Tridentate NacNac Stabilized Tin and Nickel Complexes: Access to a Monomeric Nickel Hydride and Its Catalytic Application

Abstract

The transmetalation reaction of picolyl-supported tridentate nacnac germylene monochloride [2,6-iPr2–C6H3NC(Me)CHC(Me)NH(CH2py)]GeCl (1) (py = pyridine) with SnCl2 results in an analogous stannylene chloride (2). The three-coordinated stannylenium cation [{2,6-iPr2–C6H3NC(Me)CHC(Me)NH(CH2py)}Sn]+ with SnCl3 – as a counteranion (3) has been generated through the abstraction of chloride ligand from 2 using an additional equivalent of SnCl2. Instead of forming a donor–acceptor complex, 2 undergoes a facile redox transmetalation reaction with Ni(COD)2 (COD = cyclooctadiene) and CuCl to afford analogous nickel and copper complexes [2,6-iPr2–C6H3NC(Me)CHC(Me)NH(CH2py)]MCl [M = Ni (4) and Cu (5)]. The reactions of 4 with potassium tri-sec-butylborohydride (commonly known as K-selectride) and AgSbF6 provide access to monomeric Ni(II) hydride, [2,6-iPr2–C6H3NC(Me)CHC(Me)NH(CH2py)]NiH (6) and a Ni(II) cation, [{2,6-iPr2–C6H3NC(Me)CHC(Me)NH(CH2py)}Ni][SbF6] (7), respectively. 6 was found to be an effective catalyst for the hydroboration of amides.

Hard to Handle: Extremely Labile Hydrido Nickel(II) Complexes of Cyclometalated C∧N∧N and N∧C∧N Ligands

“…Remarkably, this signal position is beyond the low-field limits of previously described Ni(II) hydrido complexes; e.g., for the complexes shown in Chart 1 values of δ (Ni−H) = −10.0/−9.9, −22.8, −6.54, and −22.73 ppm were reported. 8,14,28,31,32 In a spectrum recorded S13). No signal that could be assigned to a Ni complex was found.…”

“…An explicit comparison to the chlorido complexes is shown in Figure S20. In particular, the LUMO energies are hardly affected by the nature of the monodentate ligand H or Cl, whereas the latter substantially stabilizes the three highest occupied orbitals by 28 Sen, 14 Hu, 31 and Kemp. 32 In several of the previous reports on nickel hydrido complexes mention was made of qualitatively similar lability, yielding darkened dispersions of elemental nickel and the protonated ligand.…”

Synthesis and catalytic performance of nickel phosphinite pincer complexes in deoxygenative hydroboration of amides

“…at 40 °C), presenting a rare example of a system for catalytic deoxygenation of 2° amides under mild conditions. 6 f ,9–12 On the other hand, reactions of N -phenylbenzamide and N -phenylpropanamide with HBPin cata-lyzed by 1-BF 4 , 3-Me , 3-BH 4 , 2-OPh , 3-OPh , and 3-OAc were found to be more sluggish showing conversions in the range 10–67% (Scheme 7, entries 16–21).…”

“…6 f However, the advantages of deoxygenative hydroboration of amides in terms of the substrate scope and selectivity have been already exemp-lified with several d-block transition metal systems operating under rather mild conditions (<100 °C). 9–12 Nonetheless, only scarce examples of abundant base-metal catalysts (Mn, Fe, Co, and Ni) for deoxygenative hydroboration of amides have been reported (Fig. 1).…”

NaHBEt3-catalyzed HBpin hydroboration and deoxygenation of primary, secondary, and tertiary amides

“…[31][32][33] As the investigations intensified and more stringent reaction conditions were selected, catalysts suitable for hydroboration reactions, including those of primary amides, were gradually discovered (Scheme 1). [34][35][36][37][38][39][40][41] As it was also pointed out, Sen and co-workers reported a catalyst-free approach for the hydroboration of primary to secondary amides. However, the reaction requires high temperature and long reaction time, and the substrate scope is not very wide.…”