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d–d Dative Bonding Between Iron and the Alkaline‐Earth Metals Calcium, Strontium, and Barium
Author(s) -
Stegner Philipp,
Färber Christian,
Oetzel Jan,
Siemeling Ulrich,
Wiesinger Michael,
Langer Jens,
Pan Sudip,
Holzmann Nicole,
Frenking Gernot,
Albold Uta,
Sarkar Biprajit,
Harder Sjoerd
Publication year - 2020
Publication title -
angewandte chemie international edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.831
H-Index - 550
eISSN - 1521-3773
pISSN - 1433-7851
DOI - 10.1002/anie.202005774
Subject(s) - alkaline earth metal , chemistry , strontium , barium , intramolecular force , inorganic chemistry , metal , crystallography , stereochemistry , organic chemistry
Double deprotonation of the diamine 1,1′‐( t BuCH 2 NH)‐ferrocene ( 1 ‐H 2 ) by alkaline‐earth (Ae) or Eu II metal reagents gave the complexes 1 ‐Ae (Ae=Mg, Ca, Sr, Ba) and 1 ‐Eu. 1 ‐Mg crystallized as a monomer while the heavier complexes crystallized as dimers. The Fe⋅⋅⋅Mg distance in 1 ‐Mg is too long for a bonding interaction, but short Fe⋅⋅⋅Ae distances in 1 ‐Ca, 1 ‐Sr, and 1 ‐Ba clearly support intramolecular Fe⋅⋅⋅Ae bonding. Further evidence for interactions is provided by a tilting of the Cp rings and the related 1 H NMR chemical‐shift difference between the Cp α and β protons. While electrochemical studies are complicated by complex decomposition, UV/Vis spectral features of the complexes support Fe→Ae dative bonding. A comprehensive bonding analysis of all 1 ‐Ae complexes shows that the heavier species 1 ‐Ca, 1 ‐Sr, and 1 ‐Ba possess genuine Fe→Ae bonds which involve vacant d‐orbitals of the alkaline‐earth atoms and partially filled d‐orbitals on Fe. In 1 ‐Mg, a weak Fe→Mg donation into vacant p‐orbitals of the Mg atom is observed.