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; <b>2</b>) and N-heterocyclic carbene (NHC; <b>3</b>)). Compounds <b>2</b> and <b>3</b> are stable, isolable, and storable at 0 °C (<b>2</b>) to room temperature (<b>3</b>) under an inert atmosphere. The crystals of <b>2</b> and <b>3</b> are dark blue and red, respectively. The intense blue color of <b>2</b> arises due to the strong intramolecular charge transfer (ICT) transition from π_SiP→π*_cAAC. The electronic structure and bonding of <b>2</b>, <b>3</b> were studied by theoretical calculations. The HOMO of the molecule is located on the π_SiP bond, while the LUMO is located at the carbene moiety (cAAC or NHC). The dramatic change in color of these compounds from red (<b>3</b>, NHC) to blue (<b>2</b>, cAAC) is ascribed to the difference in energy of the LUMO within the carbenes (cAAC/NHC) due to a lower lying LUMO of cAAC