Main-chain metallopolymers at the static–dynamic boundary based on nickelocene

Abstract

General rightsThis document is made available in accordance with publisher policies. Please cite only the published version using the reference above. AbstractInteractions between metal ions and ligands in metal-containing polymers involve two bonding extremes: persistent covalent bonding, where the polymers are essentially static in nature, or labile coordination bonding, which leads to dynamic supramolecular materials.Main chain polymetallocenes based on ferrocene and cobaltocene fall into the former category due to the presence of strong metal-cyclopentadienyl bonds. Herein we describe a main chain polynickelocene formed by ring-opening polymerization of a moderately strained[3]nickelocenophane monomer, that can be switched between static and dynamic states as a result of the relatively weak Ni-cyclopentadienyl ligand interactions. This is illustrated by the observation that, at low concentration or at elevated temperature in a coordinating or polar solvent, depolymerization of the polynickelocene occurs. A study of this dynamic polymermonomer equilibrium by 1 H NMR spectroscopy allowed for determination of the associated thermodynamic parameters. Microrheology data, however, indicated that under similar conditions the polynickelocene is considered to be static on the shorter, rheological timescale.2

Enantiopure Phospha[1]ferrocenophanes: Textbook Examples of Through‐Space Nuclear Spin–Spin Coupling

“…[1] Early on, their potential as suitable monomerst oa ccessm etal-containing polymers through ring-opening polymerization (ROP) was recognized, but attempts to polymerize the phenyl-substituted species with anionic initiators failed. [10] In addition to their application as monomers, phospha[1]ferrocenophanes are interestingp hosphines and can coordinate as monodentate ligandst ot ransition metals. [4] However,t he exploration into FCPs already began a few years after the discoveryo ff errocene, [5] with the first published derivative being ac arbon-bridged [3]FCP.…”

“…[6] To date, many different ansa-sandwich compounds are known [7] and ROP of strained sandwich compounds is aw ell-established methodtoi ncorporate metals into polymers. [10] In addition to their application as monomers, phospha[1]ferrocenophanes are interestingp hosphines and can coordinate as monodentate ligandst ot ransition metals. While the carbene-stabilized compound D exhibits an unusual bonding pattern, [9] species E is the first strained sandwichcompound revealing reversible ROP.…”

Ring‐Opening Polymerisation of Low‐Strain Nickelocenophanes: Synthesis and Magnetic Properties of Polynickelocenes with Carbon and Silicon Main Chain Spacers

“…In the case of the ROP of 5 , Δ H ROP is small and negative, because the polymerisation is driven by the (albeit small) release of ring strain . To provide an interesting comparison we explored the polymerisation of tetracarba[4]nickelocenophane 8 .…”

“…The polymerisation of 5 is believed to proceed via initial coordination of pyridine to the nickel centre and subsequent cleavage of the Ni−Cp bond, a similar mechanism to that of the photolytic ROP of sila[1]ferrocenophanes, although photoexcitation of the nickel‐based monomer is unnecessary in this case, presumably due to the inherent lability of the Ni−Cp bond. Analysis of the resulting poly(nickelocenylpropylene) by MALDI‐TOF mass spectrometry revealed the presence of both cyclic and linear polymeric species, the former of which suggests that the pyridine initiator is substitutionally labile when coordinated at a [C 5 H 4 R]Ni centre, which may therefore allow for easy displacement by the propagating anionic Cp end group …”

“…Currently, the only reported high molar mass polynickelocene, poly(nickelocenylpropylene) 7 , results from the ROP of tricarba[3]nickelocenophane 5 [α=16.6(1)°] in pyridine (and a number of other polar organic solvents), Scheme . It was also demonstrated that, as a consequence of the weak Ni−Cp bonds (M−Cp dissociation energy is 250 kJ mol −1 for nickelocene vs. 305 kJ mol −1 for ferrocene), the polynickelocene 7 can exist in either a static or labile state depending on the solvent conditions and, in the latter case, forms a dynamic equilibrium with monomer 5 and oligomers 6 x / 7 (Scheme ) .…”