Complexes of Selected Main Group Element Chlorides and Fluorides with Sterically Non-Demanding Carbenes

  • Since their first isolation in 1991, N-heterocyclic carbenes (NHC) have become an established class of ligands in organometallic and coordination chemistry. In the beginning, these compounds were considered as a chemical curiosity, synthesized for fundamental studies in the laboratory. Later on, their extraordinary properties as ligands in coordination chemistry were recognized and found to be superior by means of electron donation, thermal stability and chemical inertness compared to the already established class of phosphine-ligands. Although many routes for the synthesis of carbene-coordinated transition metal complexes have become established, almost all carbene complexes of main group elements are synthesized by addition of free uncoordinated carbenes. The aim of this work was to investigate synthetic procedures to obtain main group element complexes coordinated with sterically non-demanding carbenes. As these carbene ligands are not stable in their free form, indirect routes for the synthesis of complexes thereof needed to be developed. The two synthetic methods of oxidative addition and carbene-transfer were successfully adopted for the synthesis of carbene-coordinated main group element complexes. As precursors for the oxidative addition reactions, cyclic and acyclic chloro-amidinium chlorides were chosen, which are already used for the synthesis of transition metal carbene complexes. Furthermore, the symmetric fluorine analogs α,α-difluoro-dialkylamines, as well as asymmetric α,α-difluoro-dialkylamines are introduced as carbene precursors. Neutral, hexacoordinated complexes of phosphorus(V) are presented, prepared by oxidative addition of the aforementioned fluorine-containing precursors to different phosphorus(III) compounds. The complexes are characterized and discussed by means of multinuclear NMR spectroscopy and single crystal XRD. Furthermore, three different applications for these phosphorus(V) carbene complexes are given; as an overcharge additive used in state-of-the-art lithium-ion batteries, as liquid crystal compounds and as ionic liquid precursors for carbene-phosphorus cleavage reactions using anhydrous HF. A comparative study on the carbon homologs silicon, germanium and tin was made by synthesizing chloro- and fluoro- complexes in oxidation state +IV, coordinated by cyclic and acyclic carbene ligands via oxidative addition to the respective precursors. All complexes are characterized and discussed by means of multinuclear NMR spectroscopy and by single crystal XRD. Moreover, computational (DFT) studies were made for the silicon(IV) carbene complex NHC-SiCl4 (NHC = 1,3-dimethylimidazolidin-2-ylidene), which conclude that NHC-transfer reactions are feasible using this compound. The theoretical results were proven by NHC-transfer reactions from NHC-SiCl4 to phosphorus(III) compounds to give the NHC-coordinated complexes NHC-PCl2R (R = Cl, Ph, Me), which were studied and discussed by multinuclear NMR-spectroscopy and by single crystal XRD. The complex NHC-PCl3 was oxidized to give a hexacoordinated complex of phosphorus(V), without loss of the NHC-ligand. Furthermore, NHC-transfer was made towards nickel(II) and palladium(II) chloride, to obtain the respective bis-carbene complexes (NHC)2MCl2 (M = Ni, Pd).

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Publishing Institution:IRC-Library, Information Resource Center der Jacobs University Bremen
Granting Institution:Jacobs Univ.
Author:Tobias Böttcher
Referee:Gerd-Volker Röschenthaler, Ulrich Kortz, Thomas Heine, Berthold Hoge
Advisor:Gerd-Volker Röschenthaler
Persistent Identifier (URN):urn:nbn:de:101:1-201305294668
Document Type:PhD Thesis
Date of Successful Oral Defense:2012/07/16
Year of Completion:2012
Date of First Publication:2012/08/02
PhD Degree:Chemistry
School:SES School of Engineering and Science
Library of Congress Classification:Q Science / QD Chemistry / QD450-801 Physical and theoretical chemistry / QD474 Complex compounds
Call No:Thesis 2012/23

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