Solid-State 91Zr NMR Spectroscopy Studies of Zirconocene Olefin Polymerization Catalyst Precursors

Abstract

(91)Zr (I = 5/2) solid-state NMR (SSNMR) spectra of the zirconocene compounds, Cp(2)ZrCl(2), Cp*(2)ZrCl(2) (1), Cp(2)ZrBr(2) (2), (Me(3)SiC(5)H(4))(2)ZrBr(2) (3), O(Me(2)SiC(5)H(4))(2)ZrBr(2) (4), (1,3-C(5)H(3))(SiMe(2)OSiMe(2))(2)(1,3-C(5)H(3))ZrBr(2) (5), Ind(2)ZrCl(2) (6), Cp(2)ZrMeCl (7), Cp(2)ZrMe(2) (8), and [Cp(2)ZrMe][MeB(C(6)F(5))(3)] (9) have been acquired. Static (91)Zr SSNMR spectra have been acquired for all complexes at magnetic fields of 9.4 and 21.1 T. Cp(2)ZrCl(2) and complexes 1 to 5 possess relatively narrow central transition powder patterns which allows for magic-angle spinning (MAS) (91)Zr solid-state NMR spectra to be acquired at a moderate field strength of 9.4 T. Complexes 6 to 9 possess ultrawideline central transition SSNMR spectra necessitating piece-wise acquisition techniques. From the static and MAS (91)Zr SSNMR spectra, it is possible to measure (91)Zr electric field gradient (EFG) and chemical shift (CS) tensor parameters, as well as the Euler angles which describe their relative orientation. Basis sets and methods for the accurate quantum chemical calculation of (91)Zr EFG and CS tensors have been identified. The origin of the observed EFG and CS tensor parameters are further investigated by visualization of the EFG and CS tensor orientations within the molecular frames. Correlations between the observed and calculated NMR tensor parameters and molecular symmetry and structure are made. All of these observations suggest that (91)Zr SSNMR spectroscopy can be utilized to probe the molecular structure of a variety of homogeneous and heterogeneous olefin polymerization catalysts.