Quantifying the Electronic and Steric Properties of 1,3-ImidazoleBased Mesoionic Carbenes (iMICs)

1,3-Imidazole-based mesoionic carbenes (iMICs) are a very promising class of carbon-donor ligands in synthesis and catalysis. However, a systematic study of the quantification of stereoelectronic properties of iMICs is lacking. This is most likely due to the absence of rational synthetic routes to suitable iMIC compounds. Herein, we report the synthesis of the appropriate phosphinidene (iMIC(Ar))9PPh (iMIC(Ar) = :CCH(NDipp)(2)CAr; Ar = Ph (5a), DMP (5b); DMP = 4-Me2NC6H4; Dipp = 2,6-iPr(2)C(6)H(3)), selenium (iMIC(Ar))Se (Ar = Ph (6a), DMP (6b)), and nickel carbonyl compounds (iMIC(Ar))Ni(CO)(3)(Ar = Ph (7a), DMP (7b)). The pi-accepting property of iMIC(Ar) (Ar = Ph (2a), DMP (2b)) has been evaluated by P-31 and Se-77 NMR spectroscopic analyses of 5 and 6, respectively. The overall donor property of 2 has been assessed by determining the Tolman electronic parameter (TEP) of 7. Studies suggest that iMIC(Ar) (2) are stronger 6 donors and weaker it acceptors compared to classical N-heterocyclic carbenes (NHCs). The steric profile of iMIC(Ar) (2) has been obtained by calculating the percentage buried volume (%V-bur) for (iMIC(Ar))CuX (Ar Ph, X = I (8a); Ar = DMP, X = Br (8b)).