An official website of the United States government
Interest in O 2 -dependent aliphatic carbon–carbon (C–C) bond cleavage reactions of first row divalent metal diketonate complexes stems from the desire to further understand the reaction pathways of enzymes such as DKE1 and to extract information to develop applications in organic synthesis. A recent report of O 2 -dependent aliphatic C–C bond cleavage at ambient temperature in Ni( ii ) diketonate complexes supported by a tridentate nitrogen donor ligand [(MBBP)Ni(PhC(O)CHC(O)Ph)]Cl ( 7-Cl ; MBBP = 2,6-bis(1-methylbenzimidazol-2-yl)pyridine) in the presence of NEt 3 spurred our interest in further examining the chemistry of such complexes. A series of new TERPY-ligated Ni( ii ) diketonate complexes of the general formula [(TERPY)Ni(R 2 -1,3-diketonate)]ClO 4 ( 1 : R = CH 3 ; 2 : R = C(CH 3 ) 3 ; 3 : R = Ph) was prepared under air and characterized using single crystal X-ray crystallography, elemental analysis, 1 H NMR, ESI-MS, FTIR, and UV-vis. Analysis of the reaction mixtures in which these complexes were generated using 1 H NMR and ESI-MS revealed the presence of both the desired diketonate complex and the bis-TERPY derivative [(TERPY) 2 Ni](ClO 4 ) 2 ( 4 ). Through selective crystallization 1–3 were isolated in analytically pure form. Analysis of reaction mixtures leading to the formation of the MBBP analogs [(MBBP)Ni(R 2 -1,3-diketonate)]X (X = ClO 4 : 5 : R = CH 3 ; 6 : R = C(CH 3 ) 3 ; 7-ClO4 : R = Ph; X = Cl: 7-Cl : R = Ph) using 1 H NMR and ESI-MS revealed the presence of [(MBBP) 2 Ni](ClO 4 ) 2 ( 8 ). Analysis of aerobic acetonitrile solutions of analytically pure 1–3 , 5 and 6 containing NEt 3 and in some cases H 2 O using 1 H NMR and UV-vis revealed evidence for the formation of additional bis-ligand complexes ( 4 and 8 ) but suggested no oxidative diketonate cleavage reactivity. Analysis of the organic products generated from 3 , 7-ClO4 and 7-Cl revealed unaltered dibenzoylmethane. Our results therefore indicate that N 3 -ligated Ni( ii ) complexes of unsubstituted diketonate ligands do not exhibit O 2 -dependent aliphatic C–C bond clevage at room temperature, including in the presence of NEt 3 and/or H 2 O.
more »
« less
This content will become publicly available on February 1, 2026
Pyridine vs. Thiazole in Cyclometalated N^C^N Ni(II) Complexes
Six N^C^N cyclometalated Ni(II) complexes [Ni(N^C^N)Cl] or [Ni(N^C^N’)Br] with symmetric N^C^N or non-symmetric N^C^N’ ligands in which the peripheral N-groups were varied with pyridine (Py), 4-thiazole (4Tz), 2-thiazole (2Tz), and 2-benzothiazole (2Btz) complementing the previously reported complexes with di(2-pyridyl)phenide ligands [Ni(Py(Ph)Py)X] X = Cl or Br. The non-symmetric [Ni(N^C^N’)Br] complexes were synthesized from NiBr2 and N^CH^N’ protoligands through base-assisted nickelation, while the symmetric [Ni(N^C^N)Cl] complexes were received from the N^C(Cl)^N protoligands and [Ni(COD)2] (COD = 1,5-cyclooctadiene). Introduction of 4Tz on both sides shifted the electrochemical gap ΔEexp = Eox–Ered and the long wavelength UV-vis absorption maxima of the complexes to higher energies, while 2Tz leads to a shift to lower energies. When introducing only one 4Tz or 2Tz as peripheral groups, the remaining PhPy moiety dominates the electronic properties and electrochemistry and photophysics are very similar to the Py(Ph)Py derivatives. In contrast to this, introduction of 2Btz shifts both values to lower energies, regardless of one or two 2Btz groups and the 2Btz moiety dominates the character of the frontier molecular orbitals of the complexes, as DFT calculations show. Long-wavelength UV-vis absorptions vary from 416 to 443 nm, and their energies correlate well with the first reduction potentials. Negishi-type C–C cross-coupling reactions gave total yields ranging from 1 to 60% and cross-coupling yields from 1 to 44%. The reactivities correlate roughly with the first reduction potentials. Facilitated reduction (E around –2 or higher) goes generally along with improved performance, making the thiazole-containing complexes interesting candidates for such catalysis.
more »
« less
- Award ID(s):
- 2153730
- PAR ID:
- 10635134
- Publisher / Repository:
- MDPI
- Date Published:
- Journal Name:
- Inorganics
- Volume:
- 13
- Issue:
- 2
- ISSN:
- 2304-6740
- Page Range / eLocation ID:
- 41
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
This work investigates possible mechanisms and intermediates in the reactivity of p-toluenesulfonyl fluoride with a new bidentate N-heterocyclic carbene (NHC) nickel complex, (MesNHC2oXy)Ni(COD) (Mes = 2,4,6-trimethylphenyl, oXy = ortho-xylyl, COD = cyclooctadiene). (MesNHC2oXy)Ni(COD) was synthesized from the corresponding bis(imidazolium) salt precursor, [MesNHC2oXy][Br]2, and both were structurally characterized. (MesNHC2oXy)Ni(COD) reacts with one equivalent of p-toluenesulfonyl fluoride to furnish (MesNHC2oXy)Ni(2-SO2), HF, and ½ equivalent of 4,4’-dimethylbiphenyl. (MesNHC2oXy)Ni(2-SO2) was structurally characterized and has a unique side-on SO2 coordination mode with a Ni-S-O angle of 60.49(5)°. DFT calculations of (MesNHC2oXy)Ni(2-SO2) are consistent with a Ni(II) center and an activated SO2 fragment. DFT calculations also support an initial oxidative addition at either the S-F or S-C positions, which have similar energetics.more » « less
-
Kostiantyn Marichev; Alejandro Bugarin (Ed.)Catalyst-mediated hydrogenation of ketones via hydride transfer can be directly used in the synthesis of alcohols which can exhibit great potential in the practical synthesis of pharmaceuticals. The application of Ni-NHC complexes in the hydrogenation of ketones is still limited. In a pursuit to study the effect of Ni-NHC-based complexes in the reactivity towards hydrogenation, we have studied the catalytic efficiency of a pendent-type nickel complex [Ni(NHC)2](PF6)2 constructed from a benzimidazole moiety. The hydrogenation of 2-acetylpyridine was studied with respect to catalyst loading, reaction temperature, reaction time, and solvent medium. The complex was broadly characterized by X-ray crystallography, ESI-MS, NMR, UV-Vis, and IR spectral studies.more » « less
-
Understanding H 2 binding and activation is important in the context of designing transition metal catalysts for many processes, including hydrogenation and the interconversion of H 2 with protons and electrons. This work reports the first thermodynamic and kinetic H 2 binding studies for an isostructural series of first-row metal complexes: NiML, where M = Al ( 1 ), Ga ( 2 ), and In ( 3 ), and L = [N( o -(NCH 2 P i Pr 2 )C 6 H 4 ) 3 ] 3− . Thermodynamic free energies (Δ G °) and free energies of activation (Δ G ‡ ) for binding equilibria were obtained via variable-temperature 31 P NMR studies and lineshape analysis. The supporting metal exerts a large influence on the thermodynamic favorability of both H 2 and N 2 binding to Ni, with Δ G ° values for H 2 binding found to span nearly the entire range of previous reports. The non-classical H 2 adduct, (η 2 -H 2 )NiInL ( 3 -H 2 ), was structurally characterized by single-crystal neutron diffraction—the first such study for a Ni(η 2 -H 2 ) complex or any d 10 M(η 2 -H 2 ) complex. UV-Vis studies and TD-DFT calculations identified specific electronic structure perturbations of the supporting metal which poise NiML complexes for small-molecule binding. ETS-NOCV calculations indicate that H 2 binding primarily occurs via H–H σ-donation to the Ni 4p z -based LUMO, which is proposed to become energetically accessible as the Ni(0)→M( iii ) dative interaction increases for the larger M( iii ) ions. Linear free-energy relationships are discussed, with the activation barrier for H 2 binding (Δ G ‡ ) found to decrease proportionally for more thermodynamically favorable equilibria. The Δ G ° values for H 2 and N 2 binding to NiML complexes were also found to be more exergonic for the larger M( iii ) ions.more » « less
-
Abstract A facile and efficient two‐step synthesis ofp‐substituted tris(2‐pyridylmethyl)amine (TPMA) ligands to form Cu complexes with the highest activity to date in atom transfer radical polymerization (ATRP) is presented. In the divergent synthesis,p‐Cl substituents in tris(4‐chloro‐2‐pyridylmethyl)amine (TPMA3Cl) were replaced in one step and high yield by electron‐donating cyclic amines (pyrrolidine (TPMAPYR), piperidine (TPMAPIP), and morpholine (TPMAMOR)) by nucleophilic aromatic substitution. The [CuII(TPMANR2)Br]+complexes exhibited larger energy gaps between frontier molecular orbitals and >0.2 V more negative reduction potentials than [CuII(TPMA)Br]+, indicating >3 orders of magnitude higher ATRP activity. [CuI(TPMAPYR)]+exhibited the highest reported activity for Br‐capped acrylate chain ends in DMF, and moderate activity toward C−F bonds at room temperature. ATRP ofn‐butyl acrylate using only 10–25 part per million loadings of [CuII(TPMANR2)Br]+exhibited excellent control.more » « less
