A Bismuth-Arene σ-Complex - On the Edge of Menshutkin-Type Complexes

Mes*N(SiMe3)BiCl2 (1, Mes* = 2,4,6-tri-tert-butylphenyl) can be referred to as a hidden iminobismuthane, Mes*N=BiCl, which was thought to be generated in-situ upon Me3SiCl elimination triggered by a Lewis acid such as GaCl3. Therefore, the reactivity of aminobismuthane 1 was studied to find a synthesis route for the formation of a tetrazabismuthole in a [3+2] cycloaddition reaction with a covalently bound azide. However, reaction of 1 with GaCl3 cleanly led to [Mes*N(SiMe3)BiCl][GaCl4] (2[GaCl4]), a compound with a Bi-arene sigma-complex. Utilizing Ag[WCA] salts (WCA = weakly coordinating anion) for chloride abstraction, a C-C coupling product (3) was identified. The diiodide species Mes*N(SiMe3)BiI2 (4) as precursor for a diazido species and the azido-chloride compound Mes*N(SiMe3)Bi(N-3)Cl (5) were also prepared to explore the possibility of a BiN4 heterocycle formation, again upon Me3SiX elimination (X = halogen, N-3), but 4 and 5 were unstable towards decomposition into a black precipitate and a complex product mixture. The structure and bonding of all isolated bismuth species is discussed.