Reactivity of cyclic (alkyl)(amino)carbenes (CAACs) and bis(amino)cyclopropenylidenes (BACs) with heteroallenes: comparisons with their N-heterocyclic carbene (NHCs) counterparts.
Similarly to NHCs, CAAC(a) and BAC(a) react with CO2 to give the corresponding betaines. Based on the carbonyl stretching frequencies of cis-[RhCl(CO)2(L)] complexes, the order of electron donor ability was predicted to be CAAC(a) approximately BAC(a)>NHCs. When the betaines nu(asym)(CO2) values are used, the apparent ordering is BAC(a)>NHCs approximately CAAC(a) that indicates a limitation for the use of IR spectroscopy in the ranking of ligand sigma-donating ability. Although all carbenes react with carbon disulfide to give the corresponding betaines, a second equivalent of CS2 reacts with the BAC-CS2 leading to a bicyclic thieno[2,3-diamino]-1,3-dithiole-2-thione, which results from a novel ring expansion process. Surprisingly, in contrast to NHCs, CAAC(a) does not react with carbodiimide, whereas BAC(a) exclusively gives a ring expanded product, analogous to that obtained with CS2. The intermediate amidinate can be trapped, using the lithium tetrafluoroborate adduct of BAC(b) as a carbene surrogate.
Kuchenbeiser
Glenn
G
UCR-CNRS Joint Research Chemistry Laboratory (UMI 2957), Department of Chemistry, University of California, Riverside, CA 92521-0403, USA.
Soleilhavoup
Michele
M
Donnadieu
Bruno
B
Bertrand
Guy
G
D000466:Alkadienes / Q000737:chemistry*; D000480:Alkynes / Q000737:chemistry*; D003521:Cyclopropanes / Q000737:chemistry*; D004148:Dioxolanes / Q000737:chemistry*; D006571:Heterocyclic Compounds / Q000737:chemistry*
D000466:Alkadienes; D000480:Alkynes; D003521:Cyclopropanes; D004148:Dioxolanes; D006571:Heterocyclic Compounds; C504703:aminocarbene; C025947:propadiene