Browsing by Author "Rudolf, Richard"

Now showing 1 - 4 of 4

Open Access
Leveraging N-exo substituents to tune the donor/acceptor properties of mesoionic imines (MIIs)
(2024) Rudolf, Richard; Todorovski, Andrej; Schubert, Hartmut; Sarkar, Biprajit
In this work, we show two synthetic routes to substitute the Nexo position of mesoionic imines (MIIs). By Buchwald-Hartwig amination, 5-amino-1,2,3-triazoles can be arylated at the said position, showing the versatility of amino-triazoles as building blocks for MIIs. The reaction of MIIs with electrophiles (MeI, fluoro-arenes) highlights the nucleophilic nature of MIIs as even at room temperature aromatic C-F bonds can be activated with MIIs. By combining experimental methods such as Tolman/Huynh-electronic-parameter and crystallographic interpretations with theoretical calculations, we establish that MIIs expand the nucleophilicity scale of N-donors. Contrary to the flanking substituents on the triazole scaffold, the Nexo substituent heavily influences the donating ability of MIIs: electron-withdrawing substituents will dramatically decrease the donor strength of the MII ligand. We have now established ways to functionalise not only the triazole backbone but also the Nexo position. More importantly, we show here how the substitution pattern influences the electronic structure of MIIs. Such electronic tunability should make MIIs suitable for use in various fields of chemistry.
Open Access
Mesoionic imines (MIIs) : strong donors and versatile ligands for transition metals and main group substrates
(2022) Rudolf, Richard; Neuman, Nicolás I.; Walter, Robert R. M.; Ringenberg, Mark. R.; Sarkar, Biprajit
We report the synthesis and the reactivity of 1,2,3‐triazolin‐5‐imine type mesoionic imines (MIIs). The MIIs are accessible by a base‐mediated cycloaddition between a substituted acetonitrile and an aromatic azide, methylation by established routes and subsequent deprotonation. C=O‐stretching frequencies in MII-CO2 and -Rh(CO)2Cl complexes were used to determine the overall donor strength. The MIIs are stronger donors than the N‐heterocyclic imines (NHIs). MIIs are excellent ligands for main group elements and transition metals in which they display substituent‐induced fluorine‐specific interactions and undergo C-H activation. DFT calculations gave insights into the frontier orbitals of the MIIs. The calculations predict a relatively small HOMO-LUMO gap compared to other related ligands. MIIs are potentially able to act as both π‐donor and π‐acceptor ligands. This report highlights the potential of MIIs to display exciting properties with a huge potential for future development.
Open Access
Silyl‐ and germyl‐substituted diorganophosphonites
(2023) Hettich, Thomas D.; Rudolf, Richard; Birchall, Nicholas; Nieger, Martin; Gudat, Dietrich
Reactions of metalated diorganophosphonite boranes with triorganosilyl and ‐germyl halides provided borane adducts of diorgano(tetryl)phosphonites. Further treatment with excess Et3N or DABCO yielded the borane‐free species (RO)2P‐ER′>3 (E=Si, Ge; R, R′=alkyl, aryl). The products of all reactions were characterized by elemental analyses and NMR data, and in selected cases by MS and single‐crystal XRD studies. Reactions of selected ligands with Ni(CO)4 and selenium were shown to produce Ni(CO)‐complexes or diorgano(tetryl) phosphonoselenoates (RO)(R′3E)P=Se, respectively, which were identified spectroscopically but could not be isolated. Evaluation of the TEP and 1JPSe coupling constants were used for a first assessment of the electron donor properties of the new molecules.
Open Access
Synthesis and ambiphilic reactivity of metalated diorgano‐phosphonite boranes
(2021) Hettich, Thomas D.; Rudolf, Richard; Feil, Christoph M.; Birchall, Nicholas; Nieger, Martin; Gudat, Dietrich
Unprecedented metalated phosphonite boranes were prepared from PH‐substituted precursors and silyl amides. Although potassium derivatives were thermally stable and could even be isolated and structurally characterised, lithiated analogues proved to be unstable towards self‐condensation under cleavage of LiOR at ambient temperature. Reaction studies revealed that the metalated phosphonite boranes exhibit ambiphilic character. Their synthetic potential as nucleophilic building blocks was demonstrated in the synthesis of the first stannylated phosphonite representing a new structural motif in phosphine chemistry.