A Bis(silylene)‐Substituted ortho‐Carborane as a Superior Ligand in the Nickel‐Catalyzed Amination of Arenes

Abstract

The synthesis and structure of the first 1,2-bis(NHSi)-substituted ortho-carborane [(LSi:)C]2 B10 H10 (termed SiCCSi) is reported (NHSi=N-heterocyclic silylene; L=PhC(NtBu)2 ). Its suitability to serve as a reliable bis(silylene) chelating ligand for transition metals is demonstrated by the formation of [SiCCSi]NiBr2 and [SiCCSi]Ni(CO)2 complexes. The CO stretching vibration modes of the latter indicate that the Si(II) atoms in the SiCCSi ligand are even stronger σ donors than the P(III) atoms in phosphines and C(II) atoms in N-heterocyclic carbene (NHC) ligands. Moreover, the strong donor character of the [SiCCSi] ligand enables [SiCCSi]NiBr2 to act as an outstanding precatalyst (0.5 mol % loading) in the catalytic aminations of arenes, surpassing the activity of previously known molecular Ni-based precatalysts (1-10 mol %).

Unexpected Zwitterionic Allenyls from Silylenes and a Fischer Alkynylcarbene: A Remarkable Silylene‐Promoted Rearrangement

“…[2,3] Additionally,i th as been recently found that some silylenes, particularly those stabilized by donor groups,h ave as tronger electron-donor capacity than the most basic phosphanes and even N-heterocyclic carbenes (NHCs). [4,5] This is ak ey factor of their newly reported behavior as steering ligands in homogeneous catalysis, [3,4] but, despite their strong nucleophilicity, the use of silylenes as nucleophiles for the formation of SiÀCbonds is still little developed. [1a,f,k, 6] Within the family of donor-stabilized silylenes,t hose having an amidinato fragment are being increasingly used because their syntheses are relatively easy and their electronic and steric properties can be easily tuned.…”

An Intramolecular Silylene Borane Capable of Facile Activation of Small Molecules, Including Metal‐Free Dehydrogenation of Water

“…[12] Thee lectronic structure of 1 was investigated by density functional theory (DFT) calculations,performed at the BP86/TZP level using the ADF software suite (see Supporting Information). The 29 Si NMR resonance of 1 is observed at d = 13.3 ppm, akin to the value observed for an ocarborane bridged bis-NHSi ligand.…”

Stereoselective Transfer Semi‐Hydrogenation of Alkynes to E‐Olefins with N‐Heterocyclic Silylene–Manganese Catalysts

“…Since the first report on an NHSi used in metal‐mediated catalysis in 2001, various types of NHSi ligands (e.g., monodentate A , bidentate B , and tridentate pincer‐type ligand C , see Scheme ) as donor ligands towards transition‐metals (TM) have been described . As it turned out NHSi ligands can facilitate catalytic transformations owing to their excellent control over the electronic properties of TMs in the scaffolds mainly by taking advantage of the strong σ donor ability of Si II which lowers the activation barriers of the rate limiting steps at the TM active site (e.g., oxidative addition) . Most notable, NHSi ligands can initiate cooperative effects as shown in a heterobimetallic NHSi→Ni/Cu‐catalyzed Sonogashira coupling, NHSi→Fe catalyzed hydrosilylation of ketones and NHSi→Ni catalyzed hydrogenation of olefins .…”