Synthesis and Reactivity of Nickel Hydride Complexes of an α-Diimine Ligand

Abstract

Reaction of L(0)NiBr(2) with 2 equiv of NaH yielded the Ni(II) hydride complex [(L(•-))Ni(μ-H)(2)Ni(L(•-))] (1) (L = [(2,6-iPr(2)C(6)H(3))NC(Me)](2); L(0) represents the neutral ligand, L(•-) is its radical-anionic form, and L(2-) denotes the dianion) in good yield. Stepwise reduction of complex 1 led to a series of nickel hydrides. Reduction of 1 with 1 equiv of sodium metal afforded a singly reduced species [Na(DME)(3)][(L(•-))Ni(μ-H)(2)Ni(L(•-))] (2a) (DME = 1,2-dimethoxyethane), which contains a mixed-valent core [Ni(μ-H)(2)Ni](+). With 2 equiv of Na a doubly reduced species [Na(DME)](2)[L(2-)Ni(μ-H)(2)NiL(2-)] (3a) was obtained, in which each monoanion (L(•-)) in the precursor 1 has been reduced to L(2-). By using potassium as the reducing agent, two analogous species [K(DME)(4)][(L(•-))Ni(μ-H)(2)Ni(L(•-))] (2b) and [K(DME)](2)[L(2-)Ni(μ-H)(2)NiL(2-)] (3b) were obtained. Further treatment of 3b with 2 equiv of K led to a trinuclear complex [K(DME)(THF)](2)K(2)[L(2-)Ni(μ-H)(2)Ni(μ-H)(2)NiL(2-)] (4), which contains one Ni(II) and two Ni(I) centers with a triplet ground state. When 1 and 3a were warmed in toluene or benzene, respectively, three reverse-sandwich dinickel complexes, [(L(•-))Ni(μ-η(3):η(3)-C(7)H(8))Ni(L(•-))] (5) and [Na(DME)](2)[L(2-)Ni(μ-η(3):η(3)-C(6)H(5)R)NiL(2-)] (6: R = CH(3); 7: R = H), were isolated. Reaction of 1 with Me(3)SiN(3) gave the N(3)-bridged complex [(L(•-))Ni(μ-η(1)-N(3))(2)Ni(L(•-))] (8). The crystal structures of complexes 1-8 have been determined by X-ray diffraction, and their electronic structures have been fully studied by EPR/NMR spectroscopy.

Base metal‐catalyzed hydrogen isotope exchange

“…Well‐defined nickel hydride complexes have been studied extensively in the past decade, but their applications for catalytic HIE have not been explored. Nickel hydride complexes bearing α‐diimine (DI) ligands, [( iPr DI)Ni(μ 2 ‐H)] 2 were initially characterized by Dong et al and later developed by the Chirik group for catalytic hydrosilylation and hydrogenation . Our collaboration team initially identified an α‐diimine nickel hydride complex, [( iPr DI)Ni(μ 2 ‐H)] 2 (first generation nickel hydride), as an effective catalyst for HIE.…”

High‐Frequency Fe–H Vibrations in a Bridging Hydride Complex Characterized by NRVS and DFT

“…[13] Murray has prepared Fe 3 H 3 species with a related ligand environment and high-spin iron(II) ions, but no direct spectroscopic detection of hydrides was reported. [14] Limberg and Yang have studied related nickel hydride complexes, [15],[16] but neither report assigned hydride bands in the IR spectra. In a recent paper, Ohki has described IR stretching bands for iron-hydride clusters.…”

Distinct Stepwise Reduction of a NickelNickel‐Bonded Compound Containing an α‐Diimine Ligand: From Perpendicular to Coaxial Structures

“…This experimental signal matches well the simulated one (Figure 4). Moreover, a broad signal was observed which is attributable to the nickel centers (Figure S3 in the Supporting Information) 11e. The assignment is further proven by its frozen‐solution EPR spectrum (Figure 5).…”

“…One sodium ion (Na1) interacts with the flanking aryl rings from two ligands in an η 4 /η 6 fashion, which is similar to some metalmetal‐bonded species 23. The other sodium ion (Na2) is solvated by a diethyl ether molecule and is η 4 ‐bonded to the enediamido (L 2− ) ligand, as was observed in many complexes containing dianionic diimine ligands 11e. 17a,b, 24 Notably, the monoanionic ligand does not bind a sodium ion.…”