBP)NiBr as the pre-catalyst shows selectivity for C4 products. Combined experimental and computational studies indicate that the ethylene dimerization is not initiated by Ni hydride or alkyl intermediates. Rather, our studies point to a mechanism that involves a cooperative B/Ni activation of ethylene to form a 6-membered borametallacycle intermediate. Thus, a cooperative activation of ethylene by the Ni–B unit of the (RPBP)Ni catalysts is proposed as a key element of the Ni catalysis.

Ethylene dimerization and oligomerization using bis(phosphino)boryl supported Ni complexes as homogeneous catalysts

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