Pure Molecular Inorganic Rings: Mixed Group 14/15 Metallacycles

A systematic study on the reactivity of the homodipnictogen tetrahedrane complexes [{Cp‘Mo(CO)$_2$}$_2$(μ,η$^{2:2}$-E$_2$)] (E ═ P, As, Sb; Cp‘ = η$^5$-C$_5$H$_4$tBu) towards the disilylene [L$^{Ph}$Si]$_2$ and digermylene [L$^{Ph}$Ge]$_2$ (L$^{Ph}$ = PhC(NtBu)$_2$) is presented. Depending on the specific combination of tetrel and pnictogen atom, a variety of novel silicon-pnictogen and germanium-pnictogen heterocycles in different bonding situations were obtained. This is a significant development, as these metallacycles are unprecedented and offer new possibilities for further reactivities. These three- to five-membered pure inorganic heterocycles include one Mo, one or two tetrel, and one or two pnictogen atoms in each case. Especially for the heavier pnictogen Sb, this cyclization behavior forming novel three- and four-membered Si–Sb as well as five-membered Ge–Sb ring systems has not been observed so far. These results present unique examples of heavy group 14/15 heterocycles.