The Kinetics and Mechanism of a Reaction in Which Ligand Substitution is Accompanied by a Spin-State Change: Observation of the Elusive Monodithiocarbamatonickel(II) Complex in Dimethyl Sulfoxide

Abstract

In solutions in Me₂SO containing low concentrations of diethyldithiocarbamate ion (dtc^-) and very high concentrations of Ni(Me₂SO)₆²⁺ ion, the hitherto undetected Ni(dtc)⁺ complex is kinetically stabilized and its electronic spectrum can be recorded. The mono complex is thermodynamically unstable and is converted into Ni(dtc)₂ by two independent pathways, one involving direct reaction between Ni(dtc)⁺ and dtc^-, the other being a dimerization reaction, 2Ni(dtc)⁺ → Ni²⁺ + Ni(dtc)₂.

Analysis of the mechanistic scheme

Ni²⁺ + dtc ↔ Ni(dtc)²

Ni(dtc)⁺ + dtc^- → Ni(dtc)₂

2Ni(dtc)⁺ → Ni²⁺ + Ni(dtc)₂

gives k₁ = 3 × 10³ l, mol^-1 s^-1, k_-1 ≈ 0.01 s^-1, k₂ ≈ 4 × 10⁵ l, mol^-1 s^-1 and k₃ ≈ 1 × 10³ l. mol^-1 s^-1. Coordinated dtc^- exerts a significant labilizing effect on coordinated Me₂SO molecules in Ni(dtc)⁺.