Direct Base-Assisted C‒H Cyclonickelation of 6-Phenyl-2,2′-bipyridine

Vogt, Nicolas; Sivchik, V. V.; Sandleben, Aaron; Hörner, Gerald; Klein, Axel

doi:10.3390/molecules25040997

Cited by 9 publications

(25 citation statements)

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“…The three complexes [M(Me 2 dpb)Cl] were synthesised from the protoligand 1,5-di(2-pyridyl)-2,4-dimethylbenzene (Me 2 dpbH), anhydrous NiCl 2 , [Pd(COD)Cl 2 ], or K 2 [PtCl 4 ] by using the base-assisted C‒H activation method with KOAc and K 2 CO 3 in vigorously dried aprotic solvents, as previously reported for the Ni(II) complex [Ni(dpb)Cl] (dpbH = 1,3-di(2-pyridyl)-benzene) [ 47 ] and the C , N , N coordinated derivative [Ni(phbpy)Cl] (Hphbpy = 6-phenyl-2,2′-bipyridine) [ 48 ]. The three products were characterised through elemental analyses, EI-MS(+), 1 H, and 13 C NMR spectroscopy, and additionally 195 Pt NMR for [Pt(Me 2 dpb)Cl] (see Supplementary Materials ).…”

Section: Resultsmentioning

confidence: 99%

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Photoluminescence of Ni(II), Pd(II), and Pt(II) Complexes [M(Me2dpb)Cl] Obtained from C‒H Activation of 1,5-Di(2-pyridyl)-2,4-dimethylbenzene (Me2dpbH)

et al. 2021

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The three complexes [M(Me2dpb)Cl] (M = Ni, Pd, Pt) containing the tridentate N,C,N-cyclometalating 3,5-dimethyl-1,5-dipyridyl-phenide ligand (Me2dpb−) were synthesised using a base-assisted C‒H activation method. Oxidation potentials from cyclic voltammetry increased along the series Pt < Ni < Pd from 0.15 to 0.74 V. DFT calculations confirmed the essentially ligand-centred π*-type character of the lowest unoccupied molecular orbital (LUMO) for all three complexes in agreement with the invariant reduction processes. For the highest occupied molecular orbitals (HOMO), contributions from metal dyz, phenyl C4, C2, C1, and C6, and Cl pz orbitals were found. As expected, the dz2 (HOMO-1 for Ni) is stabilised for the Pd and Pt derivatives, while the antibonding dx2−y2 orbital is de-stabilised for Pt and Pd compared with Ni. The long-wavelength UV-vis absorption band energies increase along the series Ni < Pt < Pd. The lowest-energy TD-DFT-calculated state for the Ni complex has a pronounced dz2-type contribution to the overall metal-to-ligand charge transfer (MLCT) character. For Pt and Pd, the dz2 orbital is energetically not available and a strongly mixed Cl-to-π*/phenyl-to-π*/M(dyz)-to-π* (XLCT/ILCT/MLCT) character is found. The complex [Pd(Me2dpb)Cl] showed a structured emission band in a frozen glassy matrix at 77 K, peaking at 468 nm with a quantum yield of almost unity as observed for the previously reported Pt derivative. No emission was observed from the Ni complex at 77 or 298 K. The TD-DFT-calculated states using the TPSSh functional were in excellent agreement with the observed absorption energies and also clearly assessed the nature of the so-called “dark”, i.e., d‒d*, excited configurations to lie low for the Ni complex (≥3.18 eV), promoting rapid radiationless relaxation. For the Pd(II) and Pt(II) derivatives, the “dark” states are markedly higher in energy with ≥4.41 eV (Pd) and ≥4.86 eV (Pt), which is in perfect agreement with the similar photophysical behaviour of the two complexes at low temperatures.

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Section: Resultsmentioning

confidence: 99%

“…We recently synthesised this key complex in 76% yield using anhydrous NiCl 2 and dpbH in a base-assisted direct metalation in refluxing xylene using the base combination K 2 CO 3 /KOAc. This reaction was initially developed for the C , N , N coordinating ligand 6-phenyl-2,2′-bipyridine (Hphbpy; Scheme 1 A) [ 48 ].…”

Section: Introductionmentioning

confidence: 99%

Photoluminescence of Ni(II), Pd(II), and Pt(II) Complexes [M(Me2dpb)Cl] Obtained from C‒H Activation of 1,5-Di(2-pyridyl)-2,4-dimethylbenzene (Me2dpbH)

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“…The [Ni(Phbpy)(CF 3 )] complex was synthesized from [Ni(Phbpy)Br] through a transmetalation from CF 3 (SiMe 3 ) . More recently we have obtained the parent complex [Ni(Phbpy)Br] through an alternative pathway involving base-assisted direct C–H nickelation starting from HPhbpy and NiBr 2 . In this context we also isolated the precoordinated species [Ni(κ 2 - N,N -HPhbpy)Br 2 ] 2 .…”

Section: Introductionmentioning

confidence: 99%

“…More recently we have obtained the parent complex [Ni(Phbpy)Br] through an alternative pathway involving base-assisted direct C–H nickelation starting from HPhbpy and NiBr 2 . In this context we also isolated the precoordinated species [Ni(κ 2 - N,N -HPhbpy)Br 2 ] 2 . In addition, the NCN derivatives [Ni(PyPhPy)X] (X = Cl, Br, I, OAc) were obtained recently in good yields through similar methods …”

Section: Introductionmentioning

confidence: 99%

Role of the X Coligands in Cyclometalated [Ni(Phbpy)X] Complexes (HPhbpy = 6-Phenyl-2,2′-bipyridine)

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The coligand X was varied in the organonickel complexes [Ni(Phbpy)X] (X = F, Cl, Br, I, C 6 F 5 ) carrying the anionic tridentate C ∧ N ∧ N ligand 6-(phen-2-ide)-2,2′-bipyridine (Phbpy − ) to study its effect on electronic structures of these complexes and their activity in Negishi-like C−C cross-coupling catalysis. The complexes were synthesized from the precursor [Ni(COD) 2 ] (COD = 1,5-cyclooctadiene) by chelate-assisted oxidative addition into the phenyl C−X bond of the protoligand 6-(2-halidophenyl)-2,2′-bipyridine) and were obtained as red powders. Protoligands X−Phbpy carrying the halide surrogates X = OMe, OTf (triflate) failed in this reaction. Single-crystal XRD allowed us to add the structures of [Ni(Phbpy)Cl] and [Ni(Phbpy)I] to the previously reported Br derivative. Cyclic voltammetry showed reversible reductions for X = C 6 F 5 , F, Cl, while for Br and I the reversibility is reduced through rapid splitting of X − after reduction (EC mechanism). UV−vis spectroelectrochemistry confirmed the decreasing degree of reversibility along the series C 6 F 5 > F > Cl ≫ Br > I, which parallels the "leaving group character" of the X coligands. This method also revealed mainly bpy centered reduction and essentially Ni(II)/Ni(III) oxidations, as corroborated by DFT calculations. The rather X-invariant long-wavelength UV−vis absorptions and excited states were analyzed in detail using TD-DFT and were consistent with predominant metal to ligand charge transfer (MLCT) character. Initial catalytic tests under Negishi-like conditions showed the complexes to be active as catalysts in C−C cross-coupling reactions but did not display marked differences along the series from Ni−F to Ni−I.

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“…Nickel complexes are interesting for the possibility of accepting and donating electrons in a metal‐centered manner, forming compounds in different oxidation states, Ni(IV)/Ni(III)/Ni(II)/Ni(I)/Ni(0), and in the case of non‐innocent ligands, additional transfers of electrons can also be observed with the participation of the latter. However, there are not very many isolated and characterized nickel cycles, which are assumed in ligand‐directed reactions of C−H substitution and determine the selectivity of the reaction, [44–61] and the proven structures as intermediates of specific reactions are even fewer [44] . Electrochemical and ESR data for nickelacycles are rare and incomplete, [44–48] although electrochemical properties are very important for understanding and explaining their reactivity, selectivity, in particular, in oxidative C(sp2)−H functionalization, and in recent years researchers have been trying to fill this gap.…”

Section: Cyclometalated Nickel Complexes As Key Intermediates In C(sp2)−h Bond Functionalizationmentioning

confidence: 99%

Electrochemical Insight into Mechanisms and Metallocyclic Intermediates of C−H Functionalization

Budnikova

2021

The Chemical Record

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Transition metal‐catalyzed C−H activation has emerged as a powerful tool in organic synthesis and electrosynthesis as well as in the development of new methodologies for producing fine chemicals. In order to achieve efficient and selective C−H functionalization, different strategies have been used to accelerate the C−H activation step, including the incorporation of directing groups in the substrate that facilitate coordination to the catalyst. In this review, we try to underscore that the understanding the mechanisms of the catalytic cycle and the reactivity or redox activity of the key metal cyclic intermediates in these reactions is the basis for controlling the selectivity of synthesis and electrosynthesis. Combination of the electrosynthesis and voltammetry with traditional synthetic and physico‐chemical methods allows one to achieve selective transformation of C−H bonds to functionalized C−C or C−X (X=heteroatom or halogen) bonds which may encourage organic chemists to use it in the future more often. The possibilities and the benefits of electrochemical techniques are analyzed and summarized.

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Direct Base-Assisted C‒H Cyclonickelation of 6-Phenyl-2,2′-bipyridine

Cited by 9 publications

References 57 publications

Photoluminescence of Ni(II), Pd(II), and Pt(II) Complexes [M(Me2dpb)Cl] Obtained from C‒H Activation of 1,5-Di(2-pyridyl)-2,4-dimethylbenzene (Me2dpbH)

Photoluminescence of Ni(II), Pd(II), and Pt(II) Complexes [M(Me2dpb)Cl] Obtained from C‒H Activation of 1,5-Di(2-pyridyl)-2,4-dimethylbenzene (Me2dpbH)

Role of the X Coligands in Cyclometalated [Ni(Phbpy)X] Complexes (HPhbpy = 6-Phenyl-2,2′-bipyridine)

Electrochemical Insight into Mechanisms and Metallocyclic Intermediates of C−H Functionalization

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