Origin Of The Ir-Si Bond Shortening In Ir-Nsin Complexes

The Ir-Si bond distances reported for Ir-(fac-kappa(3)-NSiNOPy) and Ir-(fac-kappa(3)-NSiN4MeOPy) species (NSiNOPy = bis(pyridine-2-yloxy)methylsilyl and NSiN4MeOPy = bis(4-methyl-pyridine-2-yloxy)methylsily) are in the range of 2.220-2.235 angstrom. These values are in the lowest limit of the Ir-Si bond distances found in the Cambridge Structural Database (CSD). To understand the origin of such remarkable shortening, a computational study of the bonding situation of representative examples of Ir-(fac-kappa(3)-NSiN) species has been carried out. It is found that the Ir-Si bond can be described as an electron-sharing (i.e. covalent) bond. Despite that, this bond is highly polarized and as a result, the contribution of the electrostatic attractions to the bonding is rather significant. Indeed, there exists a linear relationship (R-2 = 0.97) between the Ir-Si bond distance and the extent of the computed electrostatic interactions, which indicates that the ionic contribution to the bonding is mainly responsible for the observed Ir-Si bond shortening.