Formation and Structures of Hafnocene Complexes in MAO- and AlBui3/CPh3[B(C6F5)4]-Activated Systems
Full article
| Общее |
Language:
Английский,
Genre:
Full article,
Status:
Published,
Source type:
Original
|
| Journal |
Organometallics
ISSN: 0276-7333
, E-ISSN: 1520-6041
|
| Output data |
Year: 2008,
Volume: 27,
Number: 23,
Pages: 6333-6342
Pages count
: 10
DOI:
10.1021/om800664p
|
| Authors |
Bryliakov Konstantin P.
1
,
Talsi Evgenii P.
1
,
Voskoboynikov Alexander Z.
2
,
Lancaster Simon J.
3
,
Bochmann Manfred
3
|
| Affiliations |
| 1 |
Boreskov Institute of Catalysis, Siberian Branch of the Russian Academy of Sciences, 630090, Novosibirsk, Russian Federation
|
| 2 |
Department of Chemistry, Moscow State University, Lomonosovsky Prospect 1, 113000 Moscow, Russian Federation
|
| 3 |
Wolfson Materials and Catalysis Centre, School of Chemical Sciences and Pharmacy, University of East Anglia, Norwich NR4 7TJ, United Kingdom
|
|
Funding (2)
|
1
|
Russian Foundation for Basic Research
|
06-03-32700
|
|
2
|
Royal Society
|
2006/R4-IJP
|
The formation of cationic species relevant to olefin polymerization based on (SBI)HfCl2, Me2C(C5H4)(Flu)HfCl2, Ph2C(C5H4)(Flu)HfCl2, and L′HfCl2 activated by MAO, AlMe3/CPh3[B(C6F5)4], and AlBui3/CPh3[B(C6F5)4] (SBI ) rac-Me2Si(Ind)2; L′ ) C2H4(Flu)(5,6-C3H6-2-MeInd)) was studied by 1H, 13C, and 19F NMR spectroscopy. Thermally stable heterobinuclear intermediates of the type [LHf(µ-Me)2AlMe2]+[MeMAO]- and [LHf(µ-Me)2AlMe2]+[B(C6F5)4]- were identified when using MAO and AlMe3/CPh3[B(C6F5)4] as activators, respectively. The stability of these species explains the low productivity of hafnocene catalysts in the presence of AlMe3-containing activators, compared to zirconocenes. By contrast, in the ternary systems LHfCl2/AlBui3/CPh3[B(C6F5)4] hydride species were detected that must be responsible for the formation of the highly active sites in olefin polymerization. The ionic hydrido species differ significantly in stability. The formation of the mixed-alkyl complex L′Hf(Me)CH2SiMe3 proceeds with surprisingly high diastereoselectivity; the sterically more hindered isomer is produced preferentially. It reacts with CPh3[B(C6F5)4] to afford the ion pair [L′HfCH2SiMe3] +[B(C6F5)4]- as two diastereomers that exist in dynamic equilibrium. The rates of site epimerization of this ion pair indicate only small energy differences between the two isomers.