title: Cooperative Ge-N Bond activation in aluminium-functionalised aminogermanes and spontaneous imine elimination via an intermediate germyl cation.
abstract: Hydrometallation of iPr2 N-Ge(CMe3 )(C≡C-CMe3 )2 with H-M(CMe3 )2 (M=Al, Ga) affords alkenyl-alkynylgermanes in which the Lewis-acidic metal atoms are not coordinated by the amino N atoms but by the α-C atoms of the ethynyl groups. These interactions result in a lengthening of the Ge-C bonds by approximately 10 pm and a comparably strong deviation of the Ge-CC angle from linearity (154.3(1)°). This unusual behaviour may be caused by steric shielding of the N atoms. Coordination of the metal atoms by the amino groups is observed upon hydrometallation of Et2 N-Ge(C6 H5 )(C≡C-CMe3 )2 , bearing a smaller NR2 group. Strong M-N interactions lead to a lengthening of the Ge-N bonds by 10 to 15 pm and a strong deviation of the M atoms from the MC3 plane by 52 and 47 pm, for Al and Ga, respectively. Dual hydrometallation is achieved only with HAl(CMe3 )2 . In the product, there is a strong Al-N bond with converging Al-N and Ge-N distances (208 vs. 200 pm) and an interaction of the second Al atom to the phenyl group. Addition of chloride anions terminates the latter interaction while the activated Ge-N bond undergoes an unprecedented elimination of EtN=C(H)Me at room temperature, leading to a germane with a Ge-H bond. State-of-the-art DFT calculations reveal that the unique mechanism comprises the transfer of the amino group from Ge to Al to yield an intermediate germyl cation as a strong Lewis acid, which induces β-hydride elimination, with chloride binding being crucial for providing the thermodynamic driving force.
authors.affiliation: Institut für Anorganische und Analytische Chemie, Westfälische Wilhelms-Universität Münster, Corrensstrasse 30, 48149 Münster (Germany), Fax: (+49) 251-8336660. uhlw@uni-muenster.de.
authors.forename: Werner
authors.initials: W
authors.lastname: Uhl
authors.forename: Jens
authors.initials: J
authors.lastname: Tannert
authors.forename: Christian
authors.initials: C
authors.lastname: Honacker
authors.forename: Marcus
authors.initials: M
authors.lastname: Layh
authors.forename: Zheng-Wang
authors.initials: ZW
authors.lastname: Qu
authors.forename: Tobias
authors.initials: T
authors.lastname: Risthaus
authors.forename: Stefan
authors.initials: S
authors.lastname: Grimme
keywords: bond activation; density functional calculations; germanium; hydroalumination; imines