A Redox‐Switchable Germylene and its Ligating Properties in Selected Transition Metal Complexes

The synthesis, structure, and full characterization of a redox‐switchable germylene based on a [3]ferrocenophane ligand arrangement, [Fc(NMes) 2 Ge] ( 4 ), is presented. The mesityl (Mes)‐substituted title compound is readily available from Fc(NHMes) 2 ( 2 ) and Ge{N(SiMe 3 ) 2 } 2 , or from the dilithiated, highly air‐ and moisture‐sensitive compound Fc(NLiMes) 2 ⋅3 Et 2 O ( 3 ) and GeCl 2 . Cyclic voltammetry studies are provided for 4 , confirming the above‐mentioned view of a redox‐switchable germylene metalloligand. Although several 1:1 Rh I and Ir I complexes of 4 ( 5 – 7 ) are cleanly formed in solution, all attempts to isolate them in pure form failed due to stability problems. However, crystalline solids of [Mo(κ 1 Ge ‐ 4 ) 2 (CO) 4 ] ( 8 ) and [W(κ 1 Ge ‐ 4 ) 2 (CO) 4 ] ( 9 ) were isolated and fully characterized by common spectroscopic techniques ( 8 by X‐ray diffraction). DFT calculations were performed on a series of model compounds to elucidate a conceivable interplay between the metal atoms in neutral and cationic bimetallic complexes of the type [Rh(κ 1 E ‐ qE )(CO) 2 Cl] 0/+ ( qE =[Fc(NPh) 2 E] with E=C, Si, Ge). The bonding characteristics of the coordinated Fc‐based metalloligands ( qE / qE + ) are strongly affected upon in silico oxidation of the calculated complexes. The calculated Tolman electronic parameter (TEP) significantly increases by approximately 20 cm −1 (E=C) to 25 cm −1 (E=Si, Ge) upon oxidation. The change in the ligand‐donating abilities upon oxidation can mainly be attributed to Coulombic effects, whereas an orbital‐based interaction appears to have only a minor influence.