Structural Characterization of Zirconium Cations Derived from a Living Ziegler−Natta Polymerization System:  New Insights Regarding Propagation and Termination Pathways for Homogeneous Catalysts

Abstract

A canary yellow block with dimensions 0.261 x 0.167 x 0.154mm 3 was placed and optically centered on the Bruker SMART CCD system at -80°C. The initial unit cell was indexed using a least-squares analysis of a random set of reflections collected from three series of 0.3° wide ω scans (25 frames/series) that were well distributed in reciprocal space. Data frames were collected [MoKα] with 0.3° wide ω-scans, 40 seconds per frame, 606 frames per series. Five complete series were collected with an additional 160 frames a repeat of the first series for redundancy and decay purposes, with a crystal to detector distance of 4.556cm, thus providing a complete sphere of data to 2θ max =50°. A total of 38144 reflections were collected and corrected for Lorentz and polarization effects and absorption using Blessing's method as incorporated into the program SADABS 1,2 with 10464 unique [R(int)=0.0693]. Structural determination and Refinement:All crystallographic calculations were performed on a Personal computer (PC) with dual Pentium 450MHz processors and 384MB of extended memory. The SHELXTL 3 program package was now implemented, XPREP, to determine the probable space group and set up the initial files. System symmetry, lack systematic absences and intensity statistics indicated the centrosymmetric triclinic group P-1 (no.2). The structure was determined by use of Patterson methods with the successful location of the central Zirconium atom using the program XS 4 . The structure was refined with XL 5 . After the initial refinement difference-Fourier cycle, additional atoms were located and input. After several of these refinement difference-Fourier cycles, all of the atoms were refined isotropically, then anisotropically. A disordered chlorobenzene molecule was modeled and refined with three probable orientations. A centroid was calculated for the pentamethylcyclopentadienyl group. Hydrogen atoms were placed in calculated positions. The final structure was refined to convergence [∆/σ ≤ 0.001] with R(F)=8.87%, wR(F 2 )=11.43%, GOF=1.009 for all 10464 unique reflections [R(F)=4.51%, wR(F 2 )=10.21% for those 6868 data with Fo > 4σ(Fo)]. A final difference-Fourier map was featureless indicating the structure is therefore both correct and complete.The function minimized during the full-matrix least-squares refinement was Σw(Fo 2-Fc 2 ) where w=1/[σ 2 (Fo 2 )+(0.0590*P) 2 +0.0*P] and P=(max(Fo 2 ,0)+2*Fc 2 )/3. An empirical correction for extinction was also attempted but found to be negative and therefore not applied.53.78(11) N(1)-Zr(1)-C( 16) 30.17(11) CT1-Zr(1)-C( 16) 122.21( 9) O(1)-Zr(1)-C( 16) 107.16(10) C(11)-Zr(1)-C(16) 107.43(13) N(2)-Zr(1)-C(16) 29.95(10) C(5)-Zr(1)-C(16) 97.80(10) C(1)-Zr(1)-C(16) 98.40(11) C(3)-Zr(1)-C(16) 150.75(11) C(4)-Zr(1)-C(16) 125.78(11) C(2)-Zr(1)-C(16) 126.86(12) C(2)-C(1)-C(5) 107.6(3) C(2)-C(1)-C(6) 126.2(4) C(5)-C(1)-C(6) 125.9(4) C(2)-C(1)-Zr(1) 74.4(2) C(5)-C(1)-Zr(1) 73.07(19) C(6)-C(1)-Zr(1) 123.1(2) C(1)-C(2)-C(3) 108.7(3) C(1)-C(2)-C(7) 126.4(4) C(3)-C(2)-C(7) 124.3(4) C(1)-C(2)-Zr(...

Synthesis, solid state and DFT structure and olefin polymerization capability of a unique base-free dimeric methyl titanium dication

“…On the other hand, regardless of the starting m-CH 3 group geometry, the DFT structure of 6 2+ minimized to be analogous to the m-CH 3 geometry in 3 2+ and 5 The unusual geometry reported for 6 2+ is inconsistent with these other results.Although it was speculated previously23 that 6 2+ could have relevance to catalysis, this was not demonstrated, the precursor solutions decomposing at ambient temperature. The solution stability of [Cp* 2 Ti 2 {NC(Ar F2 )N i Pr 2 } 2 (m-Me) 2 ][BF 20 ] 2…”

“…2). 23 The structure of 6 2+ has attracted much attention owing to postulated implications for Ziegler-Natta catalysis, and also the very unusual reported arrangement of the Zr 2 (m-Me) 2 hydrogens. Each m-methyl group was described as having a trigonal bipyramidal geometry and an unprecedented doubly-bridging agostic C-H bond (Fig.…”

“…Fig.2The structure of [Cp* 2 Zr 2 {MeC(N t Bu)(NEt)} 2 (m-Me) 2 ] 2+ (6 2+ ) emphasising the unusual m-methyl group geometry 23. …”

Catalysts for the Living Insertion Polymerization of Alkenes: Access to New Polyolefin Architectures Using Ziegler–Natta Chemistry

“…Sita et al suggested that the barrier might be higher in the activated complex and the structural defects in the polymer were a consequence of amidinate ring flipping. To shed light on the origin of stereocontrol in this unique system, crystallographic analyses of 38 b and 38 b /[B(C 6 F 5 ) 4 ] were performed 111. Indeed, the more electrophilic metal center of the activated complex resulted in a shortening of the ZrN bonds, providing evidence that suggests a higher barrier to racemization in the active species.…”

Katalysatoren für die lebende Insertionspolymerisation von Alkenen: mit Ziegler-Natta-Chemie zu neuartigen Polyolefin-Architekturen

“…Die Aktivit‰t der Vorstufen 38 c, d bei der Polymerisation von 1-Hexen war unzureichend, vermutlich wegen der sterischen Hinderung der Komplexe. Einblicke in den Ursprung der Stereokontrolle erhielt man durch kristallographische Untersuchungen von38 b und 38 b/ [B(C 6 F 5 )4 ] [111]. Die Katalysatoraktivit‰t und das resultierende Molekulargewicht waren hˆher, und das Polymer war hoch isotaktischSchema 21.…”