Protic NHC Iridium Complexes with β-H Reactivity–Synthesis, Acetonitrile Insertion, and Oxidative Self-Activation

Abstract

Protic NHC iridium complexes, obtained from the corresponding azido-phenylene-isocyanide precursor complexes, were investigated for ligand-based reactivity. Under redox-neutral conditions, acetonitrile inserts into the N−H bonds to provide κ 2 -NHC-imidoyl ligand-based complexes, while under reductive conditions the complex also expels one N−H proton to provide the corresponding deprotonated analogues. Using zinc as a reductor activates the NHC-iridium complex to form an asymmetric bimetallic iridium hydrido complex, in which two anionic N-deprotonated NHCs bridge the bimetallic core. X-ray crystal structures are reported for the azido-phenylene-isocyanide precursor complex, the protic NHC complex, and the asymmetric bimetallic iridium hydride complex. Density functional computations and a QTAIM analysis of the bimetallic iridium hydrido complex are provided.

Cyclometallated iridium NHC complexes containing self-isomerised ligands as catalysts for hydrosilylation and transfer hydrogenation reactions

“…The Ir–C2 bond length of 1 was found to be 2.026(8) Å, a value that is similar to those observed in literature for Ir( iii )–NHC complexes (2.008–2.044). 35,36,40–42 While the cyclometallated bond length (2.117(6) Å) was longer than that of the Ir–C2 bond length (2.026(8) Å), it compares well with literature values (2.108–2.178). 35,36,43,44 The presence of an allyl bond in 1 is shown with the shorter carbon–carbon bond lengths of C5–C6 = 1.447(8) Å and C6–C8 = 1.432(9) Å, compared to C6–C7 = 1.459(9) Å.…”

“…The Ir-C2 bond length of 3 (1.997(6) Å) is shorter than that of 1 and similar bonds found in literature (2.008-2.044). 35,36,[40][41][42] This indicates a stronger coordination to the iridium metal centre. In addition, the Ir-C7 bond length of 3 (2.073(6) Å) is also shorter than that of 1, but similar to that of literature examples (2.003-2.040 Å) 53,56 showing that cyclometallation through the benzyl ring could provide additional stability.…”

Synthesis of N‐Heterocyclic Carbenes and Their Complexes by Chloronium Ion Abstraction from 2‐Chloroazolium Salts Using Electron‐Rich Phosphines

“…The 13 C{ 1 H} NMR spectra feature the characteristic C NHC resonances at δ = 171.1 and δ = 185.6 ppm (d, 1 J = 56.4 Hz) for the Ir III complex [13] and the Rh III complex and [14], respectively. These values are in good agreement with those recorded for related Ir III [21,22] and Rh III [21] complexes. The C NHC resonances are shifted to lower field in the Ir I ( [15]: δ = 192.5 ppm) and Rh I ( [16]: δ = 197.2 ppm, d, 1 J = 51.0 Hz) complexes in accord with previous observations [23,24] and theoretical predictions.…”

Synthese N‐heterocyclischer Carbene und ihrer Komplexe durch Chloroniumionabstraktion von 2‐Chlorazoliumsalzen mit elektronenreichen Phosphanen

“…Die 13 C{ 1 H}-NMR-Spektren zeigen die typischen C NHC -Resonanzen bei δ = 171.1 und δ = 185.6 ppm (d, 1 J = 56.4 Hz) für den Ir III -Komplex [13] und den Rh III -Komplex [14]. Diese Werte liegen in dem Bereich von strukturell ähnlichen Ir III - [21,22] und Rh III -Komplexen. [21] Die C NHC -Resonanzen der Ir I -( [15]: δ = 192.5 ppm) und Rh I -Komplexe ( [16]: δ = 197.2 ppm, d, 1 J = 51.0 Hz) sind, in Übereinstimmung mit vorherigen Beobachtungen [23,24] und theoretischen Voraussagen, [25] ins Tieffeld verschoben.…”

“…Diese Werte liegen in dem Bereich von strukturell ähnlichen Ir III - [21,22] und Rh III -Komplexen. [21] Die C NHC -Resonanzen der Ir I -( [15]: δ = 192.5 ppm) und Rh I -Komplexe ( [16]: δ = 197.2 ppm, d, 1 J = 51.0 Hz) sind, in Übereinstimmung mit vorherigen Beobachtungen [23,24] und theoretischen Voraussagen, [25] ins Tieffeld verschoben.…”