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Zachmanoglou CE, Docrat A, Bridgewater BM, et al. The electronic influence of ring substituents and ansa bridges in zirconocene complexes as probed by infrared spectroscopic, electrochemical, and computational studies. J Am Chem Soc. 2002;124(32):9525-46doi: 10.1021/ja020236y.
Zachmanoglou, C. E., Docrat, A., Bridgewater, B. M., Parkin, G., Brandow, C. G., Bercaw, J. E., Jardine, C. N., Lyall, M., Green, J. C., & Keister, J. B. (2002). The electronic influence of ring substituents and ansa bridges in zirconocene complexes as probed by infrared spectroscopic, electrochemical, and computational studies. Journal of the American Chemical Society, 124(32), 9525-46. https://doi.org/10.1021/ja020236y
Zachmanoglou, Cary E, et al. "The electronic influence of ring substituents and ansa bridges in zirconocene complexes as probed by infrared spectroscopic, electrochemical, and computational studies." Journal of the American Chemical Society vol. 124,32 (2002): 9525-46. doi: https://doi.org/10.1021/ja020236y
Zachmanoglou CE, Docrat A, Bridgewater BM, Parkin G, Brandow CG, Bercaw JE, Jardine CN, Lyall M, Green JC, Keister JB. The electronic influence of ring substituents and ansa bridges in zirconocene complexes as probed by infrared spectroscopic, electrochemical, and computational studies. J Am Chem Soc. 2002 Aug 14;124(32):9525-46. doi: 10.1021/ja020236y. PMID: 12167048.
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J Am Chem Soc. 2002 Aug 14;124(32):9525-46. doi: 10.1021/ja020236y.

The electronic influence of ring substituents and ansa bridges in zirconocene complexes as probed by infrared spectroscopic, electrochemical, and computational studies.

Journal of the American Chemical Society

Cary E Zachmanoglou, Arefa Docrat, Brian M Bridgewater, Gerard Parkin, Christopher G Brandow, John E Bercaw, Christian N Jardine, Mark Lyall, Jennifer C Green, Jerome B Keister

Affiliations

  1. Contribution from the Department of Chemistry, Columbia University, New York, New York 10027, USA.

PMID: 12167048 DOI: 10.1021/ja020236y

Abstract

The electronic influence of unbridged and ansa-bridged ring substituents on a zirconocene center has been studied by means of IR spectroscopic, electrochemical, and computational methods. With respect to IR spectroscopy, the average of the symmetric and asymmetric stretches (nu(CO(av))) of a large series of dicarbonyl complexes (Cp(R))(2)Zr(CO)(2) has been used as a probe of the electronic influence of a cyclopentadienyl ring substituent. For unbridged substituents (Me, Et, Pr(i), Bu(t), SiMe(3)), nu(CO(av)) on a per substituent basis correlates well with Hammett sigma(meta) parameters, thereby indicating that the influence of these substituents is via a simple inductive effect. In contrast, the reduction potentials (E degrees ) of the corresponding dichloride complexes (Cp(R))(2)ZrCl(2) do not correlate well with Hammett sigma(meta) parameters, thereby suggesting that factors other than the substituent inductive effect also influence E degrees. Ansa bridges with single-atom linkers, for example [Me(2)C] and [Me(2)Si], exert a net electron-withdrawing effect, but the effect is diminished upon increasing the length of the bridge. Indeed, with a linker comprising a three-carbon chain, the [CH(2)CH(2)CH(2)] ansa bridge becomes electron-donating. In contrast to the electron-withdrawing effect observed for a single [Me(2)Si] ansa bridge, a pair of vicinal [Me(2)Si] ansa bridges exerts an electron-donating effect relative to that from the single bridge. DFT calculations demonstrate that the electron-withdrawing effect of the [Me(2)C] and [Me(2)Si] ansa-bridges is due to stabilization of the cyclopentadienyl ligand acceptor orbital, which subsequently enhances back-donation from the metal. The calculations also indicate that the electron-donating effect of two vicinal [Me(2)Si] ansa bridges, relative to that of a single bridge, is a result of it enforcing a ligand conformation that reduces back-donation from the metal.

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