Iron in a Cage: Fixation of a Fe(II)tpy2 Complex by Fourfold Interlinking.

Thomas Brandl,Alessandro Prescimone,Sven Johannsen,Stefan Bernhard,Mario Ruben,Manuel Gruber,Nithin Suryadevara,Richard Berndt,Daniel Häussinger,Marcel Mayor

doi:10.1002/anie.202006340

Abstract

The coordination sphere of the Fe(II) terpyridine complex 1 is rigidified by fourfold interlinking of both terpyridine ligands. Profiting from an octa‐aldehyde precursor complex, the ideal dimensions of the interlinking structures are determined by reversible Schiff‐base formation, before irreversible Wittig olefination provided the rigidified complex. Reversed‐phase HPLC enables the isolation of the all‐trans isomer of the Fe(II) terpyridine complex 1, which is fully characterized. While temperature independent low‐spin states were recorded with superconducting quantum interference device (SQUID) measurements for both, the open precursor 8 and the interlinked complex 1, evidence of the increased rigidity of the ligand sphere in 1 was provided by proton T2 relaxation NMR experiments. The ligand sphere fixation in the macrocyclized complex 1 even reaches a level resisting substantial deformation upon deposition on an Au(111) surface, as demonstrated by its pristine form in a low temperature ultra‐high vacuum scanning tunneling microscope experiment.

Highlights

The coordination sphere of the Fe(II) terpyridine complex 1 is rigidified by fourfold interlinking of both terpyridine ligands
While these mechanically controlled break junction (MCBJ) based single molecule experiments showing the potential of Fe(II)tpy2 complexes as switchable subunits were encouraging, scanning tunneling microscopy (STM) may provide insights into the arrangement of the molecule at the electrode surface and its electron transport
Upon deposition on Au(111) in an ultra-high vacuum (UHV) STM set-up the complex disintegrated as clearly documented by the macrocycle spread on the metal surface (Supporting Information, Figure SI22).[11]

Summary

Introduction

The coordination sphere of the Fe(II) terpyridine complex 1 is rigidified by fourfold interlinking of both terpyridine ligands. While reaction conditions favoring the formation of the fourfold interlinked complex 2 could be found (8 equivalents of the diamine in refluxing 1,2dichloroethane (83.5 8C) for 10 days, Figure SI19 in the Supporting Information), all attempts to isolate the fourfold interlinked structure 2 failed, pointing at the lability of the imine bonds.

Results

Conclusion