Heavy cyclopropene analogues R4SiGe2 and R4Ge3 (R = SiMetBu2) – New members of the cyclic digermenes family

1H-Siladigermirene R4SiGe2 (2a) and 1H-trigermirene R4Ge3 (2b) (R = SiMetBu2) with a Gedouble bond; length as m-dashGe double bond were synthesized by the reaction of tetrachlorodigermane RGeCl2–GeCl2R with dilithiosilane R2SiLi2 and dilithiogermane R2GeLi2, respectively. The skeletal Gedouble bond; length as m-dashGe double bond of 2a is trans-bent (51.0(2)°) with a bond distance of 2.2429(6) Å. The reaction of both 2a and 2b with CH2Cl2 resulted in the formation of unusual four-membered ring compounds 5a and 5b as a result of a ring expansion reaction. 1H-Trisilirene 7a and 3H-disilagermirene 7b with an Sidouble bond; length as m-dashSi double bond also smoothly reacted with CH2Cl2 to yield the four-membered ring systems 8a and 8b, respectively.