Group 14 Metal Terminal Phosphides: Correlating Structure with |JMP|

A series of heavier group 14 element, terminal phosphide complexes, M­(BDI)­(PR2) (M = Ge, Sn, Pb; BDI = CH­{(CH3)­CN-2,6-iPr2C6H3}2; R = Ph, Cy, SiMe3) have been synthesized. Two different conformations (endo and exo) are observed in the solid-state; the complexes with an endo conformation have a planar coordination geometry at phosphorus (M = Ge, Sn; R = SiMe3) whereas the complexes possessing an exo conformation have a pyramidal geometry at phosphorus. Solution-state NMR studies reveal through-space scalar coupling between the tin and the isopropyl groups on the N-aryl moiety of the BDI ligand, with endo and exo exhibiting different JSnC values. The magnitudes of the tin–phosphorus and lead–phosphorus coupling constants, |JSnP| and |JPbP|, differ significantly depending upon the hybridization of the phosphorus atom. For Sn­(BDI)­(P­{SiMe3}2), |JSnP| is the largest reported in the literature, surpassing values attributed to compounds with tin–phosphorus multiple-bonds. Low temperature NMR studies of Pb­(BDI)­(P­{SiMe3}2) show two species with vastly different |JPbP| values, interpreted as belonging to the endo and exo conformations, with sp2- and sp3-hybridized phosphorus, respectively.