Main‐Chain Heterobimetallic Block Copolymers: Synthesis and Self‐Assembly of Polyferrocenylsilane‐b‐Poly(cobaltoceniumethylene)

Abstract

Metal-containing polymers are attracting growing attention as functional materials as a result of the useful physical and catalytic properties that arise from the presence of metal centers.[1] For example, metallopolymers with reversible redox properties are of interest for applications in electrocatalysis [2] and sensing, [3] as responsive surfaces [4] and capsules, [5] and as the active components of photonic crystal displays.[6] Block copolymers containing metal centers present additional features of considerable interest as a result of their ability to undergo self-assembly in the solid state or solution. Studies of such materials have led to applications as nanotemplates in lithography [7] and as precursors to patterned magnetic nanostructures [8] and nanocatalysts for carbon nanotube growth.[9] However, the synthesis of materials containing metalloblocks by living polymerization protocols presents substantial challenges as a result of undesirable side reactions of many metal centers with ionic and radical propagating sites. Herein, we describe our initial results on the synthesis and properties of unusual main-chain heterobimetallic diblock copolymers with different redox-active centers in each metalloblock.The ring-opening polymerization (ROP) of strained metallocenophanes 1 provides a well-studied route to functional metallopolymers 2. [10][11][12] In particular, the ROP of 18-electron sila[1]ferrocenophanes (1, M= Fe, E x R y = SiR 2 ) represents a useful route to polyferrocenylsilanes (PFSs, 2, M = Fe, E x R y = SiR 2 ) which exhibit many interesting characteristics.[13] Living anionic polymerization of sila[1]ferrocenophanes (1, M = Fe, E x R y = SiR 2 ) using organolithium initiators such as nBuLi proceeds by cleavage of the Si-Cp bond (Cp = cyclopentadienyl), and has been developed as a route to a variety of PFS block copolymers.[14] An alternative procedure, living photocontrolled ROP in the presence of cyclopentadienide anion initiators, [15] involves photoactivation and subsequent cleavage of the Fe-Cp bond. + homopolymer and also ring-opening oligomerizations of 3 appeared to proceed through Co-Cp bond cleavage. [19] The successful synthesis of PFS-b- [PCE] + block copolymers was accomplished by sequential photocontrolled ROP of 1 (M = Fe, E x R y = SiMe 2 ) and 3 followed by oxidation of the 19-electron cobaltocene centers (Scheme 1). [19][20][21][22] The living PFS blocks were synthesized by addition of sodium cyclopentadienide (NaCp) as initiator to a solution of 1 (M = Fe, E x R y = SiMe 2 ) in tetrahydrofuran (THF) under anhydrous conditions, followed by prolonged irradiation (5-24 h) of the solutions at 5 8C. The living PFS chains were then combined with 19-electron cobaltocenophane 3, and the solutions irradiated at 20 8C (to increase solubility) until the block copolymers precipitated from solution (15-24 h). The living polymer chains were quenched by, and the resulting product washed with degassed methanol, oxidized by air in the presence of ammonium triflate ([NH 4 ][OTf]), and dia...

Syntheses of Monosubstituted Rhodocenium Derivatives, Monomers, and Polymers

“…Peaks at 6.58, 6.10, and 5.93 ppm were assigned to protons from the Cp rings (protons "a, b, and c"). 13 C and 19 F NMR spectra ( Figure S10), high-resolution mass spectrum (Figure S11), and organic (C/H/N) elemental analysis results were consistent with the assigned structure.…”

Recent developments with strained metallocenophanes

“…The sequential photocontrolled ROP of ferrocenophanes and cobaltocenophanes was later demonstrated via the synthesis of PFS-b-PCE block polymers 27a and 27b (Scheme 8). The synthesis was achieved via the addition of a living PFS macroinitiator to 24 with UV irradiation, followed by subsequent oxidation of the resulting polymer [30].…”

Side-Chain Cobaltocenium-Containing Polymers: Controlled Polymerization and Applications

“…By incorporation of functional sandwich-structured metallocenes into polymer materials, metallocene-based polymers represent classical metallopolymers (3)(4)(5). Different from conventional neutral ferrocene-containing polymers (6), cobaltocenium-containing polymers are unique due to their charged state and highly stable chemical property, in other words, a novel metal-containing polyelectrolyte (7,8). However, because of the charged state, there has been a considerable challenge to synthesize mono-substituted cobaltocenium, which is the first step to prepare side-chain cobaltocenium-containing polymers (9).…”

“…For main-chain cobaltocenium-containing polymers, the readers should refer to recent work carried out by the Manners group (7,8,19,20).…”