Synthesis and Structures of Novel Low-Valent Group 14 1,3-Dimetallacyclobutanes

A series of group 14 1,3-dimetallacyclobutanes has been synthesized and structurally characterized.
The reaction of the lithium compound [Li{CH(Pri2PNSiMe3)(2-Py)}] (2) with 1 equiv of SnCl2 afforded
the tin(II) compound [Sn{CH(Pri2PNSiMe3)(2-Py)}Cl] (3). However, the reaction of 2 and MCl2 (M =
Ge, Sn, Pb) in a 2:1 ratio gave the corresponding metallacyclobutanes 1,3-[M{C(Pri2PNSiMe3)(2-Py)}]2 (4, M = Sn; 6, M = Ge; 9, M = Pb), respectively. Reaction of 2 equiv of 3 with Pb[N(SiMe3)2]2
gave the mixed-metal cyclobutane [1-Sn{C(Pri2PNSiMe3)(2-Py)}-3-Pb{C(Pri2PNSiMe3)(2-Py)}] (7).
It is noteworthy that the enantiomers of 4 and 7 containing “open-box” structures and their intermediates
were isolated and their structures have been confirmed by X-ray crystallography. Compound 3 reacts
with 1 equiv of Pb[N(SiMe3)2]2 to give [{(Pri2PNSiMe3)(2-Py)CH}Pb{N(SiMe3)2}2] (8), which can be
converted to 9 after recrystallization in diethyl ether. It is suggested that compounds 4, 6, 7, and 9 are
formed from “head-to-tail” cycloaddition of the metallavinylidene intermediate [:MC(Pri2PNSiMe3)(2-Py)] (M = Ge, Sn, Pb).,