Formation of HTi(μ-H) ₃ Ge and H ₂ M(μ-H) ₂ Ge (M = Zr and Hf) via Ge–H Bond Activation: Infrared Spectroscopic and Bonding Characterization

To precisely control reaction selectivity in hydrogermylation, it is essential to understand how transition metals activate the Ge-H bond. This study investigates Ge-H bond activation in germane using laser-ablated group IV transition metal atoms (Ti, Zr and Hf) by employing a combination of matrix isolation infrared spectroscopy and quantum chemical calculations. The reaction between Ti and germane atoms occurs in a spin-conserved manner, requiring photocatalysis and leading to the formation of HTi(μ-H)₃Ge. This product features three three-center-two-electron hydrogen-bridged bonds, arising from electron donation from the Ge-H σ bonds to the vacant d orbitals of Ti. In contrast, reactions involving Zr and Hf atoms with germane are spontaneous multistate reactions. Spin-forbidden transitions between triplet and singlet state potential energy surfaces reduce the reaction barriers along the pathways, resulting in the formation of H₂M(μ-H)₂Ge (where M represents Zr or Hf). Topological analysis reveals that H₂M(μ-H)₂Ge is characterized by an M-Ge covalent bond. Additionally, three-center-two-electron bonds are formed in H₂M(μ-H)₂Ge via hydrogen-bridged bonds. This work provides valuable theoretical insights into the activation of Ge-H bonds by transition metals.