Synthesis and characterization of open-shell Cr(II) three-coordinated paramagnetic complexes with N-heterocyclic carbenes

Postgraduate Thesis uoadl:2962508 13 Read counter

Unit:
Κατεύθυνση Ανόργανη Χημεία και Εφαρμογές της στη Βιομηχανία
Library of the School of Science
Deposit date:
2021-10-12
Year:
2021
Author:
Danopoulou Maria-Anna
Supervisors info:
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
Original Title:
Σύνθεση και μελέτη παραμαγνητικών συμπλόκων ανοιχτής στοιβάδας Cr(II) με Ν-ετεροκυκλικά καρβένια
Languages:
Greek
Translated title:
Synthesis and characterization of open-shell Cr(II) three-coordinated paramagnetic complexes with N-heterocyclic carbenes
Summary:
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:
Science
Keywords:
N-heterocyclic Carbenes, Chromium, Paramagnetic NMR, Low Coordination Number, X-ray Crystallography, Trigonal Geometry, Metal−Metal bond
Index:
Yes
Number of index pages:
3
Contains images:
Yes
Number of references:
131
Number of pages:
137

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