π Conjugation Transmitted across a d‐Electron Metallocene in Ferrocenothiaporphyrin Macrocycles

Abstract

The investigation of ferrocenophanes has been effectively stimulated by the search for useful starting building blocks for the preparation of new organometallic complexes and functional materials, efficient catalyst components, and redoxactive modifiers of biomolecules.[1] The ability of ferrocenophanes to produce functional metallopolymers by ring-opening polymerization (ROP) provides a continuous momentum to the field.[2] The electronic properties of metallocene units embedded in ansa structures are of fundamental importance in determining their overall molecular properties (Scheme 1). However, in the majority of systems explored to date, the electronic communication between externally bridged cyclopentadienyl (Cp) rings was rather limited, as shown by structural and spectroscopic data. [3][4][5] Another approach to probing the effectiveness of electronic conjugation across a sandwich complex is the incorporation of a metallocene subunit into an otherwise fully pconjugated macrocycle. However, none of conjugated ferrocenophanes reported to date revealed features characteristic of macrocyclic aromaticity. [3][4][5] More recently, we have considered heterocyclic macrocycles of the general structure 1, combining the structural features of ansa-metallocenes and porphyrinoids.[6] To date, a number of bridged pyrrolic ansaferrocene, [7] ferrocene-calixpyrrole, [8] and ferrocene-calixphyrin [6,9] hybrids have been reported (e.g., 2), [6] which were based on a similar structural paradigm except that p conjugation in the oligopyrrin chain was interrupted by sp 3 -hybridized meso bridges.We have surmised that upon achieving complete conjugation in the oligopyrrin, the metallocene unit, occasionally described as a three-dimensional equivalent of p-electron aromatic units, [10] will contribute to metallomacrocyclic aromaticity in a similar fashion as various "two-dimensional" hetero-and carbocyclic rings commonly incorporated into porphyrinoid analogues.[11] Herein we report the synthesis and characterization of ferrocenothiaporphyrin 5 and dihydroferrocenothiaporphyrin 6, which possess macrocyclic antiaromaticity and aromaticity, respectively. These two systems provide evidence for direct transmission of p-electron conjugation across a d-electron metallocene.The title compound, ferrocenothiaporphyrin ([1-4,21-24,25,29h-25,29-dihydro-25,29-dicarba-27-thiapentapyrrin-25,29-diyl]iron(II)) 5, was obtained in a [3+1] macrocyclization reaction that involved 1,1'-bis[phenyl(2-pyrrolyl)methyl]ferrocene 3 and 2,5-bis[hydroxy(p-tolyl)-methyl]thiophene 4, which were condensed under Lindsey-type conditions (Scheme 2). After oxidation with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) and column chromatography, the procedure afforded 5 as a dark brown compound in 9 % yield. Scheme 1. Incorporation of ferrocene into a porphyrinoid macrocycle.(1: X = N, NH, O, S; 2: R 1 = Me, R 2 = tolyl (Tol), 2a: R 1 = R 2 = H).Scheme 2. Synthesis and reactivity of 5 and 6 (R 1 = Ph, R 2 = Tol). The partial p-electron pathway is shown in bold.

A meso‐Tetraaryl‐21‐carbaporphyrin: Incorporation of a Cyclopentadiene Unit into a Porphyrin Architecture

“…Evidently the iron(II) cation, unambiguously originating from the ferrocene unit of 11,i sr eadily inserted into the [CNNN] core of 7,a ffording 7-Fe. [27] Thes tructure of 7 was determined by X-ray crystallography ( Figure 1). Acidic demetallation liberated 7 and the total synthetic yield of 7 was 11 %.…”

“…[26] Thereaction of 13 with n-buthyllithium yielded the 1,3-dilithium-ferrocene 14,w hich reacted with arylaldehyde to afford the 1,3bis(arylhydroxymethyl)ferrocene 10.T he diol 10 was subsequently subjected to condensation with an excess of pyrrole according to related procedures to form the 1,3-bis-(aryl(pyrrol-2-yl)methyl)ferrocene 11 as the mixture of six stereoisomers. [27] Thecondensation of 11 with pyrrole and arylaldehyde was undertaken using the conditions reported by Lindsey et al [5] and the product was oxidized using 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) to form 7 (Scheme 4). During chromatography fractions containing 7-Few ere also separated.…”

“…Still, as checked in the course of these investigations,t he analogous facile acid triggered decomposition of the ferrocene unit in the presence of acid in excess appears to be characteristic for ferrocenothiaporphyrin. [27] Thes tructure of 7 was determined by X-ray crystallography ( Figure 1). [32] Them acrocyclic pattern resembles the gold(III) meso-tetraryl-21-carbaporphyrin 7-Au.…”

Double‐Decker Ferrocene‐Type Complex of N‐Fused Porphyrin: A Model of π‐Extended Ferrocene?

“…Incidentally, ferrocenes and ruthenocenes embedded in or conjugated with porphyrinoids have been reported increasingly in recent years, and hence rapid expansion in this field would help us to understand this issue. [5,20] In summary, we have synthesized the double-decker ferrocene-type NFTPp complex 2 in a one-pot manner, and its crystal structure was determined. The properties of 2 are discussed from three viewpoints.…”

The development of artificial porphyrinoids embedded with functional building blocks

“…63 As a pioneering work, Latos-Grażyński et al employed coremodified porphyrin as a platform to investigate the electronic conjugation across metallocene in a fully conjugated macrocycle. Ferrocenothiaporphyrin 81 64 The relatively broad absorption bands at 356 nm and 455 nm changed into an intense peak at 410 nm accompanied by several weaker bands between 500-800 nm upon reduction by NaBH 4 or a controlled electrochemical reduction at potential E app = À1.35 V. Due to N-H tautomerism, the thienopyrrole unit acted as a switch to tune the aromaticity of heteroporphyrin between the stable nonaromatic 88 and 20p antiaromatic 89 under proper redox conditions. The ACID isosurface plot for 88 predicted relatively poor electron conjugation, as there is a disrupted pattern within the electronic current.…”