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

Two bis­(dithiocarbamate) (bdtc) metallamacrocyclic compounds, <b>1</b> and <b>2</b>, and the deuterated analogues <b>1</b>-<i>d</i>₈ and <b>1</b>-<i>d</i>₂₀ 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 <b>1</b>, 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 <i>para</i>-disubstituted phenylene (compound <b>1</b>) and bicyclo[2.2.2]­octane groups (compound <b>2</b>) showed rotational motion within the macrocyclic assemblies in the solid state. For compound <b>1</b>, the internal rotation of the phenylene groups was examined first by ¹³C NMR CPMAS spectroscopy using the <b>1</b>-<i>d</i>₂₀ 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 <b>1</b>-<i>d</i>₈ 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 <i>E</i>_a = 10 kcal/mol with a preexponential factor <i>A</i> = 3.9 × 10¹⁴ s^–1. For compound <b>2</b>, 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.