8. Sudipta Roy, Peter Stollberg, Regine Herbst-Irmer, Dietmar Stalke, Diego M. Andrada, Gernot Frenking, and Herbert W. Roesky. Carbene-Dichlorosilylene Stabilized Phosphinidenes Exhibiting Strong Intramolecular Charge Transfer Transition.
Abstract:
The unstable species dichlorosilylene was previously stabilized by carbene. The lone pair of electrons on the silicon atom of (carbene)SiCl2 can form a coordinate bond with metal-carbonyls. Herein we report that (carbene)SiCl2 can stabilize a phosphinidene (Ar-P, a carbone analogue) with the general formula carbene→SiCl2→P-Ar (carbene = cyclic alkyl(amino) carbene (cAAC; 2.) and N-heterocyclic carbene (NHC; 3)). Compounds 2 and 3 are stable, isolable, and storable at 0 °C (2) to room temperature (3) under an inert atmosphere. The crystals of 2 and 3 are dark blue and red, respectively. The intense blue color of 2 arises due to the strong intramolecular charge transfer (ICT) transition from πSi=P→π*cAAC. The electronic structure and bonding of 2, 3 were studied by theoretical calculations. The HOMO of the molecule is located on the πSi=P bond while the LUMO is located at the carbene moiety (cAAC or NHC). The dramatic change in color of these compounds from /red (3, NHC) to blue (2, cAAC) is ascribed to the difference in energy of the LUMO within the carbenes (cAAC/NHC) due to a lower lying LUMO of cAAC.