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• 294636-75-2 rac-(ethylene-1,2-bis(1-indenyl))Zr(CH₃)(OC(CH₃)2CH₂CH₂CHCH₂) 

Relevant academic research and scientific papers

d0 Metal olefin complexes. Synthesis, structures, and dynamic properties of (C5R5)2Zr(OCMe2CH2CH2CH=CH2)+ complexes: Models for the elusive (C5R5)2Zr(R)(Olefin)+ intermediates in metallocene-based olefin polymerization catalysis

To model the Zr-olefin interaction in the as-yet unobserved (C5R5)2Zr(R)(olefin)+ intermediates in (C5R5)2Zr(R)+-catalyzed olefin polymerization, the coordination of the tethered vinyl group in (C5R5)2Zr(OCMe2(CH2)(n)CH=CH2)+ species has been investigated. The reaction of (C5H5)2Zr(OCMe2CH2CH2CH= CH2)(Me) with B(C6F5)3 or [Ph3C][B(C6F5)4] yields the chelated olefin complex (C5H5)2Zr(OCMe2CH2CH2CH= CH2)+ as the MeB(C6F5)3- (12a) or B(C6F5)4- (12b) salts. In contrast, the reaction of (C5H5)2Zr(OCMe2CH2CH= CH2)(Me) with B(C6F5)3 in CD2Cl2 yields the MeB(C6F5)3- adduct (C5H5)2Zr(+)(OCMe2CH2CH=CH2)(μMe)B(-)(C6F5)3. The reaction of (C5H5)2Zr(OCMe2CH2CH2CH2CH=CH2)(Me) with B(C6F5)3 yields a 1.2/1 mixture (at -90 °C) of the chelated olefin complex (C5H5)2Zr(OCMe2CH2CH2CH2CH=CH2)+ and the MeB(C6F5)3- adduct (C5H5)2Zr(+)(OCMe2CH2CH2CH=CH2)(μ-Me)B(-)(C6F5)3'. The reaction of rac-(EBI)-Zr(OCMe2CH2CH2CH=CH2)(Me) (EBI = ethylene-1,2-bis(1-indenyl)) with B(C6F5)3 or [Ph3C] [B(C6F5)4] yields the chelated olefin complex rac-(EBI)Zr(OCMe2CH2CH2CH=CH2)+ as the MeB(C6F5)3- (20a) or B(C6F5)4-(20b) salts, each as a 1/1 mixture of diastereomers which differ in the relative configuration of the rac-(EBI)-Zr unit and the internal carbon of the coordinated olefin. X-ray diffraction analyses of 12a and the S,S,R/R,R,S isomer of 20a, and NMR data for 12a,b and 20a,b establish that the Zr-olefin bonding in these species is unsymmetrical and consists of a weak Zr-C(term) interaction and minimal Zr-C(int) interaction (12a, Zr-C(term) = 2.68(2), Zr-C(int) = 2.89(2) A; 20a, Zr-C(term) = 2.634(5), Zr-C(int) = 2.819(4) A). X-ray (d(C=C)), IR (v(C=C)), and NMR (1H, 13C) data show that the Zr-olefin interaction does not significantly perturb the structure of the coordinated olefin but does polarize the C=C bond such that positive charge buildup occurs at C(int). Similar unsymmetrical bonding and polarization effects may contribute to the high insertion reactivity of (C5R5)2Zr(R)(α-olefin)+ species. Dynamic NMR studies show that 12a,b and 20a,b undergo olefin face exchange in solution on the NMR time scale. The free energy barrier for face exchange of 20a (ΔG(+)(FE) = 15.4(4) kcal/mol at 43 °C) is significantly greater than that for 12a (ΔG(+)(FE) = 10.7(5) kcal/mol at -55 °C). Possible origins of this difference are discussed. The face exchange of 20a is dissociative, with minimal involvement of anion, solvent, or σ-complex intermediates.