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((Pr2P)-P-i=NSiMe3)(2-Py)}] (2) with 1 equiv of SnCl2 afforded the tin(II) compound [Sn{CH((Pr2P)-P-i=NSiMe3)(2-Py)}Cl] (3). However, the reaction of 2 and MCl2 (M = Ge, Sri, Pb) in a 2:1 ratio gave the corresponding metallacyclobutanes 1,3-[M{C((Pr2P)-P-i=NSiMe3)(2Py)}](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((Pr2P)-P-i=NSiMe3)(2-Py)}-3-Pb{C((Pr2P)-P-i=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 [{((Pr2P)-P-i=NSiMe3)(2-Py)CH}PbI{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 inter-mediate [:M=C((Pr2P)-P-i=NSiMe3)(2-Py)] (M = Ge, Sri, Pb).(1,12)