SYNTHESIS AND STRUCTURES OF NEW AMINOGALLANES WITH FOUR AND SIX MEMBERED RINGS: A NOVEL THERMOLYSIS REACTION OF THE DIAZASILAGALLETIDINE [Me2Si(NtBu)2GaCl]2

Abstract

The dimeric diazasilagalletidines, [Me₂Si(NtBu)₂GaX]₂, X = Me (1) and Cl (2), were synthesized by the reaction of gallium trichloride with the dilithiated salt of bis(t-butylamino)dimethylsilane or with the diazasilastannetidine Me₂Si(NtBu)₂Sn, respectively. By the latter method, the polycycle (MeSi)₂(NtBu),(GaCl) (3) was obtained as a by-product; compound 3 is also formed by thermolysis of 2 in vacuum. The molecular structures of 1–3 have been determined by X-ray methods. Compounds 1 and 2 crystallize in the monoclinic space group P2₁/n; compound 3 is isotypic to the previously known (MeSi)₂(NtBu)₄GaMe and the structure was solved in the space group P2₁/c. Other crystallographic data: 1. a = 11.240(6) Å, b = 8.668(4) Å, c = 15.702(8) Å, β = 100.83(3)°, Z = 2, V = 1502.7(13) ų, R = 0.052. 2, a = 9.147(5) Å, b = 18.225(9) Å, c = 9.209(5) Å, β = 107.08(4)°, Z = 2, V = 1467.4(13) ų, R = 0.058. 3 a = 9.324(9) Å, b = 14.822(15) Å, c = 19.60(2) Å, β = 110.03(7)°, Z = 4, V = 2545(4) ų, R = 0.066. In compounds 1 and 2, a four-membered Ga₂N₂ cycle forms the central ring to which two equal four-membered Si-N-Ga-N rings are fused in a trans orientation with respect to each other. The room temperature (20°C) ¹H-NMR spectrum of compound 3 exhibits only two l-butyl signals of equal intensity indicating a fast intramolecular exchange process which is inhibited only at temperatures below - 90°C (toluene). A tris(amino)gallane (Me₂Si)(NtBu)₂Ga[N(SiMe₃)₂] (4) can be obtained by reaction of 2 with lithium-bis(trimethylsilyl)amide.