Ni(i) and Ni(ii) ring-expanded N-heterocyclic carbene complexes: C–H activation, indole elimination and catalytic hydrodehalogenation

Abstract

Reaction of the bulky 6-membered N-heterocyclic carbene 6-Mes with Ni(cod)(2) gives a C-H activated 6-Mes nickel(II) complex, but the novel three-coordinate Ni(I) species Ni(6-Mes)(PPh(3))Br if the reaction is performed in the presence of Ni(PPh(3))(2)Br(2). The Ni(I) complex is a precursor for the catalytic hydrodehalogenation of aryl halides.

Hydrodefluorination of carbon–fluorine bonds by the synergistic action of a ruthenium–palladium catalyst

“…Table S2), although after 5 h of reaction the reaction was not completed (66%). At this point, it is important to mention that a very small number of examples have been reported in which HDF of fluoroarenes has been carried out using isopropyl alcohol or other secondary alcohols in basic conditions [47][48][49][50] (most of them refer to heterogenous catalysed processes), but as far as we are aware, the heterodimetallic complex 3 seems to be the most active reported to date. The monitoring of the HDF of fluorobenzene by 19 F NMR (Fig.…”

The Role of Low Valent Transition Metal Complexes in Homogeneous Catalysis: An EPR Investigation

“…In a number of examples, ring-expanded 6-, 7-and 8-membered N-aryl-substituted heterocyclic carbenes (RE-NHCs) have been found to enhance the catalytic efficiency of Ir, Pt, Cu and Au complexes [17][18][19][20][21]. Whittlesey et al [22] therefore decided to explore the possibility that a similar catalytic enhancement could be observed using low valent Ni(I)-based analogues.…”

“…Through comproportionation of [Ni-(cod) 2 ] and [Ni(PPh 3 ) 2 X 2 ] (cod = cyclooctadiene; X = Br,Cl) in the presence of RE-NHCs, Whittlesey et al, synthesized a rare example of a 3-coordinate nickel(I) complex labelled [Ni(NHC)(PPh 3 )X] [22]. In an extension of this work, EPR was used to investigate this systematic series of well-defined Ni(I) complexes bearing a set of easily modified NHC ligands (Scheme 1) in order to obtain insights into both the fundamental properties (structure and bonding) and catalytic behaviour of these 3-coordinate d 9 species.…”

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

“…11,13,14 We have recently shown that N-heterocyclic carbene (NHC) ligands based on 6-, 7-and 8-membered rings (Chart 1) and containing bulky N-aryl substituents allow access to three-coordinate Ni(I) complexes of the general formula Ni(NHC)(PPh 3 )X (X = Br, Cl). 15,16 In preliminary observations, we found that inadvertent exposure of yellow 4 solutions of these highly air-sensitive compounds to air resulted in extremely rapid changes of color to purple. We now report that for the 6-and 7-membered ring N-mesityl derived complexes, these color changes arise as a result of O 2 activation and formation of dimeric Ni(II) complexes containing NHCs that have undergone oxidation at an orthomethyl C-H group.…”