[MnBrL(CO)4] (L = Amidinatogermylene): Reductive Dimerization, Carbonyl Substitution, and Hydrolysis Reactions

The manganese(I) carbonyl complex [MnBr{Ge(iPr2bzam)tBu}- (CO)4] (1; iPr2bzam = 1,3-di(isopropyl)benzamidinate), which contains an amidinatogermylene ligand, reacts with LiPh or LitBu at room temperature undergoing a reductive dimerization process that leads to the manganese(0) dimer [Mn2{Ge(iPr2bzam)tBu}2(CO)8]. This complex and the monosubstituted derivative [Mn2{Ge(iPr2bzam)tBu}(CO)9] have also been prepared by reacting [Mn2(CO)10] with Ge(iPr2bzam)tBu at high temperature (110 °C). These binuclear complexes contain their germylene ligands in axial positions (trans to the Mn−Mn bond). The large volume of the germylene ligand clearly affects the reactivity of complex 1 with neutral two-electron donor reagents, since for bulky reagents, the CO substitution occurs trans to the germylene ligand, as in transmer-[ MnBrL{Ge(iPr2bzam)tBu}(CO)3] (L = Ge(iPr2bzam)tBu, PMe3), whereas for small reagents, the CO substitution occurs cis to the germylene ligand, as in fac-[MnBr(CNtBu){Ge(iPr2bzam)tBu}(CO)3]. The IR spectra (νCO) of these complexes have confirmed that the germylene Ge(iPr2bzam)tBu is a very strong electron-donating ligand, even stronger than the most basic trialkylphosphanes and N-heterocyclic carbenes. The hydrolysis of complex 1 leads to the salt [iPr2bzamH2][MnBr- {Ge(OH)2 tBu}(CO)4], the anion of which contains an unprecedented germanato(II) ligand, [Ge(OH)2 tBu]−, in cis to the Br atom. This hydrolysis product and its precursor 1 have been tested as catalyst precursors for the electrolytic reduction of CO2, showing no significant activity.