[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 trans-mer-[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)2tBu}­(CO)4], the anion of which contains an unprecedented germanato­(II) ligand, [Ge­(OH)2tBu]−, 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.