Chemical reduction of a pentastanna[ 1.1.1 ]propellane derivative and the synthesis and molecular structure of a bicyclo[ 1.1.1 ]pentastannane

Article abstract of DOI:10.1021/ja00180a027

Cyclic voltammetry of 2,2,4,4,5,5-hexakis(2,6-diethylphenyl)pentastanna[ 1.1.1 ]propellane (3) in THF shows two quasireversible one-electron reduction waves at E_1/2 = -1.41 and -1.93 V (V vs NHE) which correspond to the [3]/[3]^- and the [3]^-/[3]^2- redox couples, respectively. Chemical reduction of 3 with 0.5% potassium amalgam can be achieved in the presence of 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane (abbreviated as crypt) to produce the radical anion complex [3]^-[K,crypt]⁺. This radical anion has been characterized by ESR which shows g_iso = 1.92, a(^119/117Sn_1,3) = 15 G, and a(^119/117Sn_2,4,5) = 57 G for the isotropic spectrum at 410 K and g_∥ = 1.99 and g_⊥ = 1.89 for the anisotropic frozen spectrum at 130 K. Compound 3 quantitatively reacts with methyl iodide to produce 2,2,4,4,5,5-hexakis(2,6-diethylphenyl)-1-iodo3-melhylbicyclo[1.1.1]pentastannane (4), which can be isolated as deep-red crystals. Single crystals of 4 are, at 20 °C, monoclinic, space group P2₁/c-C_2h⁵ (No. 14) with a = 14.785 (2) A?, b = 20.319 (3) A?, c = 22.951 (3) A?, β = 97.63 (1)°, V = 6834 (2) A?³, and Z = 4. The tin-tin bond lengths between the bridging and bridgehead tin atoms of 4 are in the range of 2.825 (1) to 2.842 (1) A?, and the distance between the two bridgehead tin atoms is 3.361 (1) A?, The results of these investigations support the view that the central bridgehead-bridgehead bonding interaction of 3 contributes very little to the stability of this system.