Zinc thiolate complexes [ZnL n(SR)] + with azamacrocyclic ligands, part II: Mechanism of the reaction with CS 2

Johannes Notni, Stephan Schenk, Arne Roth, Winfried Plass, Helmar Görls, Ute Uhlemann, Angela Walter, Michael Schmitt, Jürgen Popp, Susana Chatzipapadopoulos, Thomas Emmler, Hergen Breitzke, Jörg Leppert, Gerd Buntkowsky, Kristian Kempe, Ernst Anders

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Abstract

The thiolate complexes [Zn([15]aneN 4)(S-CH 2-C 6H 5)]ClO 4 (1) ([15]aneN 4 = 1,4,8,12-tetraazacyclopentadecane) and [Zn(i-[14]aneN 4)(S-CH 2-C 6H 5)]ClO 4 (2) (i-[14]aneN 4 = 1,4,7,11-tetraazacyclotetradecane) have been reacted with carbon disulfide. The trithiocarbonate complexes [Zn([15]aneN 4){S-C(S)-S- CH 2-C 6H 5}]ClO 4 {1a, monoclinic, space group P2 1/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) Å 3} and [Zn(i-[14]aneN 4){S-C(S)-S-CH 2-C 6H 5}]ClO 4 {2a, orthorhombic, space group P2 12 12 1, Z = 8, a = 9.9936(1) Å, b = 22.1261(4) Å, c = 22.3192(4) Å, V = 4935.2(1) Å 3} were obtained. The reaction of 1 with CS 2 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 ΔH exp = 65.3 ± 0.7 kJ·mol -1 (ΔS exp = -49.9 ± 2.5 J·mol -1·K -1) and a free energy of activation of ΔG Dagger; = 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 of δΔG ≈ 80 kJ·mol -1. Its calculated barrier ΔG theor = 114.3 kJ·mol -1 is in reasonable agreement with the experimental value.

Original languageEnglish
Pages (from-to)2783-2791
Number of pages9
JournalEuropean Journal of Inorganic Chemistry
Issue number14
DOIs
Publication statusPublished - 17 Jul 2006
Externally publishedYes

Keywords

  • Density functional calculations
  • Enzyme models
  • Heterocumulenes
  • Macrocyclic ligands
  • Zinc

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