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.