Schröder, Jan
[VerfasserIn]
;
Böttcher, Tobias
[AkademischeR BetreuerIn]Albert-Ludwigs-Universität Freiburg Fakultät für Chemie und Pharmazie
The application of strongly σ-donating diazaboryl substituents in the design of a new class of pyridine ligands in main group chemistry
: : 2,6-bis(diazaboryl)pyridines
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Medientyp:
E-Book
Titel:
The application of strongly σ-donating diazaboryl substituents in the design of a new class of pyridine ligands in main group chemistry
:
2,6-bis(diazaboryl)pyridines
Beschreibung:
Abstract: In this work, 2,6-bis(diazaboryl)pyridines were investigated as a new class of sterically demanding pyridine ligands with enhanced N-donor strength. Quantum chemical calculations on the gas phase basicity of several representatives of the bis(diazaboryl)pyridine ligand system showed the strong σ-electron donating effect of the diazaboryl-groups. Based on the substitution pattern of the pyridine ring and the diazaboryl-groups, the new pyridines can cover a wide range of GB values. A reliable protocol for the synthesis of bis(diazaboryl)pyridines was established starting from 2,6-dibromopyridine to give 2,6-bis(B{OiPr}2)pyridine as an isolable key intermediate. Following this protocol, the four ligands (dabiPr)2py, (dabMe)2py, (dabPh)2py, and (benzodabiPr) 2py were successfully prepared and fully characterized. The application of these pyridines as ligands for reactive main group compounds was investigated. Herein, it was demonstrated that (dabiPr)2py can form neutral 1:1 adducts in the form of (dabiPr)2py•BX3 (X = H, F, Cl) and cationic 1:2 adducts in the form of [(dabiPr)2py•AlX2][AlX4] (X = Cl, Br, I). It was shown that GaCl3 and (dabiPr)2py form a Frustrated Lewis Pair at room temperature, which was used to generate p-block cations by chloride abstraction as demonstrated by the synthesis of [(dabiPr)2py•GeCl][GaCl4] and [(dabiPr)2py•SiHCl2][GaCl4]. The ligand (dabiPr)2py showed different coordination motifs, depending on the coordinated Lewis acid, either exclusively via the pyridine’s N atom or by additional coordination with one or two diazaboryl nitrogen atoms. This additional coordination was found to be hemilabile, as determined by NMR spectroscopy supported by theoretical calculations. Selected adducts of (dabPh)2py and (benzo-dabiPr)2py with BX3 (X = F, Cl, Br) were prepared and structurally characterized. Herein, it was shown that the lower basicity of the Npy and the Ndab atoms leads to a different coordination chemistry compared with (dabiPr)2py. Reduction of (dabiPr)2py with KC8 gave a room temperature stable monomeric pyridine radical anion, in which both charge and spin density were unambiguously found to be located on the pyridine moiety. Its electrochemical properties were investigated with radical scavenger reactions and CV experiments, which revealed that the radical anion is more reducing than potassium naphthanelide