2-Pyridone-stabilized iridium silylene/silyl complexes: structure and QTAIM analysis

Abstract

Iridium(III) complexes of the general formula [Ir(X)(κ²-NSi^iPr2)₂] (NSi^iPr2 = (4-methyl-pyridine-2-yloxy)diisopropylsilyl; X = Cl, 3; CF₃SO₃, 5; CF₃CO₂, 6) have been prepared and fully characterized, including X-ray diffraction studies and theoretical calculations. The presence of isopropyl substituents at the silicon atom favours the monomeric structure found in complexes 3 and 5. The short Ir–Si bond distances (2.25–2.28 Å) indicate some degree of base-stabilized silylene character of the Ir–Si bond in 3, 5 and 6 assisted by the 2-pyridone moiety. However, the shortening of these Ir–Si bonds might be a consequence of the constrained 2-pyridone geometry, and consequently the silyl character of these bonds can not be excluded. A DFT theoretical study on the nature of the Ir–Si bonds has been performed for complex 3 as well as for four other iridium complexes finding representative examples of different bonding situations between Ir and Si atoms: silylene, base-assisted silylene (both with an anionic base and with a neutral base), and silyl bonds, using the topological properties of the electron charge density. The results of these studies show that the Ir–Si bonds in Ir–NSi^iPr2 complexes can be considered as an intermediate between the base-stabilized silylene and silyl cases, and therefore they have been proposed as 2-pyridone-stabilized iridium silylene/silyl bonds.