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

Abstract

Reactions of the mesityl(amidinato)tetrylenes E(^tBu₂bzam)Mes (^tBu₂bzam = N,N′-bis(tert-butyl)benzamidinate; Mes = mesityl; E = Ge (1_Ge), Si (1_Si)) 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}] (2_Ge) and [IrCl₂(η⁵-Cp*){κ¹Ge-Ge(^tBu₂bzam)Mes}] (3_Ge), respectively, but to cyclometallated products in the case of the silylenes ([IrHCl(η⁴-cod){κ²C,Si-Si(^tBu₂bzam)CH₂C₆H₂Me₂}] (4_Si) and [IrCl(η⁵-Cp*){κ²C,Si-Si(^tBu₂bzam)CH₂C₆H₂Me₂}] (5_Si), respectively. While the cyclometallation of the germylene ligand of the iridium(I) complex 2_Ge could not be achieved by heating this complex in toluene at 90 °C, a similar treatment of the iridium(III) complex 3_Ge led to [IrCl(η⁵-Cp*){κ²C,Ge-Ge(^tBu₂bzam)CH₂C₆H₂Me₂}] (5_Ge), which is the germanium analogue of 5_Si. 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, 2_Ge) 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, 4_Si).