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Syntheses, Structures and Electronic Properties of Zwitterionic Iron(II) and Cobalt(II) Complexes Featuring Ambidentate Tris(pyrazolyl)methanide Ligands
Author(s) -
Kuzu Istemi,
Krummenacher Ivo,
Hewitt Ian J.,
Lan Yanhua,
Mereacre Valeriu,
Powell Annie K.,
Höfer Peter,
Harmer Jeffrey,
Breher Frank
Publication year - 2009
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200802317
Subject(s) - chemistry , carbanion , crystallography , ligand (biochemistry) , transition metal , cobalt , deprotonation , metal , homoleptic , tris , density functional theory , photochemistry , stereochemistry , inorganic chemistry , computational chemistry , organic chemistry , catalysis , ion , biochemistry , receptor
Zwitterionic “sandwiches” : Combined preparative, spectroscopic and theoretical studies on the syntheses, structures and electronic properties of zwitterionic iron(II) and cobalt(II) sandwich complexes [M( Me Tpmd) 2 ] containing κ 3 N ‐coordinated tris(pyrazolyl)methanide ligands ( Me Tpmd; see picture) are presented.By deprotonation of the corresponding tris(pyrazolyl)methane ( Me Tpm) precursor complexes [M( Me Tpm) 2 ][(OTf) 2 ] ( 1 and 2 ), the zwitterionic tris(pyrazolyl)methanide iron(II) ( 3 ) and cobalt(II) ( 4 ) “sandwich” complexes of the general formula [M( Me Tpmd) 2 ] are easily accessible. The structurally characterised complexes 3 and 4 are the first such homoleptic 3d transition metal species to feature two “naked”, outward pointing pyramidal carbanions. Density functional theory calculations show metal‐centred HOMOs and LUMOs with the destabilised carbanion orbitals in the energy region of the filled transition‐metal‐centred frontier orbitals. The electronic structures of these complexes have been investigated in detail by various spectroscopic techniques such as NMR, EPR, SQUID, Mössbauer, etc. Both complexes adopt a high‐spin (HS) configuration at room temperature in solution and in the solid state. A thermally induced high‐spin to low‐spin (HS–LS) transition is observed for the iron(II) complex 3 . The HS–LS transition temperature of 3 in solution differs from that in the solid state, which in turn strongly depends on the amount of solvent molecules in the crystal lattice. Electrochemical studies on the corresponding cobalt(II) complex 4 provide evidence for a HS‐Co II ⇌LS–Co III transition upon oxidation, which was confirmed by preliminary synthetic oxidation reactions. Overall, it can be concluded that the related κ 3 N ‐donor ligands tris(pyrazolyl)hydroborates (Tp R ) and R Tpmd ligands have similar bonding properties and that the metal cations experience more or less the same ligand environment.