Insertion of Benzonitrile into Al–N and Ga–N Bonds: Formation of Fused Carbatriaza-Gallanes/Alanes and Their Subsequent Synthesis from Amidines and Trimethyl-Gallium/Aluminum

Insertion of aromatic nitriles into
Al–N and Ga–N bonds are reported. Sterically less hindered
aluminum amide [PhNHAlMe2]2 (1)
undergoes CN insertion with benzonitrile to give an isomeric
mixture of tetracyclic triazaalanes {[PhNC­(Ph)­N]3[PhNC­(Ph)­NH]­Al­[AlMe]­[AlMe2]2} (2 and 3). A similar
reaction with analogous gallium amide affords a tetracyclic triazagallane
{[PhNC­(Ph)­N]3[PhNC­(Ph)­NH]­Ga­[GaMe]­[GaMe2]2} (6) along with a novel bowl shaped carbon containing
Ga–N cluster {[PhNC­(Ph)­N]­[PhN]­[GaMe]2}3 (5). On the other hand, when sterically bulky gallium
amide (Dipp on N, Dipp = 2,6-diisopropylphenyl) is employed, a tetrameric
gallium amidinate {[(Dipp)­NC­(Ph)­N]­GaMe}4 (8) is obtained. Tetracyclic triazagallazane 6 is also
synthesized from the condensation reaction of N-phenylbenzamidine
with GaMe3·OEt2. Unlike AlMe3, this reaction produces only one isomer. In case of amidines with
bulkier substituents on N such as Dipp, formation of a bicyclic triazagallane
{[(Dipp)­NC­(Ph)­NH]2[(Dipp)­NC­(Ph)­N]­[GaMe]2} (14) is also observed along with tetrameric gallium amidinate 8, whereas N-tert-butylbenzamidine
affords exclusively a tetrameric gallium amidinate {[(tert-Bu)­NC­(Ph)­N]­GaMe}4 (15) similar to its Al
analogue. However, treating N-(Dipp)­acetamidine with
GaMe3·OEt2 gives only a bicyclic triazagallane
{[(Dipp)­NC­(Me)­NH]2[(Dipp)­NC­(Me)­N]­[GaMe]2} (16). An intermediate [(tert-Bu)­N­(H) C­(Ph)­NGaMe2]2 (17), which is involved in the
formation of tetrameric gallium amidinate 15, is also
characterized. A comparison of the structural parameters of Ga–N–C
and Al–N–C frameworks synthesized in this study is reported.