Exploring the Palladium and PlatinumBis(pyridine) Complex Motif by NMR Spectroscopy, X‐ray Crystallography, (Tandem) Mass Spectrometry, and Isothermal Titration Calorimetry: Do Substituent Effects Follow Chemical Intuition?

Abstract

A series of ten palladium-bis(pyridine) complexes, as well as their corresponding platinum complexes, have been synthesized. The pyridine ligands in each series carried different σ-donor and/or π-acceptor/donor substituents at the para-position of their pyridine rings. These complexes were analysed by NMR spectroscopy, X-ray crystallography, (tandem) MS, and isothermal titration calorimetry (ITC) to validate whether these methods allowed us to obtain a concise and systematic picture of the relative and absolute thermodynamic stabilities of the complexes, as determined by the electronic effects of the substituents. Interestingly, the NMR spectroscopic data hardly correlated with the expected substituent effects but the heteronuclear platinum-phosphorus coupling constants did. Crystallographic data were found to be blurred by packing effects. Instead, tandem MS and ITC data were in line with each other and followed the expected trends.

Kinetico‐Mechanistic Insights on the Assembling Dynamics of Allyl‐Cornered Metallacycles: The PtNpy Bond is the Keystone

“…Contrarily, the 1 H– 1 H NOESY NMR spectrum of a mixture of the platinum analogue 1bL 1 c and the same L 1 c block did not show evidence of ligand exchange because cross peaks between the α pyridine proton signals of 1aL 1 c and L 1 c were not observed (Figure 3 b) even at longer mixing times (1000 ms) and at the highest recommended temperature for CDCl 3 (313 K). These observations are in line with the higher inertness of the PtN py bond when compared with the PdN py bond 14c…”

Physical networks from entropy-driven non-covalent interactions

“…In physical networks, crosslinking interactions of this sort will become less favorable (ΔΔG°> 0) with increasing temperatures, contributing to a commensurate decrease in network mechanical properties. Indeed, common physically crosslinked polymer networks based on calcium/alginate, CD/ Ad, and CB [8]/MV/Np interactions exhibit enthalpy-driven thermodynamics (ΔH°< 0; TΔS°< 0; |ΔH°| >> |TΔS°|) and network softening at elevated temperatures [28][29][30]33,37 (Supplementary Table 1).…”

“…While these materials are often required to exhibit precise mechanical properties over a range of operating temperatures such that thermal responsiveness must be considered in their design, they typically weaken (i.e., become more liquid-like, soften, and relax stress faster) with increasing temperature. Indeed, standard mathematical frameworks for describing temperature-dependent viscoelasticity of dynamically crosslinked materials such as time-temperature superposition assume network weakening at elevated temperatures [28][29][30][31][32][33][34][35][36] .…”

“…An abundance of dynamic, non-covalent crosslinking interactions have been described for building physically crosslinked polymer networks, including ionic, host-guest, hydrogen bonding, peptide-peptide, and hydrophobic interactions 6,15 . Examination of the thermodynamics of individual non-covalent interactions typically employed for crosslinking in physical networks reveals them to be enthalpy-dominated binding reactions [28][29][30]33,37 . This inclination arises because engineered binding pairs have been historically designed to be highly specific, which are by nature enthalpy driven at the cost of entropy 38 .…”

Intramolecular C(sp3)–H Imination towards Benzimidazoles Using Tetrabutylammonium Iodide and tBuOOH

“…1‐Ethyl‐2‐(4‐methoxyphenyl)‐5‐phenyl‐benzo[ d ]imidazole ( 5 ) was obtained in 85 % yield by following standard Suzuki reaction using PhB(OH) 2 (Figure b). Similarly, Sonogashira reaction was performed so synthesize 1‐ethyl‐2‐(4‐methoxyphenyl)‐5‐( p ‐tolylethynyl)‐benzo[ d ]imidazole 6 in 80 % yield. In this reaction, one alkynyl group was introduced to the benzimidazole moiety (Figure c).…”