Complexes of palladium(II) chloride with 3-(pyrazol-1-yl)propanamide (PPA) and related ligands

Trifluoromethylated 3‐(Pyrazol‐1‐yl)propanamide (PPA) Ligands

“…Complex 5 is structurally related to previously reported palladium complexes such as PdCl 2 (Me 2 PPA) 2 . [19] The PdÀ N bond lengths are 201.5(2) pm and therefore only marginally longer than in previously reported PdCl 2 (PPA) 2 -type complexes (200.2(2) -200.9(1) pm). This finding shows that the influence of the trifluoromethyl group in 3-position of the pyrazolyl ring on the ligating properties of the PPA ligand is weak.…”

“…Subsequent reaction of 1 and 2 with acrylamide following a standard protocol [14] afforded the new 3-pyrazolylpropanamides CF 3 MePPA (3) and (CF 3 ) 2 PPA (4). A great advantage of the trifluoromethylated pyrazoles is that these reactions can be easily monitored by 19 F-NMR spectroscopy. Thereby, it was found that 1 showed a reactivity toward acrylamide comparable to the unsubstituted pyrazole, and the reaction proceeded to completion after 6 h in refluxing methanol.…”

“…[9][10][11][12][13] In the course of our ongoing research on ligands based on the 3-(pyrazol-1-yl)propanamide (PPA) scaffold, we reported various transition metal complexes, showing that their coordination chemistry is diverse. [14][15][16][17][18][19] The most frequently observed coordination mode for first-row transition metals is кN,кO-chelation, [14][15][16][17][18] involving the pyrazolyl-nitrogen and amide-oxygen donor atoms (Figure 1,a). In contrast, for the less oxophilic second-row transition metals Pd [19] and Ag, [15] кN-monodentate coordination through the pyrazolyl group appeared to be most favored (Figure 1,b).…”

“…[14][15][16][17][18][19] The most frequently observed coordination mode for first-row transition metals is кN,кO-chelation, [14][15][16][17][18] involving the pyrazolyl-nitrogen and amide-oxygen donor atoms (Figure 1,a). In contrast, for the less oxophilic second-row transition metals Pd [19] and Ag, [15] кN-monodentate coordination through the pyrazolyl group appeared to be most favored (Figure 1,b). Due to the presence of amide NÀ H moieties as a potent hydrogen-bond donor, the free ligands as well as the complexes are aggregated into infinite supramolecular structures by NÀ H…”

“…[14,15,[17][18][19] This allows for the facile introduction of substituents at the ethylene backbone, [17] the pyrazolyl group, [17,18,20] or the amide nitrogen atom. [19] While these modifications influence predominantly the steric properties and/or the hydro-Supporting information for this article is available on the WWW under https://doi.org/10.1002/hlca.202000148 gen-bonding ability of the ligand, the electronic properties of all previously reported PPA derivatives did not differ very much. In the present study, we were interested in PPA ligands having trifluoromethyl as a strongly electron-withdrawing substituent at the pyrazolyl group, potentially resulting in a significantly different complex formation behavior of the ligand.…”