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

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The reaction between GeCl 2 ·dioxane and 1 equiv of {R(C 6 H 4 -2-CH 2 NMe 2 )P}K ( 5 ) yields the heteroleptic complex {R(C 6 H 4 -2-CH 2 NMe 2 )P}GeCl ( 6 ) [R = (Me 3 Si) 2 CH]. Treatment of GeI 2 with 2 equiv of the potassium salt 5 gives the homoleptic, intramolecularly base-stabilized diphosphagermylene {R(C 6 H 4 -2-CH 2 NMe 2 )P} 2 Ge ( 7 ) in good yield. In contrast, treatment of GeI 2 with 2 equiv of {R(C 6 H 4 -2-CH 2 NMe 2 )P}Li ( 4 ) in ether reproducibly yields the unusual ate complex {R(C 6 H 4 -2-CH 2 NMe 2 )P} 2 GeLi 2 I 2 (OEt 2 ) 3 ( 8 ), whereas treatment of GeI 2 or GeCl 2 ·dioxane with 3 equiv of 5 yields the cage ate complex {R(C 6 H 4 -2-CH 2 NMe 2 )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)(C 6 H 4 -2-CH 2 NMe 2 )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)(C 6 H 4 -2-CH 2 NMe 2 )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.