Nucleophilic Aromatic Substitution Reactions for the Synthesis of Ferrocenyl Aryl Ethers

作者：Korb Marcus; Swarts Pieter J; Miesel Dominique; Hildebrandt Alexander; Swarts Jannie C; Lang Heinrich^*

来源：Organometallics, 2016, 35(9): 1287-1300.

DOI：10.1021/acs.organomet.6b00157

A range of ferrocenyl aryl ethers of type Fc-O-Ar (Fc = Fe(eta(5)-C6H5)(eta(5)-C6H(n)X(4-n)); n = 2-4; X = H, P(O)(OEt)(2) SO2CF3; Ar = 2,4-(NO2)(2)-C6H3, 4-NO2-C6H4) have been successfully prepared by using the nucleophilic aromatic substitution reaction (SNAr) of Fc-OLi (1a-Li) and electron-deficient aryl fluorides, enabling a new pathway to this rarely described family of organometallic compounds. Initial studies of 1a-Li and o-phosphonato-substituted hydroxyferrocenes (1b-Li) have also been performed, indicating a low nudeophilicity of the oxygen atom. The SNAr reaction protocol tolerates ortho substituents, e.g. phosphonato and sulfonyl groups, resulting in 1,2-X,O (X = S, P) ferrocenyl ethers that can be obtained in a one pot synthesis procedure including 1,3-O -> C anionic phospho- and thia-Fries rearrangements. Within these studies, the first 1,3-diortho-functionalized ferrocenyl aryl ether could be synthesized. An electrochemical study of the redox potentials of the obtained compounds allows conclusions on the reactivity of the varying electronic properties and the electrophilicity of different aryl fluorides and the nucleophilicity of the functionalized hydroxyl ferrocenes, which is directly reflected by the potential of the first ferrocene related redox processes. Chiral-pool-based phosphonates rearrange to the aryl ethers with diastereomeric excesses of 74 and 81% after the anionic Fries rearrangement. The usage of aryl 1,2-/1,3-difluorides resulted in the synthesis of the first examples of bis(FcO)-substituted benzenes. Their electrochemical investigations reveal a splitting of the two redox processes of the ferrocenyls that decreases from 155 mV (1,2-substitution) to 130 mV (1,3-substitution) on the basis of electrostatic interactions.

• 出版日期2016-5-9