The synthesis and chemistry of the cyclophanenes and their metal complexes

Date

2018-07-04

Authors

Zhang, Limin

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Abstract

A new synthetic route to cyclophanenes 56, starting from an appropriate 2,6-dihalogen-substituted toluene via monothiacyclophanes as intermediate compounds, was developed. By this method, anti-5,8,13-16-tetramethyl [2,2] (1,3)cyclophan-1-ene, 56b, and anti-4,6,8,12,14,16-hexa-methyl [2,2] (1,3)cyclophan-1-ene, 56c, were first synthesized as well as three new monothiacyclophanes, anti-9,17-dimethyl-2-thia [3,2] (1,3) cyclophane, 72a, anti-6,9,14,17-tetramethyl-2-thia [3,2] (1,3) cyclophane, 72b, anti-5,7,9,13,15,17-hexamethyl-2-thia [3,2] (1,3) cyclophane, 72c. An X-ray structural determination of the monothiacyclophane 72a revealed an anti-stepped geometry of the molecule and that the aromatic rings were bent outward in a slightly distorted boat form. A reciprocal relationship between deviations of the inner carbons from their basal planes and distances between the inner carbons was found by comparison of X-ray data of four metacyclophanes. Several tricarbonylchromium(0) and η5-cyclopentadienyl-iron(I) complexes of cyclophanenes 56 were also prepared for the first time. The complexation effect and ring current reduction effects in these complexes were investigated through studies of their proton nmr spectra. An X-ray structure analysis of anti-8,16-dimethyl [2,2] (1,3) cyclophan-1-ene-cyclopentadienyliron(I), 105a, was determined and it was found that the bridge double bond (1.345A) has a cis geometry but with very large torsional angles: 24.7° for C-C=C-C and 41.6° for H-C=C-H. The bridge chemistry of cyclophanenes 56 and their metal complexes was investigated through some selected reactions. It was found that the cyclophanenes 56 were easily oxidized in attempted electrophilic additions to the bridge double bond. Bromination of the cyclophanene-iron complexes 105b and 105c did give the desired bromine adducts. However, it was found that the reactivity of the bridge double bond in cyclophanenes 56 is very low since most of the attempted reactions failed to give the desired products. The first synthesis of the (η6, η6-anti-4,6,8-trimethyl [2,2] (1,3) cyclophan-1,9-diene)-bis(tricarbonylchromium(0)), 133, was achieved through the dithiacyclophane route. An X-ray structure analysis of 133 was also determined and found that the two aromatic rings were inclined at 19.8° with respect to each other.

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Keywords

Cyclophanes, Metal complexes, Cyclic compounds

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