Mesityl(amidinato)tetrylenes as ligands in iridium(i) and iridium(iii) complexes: silicon versus germanium and simple κ1-coordination versus cyclometallation.

Reactions of the mesityl(amidinato)tetrylenes E(tBu2bzam)Mes (tBu2bzam = N,N'-bis(tert-butyl)benzamidinate; Mes = mesityl; E = Ge (1Ge), Si (1Si)) with the iridium precursors [Ir2(μ-Cl)2(η4-cod)2] (cod = 1,5-cyclooctadiene) and [Ir2Cl2(μ-Cl)2(η5-Cp*)2] (Cp* = 1,2,3,4,5-pentamethylcyclopentadienyl) at room temperature led to simple coordination of the tetrylene in the case of the germylenes ([IrCl(η4-cod){κ1Ge-Ge(tBu2bzam)Mes}] (2Ge) and [IrCl2(η5-Cp*){κ1Ge-Ge(tBu2bzam)Mes}] (3Ge), respectively, but to cyclometallated products in the case of the silylenes ([IrHCl(η4-cod){κ2C,Si-Si(tBu2bzam)CH2C6H2Me2}] (4Si) and [IrCl(η5-Cp*){κ2C,Si-Si(tBu2bzam)CH2C6H2Me2}] (5Si), respectively. While the cyclometallation of the germylene ligand of the iridium(i) complex 2Ge could not be achieved by heating this complex in toluene at 90 °C, a similar treatment of the iridium(iii) complex 3Ge led to [IrCl(η5-Cp*){κ2C,Ge-Ge(tBu2bzam)CH2C6H2Me2}] (5Ge), which is the germanium analogue of 5Si. DFT calculations have shown that the mononuclear κ1E-tetrylene iridium(i) complexes [IrCl(η4-cod){κ1E-E(tBu2bzam)Mes}] (E = Si, Ge; isolated only for E = Ge, 2Ge) should not participate as intermediates in the synthesis of the cyclometallated iridium(iii) derivatives [IrHCl(η4-cod){κ2C,E-E(tBu2bzam)(CH2C6H2Me2)}] (E = Ge, Si; isolated only for E = Si, 4Si).