Synthesis of Zwitterionic Group 14 Centered Complexes: Traditional Coordination and Unusual Insertion Chemistry

Novel
cationic E–Cl (E = Ge, Sn) fragments stabilized by
a bis­(phosphino)­borate ligand (2E) were synthesized by
a 1:1 stoichiometric addition of ECl2 and [Tl]­[(Ph2PCH2)2BPh2]. The metrical
parameters are consistent with dative bonds between the phosphorus
atoms and the electron-deficient group 14 element, which is in contrast
to the traditionally used aryl- and nitrogen-based ligands, which
are always covalently bound. The reaction of a second equivalent of
bis­(phosphino)­borate results
in the unexpected insertion of the main group center into the aliphatic
B–C bond of the ligand backbone to form 3E, in
addition to phosphine-borane dimer (Ph2PCH2BPh2)2 (4). The pendant phosphine on 3E was shown to possess donor ability in the coordination
of BH3 (5E).