Insertions of Cyclic and Acyclic Germanium and Tin Heterocarbenoids into Phosphorus–Chlorine Bonds: Syntheses, Structures, and Reactivities

Chloro­(organo)­phosphines are important precursors to
diphosphenes
and cyclic oligophosphines. Although chloro­(organo)­phosphines are
commonly reduced with bulk metals (e.g., Na, Mg, and Zn), these reactions
are much more selective when done homogeneously. To test whether group
14 heterocarbenoid reductions yield isolable insertion products, the
mono- and dichloro­(organo)­phosphines PhPCl2 (A), Ph2PCl (B), tBuPCl2 (C), tBu2PCl (D),
and bis­(dichlorophosphino)­methane (PCl2)2CH2 (E) were treated with the cyclic Me2Si­(μ-NtBu)2El (El =
Ge (1), Sn (2)) and the acyclic [(Me3Si)2N]2El (El = Ge (3),
Sn (4)) heterocarbenoids. The sterically least-encumbered
phosphines were more reactive, while the cyclic stannylene 2 was the most reactive and the acyclic germylene 3 was
the least reactive. All but one of the products were either mono-
or diinsertion compounds, the lone exception being a distannane derived
from 2. Semikinetic and structural data suggest that
the tetravalent group 14 compounds are formed via an insertion mechanism
whose rate depends on the steric bulk of the reaction partners and
the nature of the group 14 elements.