Synthesis and Structures of Sb[N(H)(C6H2tBu3)]3 and Bi[N(H)(C6H2tBu3)]3: Implications for the Steric Limits of Supermesityl Substitution

Syntheses and isolations of the tris(amino)stibine and tris(amino)bismuthine E[N(H)(C(6)H(2)(t)Bu(3))](3) (E = Sb, Bi) from ECl(3) and LiN(H)(C(6)H(2)(t)Bu(3)) are described, together with spectroscopic and structural characterization [crystal data for C(54)H(90)N(3)Sb, M = 903.04, space group P, a = 11.491(5) Å, b = 24.652(7) Å, c = 10.002(5) Å, alpha = 98.38(3) degrees, beta = 96.44(5) degrees, gamma = 77.25(3) degrees, V = 2724(2) Å(3), D(c) = 1.101 Mg/m(3), Z = 2, R = 0.0547; crystal data for C(54)H(90)BiN(3), M = 990.27, space group P, a = 11.511(5) Å, b = 24.785(15) Å, c = 9.981(5) Å, alpha = 98.06(5) degrees, beta = 96.50(4) degrees, gamma = 77.40(5) degrees, V = 2742(2) Å(3), D(c) = 1.200 Mg/m(3), 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 PCl(3) and AsCl(3), which have been previously shown to produce the aminoiminopnictine structures [N(H)(C(6)H(2)(t)Bu(3))]P=N(C(6)H(2)(t)Bu(3)) and [N(H)(C(6)H(2)(t)Bu(3))]As=N(C(6)H(2)(t)Bu(3)). 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.