Mechanistic Insight into H/D Exchange by a Pentanuclear Ni–H Cluster and Synthesis and Characterization of Structural Analogues of Potential Intermediates

Abstract

Experiments to gain mechanistic insight into catalytic H/D exchange of unactivated arenes by [( i Pr 3 P)-Ni] 5 H 6 (1) are described. The reaction order with respect to 1, arene substrate, and added i Pr 3 P were determined, as well as the temperature dependence of reaction rate. Site-selectivity data were obtained by monitoring the reaction of 1 with fluorobenzene and 2-methoxynaphthalene. H/D exchange competition reactions between arenes reacted with 1 were performed. The addition of an excess of Hg to a solution of 1 provided the new heterometallic cluster [( i Pr 3 P)Ni] 5 H 6 (μ 4 -Hg) (2); this species also undergoes H/D exchange with C 6 D 6 , albeit more slowly than 1. Reaction of cluster 1 with TlCp (Cp = C 5 H 5 ) gave (η 5 -Cp)Ni[( i Pr 3 P)Ni] 4 (μ 2 -H) 4 (μ 4 -Tl) (3) with the loss of H 2 . A similar transfer of cyclopentadienyl to Ni occurred when 1 was reacted with MgCp 2 , to give (η 5 -Cp)Ni[( i Pr 3 P)Ni] 4 H 6 (μ 4 -MgCp) (4), but not H 2 loss. Reaction of 1 with cyclopentadiene gave the 5-coordinate hydride complex (η 5 -Cp)Ni[( i Pr 3 P)Ni] 4 (μ 2 -H) 4 (μ 5 -H) (5). The Cp* analogue, (η 5 -Cp*)Ni[( i Pr 3 P)Ni] 4 (μ 2 -H) 4 (μ 5 -H) (6) (where Cp* = C 5 Me 5 ), was synthesized by reacting 1 with LiCp* in THF, or by reaction of 1 with pentamethylcyclopentadiene.

Formation of a Propeller-Shaped Ni4Ga3 Cluster Supported by Transmetalation of Cp* from Ga to Ni

“…The intermetallic distances, including the unprecedented formal Cp*Ni I –Ga 0 bond, are all in the range of other Ni–Ga interactions. , The M–Cp* centroid distances are distinctly different for M = Ni and Ga, with the Ni–Cp* centroid (av 1.78–1.81 Å) distance being about 0.2 Å shorter than the distance of Ga–Cp* centroid (av 2.01 Å). Both distances are consistent with the values found for comparable compounds in the literature. − The calculated bond distances at the BP86-D3/def2-TZVPP level of theory match well with the crystal structure. Different metal assignments were tested by DFT calculations, without successful convergence.…”

Nickel(0)-Induced β-H Elimination of Magnesium Alkyls: Formation and Reactivity of Heterometallic Hydrides

“…An analogous heteromultimetallic Mg–Ni hydride was also recently prepared by Crimmin et al through C–H activation of benzene by an interplay between a low-valent Mg–Mg bonded complex and Ni(0) dinitrogen compound . Notably, complex 2 featured the shortest Mg–Ni bonds [Mg1–Ni1 2.415(12) Å, Mg2–Ni1 2.380(12) Å], reported to date, which are significantly shorter than the sum of the covalent radii of Mg and Ni (Pyykkö radius, 2.49 Å; Alvarez radius, 2.65 Å) and other crystallographically characterized Mg–Ni bonds (2.455–2.947 Å). , Hydride atoms were located in a Fourier difference map and refined with isotropic displacement parameters. Both Ni–H [Ni1–H1 1.55(3) Å, Ni1–H2 1.48(4) Å] and Mg–H [Mg1–H1 1.95(4) Å, Mg2–H2 1.85(3) Å] bond distances were within the expected values for nickel hydrides and magnesium hydrides, respectively.…”

Synthesis and reactivity of heterometallic complexes containing Mg- or Zn-metalloligands

“…Johnson et al reported the reaction of [( i Pr 3 P)Ni] 5 H 6 with MgCp 2 to give (η 5 -Cp)Ni[( i Pr 3 P)Ni] 4 H 6 (μ 4 -MgCp) 7 involving the transfer of Cp to Ni during the reaction (Scheme 3). 13 The cluster 7 had six hydrides in the framework as identified by 1 H NMR integration.…”