The zwitterionic complex [Zr(CH2Ph)3{(eta6-PhCH2)B(C6F5)3}] (1) reacts smoothly at 25-degrees-C with propene and higher alpha-olefins, such as 4-methyl-1-pentene, 1-vinylcyclohexane, and allylbenzene, affording the single-insertion adducts [Zr(CH2Ph)2(CH2CHRCH2Ph)]+[B(CH2-Ph)(C6F5)3]- (R = Me, 2; R = CH2CHMe2, 4; R = C6H11, 5; R = CH2Ph, 6). Isolation and characterization of 2, 4, and 6 by NMR analysis reveal that the Zr cation is stabilized toward either further monomer insertion or beta-hydrogen elimination by back-biting eta(n)-coordination of the delta-Ph ring and by eta2-coordination of the two benzyl ligands. An analogous, less stable adduct deriving from single insertion of ethene (R = H, 3) has been detected at low temperatures by NMR. Thermolysis of 2 at 50-degrees-C, as well as addition of Lewis bases such as tetrahydrofuran, results in decomposition via beta-hydrogen elimination with formation of CH2=CMeCH2Ph. At 50-degrees-C, 2 reacts with an excess of propene affording a mixture of atactic and isotactic polypropylene, probably after beta-hydrogen elimination has occurred. In contrast, reaction of 2 with ethene proceeds already at 25-degrees-C, affording polyethylene, possibly through further insertion in 2. Compounds 2-6 are the first examples of adducts deriving from the insertion of olefins into the M-C bond of a group 4 metal complex which is an active Ziegler-Natta catalyst.

Single Insertion of Alpha-olefins Into the Cationic Complex [zr(ch2ph)3]+ Affording Isolable [zr(ch2ph)2(ch2chrch2ph)]+ Adducts - A Model For the Insertion Mechanism In Ziegler-natta Polymerization

PELLECCHIA, Claudio;GRASSI, Alfonso;ZAMBELLI, Adolfo
1994-01-01

Abstract

The zwitterionic complex [Zr(CH2Ph)3{(eta6-PhCH2)B(C6F5)3}] (1) reacts smoothly at 25-degrees-C with propene and higher alpha-olefins, such as 4-methyl-1-pentene, 1-vinylcyclohexane, and allylbenzene, affording the single-insertion adducts [Zr(CH2Ph)2(CH2CHRCH2Ph)]+[B(CH2-Ph)(C6F5)3]- (R = Me, 2; R = CH2CHMe2, 4; R = C6H11, 5; R = CH2Ph, 6). Isolation and characterization of 2, 4, and 6 by NMR analysis reveal that the Zr cation is stabilized toward either further monomer insertion or beta-hydrogen elimination by back-biting eta(n)-coordination of the delta-Ph ring and by eta2-coordination of the two benzyl ligands. An analogous, less stable adduct deriving from single insertion of ethene (R = H, 3) has been detected at low temperatures by NMR. Thermolysis of 2 at 50-degrees-C, as well as addition of Lewis bases such as tetrahydrofuran, results in decomposition via beta-hydrogen elimination with formation of CH2=CMeCH2Ph. At 50-degrees-C, 2 reacts with an excess of propene affording a mixture of atactic and isotactic polypropylene, probably after beta-hydrogen elimination has occurred. In contrast, reaction of 2 with ethene proceeds already at 25-degrees-C, affording polyethylene, possibly through further insertion in 2. Compounds 2-6 are the first examples of adducts deriving from the insertion of olefins into the M-C bond of a group 4 metal complex which is an active Ziegler-Natta catalyst.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11386/3131762
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