Synthesis and Solid-State Characterization of Self-Assembled Macrocyclic Molecular Rotors of Bis(dithiocarbamate) Ligands with Diorganotin(IV)

Two bis­(dithiocarbamate) (bdtc) metallamacrocyclic compounds, 1 and 2, and the deuterated analogues 1-d₈ and 1-d₂₀ were readily prepared through self-assembly processes involving the corresponding secondary bis­(diamines), with two equivalents each of CS₂ and dimethyltin­(IV) dichloride. Solid-state characterization using FTIR, PXRD, and TGA indicated that the solid phases of both macrocycles were amorphous solids. For compound 1, a crystalline phase could only be obtained in the form of a dichloromethane solvate; however, the corresponding crystal lattice was unstable and collapsed rapidly under ambient conditions. The bdtc ligands containing para-disubstituted phenylene (compound 1) and bicyclo[2.2.2]­octane groups (compound 2) showed rotational motion within the macrocyclic assemblies in the solid state. For compound 1, the internal rotation of the phenylene groups was examined first by ¹³C NMR CPMAS spectroscopy using the 1-d₂₀ derivative in which the hydrogen atoms of the pendant phenyl groups had been substituted with deuterium atoms and also by ²H NMR spin echo experiments using the 1-d₈ derivative in which the rotating phenylene groups have been deuterated. Line shape analysis using a log-Gaussian distribution model indicated that the central phenylene rings experience fast 2-fold flip reorientations over the sp²–sp³ carbon atom axes, overcoming an activation energy of E_a = 10 kcal/mol with a preexponential factor A = 3.9 × 10¹⁴ s^–1. For compound 2, the ¹³C CPMAS experiments suggested that the bicyclo[2.2.2]­octane moieties also undergo fast internal dynamics, which is in agreement with the higher symmetry of these fragments when compared to the phenylene spacers.