The remarkable structural diversity of alkali metal pyridine-2-thiolates with mismatched crown ethers

The metathesis reaction of butyllithium or sodium or potassium hydride with pyridine-2-thiol is effected in ethereal or hydrocarbon media, where the addition of crown ether (which is essential in the case of sodium hydride) facilitates the metalation step. The reaction is driven forward irreversibly by the evolution of a volatile component (C₄H₁₀ or H₂). It is shown that the choice of crown ether is of paramount importance in determining the solid-state structural outcome. When the cavity size of the crown ether is matched with the alkali metal ionic radius, simple monomeric formulations are identified in [Li(12C4)(NC₅H₄S-2)] (1) (12C4=[12]crown-4), [Na(15C5)- (NC₅H₄S-2)] (2) (15C5=[15]crown-5), and [K(18C6)(NC₅H₄S-2)] (3) (18C6= [18]crown-6), although the geometrical relationship between cation and anion in this series has proven to be more complex than was anticipated. The complexes resulting from the pairing of crown ethers that are either too small or too large relative to the alkali metal exhibit a rich structural diversity that is a direct function of the macrocyclic donor: dimeric [{Li(NC₅H₄S-2)}₂{18C6}] (4) and monomeric [Na(18C6)(NC₅H₄S-2)] (5) are formed in the presence of 18C6; the unprecedented metalloanionic [{Na(12C4)₂}₂{Na(NC₅ H₄S-2)₂(thf)}{Na(NC₅H₄μ-S-2) (NC₅H₄S-2)}]₂ (6), with two hitherto unknown metallates, is obtained when 12C4 is employed; and the unusual polymeric [{K(μ-NC₅H₄-μ-S-2)}₂{15C5}]∞ (7) results from the templating ability of 15C5. All complexes reported have been identified primarily through single-crystal X-ray structural analysis together with ¹H and ¹³C NMR (solubility permitting), IR spectroscopy, and melting point determination.