Organometallic polymers assembled from cation-p interactions : Use of ferrocene as a ditopic linker within the homologous series [{(Me3Si)2NM}2⋅(Cp2Fe)]∞ (M=Na, K, Rb, Cs; Cp=cyclopentadienyl)

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Morris, J. Jacob and Noll, B.C. and Honeyman, Gordon William and O'Hara, C.T. and Kennedy, A.R. and Mulvey, R.E. and Henderson, K (2007) Organometallic polymers assembled from cation-p interactions : Use of ferrocene as a ditopic linker within the homologous series [{(Me3Si)2NM}2⋅(Cp2Fe)]∞ (M=Na, K, Rb, Cs; Cp=cyclopentadienyl). Chemistry - A European Journal, 13 (16). pp. 4418-4432. ISSN 1521-3765 (https://doi.org/10.1002/chem.200700219)

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Abstract

Addition of ferrocene to solutions of alkali metal hexamethyldisilazides M(HMDS) in arenes (in which M=Na, K, Rb, Cs) allows the subsequent crystallization of the homologous series of compounds [{(Me3Si)2NM}2 (Cp2Fe)]∞ (1–4). Similar reactions using LiHMDS led to the recrystallization of the starting materials. The crystal structures of 1–4 reveal the formation of one-dimensional chains composed of dimeric [{M(HMDS)}2] aggregates, which are bridged through neutral ferrocene molecules by η5-cation–π interactions. In addition, compounds 3 and 4 also contain interchain agostic MC interactions, producing two-dimensional 44-nets. Whereas 1 and 2 were prepared from toluene, the syntheses of 3 and 4 required the use of tert-butylbenzene as the reaction media. The attempted crystallization of 3 and 4 from toluene resulted in formation of the mixed toluene/ferrocene solvated complexes [{(Me3Si)2NM)2}2 (Cp2Fe)x(Tol)y]∞ (in which M=Rb, x=0.6, y=0.8, 5; M=Cs, x=0.5, y=1, 6). The extended solid-state structures of 5 and 6 are closely related to the 44-sheets 3 and 4, but are now assembled from a combination of cation–π, agostic, and π–π interactions. The charge-separated complex [K{(C6H6)2Cr}1.5(Mes)][Mg(HMDS)3] (15) was also structurally characterized and found to adopt an anionic two-dimensional 63-network through doubly η3-coordinated bis(benzene)chromium molecules. DFT calculations at the B3 LYP/6–31G* level of theory indicate that the binding energies of both ferrocene and toluene to the M(HMDS) dimers increases in the sequence Li<Na<K. This pattern is a consequence of the larger metals allowing more open coordination spheres to support cation–π contacts. By comparison, binding of the isolated metal cations to the aromatic groups follow the reverse order K<Na<Li. A combined analysis of theoretical and experimental data suggest that ferrocene is a stronger cation–π donor than toluene for the lighter metals, but that this difference is eliminated on descending the group.

ORCID iDs

Morris, J. Jacob, Noll, B.C., Honeyman, Gordon William, O'Hara, C.T., Kennedy, A.R. ORCID logoORCID: https://orcid.org/0000-0003-3652-6015, Mulvey, R.E. ORCID logoORCID: https://orcid.org/0000-0002-1015-2564 and Henderson, K;
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