Fluorene Derivatives Bearing Halogenomethyl Groups: Synthesis, Molecular Structures, and Halogen/Hydrogen Bonding Patterns in the Crystalline State

Abstract

9,9‐Diethylfluorenes bearing chloromethyl, bromomethyl, and iodomethyl groups in the 2, 4, and 7 positions of the aromatic skeleton were prepared and their solid‐state structures determined by single‐crystal X‐ray diffraction analysis. The prepared fluorenes represent not only valuable starting materials for a wide range of fluorene‐based compounds but are also interesting objects for the analysis of the supramolecular motifs in the crystalline state. The X‐ray diffraction experiments revealed that the asymmetric unit of each structure contains one molecule, featuring similar conformations, but differ in their modes of non‐covalent intermolecular bonding. The crystal structures of the chloromethyl and bromomethyl substituted compounds 1 and 2 are primarily stabilized by Hal···Hal and C–H···Hal contacts, whereas the packing of the iodine substituted analogous compound 3 is influenced by triangular I3 synthons, C–H···π interactions and to a less degree by C–H···I contacts. The manuscript provides information about new synthetic routes, new molecules as well as about halogen/hydrogen bonding patterns and other noncovalent interactions in the crystalline state. Concerning the syntheses, the efficient one‐step synthesis of 9,9‐diethylfluorene‐2,4,7‐tricarbaldehyde (8) is also worthy of particular mention.

Fluorene Derivatives Bearing Two to Seven Phthalimidomethyl Groups: Syntheses, Crystal Structures and Conversion to Amines

“…Recently we have reported the syntheses of compounds 1 and 2 on the basis of a three-step procedure, [9] starting with the ethylation of 9H-fluorene (see Scheme 1 and Scheme S1). The 9,9-diethyl-9H-fluorene (9) was further converted into 2,7-bis (bromomethyl)-9,9-diethyl-9H-fluorene (7) and 2,4,7-tris (bromomethyl)-9,9-diethyl-9H-fluorene (8), which were finally treated with potassium phthalimide to obtain the desired compounds 1 and 2. We have now found that the incorporation Figure 1.…”

“…Fluorenes bearing halogen, formyl, or amino groups are useful starting materials for a wide range of fluorene-based acyclic and macrocyclic compounds as well as polymers. Recently, we have described the syntheses and crystal structures of halogenomethyl substituted 9,9-diethylfluorenes [8] as well as their further synthetic transformations. [8,9] For example, 2,4,7-tris(bromomethyl)-9,9diethyl-9H-fluorene was the basis for the syntheses of a series of 9,9-diethyl-9H-fluorenes bearing various functional groups, [9] some of which are shown in Figure 1a.…”

“…Recently, we have described the syntheses and crystal structures of halogenomethyl substituted 9,9-diethylfluorenes [8] as well as their further synthetic transformations. [8,9] For example, 2,4,7-tris(bromomethyl)-9,9diethyl-9H-fluorene was the basis for the syntheses of a series of 9,9-diethyl-9H-fluorenes bearing various functional groups, [9] some of which are shown in Figure 1a. Furthermore, fluorene derivatives bearing two or three aminomethyl groups have been used by us as starting materials for the preparation of acyclic and macrocyclic compounds, [9] which are exemplarily shown in Figure 1b and Figure 1c, respectively.…”

Syntheses of Acyclic and Macrocyclic Compounds Derived from 9,9‐Diethylfluorene (Part I)

“…Recently we have described the syntheses and crystal structures of halogenomethyl-substituted 9,9-diethylfluorenes 1-3 ( Figure 1), which are not only valuable starting materials for the preparation of various fluorene-based compounds, but also interesting building blocks for the formation of different supramolecular motifs in the crystalline state. [9] For example, the crystal structure of the iodomethyl substituted derivative 3 is characterized by the presence of an unusual triangular I 3 synthon consisting of two I•••I contacts with type I geometry and one I•••I contact that corresponds to the polarization-induced type II category. Regarding the synthetic applications described in our previous work, [9] the efficient one-step synthesis of 9,9-diethylfluorene-2,4,7-tricarbaldehyde (4) on the basis of 2,4,7-tris(bromomethyl)-9,9-diethylfluorene (2), providing three-fold higher yield of 4 than the known three-step reaction sequence, is worthy of particular mention.…”

“…[9] For example, the crystal structure of the iodomethyl substituted derivative 3 is characterized by the presence of an unusual triangular I 3 synthon consisting of two I•••I contacts with type I geometry and one I•••I contact that corresponds to the polarization-induced type II category. Regarding the synthetic applications described in our previous work, [9] the efficient one-step synthesis of 9,9-diethylfluorene-2,4,7-tricarbaldehyde (4) on the basis of 2,4,7-tris(bromomethyl)-9,9-diethylfluorene (2), providing three-fold higher yield of 4 than the known three-step reaction sequence, is worthy of particular mention.…”