A Palladium(II) Peroxido Complex Supported by the Smallest Steric N‐Heterocyclic Carbene, IMe = 1,3‐Dimethylimidazole‐2‐ylidene, and Its Reactivity by Oxygen‐Atom Transfer

Abstract

Stabilized with an N‐heterocyclic carbene ligand of the smallest steric profile, PdII(η2‐O2)(IMe)2 (IMe = 1,3‐dimethylimidazole‐2‐ylidene) was synthesized by the direct addition of dioxygen to Pd0(IMe)2. The peroxidopalladium complex with IMe, which was previously available only by computation, was characterized by IR spectroscopy and X‐ray crystallography. Moreover, its oxygen‐atom‐transfer reactivity was elucidated by studying its thermolysis in pyridine at 60 °C to yield 1,3‐dimethylimidazol‐2‐one (IMeO) and its reaction with oxygen‐atom‐transfer acceptors such as PPh3 and (Me3Si)2.

The key role of R–NHC coupling (R = C, H, heteroatom) and M–NHC bond cleavage in the evolution of M/NHC complexes and formation of catalytically active species

“…Oxidation of M/NHC complexes 51 , leading to formation of O–NHC bond and affording imidazoline-2-ones 52 or related substances, certainly deserves attention. 172 , 181 , 182 , 222 For example, homogeneous aerobic oxidation of Cu I /NHC complexes can be used for preparative synthesis of cyclic ureas ( Scheme 11 ). 181 The reaction is highly sensitive to the NHC steric bulkiness and possibly includes a reductive elimination step.…”

Pd-PEPPSI-IPentAn Promoted Deactivated Amination of Aryl Chlorides with Amines under Aerobic Conditions

“…The bond length of Pd–C(6) and Pd–N(1) bond lengths are 1.966 (5) and 2.107 (4) Å, respectively, which are comparable to that of the reported Pd-PEPPSI complex (Table ). ,,− , It is noteworthy that the N -aryl moieties derived from carbene ligand are oriented nearly perpendicularly to the coordination plane with dihedral angles of 79.41 and 84.15°, respectively. These results suggest that the bulky alkyl chain would effectively protect the palladium center.…”

“…Despite these compelling advances in phosphine-free catalyst design, several drawbacks still limit their utility. First, the transformation is highly challenging when hindered aryl chlorides and sterically demanding anilines or heterocyclic amines were selected as coupling partners in air conditions. , The catalytic processes generally need strict oxygen- and moisture-free operation, whereas trace of oxygen would trap the LPd(0) to form the unreactive LPd­(O 2 ) . To ensure the stabilization of the low-valent active species in aerobic conditions, the ligand with bulky substituted groups is required .…”

A Highly Substitutable Palladium(II) Complex Stabilized by the Smallest Steric N‐Heterocyclic Carbene, IMe (IMe = 1,3‐Dimethylimidazole‐2‐ylidene)

“…Therefore, the access to a mono‐ligated NHC complex with weakly coordinating ligands is very limited . To overcome the problematic metalation of NHC, we have utilized the smallest steric NHC and successfully prepared mono‐ligated palladium(II) complex with a weakly coordinating anion and tetrahydrofuran (THF) . Here, we report the preparation and full characterization of a mono‐ligated palladium(II) complex supported by I Me ( I Me = 1,3‐dimethylimidazole‐2‐ylidene), triflate, and THF.…”

“…3,11 However, most of mono-ligated NHC palladium complexes contain bulky NHCs with relatively strongly bound anions such as acetate anions, or halide-or carboxylate-bridged palladium dimers are obtained. 17,18 Here, we report the preparation and full characterization of a mono-ligated palladium(II) complex supported by IMe (IMe = 1,3-dimethylimidazole-2-ylidene), triflate, and THF. 14 Therefore, the access to a mono-ligated NHC complex with weakly coordinating ligands is very limited.…”