A stepwise assembly of a molecular box from 16-electron half-sandwich precursors [Cp*M(pdt)] (M = Rh, Ir).

The coordinatively-unsaturated 16-electron half-sandwich precursors [Cp*M(pdt)] (M = Rh, Ir; pdt = pyrazine-2,3-dithiol) have been synthesized. X-ray crystallography in combination with (1)H NMR analysis was used to elucidate the nature of the precursors. The Rh(iii) precursor displays a dimeric form in the trans arrangement in the solid state, formulated as [(Cp*Rh)2(μ(S)-pdt)2] (), in which covalent Rh-S bonds bridge the metal centers. In solution, however, dimers and monomers coexist in equilibrium. The dissociation equilibrium of in DMSO-d6 was evaluated by (1)H NMR at several temperatures between 20 and 80 °C. The Ir(iii) precursor [Cp*Ir(pdt)] () is the monomeric form, and stable in the solid state and solution. Due to their unsaturation and bridging properties, these precursors were further used in stepwise assembly reactions with the binuclear building blocks to give open macrocycles and a closed molecular box.