Branching the Electron-Reservoir Complex [Fe(η⁵-C₅H₅)(η⁶-C₆Me₆)][PF₆] onto Large Dendrimers: “Click”, Amide, and Ionic Bonds

Abstract

Several strategies have been used to functionalize 1,3,5-trisubstituted arene-cored dendrimers with the organometallic electron-reservoir moiety [Fe(eta(5)-C(5)H(5))(eta(6)-C(6)Me(6))](+), 1, to provide dendritic multielectron reservoirs. They all start from the carboxylic acid [Fe(eta(5)-C(5)H(4)COOH)(eta(6)-C(6)Me(6))][PF(6)], 2, or its acyl chloride derivative [Fe(eta(5)-C(5)H(4)COCl)(eta(6)-C(6)Me(6))][PF(6)], 3. For this purpose, a series of new polyamine dendrimers from G(0) to G(2) with 1--> 3 C connectivity of the branching to the core have been synthesized. Amide, "click" and ionic ammonium carboxylate linkage successfully provided G(0), G(1), and G(2) metallodendrimers with 9, 27, and 81 cationic terminal organoiron groups respectively. Further construction of large metallodendrimers up to G(7) with approximately 14 000 organoiron termini was only possible by combining amide, "click", and tether lengthening strategies to avoid steric bulk at the dendrimer periphery. Reduction of the 18-electron Fe(II) metallodendrimers, exemplified by a G(4)-DAB-64-Fe(II) complex, was achieved exergonically using the parent electron-reservoir complex [Fe(eta(5)-C(5)H(5))(eta(6)-C(6)Me(6))], 1a, at -30 degrees C in MeCN, which allowed further reduction of 64 equiv of C(60) to C(60)(*-) using the 19-electron Fe(I) metallodendrimer.

ROMP Synthesis and Redox Properties of Polycationic Metallopolymers Containing the Electron-Reservoir Complex [Fe(η5-C5H5)(η6-C6Me6)][PF6]

“…Furthermore, the IR ( Figure S4) and UV−vis. ( Figure S5) spectra are also consistent with the structure of 3 including the mixed-sandwich complex [FeCp(η 6 -C 6 Me 6 )][PF 6 ].…”

“…5 However, only a few dendritic molecules containing the complex [FeCp(η 6 -C 6 Me 6 )] [PF 6 ] connected to the branch termini have so far been reported, due to the difficulty related to the weak solubility resulting from the simultaneous presence in this complex of the positive charge and large bulk of the arene ligand. 6 We therefore envisaged to introduce this complex on the side branches of polymers given the fast and living polymerization provided by the third-generation Grubbs ruthenium ring-opening metathesis polymerization (ROMP) catalyst. 7 The use of this very useful ROMP catalyst 4 for poly(alkyl)metallocene synthesis has been initiated in 2012, 8 and these seminal studies have been followed by reports of other polymetallocene derivatives using this catalyst.…”

Design of blue fluorescence emitter star-shaped macromolecules based on pyrene and anthracene

“…[1][2][3][4] In particular, the incorporation of the transition-metal sandwich complexes within macromolecular structures is of great interest due to the stereoelectronic characteristics of the delocalized π-cyclic ring ligands. [5][6][7][8] The presence of many equivalent, noninteracting redox-active units affords the simultaneous exchange of a large number of electrons that increase the electron transfer rate. [9] The focus of our research group has been on the use of η 6 -aryl-η 5 -cyclopentadienyliron (II) complexes in the design of many classes of macromolecules which included linear polymers, [10] starshaped macromolecules, [11,12] dendrimers, [13,14] and hyperbranched polymers.…”

The Redox Functions of Metallodendrimers

“…In this series, dendrimers have recently been reported with the sandwich group linked to the dendritic core via the Cp [130] or via the arene ligand [131]. Star-shape hexametallic complexes bearing [Fe(g 5 -C 5 H 4 R)(g 6 -arene)][PF 6 ] termini were shown to serve as redox catalysts for nitrate and nitrite reduction to ammonia in basic aqueous medium [132,133].…”

“…per dendrimer branch) led to the transfer of one electron to C 60 per branch [144] and to the formation of a dendrimer with 64 [Fe(II)(g 5 -C 5 H 4 R)(g 6 -C 6 Me 6 )] ? (C 60 ) -termini [130].…”