Synthesis and Structures of Cadmium Carboxylate and Thiocarboxylate Compounds with a Sulfur-Rich Coordination Environment: Carboxylate Exchange Kinetics Involving Tris(2-mercapto-1‑<i>t</i>‑butylimidazolyl)hydroborato Cadmium Complexes, [Tm^{Bu^t}]Cd(O₂CR)

A series
of cadmium carboxylate compounds in a sulfur-rich environment
provided by the tris­(2-tert-butylmercapto­imidazolyl)­hydroborato
ligand, namely, [TmBut]­CdO2CR, has been synthesized
via the reactions of the cadmium methyl derivative [TmBut]­CdMe with RCO2H. Such compounds mimic aspects of cadmium-substituted
zinc enzymes and also the surface atoms of cadmium chalcogenide crystals,
and have therefore been employed to model relevant ligand exchange
processes. Significantly, both 1H and 19F NMR
spectroscopy demonstrate that the exchange of carboxylate groups between
[TmBut]­Cd­(κ2-O2CR) and the
carboxylic acid RCO2H is facile on the NMR time scale,
even at low temperature. Analysis of the rate of exchange as a function
of concentration of RCO2H indicates that reaction occurs
via an associative rather than dissociative pathway. In addition to
carboxylate compounds, the thiocarboxylate derivative [TmBut]­Cd­[κ1-SC­(O)­Ph] has also been synthesized via the reaction
of [TmBut]­CdMe with thiobenzoic acid. The molecular structure
of [TmBut]­Cd­[κ1-SC­(O)­Ph] has been determined
by X-ray diffraction, and an interesting feature is that, in contrast
to the carboxylate derivatives [TmBut]­Cd­(κ2-O2CR), the thiocarboxylate ligand binds in a κ1 manner via only the sulfur atom.