Mechanistic Studies of Ethylene and alpha-Olefin Co-Oligomerization Catalyzed by Chromium-PNP Complexes

作者：Do Loi H; Labinger Jay A^*; Bercaw John E

来源：Organometallics, 2012, 31(14): 5143-5149.

DOI：10.1021/om300492r

To explore the possibility of producing a narrow distribution of mid- to long-chain hydrocarbons from ethylene as a chemical feedstock, co-oligomerization of ethylene and linear alpha-olefins (LAOs) was investigated, using a previously reported chromium complex, [CrCl3(PNPOMe)] (1, where PNPOMe = N,N-bis(bis(o-methoxyphenyl)phosphino)methylamine). Activation of 1 by treatment with modified methylaluminoxane (MMAO) in the presence of ethylene and 1-hexene afforded mostly C-6 and C-10 alkene products. The identities of the C-10 isomers, assigned by detailed gas chromatographic and mass spectrometric analyses, strongly support a mechanism that involves five- and seven-membered metallacyclic intermediates comprised of ethylene and LAO units. Using 1-heptene as a mechanistic probe, it was established that 1-hexene formation from ethylene is competitive with formation of ethylene/LAO cotrimers and that cotrimers derived from one ethylene and two LAO molecules are also generated. Complex 1/MMAO is also capable of converting 1-hexene to C-12 dimers and C-18 trimers, albeit with poor efficiency. The mechanistic implications of these studies are discussed and compared to previous reports of olefin cotrimerization.

• 出版日期2012-7-23