Synthesis, characterization, and redox behavior of new selenium coronands and of copper(I) and copper(II) complexes of selenium coronands.

Abstract

The synthesis and characterization of new selenium coronands and of copper(I) and copper(II) complexes of selenium coronands are reported. Molecular structures in the solid state have been determined by X-ray crystallography. The molecular structures of 6,7,13,14-dibenzo-1,5,8,12-tetraselenacyclotetradecane (dibenzo-14Se4 (1)) and 1,5,9-triselenacyclododecane (12Se3 (2)) adopt conformations which maximize the number of possible gauche C−Se−C−C bond torsion angles. 1: T = 190 K; orthorhombic, space group Pca21; fw = 552.19; Z = 4; a = 9.645(3) Å; b = 12.679(6) Å; c = 15.332(4) Å; V = 1874.9 Å3; RF = 0.027 for 1732 data (Io ≥ 2.5σ(Io)) and 200 variables. 2: T = 190 K; orthorhombic, space group Pn21a; fw = 363.12; Z = 4; a = 14.943(4) Å; b = 5.638(2) Å; c = 14.229(3) Å; V = 1198.8 Å3; RF = 0.026 for 862 data (Io ≥ 2.5σ(Io)) and 111 variables. The molecular structures of 1,5-diselena-9,13-dithiacyclohexadecane (16Se2S2 (3)) and [Cu(16Se2S2)][SO3CF3]2 (4) correspond to those displayed by both of the analogous tetrathia and tetraselena macrocycles. Compound 3 adopts a [3535] quadrangular conformation. Compound 4, [Cu(16Se4(OH)2][SO3CF3]2 (5) (where 16Se4(OH)2 = cis-1,5,9,13-tetraselenacyclohexadecane-3,11-diol), and [Cu(8Se2(OH))2][SO3CF3]2 (6) (where 8Se2(OH) = 1,5-diselenacyclooctan-3-ol) have typical tetragonally distorted octahedral coordination environments of Cu(II). Compounds 4 and 5 both display a c,t,c configuration of the coronand. Compound 5 has only one hydroxyl group coordinated in an axial position, which requires that the corresponding Se−Cu−Se−C−C−C ring be locked into a boat rather than a chair conformation. The hydroxyl groups in 6 occupy the axial coordination positions. 3: T = 200 K; monoclinic, space group C2/c; fw = 390.36; Z = 12; a = 24.202(9) Å; b = 18.005(7) Å; c = 16.235(5) Å; β = 138.23(3)°; V = 4713 Å3; RF = 0.052 for 1881 data (Io ≥ 2.5σ(Io)) and 172 variables. 4: T = 297 K; monoclinic, space group P21/n; fw = 752.03; Z = 2; a = 8.882(2) Å; b = 10.874(2) Å; c = 13.360(2) Å; β = 97.95(2)°; V = 1277.9 Å3; RF = 0.028 for 1610 data (Io ≥ 2.5σ(Io)) and 176 variables. 5: T = 190 K; monoclinic, space group P21/n; fw = 877.84; Z = 4; a = 8.412(5) Å; b = 20.924(5) Å; c = 15.021(5) Å; β = 100.82(4)°; V = 2597 Å3; RF = 0.059 for 2152 data (Io ≥ 2.5σ(Io)) and 185 variables. 6: T = 195 K; monoclinic, space group P21/c; fw = 877.84; Z = 2; a = 6.875(2) Å; b = 10.945(2) Å; c = 17.496(2) Å; β = 96.76(2)°; V = 1307.3 Å3; RF = 0.023 for 1816 data (Io ≥ 2.5σ(Io)) and 159 variables. [Cu(16Se2S2)][SO3CF3] (7) and [Cu(16Se4(OH))][SO3CF3] (8) (where 16Se4(OH) = 1,5,9,13-tetraselenacyclohexadecan-3-ol) are both tetrahedral Cu(I) coronand complexes with typical t,t,t configurations. 7: T = 205 K; triclinic, space group P1̄; fw = 602.97; Z = 2; a = 10.512(3) Å; b = 10.674(2) Å; c = 10.682(3) Å; α = 101.47(2)°; β = 116.82(2)°; γ = 93.59(2)°; V = 1032.3 Å3; RF = 0.029 for 2237 data (Io ≥ 2.5σ(Io)) and 264 variables. 8: T = 297 K; monoclinic, space group P21/n; fw = 712.77; Z = 4; a = 13.695(2) Å; b = 11.202(2) Å; c = 14.163(3) Å; β = 92.35(2)°; V = 2170.9 Å3; RF = 0.035 for 2086 data (Io ≥ 2.5σ(Io)) and 189 variables. Compounds 5, 6, and 8 all display hydrogen bonding between hydroxyl groups and the SO3CF3- ions. Isotropic 13C and 77Se chemical shifts have been obtained in the solid state for 2, 3, 1,5,9,13-tetraselenacyclohexadecane-3,11-diol (16Se4(OH)2 (9)), 1,5,9,13-tetraselenacyclohexadecan-3-ol (16Se4(OH) (10)), and the dicationic complex 1,5,-(diseleniacyclooctane trifluoromethanesulfonate (8Se2(SO3CF3)2 (11)). In addition, the 77Se chemical shift anisotropies have been determined for 10 and 11. The dicationic compound 11 resonates at lower field, reflective of a contribution from the transannular Se−Se bond. The redox behavior of 1−8 has been examined by means of cyclic voltammetry. Redox behavior of the copper complexes 4, 5, and 6 indicates the presence of two different conformational isomers of the Cu(I) complexes that are oxidized at different potentials, analogous to Rorabacher's copper(II/I) complexes that follow a dual-pathway square-scheme mechanism. The quasi-reversible cyclic voltammograms observed for the Cu(II) complexes of selenium coronands reflect the configurational changes between Cu(II) complexes (octahedral or tetragonal configurations) and Cu(I) complexes (tetrahedral configurations) and indicate that the configurational changes are slower than the electron transfers to the electrode.