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.