Coulombic inter-ligand repulsion effects on the Pt(ii) coordination chemistry of oligocationic, ammonium-functionalized triarylphosphines

Abstract

The Pt(II) coordination chemistry of oligocationic ammoniomethyl- and neutral aminomethyl-substituted triarylphosphines (L) is described. Complexes of the type PtX(2)(L)(2) (X = Cl, I) have been isolated and characterized. For the hexa-meta-ammoniomethyl-substituted ligands [1](6+) and [2](6+), two ligands always occupy a trans-configuration with respect to each other in complexes of the type PtX(2)(L)(2), while for the tri-para-ammoniomethyl-substituted ligand [7](3+), the trans/cis ratio is dependent on the ionic strength of the solution. This behaviour was not observed for the neutral aminomethyl-substituted ligands. In the crystal structure of trans-[PtI(2)(1)(2)]I(12), the geometrical parameters of the phosphine ligand [1](6+) are very similar to those found in the analogous complex of the benchmark ligand PPh(3), i.e. trans-PtI(2)(PPh(3))(2), indicating that no significant increase in the steric congestion is present in the complex. Instead, the coordination chemistry of this class of phosphine ligands is dominated by repulsive Coulombic inter-ligand interactions.

Water-soluble complexes MX2L2 (M = Pd, Pt; L = PPh2(C6H4-p-SO3K)): Synthesis, stereoisomerism, and catalytic activities for aromatic cyanation in n-heptane/water biphasic solution

“…For PtI 2 {PPh 2 (C 6 H 4 -p-SO 3 K)} 2 with KI, the trans/cis ratio considerably changed from 6/5 to 3/7. These results are consistent with the recent report that the trans/cis ratio decreases with increasing the ionic strength of solution [49]. Thus the observed results for the stereoisomeric ratio may be attributed to a strong intramolecular interligand Coulombic repulsion between the ionic phosphine ligands, which disfavors the cis-isomer.…”

“…Since intramolecular interligand Coulombic repulsion is diminished at higher ionic strengths due to shielding of the charges [41,49], further experiments on the stereoisomers were performed in potassium halide solution of DMSO. Treatment of DMSO-d 6 solution of PdCl 2 {PPh 2 (C 6 H 4 -p-SO 3 K)} 2 (the trans/cis ¼ ca.…”

“Anti‐Electrostatic” Halogen Bonding

“…[28] In addition, several halometallates exhibit halogen-halogen contacts in the solid state either by self-association or by coordination to (poly)halides. [29] These contacts are typically very weak, however, and it is unclear whether they should be characterized as XB. [30] Polyhalides 2À ,w hich form linear XB adducts in crystal structures if the terminal halides are coordinated by further interactions,m ay also feature AEXBs.…”

Steric, Electronic, and Secondary Effects on the Coordination Chemistry of Ionic Phosphine Ligands and the Catalytic Behavior of Their Metal Complexes

“…It was thus concluded that the intramolecular, interA C H T U N G T R E N N U N G liA C H T U N G T R E N N U N G gand Coulombic repulsion disfavors the cis isomer and is attenuated at higher ionic strengths due to shielding of the charges. [113] Through further measurements of the trans/cis equilibrium position at different temperatures, the thermodynamic parameters for trans-cis isomerization were determined at À22.0 kJ mol À1 for [NaI] = 0.0 m and À32.3 kJ mol À1 for [NaI] = 0.2 m. Thus, trans-cis conversion results in a significantly larger negative enthalpy change in the presence of 0.2 m NaI, confirming the stabilization of the cis isomer by the added NaI.…”

“…In contrast, sterically similar, neutral aminomethyl-substituted analogues of these ligands lead to formation of the corresponding cis complexes. [113] In the case of complex [PtI 2 (11) 2 ] (Scheme 10), a mixture of cis and trans stereoisomers was obtained. Importantly, the trans/cis ratio was found to be dependent on the ionic strength of the solution, with a higher ionic strength leading to a lower trans/cis ratio (Figure 1).…”