A Dimeric Gallium Hydrazide as an Active Lewis Pair - Complexation and Activation of Me2GaH and Various Heterocumulenes

Uhl W., Willeke M., Hepp A., Pleschka D., Layh M.

Abstract

Treatment of the dimeric gallium hydrazide [Me2Ga-N(2-Ad)-NC5H10]2 (5) with Me2GaH resulted in the formation of an adduct 6 by Ga-N bond cleavage and coordination of the metal hydride via a Ga-N and a 3c-2e Ga-H-Ga bond. This reaction reflects the typical behavior of frustrated Lewis pairs. Reactions with heterocumulenes R-N=C=X (R = Ph, CMe3, Dipp, X = O; R = Ph, X = S) or X=C=X (X = O, S) resulted in the formation of the cyclic Ga-N insertion products Me2Ga-N(R)C(O)N(2-Ad)-NC5H10 (7a-c), Me2GaS2C-N(2-Ad)-NC5H10 (8) or Me2GaX2C-N(2-Ad)-NC5H10 [X = O (9); S (10)] in moderate to good yields. Three different structural motifs were observed in the solid state: Five-membered GaNCN2 heterocycles with exocyclic C=O bonds for compounds 7a-c, four-membered GaSCN or GaSCS heterocycles for compounds 8 and 9 (chelating coordination of the Ga atoms by SCN and CS2 ligands) and an eight-membered (GaOCO)2 heterocycle for the dimeric CO2 insertion product 10. Treatment of 5 with PhCN or Ph2CO resulted in a completely different reaction and afforded a dimeric Ga imide 11a or an alcoholate 11b. These reactions may start by retro-hydrogallation with the formation of H10C5N-N=C(C9H14) and Me2GaH and proceed by addition of the metal hydride to the polar multiple bonds of the nitrile or ketone.