Heavy Alkali Metal Arenedithiocarboxylates: A Facile Synthesis, Dimeric Structure, and Nonbonding Interaction between the Metals and Aromatic Ring Carbons

Dithiocarboxylic acids and their trimethylsilyl esters were found to readily react with potassium, rubidium, and
cesium fluorides to give the corresponding alkali metal dithiocarboxylates 3−5 in moderate to good yields. A
series of tetramethylammonium dithiocarboxylates 8 have been prepared in good yields by the reaction of sodium
dithiocarboxylates 7 with tetramethylammonium chloride. The structures of potassium (3b), rubidium (4g), cesium
(5f), and tetramethylammonium 4-methylbenzenecarbodithioates (8e) and tetramethylammonium 2-methoxybenzenecarbodithioate (8f) were characterized crystallographically. These heavier alkali metal salts (3b, 4g, 5f) have
a dimeric structure [(RCSSM)2, M = K, Rb, Cs] in which the two dithiocarboxylate groups are chelated to the
metal cations which are located on the upper and lower sides of the plane involving the two opposing
dithiocarboxylate groups. The K+ cations interact with the tolyl fragment of a neighboring molecule, while the
Rb+ and Cs+ cations interact with two neighboring tolyl fragments, in which the ipso and ortho carbons are
positioned close to the metals. The interaction number of the metals with surrounding atoms is 8 for K+ and Rb+
and 12 for Cs+. The C−S distances of the dithiocarboxylate group are different for the potassium salt 3b. In
contrast, those of the rubidium salt 4g and cesium salt 5f are equal. Similarly, the chelating sulfur−metal bond
distances of 3b are different, while those of 4g and 5f are almost equal. The dihedral angles of the phenyl ring
and dithiocarboxylate plane increase in the order of the K, Rb, and Cs salts. The structural analysis of sodium
4-methylbenzenecarbodithioate (7g) revealed the presence of 4-CH3C6H4CS2Na0.36. In contrast, the tetramethylammonium salts 8 are monomeric where the cation moieties are located out of the dithiocarboxylate plane. The
potassium 3, rubidium 4, and cesium dithiocarboxylates 5 readily reacted with methyl iodide or triorganotin
chlorides at room temperature to give the corresponding methyl 9 and triorganotin dithioesters 10 in good yields.
At 0 °C, the reactivity of the rubidium 4 and cesium salts 5 to methyl iodides decreases dramatically compared
with those of the sodium salts 7 and potassium salts 3.