Synthesis and Structures of Sb[N(H)(C₆H₂^tBu₃)]₃ and Bi[N(H)(C₆H₂^tBu₃)]₃: Implications for the Steric Limits of Supermesityl Substitution

Syntheses and isolations of the tris(amino)stibine and tris(amino)bismuthine E[N(H)(C6H2tBu3)]3 (E = Sb, Bi) from ECl3 and LiN(H)(C6H2tBu3) are described, together with spectroscopic and structural characterization [crystal data for C54H90N3Sb, M = 903.04, space group P1̄, a = 11.491(5) Å, b = 24.652(7) Å, c = 10.002(5) Å, α = 98.38(3)°, β = 96.44(5)°, γ = 77.25(3)°, V = 2724(2) Å3, Dc = 1.101 Mg/m3, Z = 2, R = 0.0547; crystal data for C54H90BiN3, M = 990.27, space group P1̄, a = 11.511(5) Å, b = 24.785(15) Å, c = 9.981(5) Å, α = 98.06(5)°, β = 96.50(4)°, γ = 77.40(5)°, V = 2742(2) Å3, Dc = 1.200 Mg/m3, Z = 2, R = 0.0619]. The compounds bear the “bulky” 2,4,6-tri-tert-butylphenyl substituent (known as supermesityl or Mes*), and their formation is considered in the context of the same reactions for PCl3 and AsCl3, which have been previously shown to produce the aminoiminopnictine structures [N(H)(C6H2tBu3)]PN(C6H2tBu3) and [N(H)(C6H2tBu3)]AsN(C6H2tBu3). The observations establish the limits of the steric control by the supermesityl substituent and provide qualitative support for the thermodynamic significance of substituent steric strain.