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Metallocene-Terminated Allylium Salts: The Effect of End Group on Localization in Polymethines

Barlow, Stephen and Henling, Lawrence M. and Day, Michael W. and Schaefer, William P. and Green, Jennifer C. and Hascall, Tony and Marder, Seth R. (2002) Metallocene-Terminated Allylium Salts: The Effect of End Group on Localization in Polymethines. Journal of the American Chemical Society, 124 (22). pp. 6285-6296. ISSN 0002-7863. doi:10.1021/ja012472z.

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A range of 1,3-di(metallocenyl)allylium salts [Mc(CH)_3Mc‘]+[X]- {Mc, Mc‘ = ferrocenyl (Fc), 2,3,4,5,1‘,2‘,3‘,4‘-octamethylferrocen-1-yl (Fc‘ ‘), ruthenocenyl (Rc); X = BF_4, PF_6} was synthesized by reaction of (2-lithiovinyl)metallocenes with formylmetallocenes, followed by treatment of the resulting alcohols with HX. Two salts with X = BAr‘_4 {Ar‘ = 3,5-(CF_3)_2C_6H_3} were synthesized by anion metathesis from the corresponding PF_6 salts. The crystal structure of [Fc‘‘(CH)_3Fc‘‘]+[PF_6]- contains symmetrical termethine cations, while the same appears to be true in the disordered structure of [Fc(CH)_3Fc]+[PF_6]-. The formally unsymmetrical cation in [Fc(CH)_3Fc‘‘]+[BF_4]- is only slightly unsymmetrical with little bond-length alternation in the allylium bridge. In contrast, the crystal structures of [Rc(CH)_3Rc]+[PF_6]- and [Rc(CH)_3Rc]+[BAr‘_4]- both contain a bond-alternated “Peierls-distorted” cation, which can be considered as a ruthenocene bridged to a [(η^6-fulvene)(η^5-cyclopentadienyl)ruthenium] cation by a vinylene moiety. The strong similarity between solid-state and solution infrared and Raman spectra of [BF_4]^-, [PF_6]^-, and [BAr‘_4^- salts of [Rc(CH)_3Rc]^+ indicates that the C−C stretching constant in the allylium chain and, therefore, the structure, of this ion are largely independent of the local environment, suggesting that the unsymmetrical structures observed in the crystal structures are not simply an artifact of packing. Differences in the solvatochromism of [Rc(CH)_3Rc]+ and [Fc(CH)_3Fc]^+ also suggest a localized structure for the former cation in solution. Electrochemistry, UV−visible−NIR spectroscopy, and DF calculations give insight into the electronic structure of the metallocene-terminated allylium cations. Using an analogy between polymethines and mixed-valence compounds, the difference between the behaviors of [Fc(CH)_3Fc]+ and [Rc(CH)_3Rc]^+ is attributed to larger reorganization energy associated with the geometry differences between metallocene and [(η^6-fulvene)(η^5-cyclopentadienyl)metal] structures in the ruthenium case.

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Additional Information:© 2002 American Chemical Society. Received 5 November 2001. Published online 8 May 2002. Published in print 1 June 2002. Support from the National Science Foundation, Air Force Office of Scientific Research (AFOSR) at Caltech is gratefully acknowledged. The research described in this paper was performed in part by the Jet Propulsion Laboratory (JPL), California Institute of Technology, as part of its Center for Space Microelectronics Technology and was supported by the Ballistic Missile Defense Initiative Organization, Innovative Science and Technology Office through an agreement with the National Aeronautics and Space Administration (NASA). We thank Kenneth Calgren for his assistance with Raman measurements, Dr. Paul Roussel for his assistance with low-temperature NMR experiments, Dr. Andrew Cowley for his efforts with a highly disordered crystal of 3c·xCH_2Cl_2, and Johnson Matthey for a loan of ruthenium precursors. We also thank the reviewers of the manuscript for helpful comments.
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Ballistic Missile Defense OrganizationUNSPECIFIED
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Official Citation:Metallocene-Terminated Allylium Salts:  The Effect of End Group on Localization in Polymethines Stephen Barlow, Lawrence M. Henling, Michael W. Day, William P. Schaefer, Jennifer C. Green, Tony Hascall, and Seth R. Marder Journal of the American Chemical Society 2002 124 (22), 6285-6296 DOI: 10.1021/ja012472z
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:75819
Deposited By: Ruth Sustaita
Deposited On:07 Apr 2017 16:08
Last Modified:15 Nov 2021 16:55

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