Stereoelectronic Effects in C–H Bond Oxidation Reactions of Ni(I) N-Heterocyclic Carbene Complexes

Abstract

Activation of O 2 by the three-coordinate Ni(I) ring-expanded N-heterocyclic carbene complexes Ni(NHC)(PPh 3 )Br (NHC = 6-Mes, 7-Mes) produced the dimeric Ni(II) complexes Ni(6-Mes)(Br)(µ-OH)(µ-O-6-Mes′)NiBr (3) and Ni(7-Mes)(Br)(µ-OH)(µ-O-7-Mes′)NiBr (4) containing oxidized ortho-mesityl groups from one of the carbene ligands. Mass spectrometry was consistent with bis-µ-aryloxy compounds also being formed in these reactions. Low temperature UV-visible spectroscopy showed that the reaction between Ni(6-Mes)(PPh 3 )Br and O 2 was too fast even at ca. -80 °C to yield any observable intermediates. Addition of O 2 to Ni(I) precursors containing a less donating diamidocarbene (6-MesDAC) or the less bulky 6-/7-membered ring diaminocarbene ligands (6-/7-o-Tol) proceeded quite differently, affording phosphine and carbene oxidation products (Ni(O=PPh 3 ) 2 Br 2 and (6-MesDAC)=O) and mononuclear dibromido Ni(II) complexes (Ni(6-/7-o-Tol)(PPh 3 )Br 2 ) respectively.3

A Comparison of the Stability and Reactivity of Diamido‐ and Diaminocarbene Copper Alkoxide and Hydride Complexes

“…To prove that 5 wasn ot formed by just slow hydrolytic decomposition resulting from adventitious moisture, water (4.5 equivalents) was added to aT HF solution of 1. [20] The orange solution turned instantly dark red and then, within seconds, afforded ay ellow suspension. Thes olid component was identified by powder X-ray diffraction as nanoparticulate Cu 2 O( see the Supporting Information), whereas the 1 HNMR spectrum of the solution showedt he presence of as ingle copper-containing species( present alongside tBuOH), which was characterised by X-ray diffraction as ad ifferent ringopenedc arbene product, [(6-MesDAC)Cu(OC(O)CMe 2 C(O)N(H)- (1)ÀC (1) 1.874(2), Cu(1)ÀO (1) 1.8016 (15), O(1)ÀC (23)1 .407(3), C(1)ÀCu (1)-O(1) 175.31(8), Cu(1)-O(1)-C(23) 124.75 (13).…”

Mono- and dinuclear Ni(i) products formed upon bromide abstraction from the Ni(i) ring-expanded NHC complex [Ni(6-Mes)(PPh3)Br]

“…1,2 In terms of monodentate ligands, the early dependence on tertiary phosphines to stabilise Ni(I) 3,4 has largely been superseded by the use of N-heterocyclic carbenes (NHCs) and these have facilitated the isolation of a wide range of fully characterised four-, three-and even two-coordinate Ni(I) species. 5,6 Over the last few years, we have used so-called ringexpanded NHCs (RE-NHCs; carbenes with ring sizes >5) for the preparation of three-and two-coordinate Ni(I) complexes with interesting stoichiometric 7 and catalytic chemistry, 8 as well as novel magnetic properties. 9 In all cases, the starting point for our chemistry has been the three-coordinate species…”

Silver(I) and Nickel(II) Complexes with Oxygen‐ or Nitrogen‐Functionalized NHC Ditopic Ligands and Catalytic Ethylene Oligomerization

“…In 2014, Whittlesey and co-workers obtained a complex containing the Ni II anion [NiBr 3 (PPh 3 )]as a byproduct in the formation of a Ni II NHC complex by deprotonation of a N-aryl-substituted six-membered imidazolium ring followed by the addition of [NiBr 2 (PPh 3 ) 2 ] (Figure 8). [23] The 1 H NMR resonances of the associated imidazolium cation were observed between 19.55 and -4.85 ppm. In 2017, Fout and co-workers [21] isolated a [NiBr 3 (NHC)]complex from the chemical oxidation of a bidentate NHC-η 2 -iminoacyl Ni II complex by [Ph 3 CBr] and its 1 H NMR signals ranged from 87.29 to -22.21 ppm (Figure 8).…”