Synthesis, Characterization, and PGSE (¹H and ¹⁹F) NMR Diffusion Studies on Cationic (η⁶- Arene)Mn(CO)₃⁺ Complexes:  Boron Counterion, Ion Pairing, and Solvent Dependences

The synthesis, characterization, and PGSE (¹H and ¹⁹F) NMR diffusion studies on the cationic [(η⁶-arene)Mn(CO)₃][X] (arene = anisole, 4-chloroanisole, and 1,3,5-trimethoxybenzene; X = BPh₄ and BArF) are reported. The tetraphenyl borate complexes of anisole and 4-chloroanisole show surprisingly strong ion pairing in dichloromethane solution, whereas the BArF salts do not. ¹H,¹H-NOESY data support this anion selectivity. In chloroform solution one finds the usual strong ion pairing for both anions. The solid-state structure of [(η⁶-1,3,5-trimethoxybenzene)Mn(CO)₃][BPh₄] has been determined. ¹³C NMR and IR data for the new complexes are reported. The observed IR frequencies are higher for the BArF complexes than for the BPh₄ complexes.