Cationic (tripyrrinato)palladium(II) complexes

The formation of cationic palladium(II)complexes [TrpyPd^II]⁺X⁻ by salt metathesis of the respective trifluoroacetates with different salts of weakly coordinating anions X⁻ was investigated. With non-hydrolizable counterions, cationic mono- and dinuclear complexes are observed depending on the nature of the anion X⁻ and the solvent. The mononuclear cations, which are only formed with X = BAr^F, most probably carry a weakly bound molecule of dichloromethane at the fourth coordination site of Pd^II. When treated with diazoalkanes, only these are sufficiently reactive to form carbene complexes. Four- and five coordinate Lewis base adducts [TrpyPd^IIL]⁺ with L = CH₃NC, tBuNH₂, PMe₃, PEt₃ and PiPr₃ and [TrpyPd^IIL₂]⁺ with L = PMe₃ were prepared from the mononuclear cations [TrpyPd^II]⁺BAr^F−. From structural studies it becomes apparent, that the formation of stable five coordinate Pd^II species is restricted to medium size ligands and depends on the delicate balance between the steric influence of L and the strain, which is induced on the TrpyPd^II unit.     

Reactivity of chloro(N-methyliminodiacetato)palladium(II) and chloro(pyridyl-2,6-dicarboxylato)palladium(II) complexes with purine based 5′-nucleotides and glutathione: antitumor activity of platinum(II)-analogs

The interaction of [Pd^II(mida)(Cl)]⁻ (1) (mida²⁻ = N-methyliminodiacetate) and [Pd^II(pydc)(Cl)]⁻ (2) (pydc²⁻ = pyridyl-2,6-dicarboxylate) with adenosine-5′-monophosphate (AMP), inosine-5′-monophosphate (IMP) and glutathione (GSH) was studied kinetically as a function of [L] (L = AMP, IMP, GSH) and [Cl⁻] and temperatures (10-35 °C) at pH 4.0. The kinetic results suggest that the reaction of 1 and 2 with the 5′-nucleotides (AMP, IMP) is characterized by the hydrolysis of chloro-complexes followed by the aquo-substitution with purine based 5′-nucleotides through its N7 atom. The reaction of 1 and 2 with GSH takes place through the direct chloride replacement with GSH. Kinetic data and activation parameters are interpreted in terms of an associative mechanism and discussed in reference to the data reported earlier. The [Pt^II(mida)(Cl)]⁻ (3) and [Pt^II(pydc)(Cl)]⁻ (4) complexes were prepared and allowed to interact with AMP and IMP and their reaction products were characterized by ¹H NMR studies. The antitumor activity of 3 and 4 was examined against MCF-7 (breast cancer), NCI-H460 (lung cancer) and SF-268 (CNS) cell lines.     

Water soluble platinum(II) and palladium(II) complexes of alkyl sulfonated phosphines

The reactions of the alkylsulfonated phosphines LM=Ph₂P(CH₂)_nSO₃Na/K (n=2, 3, 4) with K₂PtCl₄ and K₂PdCl₄ have been studied in homogeneous aqueous solution as a function of pH. In homogeneous acidic solution the protonated phosphines react to give cis- and trans-PtCl₂(LH)₂. The biphasic reaction between 1,5-cyclooctadiene platinum(II) chloride in dichloromethane and acidified aqueous LNa/K gives a higher proportion of the cis isomer. In neutral solution the initial reaction to give [PtCl(LNa/K)₃]⁺Cl⁻ is followed by slow formation of cis-PtCl₂(LNa/K)₂. K₂PdCl₄ reacts more rapidly to give PdCl₂(LNa/K)₂. In homogeneous alkaline solution rapid oxidation of the phosphine occurs with only small amounts of platinum complex being observable. The biphasic reaction yields phosphine oxide in the aqueous layer and a small amount of the chelate complexes PtL₂ in the organic. Representative complexes have been isolated and characterised and the mechanisms for the reactions discussed. The electrospray mass spectra of solutions of the isolated complexes have been recorded in both positive and negative ionisation modes. The positive ionisation spectra are complicated, but platinum and palladium containing ions derived from loss of chloride, H⁺ and HCl are observed in the negative ionisation spectra.     

Tetracoordinate diamidato-bis(phosphanyl) metal systems: Synthesis, characterization, and electrochemical analysis of palladium(II) complexes

Square planar diamidato-bis(phosphanyl) palladium(II) complexes have been prepared and characterized. Most products precipitate out of THF solution on reaction of the parent ligand with Pd(OAc)₂ in the presence of 2 equiv. of base at 50 °C overnight. The solution and solid state structure of each complex is reported based on multinuclear NMR and X-ray analyses, respectively. The effects of carboxamido nitrogen coordination on the stabilization of the metal center from reduction were studied using cyclic voltammetry. The irreversible peak reduction potential of each complex was greater by approximately −340 mV to −590 mV as compared to Pd(PPh₃)₂Cl₂ indicating that carboxamido nitrogen coordination protects the Pd(II) center from reduction.     

Synthesis, spectroscopy, structure and photophysical properties of dinaphthylmethylarsine complexes of palladium(II) and platinum(II)

Dinaphthylmethylarsine complexes of palladium(II) and platinum(II) with the formulae [MX₂L₂] (M = Pd, Pt; L = di(1-naphthyl)methylarsine = Nap₂AsMe and X = Cl, Br, I), [M₂Cl₂(μ-Cl)₂L₂], [PdCl(S₂CNEt₂)L], [Pd₂Cl₂(μ-OAc)₂L₂] and [MCl₂(PR₃)L] (PR₃ = PEt₃, PPr₃, PBu₃, PMePh₂) have been prepared. These complexes have been characterized by elemental analyses, IR, Raman, NMR (¹H, ¹³C, ³¹P) and UV-vis spectroscopy. The stereochemistry of the complexes has been deduced from the spectroscopic data. The crystal structures of trans-[PdCl₂(PEt₃)(Nap₂AsMe)] and of [Pd(S₂CNEt₂)₂], a follow-up product, were determined. The UV-vis spectra of [MX₂L₂] complexes show a red shift on going from X = Cl to X = I. The complexes [PdX₂L₂] and [PtX₂L₂] are strongly luminescent in fluid solution and in the solid at ambient temperature.     

Cationic palladium(II) complexes of the sterically hindered bis(4-methylthiazolyl)isoindoline (4-Mebti) with neutral group XVI donor ligands

A series of cationic palladium complexes [(4-Mebti)PdL]⁺ with 4-Mebti = anion of bis(4-methylthiazolylimino)isoindoline and L = neutral ligand with group 16 donor atom has been prepared from the chlorido derivative [(4-Mebti)PdCl] and NaBAr^F (BAr^F = tetrakis(3,5-bis(trifluoromethyl)phenyl)boranate) in the presence of the respective donor ligand. Crystallographic and spectroscopic analyses were achieved for species with L = SMe₂, SeMe₂, dmf, acetamide, diphenylurea, and formiate. The latter two complexes represent products from hydrolyses of phenyl isocyanate and dmf, respectively, which occur during the ligand exchange reactions. Several other O-donor ligands like thf, acetone, Me₂O, water, and others are not bound to the palladium ion, and the dinuclear μ-chlorido derivative [{(4-Mebti)Pd}₂Cl]⁺ is isolated in these cases instead. The crystallographic analyses prove the expected presence of distorted, pseudo-planar palladium chelates, and the degree of distortion correlates well with the chemical shifts observed for the proton nuclei of the terminal methyl groups in the ¹H NMR experiment.     

Synthesis, characterization and structural studies of new palladium(II) complexes including non-symmetric phosphorus ylides

The reaction of the non-symmetric phosphorus ylides, Ph₂P(CH₂)_nPPh₂C(H)C(O)PhR [Y₁-Y₄: n = 1, R = Cl, Br, NO₂, OCH₃ and Y₅-Y₈: n = 2, R = Cl, Br, NO, OCH₃] with dichloro(1,5-cyclooctadiene)palladium(II) in dichloromethane under mild conditions afford the monomeric P-C chelated complexes, [(Y)PdCl₂] (Y = Y₁-Y₈). These complexes were fully characterized by elemental analysis and spectroscopic techniques such as IR, ¹H, ³¹P, and ¹³C NMR. In addition, the identity of complexes [(Y₅)PdCl₂] (1b) and [(Y₈)PdCl₂] (4b) was unequivocally determined by single crystal X-diffraction techniques, both structures consisting of six-membered rings formed by coordination of the ligands through the phosphine group and the ylidic carbon atom to the metal center. The coordination geometry around the Pd atoms in both these complexes be defined as slightly distorted square planar. Furthermore, their electrochemical behavior was also investigated by cyclic voltammeters, thus the cyclic voltammetry of complex [(Y₁)PdCl₂], in dichloromethane solution with Pt electrode, shows that the redox reaction of the pair Pd(II)/Pd(0) is irreversible with the cathodic peak potential at −1.08 V versus Ag wire.     

The synthesis of substituted bis[(diarylphosphinomethyl)cyclopentadienyl]zirconocene dichloride complexes for the preparation of heterodimetallic complexes containing early/late transition metal combinations

Fulvenes (1a–e) derived from condensation of cyclopentadiene with acetone or a variety of aldehydes were treated with LiPAr₂ (Ar = phenyl, p-tolyl) to yield the respective substituted (diarylphosphinomethyl)cyclopentadienides (2, 3). Subsequent reaction with ZrCl₄(THF)₂ gave the respective bis[(diarylphosphinomethy])cyclopentadienyl]zirconium dichlorides ( Ar = phenyl (4), p-tolyl (5)). The complex rac-[C₅H₄-CH(CH₃)-PPh₂]₂ZrCl₂ (rac-4b) was characterized by X-ray diffraction. The reaction of complexes 4a and 5a [(Cp-CMe₂-PAr₂)₂ZrCl₂] with PdCl₂(NCPh)₂ or PtCl₂(NCPh)₂ leads to the formation of the trans-(metallocene-chelate-phosphane)metal complexes 6–9 (e.g. trans-Cl₂Pd(Ph₂P-CMe₂-Cp)₂ZrCl₂]. Chloride abstraction from the reaction product of [Cp-CH(CMe₃)PPh₂]₂ZrCl₂ with PdCl₂(NCPh)₂ eventually gave the cationic complex [meso,trans-(Cp-CH(CMe₃)PPh₂)₂(Cl)Zr(μ-Cl)Pd(Cl)]⁺ (10) that was also characterized by X-ray diffraction. It features a dimetallabicyclic framework with two Cp-CHR-PPh₂ ligands and a chloride bridging between the early and the late transition metal center.     

Synthesis and spectroscopy of diethyl (pyridinylmethyl)phosphates and their palladium (II) complexes: X-ray crystal structures of Pd(II) complexes

The synthesis of diethyl (pyridin-2-, -3-, -4-ylmethyl)phosphate (2-pmOpe, 3-pmOpe, 4-pmOpe) ligands and their palladium (II) complexes of general formula trans-[PdCl₂L₂] (L = 2-pmOpe, 3-pmOpe,4-pmOpe) has been described. Pyridine phosphate derivatives were synthesized via the condensation of phosphorochloridic acid diethyl ester with an appropriate pyridinylmethanol in the presence of triethylamine. The compounds have been identified and characterized by IR, far-IR, ¹H NMR, ³¹P NMR, ³¹P CP-MAS NMR and elemental analyses. The crystal and molecular structures of palladium (II) complexes, i.e., [PdCl₂(2-pmOpe)₂] and [PdCl₂(4-pmOpe)₂] determined by the X-ray diffraction method, are presented. In both structures, Pd(II) ions are four-coordinated by two chlorine atoms and two pyridine nitrogen atoms. The geometry of complexes is square-planar and adopt a trans configuration, which is consistent with preparation method.     

Reactivity of palladium(II) methyl complexes towards CO2: formation of carbonate complexes

Treatment of a benzene solution of (tmeda)PdMe₂ or (dppe)PdMe₂ with carbon dioxide gives the corresponding methyl bicarbonate complex, (L-L)PdMe(O₂COH). These were characterised by NMR spectroscopy and elemental analysis. Under strictly dry conditions no reaction was observed. Recrystallisation of the tmeda bicarbonate complex from acetone yields the corresponding η²-carbonate complex, which was characterised by X-ray crystallography. The reaction probably proceeds through attack by free carbonic acid on the dimethyl complex.     

Symmetrical bis-(NHC) palladium(II) complexes: Synthesis, structure, and application in catalysis

The synthesis and characterization of symmetrically substituted bis-N-heterocyclic carbene palladium(II) complexes with a functional group attached to the bridging moiety is described, as well as the immobilization of one of them on polystyrene Wang resin. The resulting complexes were tested both in homogeneous and heterogeneous Suzuki-Miyaura cross-coupling reactions.     

Synthesis, characterization and in vitro cytotoxicity of the first palladium(II) oxalato complexes involving adenine-based ligands

The first [Pd(Lⁿ)₂(ox)] xH₂O oxalato(ox) complexes involving 2-chloro-N6-(benzyl)-9-isopropyladenine (L¹; complex 1), 2-chloro-N6-(4-methoxybenzyl)-9-isopropyladenine (L²; 2), 2-chloro-N6-(2,3-dimethoxybenzyl)-9-isopropyladenine (L³; 3), 2-chloro-N6-(2,4-dimethoxybenzyl)-9-isopropyladenine (L⁴; 4), and 2-chloro-N6-(4-methylbenzyl)-9-isopropyladenine (L⁵; 5) have been synthesized by the reactions of potassium bis(oxalato)palladate(II) dihydrate, [K₂Pd(ox)₂]·2H₂O, with the mentioned organic compounds (H₂ox = oxalic acid; x = 0 for 1-3 and 5 or 2 for 4). Elemental analyses (C, H, N), FTIR, Raman and NMR (¹H, ¹³C, ¹⁵N) spectroscopies, conductivity measurements and thermal studies (thermogravimetric and differential thermal analyses, TG/DTA) have been used to characterize the prepared complexes. The molecular structures of [Pd(L²)₂(ox)] (2) and [Pd(L⁵)₂(ox)]·L⁵·Me₂CO (5·L⁵·Me₂CO) have been determined by a single crystal X-ray analysis. The geometry of these complexes is slightly distorted square-planar with two appropriate Lⁿ (n = 2 or 5) molecules mutually arranged in the head-to-head (2) or head-to-tail (5) orientation. The Lⁿ ligands are coordinated to the central Pd(II) ion via the N7 atoms. The same conclusions regarding the binding properties of L¹-L⁵ ligands can be made based on multinuclear NMR spectra. In vitro cytotoxicity of the complexes 1-5 has been evaluated against human chronic myelogenous leukaemia (K562) and human breast adenocarcinoma (MCF7) cancer cell lines. Significant cytotoxicity has been determined for the complexes 3 (IC₅₀ = 6.2 μM) and 5 (IC₅₀ = 6.8 μM) on the MCF7 cell line, which is even better than that found for the well-known and widely-used platinum-bearing antineoplastic drugs, i.e. oxaliplatin and cisplatin.     

Kinetics and mechanism of the oxidation of ammineruthenium(II) complexes by bromine

The reactions of Ru(NH₃)₅py²⁺, Ru(NH₃)₄bpy²⁺, Ru₂(NH₃)₁₀pz⁵⁺, RuRh(NH₃)₁₀pz⁵⁺ and Ru(NH₃)₅pz²⁺ with bromine are first-order in ruthenium and first-order in bromine. The rates decrease with increasing bromide ion concentration and, except for Ru(NH₃)₅pz²⁺, are independent of hydrogen ion concentration. The reactions are postulated to proceed via outer-sphere, one-electron transfer from Ru(II) to Br₂ with the formation of Br₂⁻ as a reactive intermediate. The bromide inhibition is ascribed to the formation of Br₃⁻ which is unreactive in outer-sphere reactions because of the barrier imposed by the need to undergo reductive cleavage. The reaction of Ru(NH₃)₅pz²⁺ is inhibited by hydrogen ions. The hydrogen ion dependence shows that Ru(NH₃)₅pzH³⁺ has a pK_a of 2.49 and is at least 500 times less reactive than Ru(NH₃)₅pz²⁺. The reaction of Ru₂(NH₃)₁₀pz⁴⁺ with bromine is biphasic. The second phase has a rate identical to that of the Ru₂(NH₃)₁₀pz⁵⁺-Br₂ reaction. A detailed analysis shows that the reaction of Ru₂(NH₃)₁₀pz⁴⁺ with bromine proceeds by a sequence of one-electron steps, Br₂⁻ being produced as an intermediate. A linear free energy relationship between rate constants and equilibrium constants, obeyed for all the reactions studied, provides an estimate of 1.5 × 10² M⁻¹ s⁻¹ for the self-exchange rate constant of the Br₂/Br₂⁻ couple.     

2-Mercapto-1-t-butylimidazolyl as a bridging ligand: Synthesis and structural characterization of nickel and palladium paddlewheel complexes

Nickel and palladium paddlewheel complexes that feature 2-mercapto-1-t-butylimidazolyl (mim^But) bridging ligands, namely Ni₂[mim^But]₄ and Pd₂[mim^But]₄, have been synthesized and structurally characterized by X-ray diffraction. Since the mim^But ligand bridges in an asymmetric manner via a sulfur and nitrogen donor, paddlewheel compounds of the type M₂[mim^But]₄ may exist as isomers that are distinguished by the relative orientations of the ligands. In this regard, the (4,0)-Ni₂[mim^But]₄ and trans-(2,2)-Ni₂[mim^But]₄ isomers have been isolated for the nickel system, while the (4,0)-Pd₂[mim^But]₄ and (3,1)-Pd₂[mim^But]₄ isomers have been isolated for the palladium system.     

Nickel(II) and copper(II) complexes of mixed benzene-triazolehemiporphyrazines

The kinetics of substitution reactions of [η-CpFe(CO)₃]PF₆ with PPh₃ in the presence of R-PyOs have been studied. For all the R-PyOs (R = 4-OMe, 4-Me, 3,4-(CH)₄, 4-Ph, 3-Me, 2,3-(CH)₄, 2,6-Me₂, 2-Me), the reactions yeild the same product [η⁵-CpFe(CO)₂PPh₃]PF₆, according to a second-order rate law that is first order in concentrations of [η⁵-CpFe(CO)₃]PF₆ and of R-PyO but zero order in PPh₃ concentration. These results, along with the dependence of the reaction rate on the nature of R-PyO, are consistent with an associative mechanism. Activation parameters further support the bimmolecular nature of the reactions: ΔH^≠ = 13.4 ± 0.4 kcal mol⁻¹, ΔS^≠ = −19.1 ± 1.3 cal k⁻¹ mol⁻¹ for 4-PhPyO; ΔH^≠ = 12.3 ± 0.3 kcal mol⁻¹, ΔS^≠ = 24.7 ±1.0 cal K⁻¹ mol⁻¹ for 2-MePyO. For the various substituted pyridine N-oxides studied in this paper, the rates of reaction increase with the increasing electron-donating abilities of the substituents on the pyridine ring or N-oxide basicities, but decrease with increasing ¹⁷O chemical shifts of the N-oxides. Electronic and steric factors contributing to the reactivity of pyridine N-oxides have been quantitatively assessed.     

Synthesis, spectroscopic properties and structural characterisation of Pd(II) and Pt(II) complexes with 1,3,5-pyrazole derived ligands. Rotation around the metal-N bond

Reactions of ligands 1-ethyl-5-methyl-3-phenyl-1H-pyrazole (L¹) and 5-methyl-1-octyl-3-phenyl-1H-pyrazole (L²) with [PdCl₂(CH₃CN)₂ and K₂PtCl₄ gave complexes trans-[MCl₂(L)₂] (L = L¹, L²). The new complexes were characterised by elemental analyses, conductivity measurements, infrared, ¹H and ¹³C{¹H} NMR spectroscopies and X-ray diffraction. The NMR study of the complex [PdCl₂(L¹)₂], in CDCl₃ solution, is consistent with a very slow rotation of ligands around the Pd-N bond, so that two conformational isomers can be observed in solution (syn and anti). Different behaviour is observed for complexes [PdCl₂(L²)₂] and [PtCl₂(L)₂] (L = L¹, L²), which present an isomer in solution at room temperature (anti). The crystal structure of [PdCl₂(L¹)₂] complex is described, where the Pd(II) presents a square planar geometry with the ligands coordinated in a trans disposition.     

One-dimensional chain structures constructed from tetra(acetamidato)dirhodium(II,III) complexes and square planar platinum and palladium complexes

The reaction of [Rh₂(acam)₄(H₂O)₂]ClO₄ (1) (Hacam = acetamide) with K₂PtCl₄ in aqueous solution gave crystals of [Rh₂(acam)₄(H₂O)₂][Rh₂(acam)₄{(μ-Cl)₂PtCl₂}] · 2H₂O (2). The reaction of 1 with K₂PdCl₄ produced the palladium analog [Rh₂(acam)₄(H₂O)₂][Rh₂(acam)₄{(μ-Cl)₂PdCl₂}] · 2H₂O (3) and a small amount of an aquated palladium complex [Rh₂(acam)₄{(μ-Cl)₂PdCl(H₂O)}] · H₂O (4). Complexes 2 and 3 have anionic chains of [Rh₂(acam)₄{(μ-Cl)₂MCl₂}]⁻ (M = Pt, Pd), while 4 includes neutral chains of [Rh₂(acam)₄{(μ-Cl)₂PdCl(H₂O)}]. Although all of the structures include infinite chains of (-Rh-Rh-Cl-M-Cl-)_n (M = Pt, Pd), the chain structures are different; zigzag for 2 and 3 and helical for 4. In the structures of 2 and 3, the counter cation [Rh₂(acam)₄(H₂O)₂]⁺ made a hydrogen-bonded chain with the crystallization water molecules. The cationic chains and the anionic chains are connected with hydrogen bonds. In the structure of 4, the chains are also linked together by direct hydrogen bonds between the chains and those with the crystallization water molecules. ESR spectra of the powdered samples of 2 and 3 at 77 K were consistent with a rhombic structure: for 2, g₁ = 2.111, g₂ = 2.054, g₃ = 2.004; for 3, g₁ = 2.115, g₂ = 2.057, g₃ = 2.007. These results indicate that there is a spin flip-flop exchange between the cations, [Rh₂(acam)₄(H₂O)₂]⁺, and the units in the anionic chains. The electrical conductivities of 2 and 3 were in the order of 10⁻⁷ S cm⁻¹ at room temperature.     

New mononuclear Pd(II) complexes of sterically hindered bispyrazolylmethanes

Three new palladium(II) complexes incorporating the bispyrazolylmethane core have been synthesised and fully characterised in the solution and solid state. Single crystal X-ray studies revealed almost complete blocking of the upper face of the palladium ion by the substituents at the 3- and 5-positions of the pyrazole rings. Preliminary screening of the complexes for palladium(II) mediated catalysis revealed good catalytic activity for the Heck coupling reaction.     

Synthesis, structure, and hydrolytic reaction of trans-dichlorobis(diethanolamine-N)palladium(II) with N-acetylated L-histidylglycine dipeptide

The reaction of PdCl2, or K2PdCl4, with diethanolamine (DEA), in the molar ratio 1:2, affords the trans-[PdCl2(DEA)2] complex. X-ray structure analysis of this complex confirmed the formation of the trans-isomer. The complex crystallizes in the space group P42bc. The central Pd(II) ion is coordinated in an almost ideal square-planar fashion with a small deformation of the Cl-Pd-Cl angle (175.6(7) degrees) due to N-H...Cl hydrogen bonding. The N-H group participates in a bifurcated interaction with the two symmetry related Cl- anions. The hydroxyl groups of the diethanolamine ligand form very strong hydrogen bonds between the complex units, thus leading to infinite zigzag (O-H...O-H...O-H..) chains in the crystal packing. The complex units are further connected by weaker intermolecular hydrogen bonds of the N-H...Cl type in a way to form layers parallel to the crystallographic (001) plane. The reaction between the trans-[PdCl2(DEA)2] or trans-[Pd(H2O)2(DEA)2]2+ complex and MeCOHis-Gly dipeptide at 1.5 < pH < 2.0 and at 25 degrees C leads to the regioselective cleavage of the amide bond involving the carboxylic group of the histidine. The cleavage of the substrate was fast and went almost to completion within less than one hour.     

Diffusion NMR studies on neutral and cationic square planar palladium(II) complexes

Diffusion NMR investigations were carried out in CD₂Cl₂ for a series of neutral (1-7) and cationic (8-10) square planar palladium complexes. Diffusion data were elaborated through a modified Stokes-Einstein equation that takes into account the size and shape of molecules. The hydrodynamic volume at infinite dilution of all complexes was found to be similar to the crystallographic volume and always much larger than the van der Waals volume. The self-aggregation tendency of [Pd(N,C⁻)(N,N)][PF₆] ionic complexes [(N,C⁻) = (C₆H₄-(Ph)C(O)-CN-Et); 8, (N,N) = 2,2′-bipirydine; 9, (N,N) = (2,6-(iPr)₂-C₆H₃)NC(Me)-C(Me)N(2,6-(iPr)₂-C₆H₃); 10, (N,N) = (2,6-(iPr)₂-C₆H₃)NC(R′)-C(R′)N(2,6-(iPr)₂-C₆H₃), R′₂ = naphthalene-1,8-diyl] was investigated by performing ¹H and ¹⁹F diffusion experiments as a function of the concentration. Clear evidence for the formation of ion triples containing two cationic units was obtained for 8, most likely due to the establishment of a weak Pd?O interaction. The tendency to form ion triples was much reduced in 9 and 10, having an increased steric hindrance in the apical positions. While 9 showed the usual tendency to afford a mixture of free ions and ion pairs, solvated ions were the predominant species in the case of 10 even at high concentration values (approaching 100 mM).