Bowl vs Saddle Conformations in Cyclononatriene-Based Anion Binding Hosts

The synthesis of organometallic complexes [{Ru(p-MeC₆H₄CHMe₂)}_n(C₂₁H₂₄S₃)][CF₃SO₃]_2n (n = 1, 6; n = 2, 7) and [{Ir(C₅Me₅)}₂(C₂₁H₂₄S₃)][CF₃SO₃]₄ (9) based upon the trimeric macrocycle cyclotris(dimethylthiophenylene) (4) is reported. A saddle conformation is identified for the free ligand 4 and complexes 6 and 9 by X-ray crystallography. The anion complexation behavior of complex 9 is compared with the related cyclotriveratrylene complex [{Ru(p-MeC₆H₄CHMe₂)}₂(C₂₇H₃₀O₆)][CF₃SO₃]₄ (2), which possesses a bowl-shaped conformation, by ¹H NMR titration studies in a variety of solvents. While host 2 displays a significant affinity for halides with binding constants of up to 1.25(7) × 10³ M^-1 in nitromethane solution, the absence of a molecular cavity in 9 results in very little specific anion affinity. The 1,3-alternate calix[4]arene complex [{Ru(η⁶-p-MeC₆H₄CHMe₂)}₂(η⁶:η⁶-C₄₀H₄₈)][BF₄]₄ (11) is also reported and shown to bind anions in an unusual C−H···anion hydrogen-bonding fashion by X-ray crystallography and ¹H NMR.