Amidinatogermylene Metal Complexes as Homogeneous Catalysts in Alcoholic Media

A series of transition-metal complexes containing the bulky amidinatogermylene Ge­(^tBu₂bzam)^tBu (1; ^tBu₂bzam = N,N′-bis­(tert-butyl)­benzamidinate) as a ligand have been prepared and characterized. While the hydrolytic degradation of the germylene ligand of the square-planar complexes [MCl­(η⁴-cod)­{Ge­(^tBu₂bzam)^tBu}] (M = Rh (2), Ir (3); cod = 1,5-cyclooctadiene) and [PdCl­(η³-metallyl)­{Ge­(^tBu₂bzam)^tBu}] (4; metallyl = 2-methylallyl) is slow but clearly evident in carefully dried aprotic solvents, the octahedral complexes [RuCl₂(η⁶-cym)­{Ge­(^tBu₂bzam)^tBu}] (5; cym = p-cymene) and [IrCl₂(η⁵-Cp*)­{Ge­(^tBu₂bzam)^tBu}] (6; Cp* = pentamethylcyclopentadienyl) have proven to be stable even in alcoholic solvents. These latter complexes have been tested as catalyst precursors of reactions involving alcohols as substrates and/or solvents, and remarkably, they have been found to be active in the transfer hydrogenation of cyclohexanone with isopropyl alcohol (5 and 6), the N-alkylation of aniline with benzyl alcohol (5 and 6), and the deuteriation of acetophenone with CD₃OD (6). The use of heavier carbene metal complexes as catalyst precursors of reactions involving alcohols as solvents is unprecedented.