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

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*(IrNBu)-Bu-t] (Cp* = C5Me5) gave the corresponding imido-and silylmethyl-bridged heterobimetallic Lu-Ir complexes [Cp*Ir(mu-(NBu)-Bu-t)(mu-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*(IrNBu)-Bu-t] yielded the imido-and trimethylsilylmethylidene-bridged Sc-Ir complex [Cp*Ir(m-NtBu)( mu-CHSiMe3)ScCp'] (3) through the C-H bond activation of the alpha-CH2 unit in a CH2SiMe3 group. Recrystallization of 3 from toluene in the presence of pyridine gave the pyridine-coordinated complex [Cp*Ir(mu-(NBu)-Bu-t)(mu-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(mu-(NBu)-Bu-t)(mu-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(mu-(NBu)-Bu-t)(mu-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(mu-NtBu)(mu-CH2SiMe2C(=CH2)O)LuCp*] (6), which upon reaction with PhCN gave an adduct complex [Cp*Ir(mu-(NBu)-Bu-t)(mu-CH2SiMe2C(=CH2)O)Lu(NCPh)Cp*] (6') through coordination of PhCN to the Lu atom. The reaction at the bridging imido ligand (NBu)-Bu-t was not observed in any case.