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.