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(Pr i 2 P=NSiMe 3 )(2-Py)}] (2) with 1 equiv of SnCl 2 afforded the tin(II) compound [Sn{CH(Pr i 2 P=NSiMe 3 )(2-Py)}Cl] (3). However, the reaction of 2 and MCl 2 (M = Ge, Sn, Pb) in a 2:1 ratio gave the corresponding metallacyclobutanes 1,3-[M{C(Pr i 2 P=NSiMe 3 )(2-Py)}] 2 (4, M = Sn; 6, M = Ge; 9, M = Pb), respectively. Reaction of 2 equiv of 3 with Pb[N(SiMe 3 ) 2 ] 2 gave the mixed-metal cyclobutane [1-Sn{C(Pr'2P=NSiMe3)(2-Py)}-3-Pb{C(Pr i 2 P=NSiMe 3 )(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(SiMe 3 ) 2 ] 2 to give [{(Pr i 2 P=NSiMe 3 )(2-Py)CH}Pb{N(SiMe 3 ) 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(Pr i 2 P=NSiMe 3 )-(2-Py)] (M = Ge, Sn, Pb). 1,12 .