Periodic Reporting for period 1 - POLY-SAAR (Conjugated Hybrid Polymers from Unsaturated Heavier Group 14 Building Blocks)
Reporting period: 2019-07-01 to 2021-06-30
In order to synthesize Janus head-type bis(germylenes) (and eventually apply them in polymer synthesis), a reported NHC-coordinated four-membered germylene with an exocyclic imino functionality and a chloro substituent was subjected to 2e– reduction by potassium graphite (KC8), which afforded potassium silagermenide instead of the targeted sp3 silyl anion. X-ray diffraction analysis on single crystals revealed that potassium silagermenide forms a 1D coordination polymer in the solid state. The potassium silagermenide is also used as valuable synthon for the synthesis of functional silagermenes.
With a view to hitherto unknown organometallic polymers with silagermenylidene repeat units, the reactivity of a literature-known silagermenylidene towards a variety of transition metal precursors was investigated. Specifically, the treatment of silagermenylidene [R2(Cl)Si−(R)Si(NHC)Ge:] with [Ni(COD)2] (R = 2,4,6-triisopropylphenyl; NHC = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene; COD= 1,5-cyclooctadiene) afforded the first transition metal complex of a heavier allylic pi-system. The reaction of the latter with one equivalent of NHC produced the first heavier cyclopropene-transition metal complexes. Notably, the coordination mode in these complexes is different from the metallacyclopropane and pi-complex extremes of the Dewar-Chatt-Duncanson model: the sigma-component of the Ge=Si double bond acts as donor and acceptor leaving behind a nearly unsupported Si–Ge pi-bond.
List of publications:
1. P. K. Majhi, M. Zimmer, B. Morgenstern, V. Huch, D. Scheschkewitz, “Transition Metal Complexes of Heavier Vinylidenes: Allylic Coordination vs Vinylidene-Alkyne Rearrangement at Nickel” J. Am. Chem. Soc. 2021, DOI:10.1021/jacs.1c06453.
2. P. K. Majhi, V. Huch, D. Scheschkewitz, “A Mixed Heavier Si=Ge Analogue of a Vinyl Anion” Angew. Chem. 2021, 133, 246-250; Angew. Chem. Int. Ed. 2021, 60, 242-246.
3. P. K. Majhi, M. Zimmer, B. Morgenstern, D. Scheschkewitz, “Transition Metal Complexes of Heavier Cyclopropenes: non-Dewar-Chatt-Duncanson Coordination and Facile Si=Ge Functionalization” J. Am. Chem. Soc. 2021, 143, 8981-8986. (This work was also highlighted by David Schilter in Nature Reviews Chemistry, 2021, 5, 446).