Copper-Mediated Polycondensations of Substituted Diiodoferrocenes and Bis(stannyl)ferrocenes:  Synthesis and Properties of Soluble Polyferrocenylenes Containing Trimethylsilyl or Methyl Groups

Abstract

Low to moderate molecular weight substituted polyferrocenylenes [(η 5 -C5H3X)Fe(η 5 -C5H3X)]n (where 3a-3c, X ) H, SiMe3, Me) were prepared from the Ullmann coupling reaction of the diiodoferrocenes, (η 5 -C5H3XI)2Fe (2a-2c), with an excess of copper metal or alternatively CuCl-facilitated coupling of the bis(stannyl)ferrocene, (η 5 -C5H3SiMe3SnBu3)2Fe (1b). The new monomers were characterized by 1 H and 13 C NMR spectroscopy, elemental analysis and mass spectrometry. A single-crystal X-ray diffraction study (η 5 -C5H3SiMe3I)2Fe (2b) shows the disubstituted cyclopentadienyl rings are eclipsed with the substituents staggered by 20°. The molecular weights (Mw) for the soluble homopolymers 3b and 3c were estimated by gel permeation chromatography in THF vs polystyrene standards and were found in the range from 2.0 × 10 3 to 1 × 10 4 with generally broad polydispersities (PDI > 2). Polymers 3b and 3c were characterized by 1 H and 13 C NMR spectroscopy and elemental analysis. The polymer thermal transition behavior and morphology of 3a-3c were examined by differential scanning calorimetry (DSC) and by powder X-ray diffraction (PXRD). The amorphous nature of the disubstituted polymers 3b and 3c was evident by the presence of weak glass transitions and the absence of any melt transitions. In contrast, the semicrystalline nature of the largely insoluble polyferrocenylene 3a led to the presence of a strong melt transition by DSC in addition to three sharp peaks in its the PXRD spectrum. The polymers 3b and 3c as well as their I 2 and TCNE oxidized products (4b, 4c and 5b, 5c) were characterized by UV/vis/NIR spectroscopy. The neutral polymers 3b and 3c showed only weak d-d visible transition centered near λ ) 480 nm, while the partially oxidized derivatives showed strong charge-transfer peaks in the visible λ ) 630-700 nm) and broad intervalence charge-transfer transitions between λ ) 850 and 1900 nm. Cyclic voltammetry of the neutral polymers 3b and 3c showed two well-separated oxidation waves with ∆E 1/2 values of 485 and 460 mV s -1 respectively and were consistent with substantial interaction between neighboring metal centers. Mo ¨ssbauer data of the partial oxidized dimethylferrocene polymer 5c with TCNE at room temperature indicates that electron transfer is valence trapped with distinct Fe 2+ and Fe 3+ sites.

Main‐Chain Polymetallocenes with Short Spacer Groups

“…3.4) [40]. 10 ±7 s) [40]. These polymers possess molecular weights in the range of M n & 1500±3600 (PDI & 1.5±3.0).…”

Sandwich Complex‐Containing Macromolecules: Property Tunability Through Versatile Synthesis

“…The T g s of this series of polymers decreased as the size of the substituent on the Cp rings increased; indeed, polymer 58 , without a substituent, featured a T m (Table ) and was crystalline, as suggested from powder X‐ray diffraction (p‐XRD) analysis. Cyclic voltammograms of the polymers showed two resolved and reversible CV waves separated by about 0.5 V, which the authors attributed to enhanced electronic communication between the iron centers …”

“…Like other macromolecules, sandwich complex‐containing macromolecules can be obtained through step polymerization mechanisms, which include esterification, hydrosilylation, amidation, and aromatic substitution, as well as other substitution reactions. These step polymerization reactions offer the opportunity to tune the properties of the sandwich complex‐containing macromolecule through the incorporation of various spacers . Electronics as well as the structure of the spacers tunes electronic interaction between the metal centers, solubility, and thermal properties of the resulting polymer.…”

“…[ 38 ] Facilitated by the appreciable susceptibility of the Cp rings to nucleophilic substitution and addition reaction, metal-mediated coupling reaction of dihaloferrocenes is a widely employed synthetic methodology for the synthesis of ferrocene-containing macromolecules. [74][75][76][77]80,86 ] A copper-or magnesium-mediated Ullmann coupling of diiodoferrocenes yielded poly(ferrocenylene)s ( 58 , 61, and 62 ) that were characterized by broad PDI (PDI = 1.30-3.01) and low to moderate molecular weights (M n = 1840-10 650 g mol −1 ) (Scheme 7 ). [ 86 ] The T g s of this series of polymers decreased as the size of the substituent on the Cp rings increased; indeed, polymer 58 , without a substituent, featured a T m ( Table 2 ) and was crystalline, as suggested from powder X-ray diffraction Figure 11.…”

“…[74][75][76][77]80,86 ] A copper-or magnesium-mediated Ullmann coupling of diiodoferrocenes yielded poly(ferrocenylene)s ( 58 , 61, and 62 ) that were characterized by broad PDI (PDI = 1.30-3.01) and low to moderate molecular weights (M n = 1840-10 650 g mol −1 ) (Scheme 7 ). [ 86 ] The T g s of this series of polymers decreased as the size of the substituent on the Cp rings increased; indeed, polymer 58 , without a substituent, featured a T m ( Table 2 ) and was crystalline, as suggested from powder X-ray diffraction Figure 11. Structures of silane-( 45 and 46 ) [ 103 ] and siloxane-bridged ( 47 ) [ 104 ] oligo(ferrocene)s. Measured in a THF solution containing about 1 × 10 −3 M of the monomer unit and 0.1 M of [( n -Bu) 4 N]PF 6 .…”