Rare-earth–iridium heterobimetallic complexes with bridging imido and silylmethyl ligands: synthesis, structure and reactivity

Abstract

The reaction of the half-sandwich lutetium dialkyl complexes [(C₅Me₄R)Lu(CH₂SiMe₃)₂(THF)] (1-Lu: R = Me, 1′-Lu: R = SiMe₃) with 1 equiv. of the iridium imido complex [Cp*IrN^tBu] (Cp* = C₅Me₅) gave the corresponding imido- and silylmethyl-bridged heterobimetallic Lu–Ir complexes [Cp*Ir(μ-N^tBu)(μ-CH₂SiMe₂CH₂)Lu(C₅Me₄R)] (2a: R = Me, 2b: R = SiMe₃), with the release of SiMe₄ through C–H bond activation (hydrogen abstraction) of a methyl group in one CH₂SiMe₃ group by another CH₂SiMe₃ group. A similar reaction of the scandium dialkyl complex [Cp′Sc(CH₂SiMe₃)₂(THF)] (1-Sc) (Cp′ = C₅Me₄SiMe₃) with [Cp*IrN^tBu] yielded the imido- and trimethylsilylmethylidene-bridged Sc–Ir complex [Cp*Ir(μ-N^tBu)(μ-CHSiMe₃)ScCp′] (3) through the C–H bond activation of the α-CH₂ unit in a CH₂SiMe₃ group. Recrystallization of 3 from toluene in the presence of pyridine gave the pyridine-coordinated complex [Cp*Ir(μ-N^tBu)(μ-CHSiMe₃)Sc(NC₅H₅)Cp′] (3′). The reaction of the Lu–Ir heterobimetallic complex 2a with two equivalents of PhCN afforded the enamido complex [Cp*Ir(μ-N^tBu)(μ-CH₂SiMe₂)N(C(CH₂)Ph)Lu(PhCN)Cp*] (4) through the insertion of one molecule of PhCN into the terminal Lu–CH₂ bond in 2a and the coordination of another molecule of PhCN to the Lu atom. The intramolecular nucleophilic addition of the enamido unit to the coordinated PhCN in 4 then yielded the diazalutenacyclohexadienyl complex [Cp*Ir(μ-N^tBu)(μ-CH₂SiMe₂NC(Ph)CHC(Ph)NH)LuCp*] (5) after isomerization (1,3-hydrogen shift). The reaction of 2a with carbon monoxide (1 atm) at room temperature afforded the enolate complex [Cp*Ir(μ-N^tBu)(μ-CH₂SiMe₂C(CH₂)O)LuCp*] (6), which upon reaction with PhCN gave an adduct complex [Cp*Ir(μ-N^tBu)(μ-CH₂SiMe₂C(CH₂)O)Lu(NCPh)Cp*] (6′) through coordination of PhCN to the Lu atom. The reaction at the bridging imido ligand N^tBu was not observed in any case.