Selective Ion Pairing in [Ir(bipy)H₂(PRPh₂)₂]A (A = PF₆, BF₄, CF₃SO₃, BPh₄, R = Me, Ph):  Experimental Identification and Theoretical Understanding

Abstract

NMR studies of the title compounds show that selective tight ion pairing occurs with the anion binding site being located in an intuitively unexpected region of the cation: on the side of the bipyridyl ligand remote from the metal instead of being closest to the metal near the MH 2 group. The interaction specificity falls off with increasing anion size. ONIOM (QM/ MM) calculations represent the cation structure very well, and natural population analysis calculations identify the predominant location of the positive charge at the bipyridyl ring carbons that take part in the inter-ring C-C bond (C-2 and C-2′). This is fully consistent with tight ion pairing near these and the adjacent carbons, C-3 and C-3′. The electrostatic potential calculated for the cation confirms the location of the preferred binding site.

Applications of NMR diffusion methods with emphasis on ion pairing in inorganic chemistry: a mini‐review

“…In connection with the observation that changing the anion can affect reaction chemistry and specifically the products and rates of homogeneously catalyzed reactions, NOE and diffusion NMR studies have addressed and helped to rationalize observations concerned with An anion‐dependent selectivity connected with the C–H activation mechanism in the reaction of an imidazolium salt with IrH 5 [(PPh 3 ) 2 ] Ion pairing effects in intramolecular heterolytic H 2 activation in an iridium complex The influence of ion pairing on styrene hydrogenation using a η 6 ‐arene β‐diketiminato‐ruthenium salt The role of the BPh 4 − anion in ion pairing and allyl dynamics in a series of palladium salts Counter ion effects in palladium catalyzed styrene/CO copolymerization 128 Detecting positional anion effects in several chiral rhodium salts containing bulky P donors and Understanding the anion effect in cyclopentadienyl ruthenium‐based Diels–Alder chemistry …”

Ion pairing using PGSE diffusion methods

“…Moreover, it is not possible to use conductivity data, even qualitatively, to estimate the extent of ion pairing. The diffusion data from the NMR experiments, when taken together with (NOESY or HOESY) Overhauser studies, which allow one to place the anion in three-dimensional space relative to the cation [110][111][112][113][114][115][116][117][118][119][120][121][122][123], frequently determine the structural details for the ion pair. This is yet another advantage of this NMR approach to ion pairing.…”

Cationic olefin Pd(II) complexes bearing α-iminoketone N,O-ligands: synthesis, intramolecular and interionic characterization and reactivity with olefins and alkynes

“…3). This can be due to a higher accumulation of positive charge on the pyridine-ring [23] respect to the phenyl ring and/or to a repulsion exerted by the lone pair on the carbonyl-oxygen. Going from 3/3a to 2/2a compounds, -C(Me)@N(2,6-(i-Pr) 2 -C 6 H 3 ) moiety substitute the pyridine-ring and the anion shift toward the O-arm (Fig.…”