Synthesis and Investigation of Carbocyclic Silylenes, Radicals, Diradicaloids, and Anions

• Applicant: Privatdozent Dr. Rajendra S. Ghadwal
• Subject Area: Inorganic Molecular Chemistry - Synthesis and Characterisation
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 549520861

The central objectives of this project are (i) the synthesis of thermally stable carbocyclic silylenes, radicals, diradicaloids, and anions based on anionic dicarbene (ADC = ArC{N(Dipp)C}2; Ar = aryl group, Dipp = 2,6-iPr2C6H3) frameworks and (ii) the investigation of their structure and reactivity. The proposed annulated tricyclic silicon compounds feature the central 1,4-Si2C4 ring fused between two peripheral 1,3-imidazole units. The starting materials, the cyclic Si(IV) precursors [(ADC)SiCl3]2, will be prepared by reacting our recently reported N-ethynylformimidamide (eFIM) derivatives (eFIM = (Dipp)N=C(Ar)N(Dipp)C=CSiMe3) with SiCl4 via Me3SiCl elimination and subsequent ring-closing reactions. Reductions of [(ADC)SiCl3]2 with an appropriate amount of KC8 will yield cyclic bis-chlorosilylenes [(ADC)SiCl]2 and 1,4-disilabenzene compounds [(ADC)Si]2 (i.e Si(I) diradicaloids). Other functionalized silylenes [(ADC)SiR]2 will be prepared by salt metathesis reactions of [(ADC)SiCl]2. Cyclic voltammetry studies of [(ADC)Si]2 will be performed to obtain information about the viability and stability of other oxidation states. Sequential one-electron oxidations of [(ADC)Si]2 are expected to afford radical cations [(ADC)Si]2O+ and dicationic bis-silylenes [(ADC)Si]22+ with two-coordinated silicon atoms. Similarly, one-electron reductions of [(ADC)Si]2 with appropriate agents will be carried out to prepare radical anions [(ADC)Si]2O - and dianions [(ADC)Si]22 - . In addition to thorough structural characterization of the proposed compounds using experimental (NMR, IR, EPR, UV-Vis spectroscopy, mass-spectrometry, X-ray diffraction) and computational methods, reactivity studies of the key compounds with small molecules (e.g. H2, CO, CO2, NH3, P4), organic substrates, and transition metal species will be carried out. The outcome of this project will be valuable in identifying the potential of anticipated and related silicon compounds in synthesis, catalysis, and beyond.

• DFG Programme: Research Grants