Synthesis, Geometry, and Bonding Nature of Heptacoordinate Compounds of Silicon and Germanium Featuring Three Phosphine Donors

Structural studies were performed on heptacoordinate compounds of silicon {(o-Ph2P)C6H4}3SiX (X = F (1), Cl (3), H (5)) and germanium {(o-Ph2P)C6H4}3GeX (X = F (2), Cl (4), H (6), Me (7)) compounds featuring three phosphine donors. We found that 5, 6, and 7 have approximately a C3 symmetry similar to Corriu’s compounds (heptacoordinate silane {(o-Me2NCH2)C6H4}3SiX (X = F (8), H) and germane {(o-Me2NCH2)C6H4}3GeX (X = H, F) with three nitrogen donors coordinating to the central Si/Ge trans to the Cipso atoms). In contrast, the Si compounds 1 and 3 and the Ge compounds 2 and 4 have novel heptacoordinate geometries; the incorporation of such electronegative substituents as F and Cl results in the change of one phosphine donor from the position trans to the Cipso atom to that trans to the X atom. Compounds 1–4 retain this unprecedented geometry in solution but show dynamic behavior. The structural modification observed upon changing the substituent at Si and Ge is rationalized by electrostatic and charge tran...