Synthesis, characterization, and stereochemistry of S-bridged CoIIIMCoIII (M = PdII, PtII) trinuclear complexes containing two non-bridging thiolato groups: building blocks for the construction of chiral heterometallic aggregates

Abstract

The reaction of fac(S)-[Co(aet)₃] (aet = aminoethanethiolate) with [PdCl₄]²⁻ in a 2∶1 ratio in water gave an S-bridged Co^IIIPd^IICo^III trinuclear complex composed of two mer(S)-[Co(aet)₃] units, [Pd{Co(aet)₃}₂]²⁺ ([1]²⁺). In [1]²⁺, each of the two mer(S)-[Co(aet)₃] units is bound to a square-planar Pd^II ion through two of three thiolato groups, leaving two non-bridging thiolato groups at the terminal. Of two geometrical forms, syn and anti, possible for [Pd{Co(aet)₃}₂]²⁺, which arise from the difference in arrangement of two terminal non-bridging thiolato groups, [1]²⁺ afforded only the syn form. A similar reaction of fac(S)-[Co(aet)₃] with [PtCl₄]²⁻ or trans-[PtCl₂(NH₃)₂] produced an analogous Co^IIIPt^IICo^III trinuclear complex, [Pt{Co(aet)₃}₂]²⁺ ([2]²⁺), but both the syn and anti forms were formed for [2]²⁺. Complexes [1]²⁺ and syn- and anti-[2]²⁺, which exclusively exist as a racemic (ΔΔ/ΛΛ) form, were successfully optically resolved with use of [Sb₂(R,R-tartrato)₂]²⁻ as the resolving agent. The reaction of syn-[2]²⁺ with [AuCl{S(CH₂CH₂OH)₂}] led to the formation of an S-bridged Co^III₄Pt^II₂Au^I₂ octanuclear metallacycle, [Au₂{Pt[Co(aet)₃]₂}₂]⁶⁺ ([3]⁶⁺), while the corresponding reaction of anti-[2]²⁺ afforded a different product ({[4]³⁺}_n) that is assumed to have a polymeric structure in {[Au{Pt[Co(aet)₃]₂}]³⁺}_n.