Cooperative Ge–N Bond Activation in Hydrogallation
Products of Alkynyl(diethylamino)germanes (Et<sub>2</sub>N)<sub><i>n</i></sub>Ge(CC<sup><i>t</i></sup>Bu)<sub>4–<i>n</i></sub>
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Abstract
Treatment
of the alkynyl(diethylamino)germanes Et<sub>2</sub>NGe(CC<sup><i>t</i></sup>Bu)<sub>3</sub> (<b>1</b>) and (Et<sub>2</sub>N)<sub>2</sub>Ge(CC<sup><i>t</i></sup>Bu)<sub>2</sub> (<b>2</b>) with dialkylelement hydrides <sup><i>t</i></sup>Bu<sub>2</sub>MH (M = Al, Ga) afforded in high yields
the hydrometalation products (<sup><i>t</i></sup>BuCC)<sub>2</sub>(Et<sub>2</sub>N)Ge[C(M<sup><i>t</i></sup>Bu<sub>2</sub>)C(H)<sup><i>t</i></sup>Bu] (<b>3</b>), (<sup><i>t</i></sup>BuCC)(Et<sub>2</sub>N)Ge[C(M<sup><i>t</i></sup>Bu<sub>2</sub>)C(H)<sup><i>t</i></sup>Bu]<sub>2</sub> (<b>4</b>) and (<sup><i>t</i></sup>BuCC)(Et<sub>2</sub>N)<sub>2</sub>Ge[C(Ga<sup><i>t</i></sup>Bu<sub>2</sub>)C(H)<sup><i>t</i></sup>Bu] (<b>6</b>). The Lewis acidic aluminum and gallium
atoms showed a close contact to the nitrogen atoms of the amino groups
attached to germanium, which resulted in relatively long Ge–N
bonds and short Al–N or Ga–N distances. The structures
of these molecules and the strengths of the interactions were investigated
by dispersion-corrected density functional theory. This activation
of the Ge–N bonds caused an unprecedented reactivity of compounds <b>4b</b> and <b>6</b>. <b>4b</b> reacted with PhCCH
under mild conditions and elimination of HNEt<sub>2</sub> to give
the mixed dialkynyl compound (<sup><i>t</i></sup>BuCC)(PhCC)Ge[C(Ga<sup><i>t</i></sup>Bu<sub>2</sub>)C(H)<sup><i>t</i></sup>Bu]<sub>2</sub> (<b>5</b>), while facile insertion of
RNCX into a Ge–N bond of <b>6</b> led
to the formation of the six-membered Ge–C–Ga–X–C–N
heterocycles <b>7</b> (R = Ph, Et; X = O, S)