d(0) metal olefin complexes. Synthesis, structures, and dynamic propertiesof (C5R5)(2)Zr(OCMe2CH2CH2CH=CH2)(+) complexes: Models for the elusive (C5R5)(2)Zr(R)(olefin)(+) intermediates in metallocene-based olefin polymerization catalysis

To model the Zr-olefin interaction in the as-yet unobserved (C5R5)(2)Zr(R)( olefin)(+) intermediates in (C5R5)(2)Zr(R)(+)-catalyzed olefin polymerizati on, the coordination of the tethered vinyl group in (C5R5)(2)Zr(OCMe2(CH2)( n)CH=CH2)(+) species has been investigated. The reaction of (C5H5)(2)Zr(OCM e2CH2CH2CH= CH2)(Me) with B(C6F5)(3) or [Ph3C][B(C6F5)(4)] yields rhechelat rd olefin complex (C5H5)(2)Zr(OCMe2CH2CfI2CH= CH2)(+) as the MeB(C6F5)(3)(- ) (12a) or B(C6F5)(4)(-) (12b) salts. In contrast, the reaction of (C5H5)(2 )Zr(OCMe2CH2CH= CH2)(Me) with B(C6F5)(3) in CD2Cl2 yields the MeB(C6F5)(3)( -) adduct (C5H5)(2)Zr(+)(OCMe2CH2CH=CH2)(mu-Me)B(-)(C6F5)(3) The reaction o f (C5H5)(2)Zr(OCMe2CH2CH2CH2CH=CH2(Me) with B(C6F5)(3) yields a 1.2/1 mixtu re (at -90 degrees C) of the chelated olefin complex (C5H5)(2)Zr(OCMe2CH2CH 2CH2CH=CH2)(+) and the MeB(C6F5)(3)(-) adduct (C5H5)(2)Zr(+)(OCMe2CH2CH2CH= CH2)(mu-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 th e MeB(C6F5)(3)(-) 20a) or B(C6F5)(3)(-)(20a) salts, each as a 1/1 mixture o f diastereomers which differ in the relative configuration of the mc-(EBI)Z r 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 unsymmet rical and consists of a weak Zr-C-term interaction and minimal Zr-C-int int eraction (12a, Zr-C-term = 2.68(2), Zr-C-int = 2.89(2) Angstrom; 20a, Zr-C- term = 2.634(5),Zr-C-int = 2.819(4) Angstrom). X-ray (d(C-C)),IR ((C-C)), a nd NMR (H-1,C-13) data shaw that the Zr-olefin interaction does not signifi cantly perturb the structure of the coordinated olefin but does polarize th e C=C bond such that positive charge buildup occurs at C-int. Similar unsym metrical bonding and polarization effects may contribute to the high insert ion reactivity of (C5R5)(2)Zr-(R)(alpha-olefin)(+) species. Dynamic NMR stu dies show that 12a,b and 20a,b undergo olefin race exchange in solution on the NMR time scale. The free energy barrier for face exchange of 20a (Delta G(FE)(double dagger ) = 15.4(4) kcal/mol at 43 degrees C) is significantly greater than that fo r 12a (Delta G(FE)(double dagger) =10.7(5) kcal/mol at -55 degrees C). Poss ible origins of this difference are discussed. The face exchange of 20a is dissociative, with minimal involvement of anion, solvent, or a-complex inte rmediates.