Chromium(III) complexes bearing 2-benzazole-1,10-phenanthrolines: synthesis, molecular structures and ethylene oligomerization and polymerization

Abstract

The 2-benzazole-1,10-phenanthrolines and their chromium(III) complexes were synthesized and characterized by elemental and spectroscopic analyses as well as by single-crystal X-ray crystallography. X-Ray crystallographic analyses of C6 and C8 reveal an octahedral geometry around both chromium centers. The electronic spectra of the chromium complexes exhibit d-d transitions typically of a pseudo-octahedral coordinated d(3) ion, falling into the region nu(1)(4)A(2g)-->(4)T(2g) 600-700 nm,nu(2)(4)A(2g)-->(4)T(1g)(F) 430-470 nm, and the 10Dq values between 15674 and 16529 cm(-1). The variation of the heteroatoms (X = N, O, S) in benzazole group shows regular influence on the 10Dq values as 10Dq (O) > 10Dq (N) > 10Dq (S), which reflects the sigma-donor/pi-acceptor properties of these benzazole ligands. Upon activation with modified methylaluminoxane (MMAO), these complexes exhibited high activities for ethylene oligomerization (up to 7.36 x 10(6) g mol(-1) (Cr) h(-1)) and ethylene polymerization (up to 1.28 x 10(6) g mol(-1) (Cr) h(-1)). The effects of non-coordinated N, O or S heteroatoms in the ligands have been examined, and interestingly catalytic activities also strictly adhered to the trend O > N > S under various ethylene pressures. Reaction conditions significantly influenced the catalytic properties of the complexes.

Oligomerization of Olefins

“…Chart 5.3 summarizes the complex with the tridentate ligand, 3a [64], 3b [65], 3c [66], 3d [67][68][69], and 3e [70] (Table 5.1 run 24). Most of the complexes afford oligomers with SchulzFlory distribution.…”

Ethylene tetramerization with a highly active and long-lifetime trinuclear diphenylphosphinoamine/Cr(III)/MAO catalyst

“…The ligand 1 was prepared according to a published procedure [9]. Cis,cis-1,3,5-cyclohexanetricarboxylic acid, diphenylphosphoryl azide(DPPA) and Cr(acac) 3 were purchased from Sigma-Aldrich(Pennsylvania, USA) and used as received. Polymerization grade ethylene was obtained from Daqing Petro-Chemical Ltd. (Daqing, China).…”

“…In recent years there has been a substantial acceleration in research activity concerned with homogeneous transition metal catalysts for ethylene oligomerization and polymerization. Chromium catalysts play an important role in both of these processes [1][2][3][4][5][6][7][8]. Since the first report of ethylene tetramerization to form 1-octene using Cr-bis(diphenylphosphino)amine (PNP) catalysts [9], numerous studies have investigated the relationship between ligand structure and catalytic properties.…”

Recent Research Progress in Preparation of Ethylene Oligomers with Chromium-Based Catalytic Systems

“…In order to investigate this kind of catalyst in detail, Zhang and co-workers did research and reported their investigation on bis(benzimidazolyl)pyridine ligands [22]. They prepared a series of these ligands (Fig.…”

“…Chromium complexes bearing NNN ligands exhibited high catalytic activities in ethylene oligomerization and polymerization [15,21,22]. It is reported that chromium complexes ligated by NNN species such as bis(imino)pyridine, (2-pyridylmethyl)amines, β-diketimate and pyrrolide-imine ligands can polymerize or oligomerize ethylene with great activity [21,[23][24][25].…”