Insight into the Decomposition Mechanism of Donor-Acceptor Complexes of EH2 (E = Ge and Sn) and Access to Germanium Thin Films from Solution

Electron-donating N-heterocyclic carbenes (Lewis bases, LB) and electron-accepting Lewis acids (LA) have been used in tandem to yield donor-acceptor complexes of inorganic tetrelenes LB center dot EH2 center dot LA (E = Si, Ge, and Sn). Herein, we introduce the new germanium (II) dihydride adducts ImMe(2)center dot GeH2 center dot BH3 (ImMe(2) = (HCNMe)(2)C:) and Im(i)Pr(2)Me(2)center dot GeH2 center dot BH3 (Im(i)Pr(2)Me(2) = ((MeCNPr)-Pr-i)(2)C:), with the former complex containing nearly 40 wt % germanium. The thermal release of bulk germanium from ImMe(2)center dot GeH2 center dot BH3 (and its deuterated isotopologue ImMe(2)center dot GeD2 center dot BD3) was examined in solution, and a combined kinetic and computational investigation was undertaken to probe the mechanism by which Ge is liberated. Moreover, the thermolysis of ImMe(2)center dot GeH2 center dot BH3 in solution cleanly affords conformal nanodimensional layers of germanium as thin films of variable thicknesses (20-70 nm) on silicon wafers. We also conducted a computational investigation into potential decomposition pathways for the germanium(II)- and tin(II)dihydride complexes NHC center dot EH2 center dot BH3 (NHC = [(HCNR)(2)C:]; R = 2,6-(Pr2C6H3)-Pr-i (Dipp), Me, and H; and E = Ge and Sn). Overall, this study introduces a mild and convenient solution-only protocol for the deposition of thin films of Ge, a widely used semiconductor in materials research and industry.