Charged Behaviour from Neutral Ligands: Synthesis and Properties of N‐Heterocyclic Pseudo‐amides

Abstract

Deprotonation of the 1-isopropyl-3-(phenylamino)pyridin-1-ium iodide gives the corresponding neutral betaine, which is formalised as a pyridinium-amido ligand when coordinated to a metal. Spectroscopic, structural and theoretical methods have been used to investigate the metal-ligand bonding, ligand dynamics and electron distribution. Collectively, the data show that the ligand can be characterised as a pseudo-amide and is a strong donor akin to alkyl phosphines and N-heterocyclic carbenes. Furthermore, rotation about both N substituent C-N bonds occurs, which is in contrast to the two alternative pyridinium positional isomers that exhibit neutral resonance structures. For comparison, compounds and complexes derived from norharman were prepared, which contain an additional C-C bond supporting conjugation and the accessibility of a neutral resonance structure. Notwithstanding the formal neutral structure, norharman-derived ligands are comparably strong donors, and have the additional advantage of exhibiting stability to dioxygen and water.

Adaptive N-Mesoionic Ligands Anchored to a Triazolylidene for Ruthenium-Mediated (De)Hydrogenation Catalysis

“…Under a N 2 atmosphere, the acid 2 (2.835 g, 15 mmol) was refluxed in SOCl 2 (15 mL) for 3 h. Excess SOCl 2 was removed under reduced pressure in a well-ventilated fumehood. The residue was dissolved in dry CH 2 Cl 2 (60 mL), then DIPEA (3.14 mL, 18 mmol) and 4-aminopyridine (1.41 g, 15 mmol) were added, and the reaction mixture was stirred at room temperature for 18 Pyridinium-triazolium Triflate 4. The triazole 3 (1.281 g, 4.8 mmol) was suspended in CH 2 Cl 2 (50 mL) and stirred at 0°C for 10 min.…”

Optimization of Synthetically Versatile Pyridylidene Amide Ligands for Efficient Iridium‐Catalyzed Water Oxidation

“…An ortho-PYAs ystem will feature an eutral limiting resonance structure, [24] although the proximity of the N-methyl group and the amide C=Ou nit is expected to induce ad ihedrals train (Scheme 2A). Although complex 1 may be considered as a para-PYA unit with the amide in the para positiont ot he pyridyl nitrogen, derivatives with the amide in meta or ortho substitution will have considerably different electronic properties.…”

Filling a Niche in “Ligand Space” with Bulky, Electron‐Poor Phosphorus(III) Alkoxides

“…The electronic properties of ligands have been assessed using a variety of methods, all of which have positive and negative aspects. A convenient approach, which we have used previously to assess the donor properties of very electron‐rich ligands, has been proposed by Gusev et al ,,,. This involves geometry optimizations and vibrational frequency analyses of [(η 5 ‐C 5 H 5 )Ir(CO)L] complexes (in which L is the desired ligand), using DFT methods to obtain CO stretching frequencies and C−O bond lengths that vary as a function of the donor/acceptor properties of L. The use of this complex, as opposed to other commonly used gauges of electronic properties {for example, [Ni(L)(CO) 3 ]}, allows the comparison of a large range of different ligand classes using the same scale.…”