An Intramolecularly Base-Stabilized Diphosphagermylene and Two Unusual Germanium(II) Ate Complexes: A Structural, NMR, and DFT Study

The reaction between GeCl2·dioxane and 1 equiv of {R(C6H4-2-CH2NMe2)P}K (5) yields
the heteroleptic complex {R(C6H4-2-CH2NMe2)P}GeCl (6) [R = (Me3Si)2CH]. Treatment of
GeI2 with 2 equiv of the potassium salt 5 gives the homoleptic, intramolecularly base-stabilized diphosphagermylene {R(C6H4-2-CH2NMe2)P}2Ge (7) in good yield. In contrast,
treatment of GeI2 with 2 equiv of {R(C6H4-2-CH2NMe2)P}Li (4) in ether reproducibly yields
the unusual ate complex {R(C6H4-2-CH2NMe2)P}2GeLi2I2(OEt2)3 (8), whereas treatment of
GeI2 or GeCl2·dioxane with 3 equiv of 5 yields the cage ate complex {R(C6H4-2-CH2NMe2)P}3GeK (9). The solid-state structures of 7−9 have been determined by X-ray crystallography,
and the dynamic behavior of 6−9 in solution has been studied by multielement and variable-temperature NMR experiments. DFT calculations on the model complex {(Me)(C6H4-2-CH2NMe2)P}GeCl (6a) indicate that inversion at germanium via a planar transition state is
disfavored [Einv = 38.5 kcal mol-1] with respect to inversion at phosphorus [Einv = 21.0 kcal
mol-1]; inversion at germanium is calculated to proceed via an edge-inversion rather than
vertex-inversion process. For the model diphosphagermylene {(Me)(C6H4-2-CH2NMe2)P}2Ge (7a) the lowest energy process for epimerization is calculated to be inversion at germanium
via a pseudo-trigonal bipyramidal intermediate [Einv = 3.0 kcal mol-1]. Inversion at
germanium (via a vertex-inversion process) is calculated to have a barrier of 48.0 kcal mol-1,
whereas the barriers to inversion at phosphorus are 24.0 and 18.5 kcal mol-1 for the chelating
and terminal phosphorus atoms, respectively.