Isocyanide and Phosphine Oxide Coordination in Binuclear Chromium Pacman Complexes.
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ABSTRACT:
SUBMITTER: Stevens CJ
PROVIDER: S-EPMC3905932 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:A series of Cr-based complexes 6-10 bearing aminophosphine (P,N) ligands Ph2P-L-NH2 [L = CH2CH2 (1), L = CH2CH2CH2 (2), and L = C6H4CH2 (3)] and phosphine-imine-pyrryl (P,N,N) ligands 2-(Ph2P-L-N=CH)C4H3NH [L = CH2CH2CH2 (4) and L = C6H4CH2 (5)] were prepared, and their catalytic properties were examined for ethylene tri/tetramerization. X-ray crystallographic analysis of complex 8 indicated the κ2-P,N bidentate coordination mode at the Cr(III) center and the distorted octahedral geometry of monomeric P,N-CrCl3. Upon activation by methylaluminoxane (MAO), complexes 7-8 bearing P,N (PC3N backbone) ligands 2-3 showed good catalytic reactivity for ethylene tri/tetramerization. On the other hand, complex 6 bearing the P,N (PC2N backbone) ligand 1 was found active for non-selective ethylene oligomerization, while complexes 9-10 bearing P,N,N ligands 4-5 only produced polymerization products. In particular, the high catalytic activity of 458.2 kg/(g·Cr·h), excellent selectivity of 90.9% (1-hexene and 1-octene combined), and extremely low PE content of 0.1% were obtained with complex 7 in toluene at 45 °C and 45 bar. These results suggest that rational control of P,N and P,N,N ligand backbones, including a carbon spacer and rigidity of a carbon bridge, can lead to the high-performance catalyst for the ethylene tri/tetramerization process.
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