Complexes [Pd(η1,η2-C8H12OMe)bipy]+X- (2a−f) (where X = BPh4 - (a), CF3SO3 - (b), BF4 - (c), PF6 - (d), SbF6 - (e), and B(3,5-(CF3)2C6H3)4 - (f); bipy = 2,2‘-bipyridine; C8H12OMe = cyclooctenylmethoxy group) were synthesized by the reaction of the dimer [Pd(η1,η2-C8H12OMe)Cl]2 (1) with the bipy ligand in methanol containing Y+X- salts. They were characterized in solution by multinuclear and multidimensional NMR spectroscopy. The solid-state structure of complex 2d was obtained by X-ray single-crystal investigation. The catalytic activity of complexes 2 toward CO/styrene copolymerization in methylene chloride was tested and related to the type of counterion. The order of the catalytic activity of complexes 2a−f is the following:  BPh4 - ≪ CF3SO3 - < BF4 - < PF6 - < SbF6 - < B(3,5-(CF3)2C6H3)4 -. If the copolymerization reactions are carried out in the presence of an excess of the bipy ligand, the anion effect is less important and the order is the following:  BPh4 - ≪ CF3SO3 - < BF4 - ≈ B(3,5-(CF3)2C6H3)4 - ≈ PF6 - ≈ SbF6 -. The interionic structure of all complexes was investigated in CD2Cl2 at room and low temperature by 19F{1H} HOESY and 1H NOESY NMR spectroscopies. In solution, the counterions are located above or below the bipy ligand shifted toward the pyridine ring trans to the Pd−C σ bond, while in the crystal structure of 2d, they are settled sideways to the cationic moiety. The best anion in catalysis is the least strong coordinating one that shows the weakest interionic contacts in the 19F{1H} HOESY or 1H NOESY NMR spectra. The dynamic process that exchanges the two pyridyl rings was investigated by variable-temperature NMR spectroscopy in CD2Cl2. The activation parameters were determined. ΔG ⧧ 298 values range from 54 to 58 kJ/mol. The negative values of ΔS ⧧ (−58/−108 J K-1 mol-1), for all compounds, with the exception of 2f, suggest an associative mechanism.

The interionic structure of complexes [Ru( 6 -Arene){(2-R-C6H4)N=C(Me)-C(Me)=N(2-R-C6H4)}Cl]X was investigated by an integrated experimental (PGSE diffusion and NOE NMR spectroscopy and X-ray single crystal studies) and theoretical (DFT and ONIOM calculations) approach.PGSE NMR experiments indicated that ion pairing is the main aggregative process in CD2Cl2 and solvents with higher relative permittivity. They also showed that the tendency to ion pairing for isodielectric solvents is higher when the latter are protic. NOE interionic contacts were observed in 2propanol-d8 even for BARFsalts. Ion pairing was favoured by more coordinating counterions and an increase in concentration. An equilibrium between ion pairs and ion quadruples was observed by PGSE measurements in chloroform-d and benzene-d6. Such equilibrium is shifted toward ion quadruples by an increase in the concentration or when least coordinating counterions are used. For small fluorinated counterions, NOE studies located ion pairs above the plane containing the C=N imine moieties. ONIOM calculations found that this anion-cation orientation was at least 35.9 kJ/mol lower in energy than a second orientation with the anion close to cymene, which, in some cases, was observed in the solid state. NOE investigations on complexes with BPh4counterion did not allow a single orientation capable of explaining the observed NOEs to be found. X-ray studies showed that one cation is surrounded by two anions. ONIOM calculations found that these two anion-cation orientations have similar energies. X-ray and NOE NMR data strongly suggest that ion quadruples with BPh4anions are constituted by an alternation of cations and anions. Interionic NOE intensities are almost invariant on passing from ion pairs to ion quadruples with small fluorinated counterions. X-ray studies suggested at least four possible structures of ion quadruples differing in both disposition and orientation of the ionic moieties. Three structures considered by ONIOM calculations, were similar in energy, but more stable than the separated ion pairs.