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. [ABSTRACT FROM AUTHOR]