Κατεύθυνση Ανόργανη Χημεία και Εφαρμογές της στη ΒιομηχανίαLibrary of the School of Science
Ανδρέας Α. Δανόπουλος, Καθηγητής, Εθνικό και Καποδιστριακό Πανεπιστήμιο Αθηνών
Παναγιώτης Κυρίτσης, Καθηγητής, Εθνικό και Καποδιστριακό Πανεπιστήμιο Αθηνών
Πατρίνα Παρασκευοπούλου, Αναπλ. Καθηγήτρια, Εθνικό και Καποδιστριακό Πανεπιστήμιο Αθηνών
Σύνθεση και μελέτη παραμαγνητικών συμπλόκων ανοιχτής στοιβάδας Cr(II) με Ν-ετεροκυκλικά καρβένια
Synthesis and characterization of open-shell Cr(II) three-coordinated paramagnetic complexes with N-heterocyclic carbenes
In the following thesis presenting, we synthesized and characterized a group of open-shell Cr(II) (d4) three-coordinated paramagnetic complexes, using a series of N−heterocyclic carbenes as ligands. The carbenes that we used were the IMes = 1,3-bis-(2,4,6-trimethylphenyl)-imidazol-2-ylidene, IPr = 1,3-bis-(2,6-diisopropylphenyl)-imidazol-2-ylidene, CAACMe2 = 5,5-dimethyl-3,3-dimethyl-2-(2′,6′-diisopropylphenyl)-pyrrolidine-1-ylidene and IPr* = 1,3-bis(2,6-dibenzhydryl-4-methylphenyl)imidazol-2-ylidene, which differ from each other in their stereoelectronic (σ-donating, π-accepting) properties.
We synthesized nine metal complexes of the type [Cr(II)Χ2Y] where X = −CH2C6H5 and −N(SiMe3)2 group, and Y= NHC seven of which have not been reported in the literature yet. The complexes are all paramagnetic and the molecular geometry model is distorted trigonal−planar around the centered metal ion, which is very interesting for the CrII chemistry because it’s usually unstable to isolate in low coordination geometries. A new tetra-nuclear complex of type [(Cr(κΝ,μ2−Ν(SiMe3)(SiMe2(κC,μ’2−CH2)))4] was also synthesized by a thermolysis reaction of the [Cr(N(SiMe3)2)2)(THF)2] complex possibly via a C−H bond activation of the −N(SiMe3)2 group. The four chromous centers are on the edges of the square-planar geometry coordinated by two N atoms and two C atoms. The small dimetallic distance between two metal centers reveals the existence of a quadruple bond.
All metal-complexes were characterized by paramagnetic 1H NMR, X-ray crystallography and UV−vis spectroscopy. Due to the paramagnetic behavior, the magnetic susceptibility μeff was measured for several complexes using the Evans method. The results showed that for the three-coordinated complexes the number of unpaired electrons is four (S = 2) while in the tetra-nuclear metal complex the μeff value was found relatively low.
Main subject category:
N-heterocyclic Carbenes, Chromium, Paramagnetic NMR, Low Coordination Number, X-ray Crystallography, Trigonal Geometry, Metal−Metal bond
Number of references:
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