An intramolecularly base-stabilized diphosphagermylene and two unusual germanium(II) ate complexes: A structural, NMR, and DFT study

The reaction between GeCl2 center dot 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)(2)CH]. Treatment of GeI2 with 2 equiv of the potassium salt 5 gives the homoleptic, intramolecularly base-stabilized diphosphagermylene {R(C6H4-2-CH2NMe2)P}(2)Ge (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}(2)GeLi2I2(OEt2)(3) (8), whereas treatment of GeI2 or GeCl2 center dot dioxane with 3 equiv of 5 yields the cage ate complex {R(C6H4-2-CH2NMe2)P}(3)GeK (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 [E-inv = 38.5 kcal mol(-1)] with respect to inversion at phosphorus [E-inv = 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}(2)Ge (7a) the lowest energy process for epimerization is calculated to be inversion at germanium via a pseudo-trigonal bipyramidal intermediate [E-inv = 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.