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Ringexpansion of N-Heterocyclic Carbenes

Subject Area Inorganic Molecular Chemistry - Synthesis and Characterisation
Term from 2016 to 2024
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 316481056
 
Final Report Year 2024

Final Report Abstract

Within the project „Ringerweiterung N-Heterozyklischer Carbene“, ring-expansion reactions (RERs) of N-heterocyclic carbenes (NHCs) in main group element chemistry, especially in the chemistry of main group element hydrides of group 13 and 14 elements and of diboron(4) ethers, have been explored. The main results of this project are the following: 1) RERs of NHCs in hydrides of group 13, 14 and 15 elements have been systematically explored and established in main group element chemistry. One focus of the project was on investigations aiming at the chemistry of hydrides of the elements aluminum/gallium (group 13), germanium/tin (group 14) and phosphorous (group 15). Mechanisms for this kind of RERs have been established. 2) For selected NHC alane adducts, novel decomposition pathways of NHCs with loss of the 5-ring scaffold have been established, which lead to decarbonization of the NHC-ligand with (i) loss of the carbene carbon atom or (ii) loss of the backbone of the 5-membered ring. 3) RERs of NHC adducts of diborane(4) ethers were explored systematically and have been established in the chemistry of this class of compounds. Mechanisms for this kind of RER have been established. 4) We provided the first example of a RER at cyclic (alkyl)(amino)carbenes (cAACs) and a related reaction at cyclic (amino)(aryl)carbenes (cAArCs). 5) We demonstrated that cAACMe reacts with selected arylboronic acid esters under reversible oxidative addition. Thus, carbenes :CR2 react analogously to their isolobal transition metal counterparts C2v-d8-ML4 or C2v-d10-ML2. 6) We demonstrated that NHCs are useful hydrogen acceptors for the dehydrocoupling of main group element hydrides and provided specific examples for dehydrogenative coupling of hydrides of the heavier group 14 elements and of phosphorous. 7) We demonstrated that NHCs and/or cAACs are in principle useful reagents for the dehydrogenation of group 13 element hydrides to obtain low-valent compounds of these elements. 8) We demonstrated how NHC adducts of alanes and galanes can be stabilized with respect to RER and thus how they can be used in synthesis. Furthermore, we provided specific examples for the application of adducts (NHC)·EH2X and (NHC)∙EHX2 (E = Al, Ga) in contemporary chemistry of Al and Ga.

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