Confinement‐Induced Selectivities in Gold(I) Catalysis—The Benefit of Using Bulky Tri‐(ortho‐biaryl)phosphine Ligands

Abstract

The confinement of a catalytic site is an efficient strategy to control a reaction and modulate its selectivity. In the present work, a new class of structurally simple and easily accessible bulky tri-(ortho-biaryl)phosphine ligands were accessed, and their gold(I) complexes synthesized. Their X-ray diffraction analysis and the comparative evaluation of their V Bur % and G steric parameters against a series of gold complexes commonly employed in catalysis demonstrated their confined nature. Despite their notable steric congestion, these complexes exhibited remarkable catalytic activities and unusual selectivities, both in nature and level, that make them unique in the field of synthetic homogeneous gold catalysis.

A Cavity-Shaped Gold(I) Fragment Enables CO2 Insertion into Au–OH and Au–NH Bonds

“…In previous studies, we have demonstrated that the cavity-shaped protection enforced by the exceptionally bulky tris-2-(4,4′-di- tert -butylbiphenylyl)phosphine provides a remarkable kinetic stabilization to otherwise unstable compounds, such as the corresponding gold(I)–ethylene and gold(I)-carbonyl complexes of type [(P-ligand)AuL] + (L = C 2 H 4 , CO). 13 On this bases, we now sought to utilize this ligand to access a monomeric Au(I) hydride species, 17 examples of which have been isolated only using strong donor N-heterocyclic carbenes (NHCs) 9a , 18 and NHC-coordinated diphosphene ligands. 19 Gold hydrides have been considered as intermediates in numerous gold-catalyzed organic transformations.…”

“…For elemental analyses, a LECO TruSpec CHN elementary analyzer was utilized. Complex 1 was prepared according to a literature procedure . All other reagents were used as received from commercial suppliers.…”

“…Complex 1 was prepared according to a literature procedure. 13 All other reagents were used as received from commercial suppliers. The yields obtained for complexes 3 , 4 , 7 , 8 , and 12 have been calculated taking into account the amount of residual pentane observed by 1 H and 13 C NMR spectroscopy in the samples.…”

“…However, the use of phosphine ligands to prepare this type of species has been scarcely described, most likely due to their relatively weaker donor capacity and their conical structure with lesser protection on the metal center . In previous studies, we have shown that the use of the exceptionally bulky tris-2-(4,4′-di- tert -butylbiphenylyl)­phosphine generates a protective cavity around the gold center that provides a remarkable kinetic stability to otherwise unstable compounds Herein, we describe the preparation of the corresponding gold hydroxide synthon and explore its reactivity toward different substrates, showing the ability of the extremely bulky phosphine to stabilize unusual monomeric gold species.…”