Fluoride-free Hiyama coupling by palladium abnormal N-heterocyclic carbene complexes

Abstract

A series of palladium complexes of the abnormal N-heterocyclic carbene ligands of the type (a-NHC)PdI2(L) [L = NC5H5(1-3)b and PPh3(1-3)c] effectively catalyzed the Hiyama coupling of aryl bromides and iodides with PhSi(OMe)3 under the highly desired fluoride-free conditions. Interestingly enough, the pyridine based trans-(1-3)b complexes and a PPh3 derived cis-3c complex exhibited higher yields than the related PPh3 derived trans-(1-2)c complexes. The superior performances of the pyridine based trans-(1-3)b complexes and the PPh3 derived cis-3c complex have been correlated to a tighter binding of the a-NHC ligand to the palladium center in these complexes, leading to a greater (a-NHC) ligand influence on the metal center partaking in the catalysis.

Palladium Acyclic Diaminocarbene (ADC) Triflate Complexes as Effective Precatalysts for the Hiyama Alkynylation/Cyclization Reaction Yielding Benzofuran Compounds: Probing the Influence of the Triflate Co‐Ligand in the One‐Pot Tandem Reaction

“…With our interest lying in exploring the potential of transition metal N‐heterocyclic carbene complexes in homogeneous catalysis and in biomedical applications, we have explored the utility of various type of singlet carbene ligand scaffolds namely, the imidazole, benzimidazole, 1,2,4‐triazole based ones,, abnormal carbenes, bicyclic and the tricyclic carbene systems . In this connection, we became interested in another new motif, particularly that of the acyclic diaminocarbene ligands, for their utility in time efficient tandem reactions ,.…”

Suzuki–Miyaura and Hiyama coupling catalyzed by PEPPSI-type complexes with non-bulky NHC ligand

“…In contrast, their applications in the Hiyama coupling are rather scarce [25][26][27]. This is surprising because these two methods, the Suzuki-Miyaura and the Hiyama reactions, present alternative pathways leading to biaryl compounds and, therefore, it could be interesting to estimate their relative applicability under similar reaction conditions.…”

Chiral Oxazolidine‐Fused N‐Heterocyclic Carbene Complexes of Rhodium and Iridium and Their Utility in the Asymmetric Transfer Hydrogenation of Ketones

“…Despite their promise, the multistep sequences required for the synthesis of these fused bicyclic oxazolidine N‐heterocyclic carbene ligands has somewhat restricted the larger applicability of these ligands, and this has attracted our attention. Specifically, owing to our interest in the exploration of the catalytic utility N‐heterocyclic carbene ligands with different ring types, spanning from the ubiquitous five‐membered cyclic imidazole‐ and triazole‐based ones to less common varieties such as acyclic six‐membered N‐heterocyclic carbenes, bicyclic imidazo[1,2‐ a ]pyridines,, and tricyclic triazolooxazine‐derived ones, we became interested in exploring the catalytic exploits of one such less frequently encountered type, that is, chiral bicyclic oxazolidine‐fused N‐heterocyclic carbene ligands. Furthermore, as much of the catalytic studies reported for these bicyclic oxazolidine‐fused N‐heterocyclic‐carbene‐based systems were performed under in situ LAC conditions and there are no known examples of well‐defined transition‐metal complexes, we decided to employ structurally characterized molecular complexes for our study in asymmetric catalysis to obtain a better insight into the mode of action of these catalysts.…”