Zinc Thiolate Complexes [ZnLn(SR)]+ with Azamacrocyclic Ligands, Part II: Mechanism of the Reaction with CS2

Abstract

AbstractThe thiolate complexes [Zn([15]aneN4)(S–CH2–C6H5)]ClO4 (1) ([15]aneN4 = 1,4,8,12‐tetraazacyclopentadecane) and [Zn(i‐[14]aneN4)(S–CH2–C6H5)]ClO4 (2) (i‐[14]aneN4 = 1,4,7,11‐tetraazacyclotetradecane) have been reacted with carbon disulfide. The trithiocarbonate complexes [Zn([15]aneN4){S–C(S)–S–CH2–C6H5}]ClO4 {1a, monoclinic, space group P21/n, Z = 8, a = 13.2338(1) Å, b = 12.9251(2) Å, c = 30.1669(4) Å, β = 101.463(1)°, V = 5057.1(1) Å3} and [Zn(i‐[14]aneN4){S–C(S)–S–CH2–C6H5}]ClO4 {2a, orthorhombic, space group P212121, Z = 8, a = 9.9936(1) Å, b = 22.1261(4) Å, c = 22.3192(4) Å, V = 4935.2(1) Å3} were obtained. The reaction of 1 with CS2 is second order with a rate constant of k = (57.6 ± 2.4) × 10–3 M–1·s–1 at 25 °C. The experimentally determined Eyring activation barrier is ΔHexp‡ = 65.3 ± 0.7 kJ·mol–1(ΔSexp‡ = –49.9 ± 2.5 J·mol–1·K–1) and a free energy of activation of ΔG‡ = 80.2 ± 1.5 kJ·mol–1 at 25 °C. To discriminate between an associative and a dissociative mechanism the barriers for both processes were calculated using density functional theory at the C‐PCM(B98/G3MP2Large)//B3LYP/6‐311+G(d) level. The associative mechanism is clearly favored with a difference in free energies of activation ofδΔG‡ ≈ 80 kJ·mol–1. Its calculated barrier ΔGtheor‡ = 114.3 kJ·mol–1 is in reasonable agreement with the experimental value. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)