Intermolecular Interactions of CpFePPh3(CO)CO(CH2)5CH3: From a Crystalline Solid to a Supramolecular "Iron-Truss" Polymer

Aromatic Embrace Motifs for Bulk Supramolecular Polymers

Frequently encountered in crystalline materials, aromatic embraces (AEs) are formed when arylated molecules interact through multiple concerted aromatic interactions. AEs are a robust motif that is suitable for the preparation of amorphous bulk supramolecular polymers (BSPs). Crystal engineering revealed that the polymorphic compound (PPh₃ )(Cp)Fe(CO){CO(CH₂ )₅ CH₃ } (Cp=cyclopentadienyl), known as FpC₆ , assembled into various chain structures through several AE motifs. Upon melting, FpC₆ always adopted the same AE motif, which extended into the corresponding embracing "ladder" chains. The resultant BSP displayed typical polymer behaviour, including the presence of a glass transition and viscoelasticity, which allowed the effect of thermal history on the polymerisation behaviour to be explored. The ladder chains formed by the AE remain assembled at temperatures of up to 130 °C and were able to effectively suppress crystallisation during cooling. The ability of the AE to form chains at high temperatures and suppress crystallisation is a new opportunity to advance the field of BSPs and supramolecular chemistry.

Iron-Carbonyl Aqueous Vesicles (MCsomes) by Hydration of [Fe(CO){CO(CH2)5CH3}(Cp)(PPh3)] (FpC6): Highly Integrated Colloids with Aggregation-Induced Self-Enhanced IR Absorption (AI-SEIRA)

Self-assembly of hydrophobic molecules into aqueous colloids contradicts common chemical intuition, but has been achieved through hydration of [Fe(CO){CO(CH2)5CH3}(Cp)(PPh3)] (FpC6). FpC6 has no surface activity, no NMR signals in D2O and no critical aggregation concentration (CAC) in H2O. The molecule, however, contains both acyl and terminal CO groups that are prone to being hydrated. By adding water to a solution in THF, self-assembly of FpC6 can be initiated through water-carbonyl interactions (WCIs) with the highly polarized acyl CO groups. This aggregation subsequently enhances the hydration of the acyl CO groups and also induces the WCI of otherwise unhydrated terminal CO groups. The resultant metal-carbonyl aggregates have been proved to be bilayer vesicles with iron complexes exposed towards water and alkyl chains forming inner walls (MCsomes). These MCsomes show high structure integration upon dilution due to the hydrophobic nature of the building blocks. The highly polarized CO groups on the surface of the MCsomes result in a negative zeta potential (-65 mV) and create a local electric field, which significantly enhances the IR absorption of CO groups by more than 100-fold. This is the first discovery of aggregation-induced self-enhanced IR absorption (AI-SRIRA) without the assistant of external dielectric substrates. Highly integrated MCsomes are, therefore, promising as a novel group of materials, for example, for IR-based sensing and imaging.

End Group Functionalization of PFpP Macromolecules Via Fp Migration Insertion Reactions

PFpP macromolecules, synthesized via migration insertion polymerization of CpFe(CO)2 (CH2)3 PPh2 (FpP), exhibit reactive Fp end groups for further migration insertion reactions in the presence of phosphines. A number of alkyl diphenylphosphines with varied alkyl length, Ph2PCn (n = 6, 10, 18), have been prepared for the reaction, resulting in PFpP-PPh2Cn (n = 6, 10, 18) amphiphiles. The phosphines with longer alkyl chains impose steric hindrance for the reaction and therefore require longer reaction times and excess phosphines relative to PFpP.