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

Abstract

The synthesis, characterization, and PGSE ((1)H and (19)F) NMR diffusion studies on the cationic [(eta(6)-arene)Mn(CO)(3)][X] (arene = anisole, 4-chloroanisole, and 1,3,5-trimethoxybenzene; X = BPh(4) 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. (1)H,(1)H-NOESY data support this anion selectivity. In chloroform solution one finds the usual strong ion pairing for both anions. The solid-state structure of [(eta(6)-1,3,5-trimethoxybenzene)Mn(CO)(3)][BPh(4)] has been determined. (13)C NMR and IR data for the new complexes are reported. The observed IR frequencies are higher for the BArF complexes than for the BPh(4) complexes.

Ion pairing using PGSE diffusion methods

“…The gas phase r H value for the BArF À anion of ca. 5.8 Å [139], calculated via the molecular modeling program Chem3D, is somewhat smaller than the r H value of 6.3 Å for Na(BArF) in methanol. Consequently, the observed r H value of 6.6 Å is suggestive of only a small amount of ion pairing.…”

“…Along the same lines, one finds a substantial difference In the diffusion characteristics between the two related p-arene Table 9 Values for the diffusion coefficient, D (·10 À10 m 2 s À1 ), and the hydrodynamic radius, r H , (Å ) for 2 mM solutions of the Ru-aquo salts in H 2 O and acetone [ [Mn(CO) 3 (g 6 -p-Cl-C 6 H 4 -OMe)] tetraphenyl borate salts, 17, X ¼ BPh 4 À and BArF À , in dichloromethane solution (see Table 10) [139]. The relatively large BArF À anion does not…”

“…However, the BPh 4 À analogue seems to strongly ion pair, with the result that the r H value for the cation markedly increases. The r H value for the ''free'' BPh 4 À anion is estimated to be about 5.1 Å , based on both X-ray and PGSE studies [139]. It is not immediately obvious that the eight CF 3 groups of the BArF À anion will play such a marked role with respect to minimizing the ion pairing.…”

“…It is not immediately obvious that the eight CF 3 groups of the BArF À anion will play such a marked role with respect to minimizing the ion pairing. However, the ''difference'' in ion pairing between these two tetraphenyl borate species is almost non-existent in chloroform solution where, for both boron anions, the ion pairing now approaches 100% [139].…”

“…Values a for the diffusion coefficient, D (·10 À10 m 2 s À1 ), and the hydrodynamic radius, r H (Å ), for 2 mM solutions of the manganese carbonyl complexes, R-T in several solvents[139] Viscosity, g (299 K, kg s À1 m À1 ): CH 2 Cl 2 = 0.414; acetone = 0.306; CDCl 3 = 0.534.Table A16Values a for the diffusion coefficient, D (·10 À10 m 2 s À1 ), and the hydrodynamic radius, r H (Å ), for 2 mM solutions of the RuCl(BINAP) Salts, 16, in several solvents[138] The viscosities used in the calculations (300 K) are those of the pure solvents: CH 2 Cl 2 = 0.405, CHCl 3 = 0.529 (0.542), CH 3 OH = 0.526, (0.547), (CH 3 ) 2 CO = 0.303; H 2 O = 1.002.Table A17Values for the diffusion coefficient, D (·10 À10 m 2 s À1 ), and the hydrodynamic radius, r H (Å ), for 2 mM solutions of the salts Ru(CH 3 CN)(BINAP), U, in several solvents (400 MHz)[147] Table A18 Diffusion coefficients (10 10 D t m 2 s À1 ), hydrodynamic Radii (r H , Å ), c factors, and aggregation numbers (N) for compounds V, W, and X as a function of solvent (e r at 25°C) and concentration (C, mM)[24] …”