Group 14 Metal Terminal Phosphides: Correlating Structure with |<i>J</i>_MP|

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.一系列第14族重元素末端膦化物配合物M(BDI)(PR₂)（其中M=Ge、Sn、Pb；BDI=CH{(CH₃)CN-2,6-iPr₂C₆H₃}₂；R=Ph、Cy、SiMe₃）已被成功合成。在固态下可观测到两种不同构象：内型（endo）与外型（exo）。当M=Ge、Sn且R=SiMe₃时，具有内型构象的配合物的磷原子配位几何呈平面结构，而具有外型构象的配合物的磷原子配位几何则为锥型结构。溶液态核磁共振（NMR）研究显示，BDI配体的N-芳基片段上的锡原子与异丙基之间存在空间标量耦合，内型与外型构象的J_SnC数值存在显著差异。锡-磷与铅-磷的耦合常数|J_SnP|和|J_PbP|的大小，会随磷原子的杂化方式不同而出现显著差异。其中，配合物Sn(BDI)(P{SiMe₃}₂)的|J_SnP|为目前文献报道的最大值，甚至超过了含锡-磷多重键化合物的耦合常数数值。对Pb(BDI)(P{SiMe₃}₂)的低温核磁共振研究表明，存在两种|J_PbP|数值相差悬殊的物种，分别被归因为内型与外型构象，对应磷原子分别为sp²与sp³杂化。