Computational and experimental investigations of CO2 and N2O fixation by sterically demanding N-heterocyclic carbenes (NHC) and NHC/borane FLP systemsElectronic supplementary information (ESI) available: X-ray structure of compound 6, selected NMR spectra and computational details. CCDC 963622-963628 and 964196 (6). For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c3dt52742e

The sterically demanding NHCs 1,3-di- tert -butylimidazolin-2-ylidene ( 1a ), 1,3-di- tert -butyl-4,5-dimethylimidazolin-2-yildene ( 1b ), and also the corresponding frustrated Lewis pair combinations 1a,b /B(C 6 F 5 ) 3 react readily with CO 2 to form the NHC·CO 2 ( 5a,b ) and the NHC·CO 2 ·B(C 6 F 5 ) 3 ( 9a,b ) adducts, respectively. However, N 2 O activation and isolation of the NHC·N 2 O adduct ( 6 ) was only possible for NHC 1a . On heating, the NHC·N 2 O adduct 6 degrades to 1a , N 2 O, N 2 and the urea derivative 7 . Nevertheless, an NHC·N 2 O adduct of 1b was obtained with the FLP system 1b /B(C 6 F 5 ) 3 . In contrast, for the FLP combination 1a /B(C 6 F 5 ) 3 , N 2 O coordination appears to be slower than the self-deactivation. Hence, only the self-deactivation product 3 was observed under an N 2 O atmosphere. DFT calculations give insights into the CO 2 and N 2 O activation process with 1a,b and 1a,b /B(C 6 F 5 ) 3 . N-heterocyclic carbenes alone and their frustrated Lewis pair combination with B(C 6 F 5 ) 3 allows trapping of the greenhouse gases CO 2 and N 2 O.