Synthesis and Characterization of Dimethylbis(2-pyridyl)borate Nickel(II) Complexes: Unimolecular Square-Planar to Square-Planar Rotation around Nickel(II)

Celaje, Jeff Joseph A.; Pennington‐Boggio, Megan K.; Flaig, Robinson W.; Richmond, Michael G.; Williams, Travis J.

doi:10.1021/om500173j

Cited by 9 publications

(26 citation statements)

References 70 publications

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“…The negative Δ S ‡ of activation for this reaction is particularly noteworthy and indicates an ordered transition state that is inconsistent with a rate-limiting ligand-dissociation event. This suggestion is further corroborated by the fact that the decomposition of 2 is not measurably affected by the addition of up to 8 equiv of free CNAr Mes2 (Table ) . Accordingly, the kinetic data for 2 indicate that β-Cl elimination may not require an in-plane, open coordination site in Group 10 metal polymerization systems.…”

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confidence: 58%

Direct Observation of β-Chloride Elimination from an Isolable β-Chloroalkyl Complex of Square-Planar Nickel

et al. 2014

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Reported here are the isolation, structural characterization, and decomposition kinetics of the four-coordinate pentachloroethyl nickel complex, NiCl(CCl2CCl3)(CNAr(Mes2))2 (Ar(Mes2) = 2,6-(2,4,6-Me3C6H2)2C6H3). This complex is a unique example of a kinetically persistent β-chloroalkyl in a system relevant to coordination-insertion polymerization of polar olefins. Kinetic analysis of NiCl(CCl2CCl3)(CNAr(Mes2))2 decomposition indicates that β-chloride (β-Cl) elimination proceeds by a unimolecular mechanism that does not require initial dissociation of a CNAr(Mes2) ligand. The results suggest that a direct β-Cl elimination pathway is available to four-coordinate, Group 10 metal vinyl chloride polymerization systems.

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confidence: 58%

Direct Observation of β-Chloride Elimination from an Isolable β-Chloroalkyl Complex of Square-Planar Nickel

et al. 2014

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“…(b) The σ-complex-assisted metathesis (σ-CAM). As some Ni(II) complexes were found in the triplet state, [39][40][41] geometry optimization, the H 2 simply dissociated away from the Ni. In the [NiFe] hydrogenase model study, Keith and Hall also reported that while the triplet state was possible for the Ni(II), H 2 binding to the high spin Ni was not found.…”

Section: B C-o Bond Hydrogenolysismentioning

confidence: 99%

Mechanism of Ni N-heterocyclic carbene catalyst for C–O bond hydrogenolysis of diphenyl ether: a density functional study

et al. 2014

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Catalysts for aromatic C-O bond activation can potentially be used for the lignin degradation process. We investigated the mechanisms of C-O bond hydrogenolysis of diphenyl ether (PhOPh) by the nickel N-heterocyclic carbene (Ni-SIPr) complex to produce benzene and phenol as products. Our calculations revealed that diphenyl ether is not only a substrate, but also serves as a ligand to stabilize the Ni-SIPr complex. The Ni(SIPr)(η(6)-PhOPh) complex is initially formed before rearranging to Ni(SIPr)(η(2)-PhOPh), the active species for C-O bond activation. The catalytic reaction has three steps: (i) oxidative addition of Ni(SIPr)(η(2)-PhOPh) to form [Ni(SIPr)(OPh)(Ph)](0), (ii) σ-complex-assisted metathesis, in which H2 binds to the nickel to form [Ni(SIPr)(OPh)(Ph)(H2)](0), and then benzene (or phenol) is eliminated, and (iii) reductive elimination of phenol (or benzene) and the binding of PhOPh to regenerate Ni(SIPr)(η(2)-PhOPh). As the rate determining step is the oxidative addition step (+24 kcal mol(-1)), we also calculated the free energy barriers for the oxidative addition of diaryl ether containing a trifluoromethyl electron withdrawing group (PhOC6H4CF3) and found that C-O bond activation at the carbon adjacent to the aryl ring that contains the electron withdrawing substituent is preferred. This is in agreement with the experimental results, in that the major products are phenol and trifluoromethylbenzene. Moreover, the hydrogenation of benzene via Ni(SIPr)(η(2)-C6H6) requires a high energy barrier (+39 kcal mol(-1)); correspondingly, the hydrogenation products, e.g. cyclohexane and cyclohexadiene, were not observed in the experiment. Understanding the reaction mechanisms of the nickel catalysts for C-O bond hydrogenolysis of diphenyl ether will guide the development of catalytic systems for aromatic C-O bond activation to achieve the highest possible selectivity and efficiency.

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“…Since early reports by Hodgkins in 1993 on bis(pyridyl)borates ( 1 ) and Jäkle in 2012 on tris(pyridyl)borates ( 2 ), − there has been growing interest in poly(pyridyl)borates, − which represent a new addition to the very popular scorpionate family. , These poly(pyridyl)borates have several attractive features over the better-known poly(pyrazolyl)borates as they have more thermally stable B–C linkages (compared to the relatively polar B–N linkages of the latter), four-substitutable positions on pyridyl groups ( vs three on pyrazolyl moieties), a closer proximity of the heterocyclic ring substituent to the metal site, and are believed to be better σ-donor ligands . Interestingly, despite several emerging applications, the reported poly(pyridyl)borates were limited to the parent systems based on unsubstituted pyridyl moieties ( e.g.…”

Section: Introductionmentioning

confidence: 99%

Copper(I), Silver(I), and Gold(I) Ethylene Complexes of Fluorinated and Boron-Methylated Bis- and Tris(pyridyl)borate Chelators

et al. 2023

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Bis- and tris-pyridyl borate ligands containing pyridyl donor arms, a methylated boron cap, and a fluorine-lined coordination pocket have been prepared and utilized in coinage metal chemistry. The tris(pyridyl)borate ligand has been synthesized using a convenient boron source, [NBu4][MeBF3]. These N-based ligands permitted the isolation of group 11 metal–ethylene complexes [MeB(6-(CF3)Py)3]M(C2H4) and [Me2B(6-(CF3)Py)2]M(C2H4) (M = Cu, Ag, Au). The gold complexes display the largest coordination-induced upfield shifts of the ethylene 13C resonance relative to that of the free ethylene in their NMR spectra, while the silver complexes show the smallest shift. Solid-state structures of five of these metal–ethylene complexes as well as the related free ligands were established by X-ray crystallography. Surprisingly, all three [MeB(6-(CF3)Py)3]M(C2H4) adopt the rare κ2 coordination mode rather than the typical κ3 coordination mode of facial capping tridentate ligands. Computational analyses indicate that κ2 coordination mode is favored over the κ3-mode in these coinage metal–ethylene complexes and point to the effects CF3-substituents have on κ2/κ3-energy difference. The M–C and M–N bond distances of [MeB(6-(CF3)Py)3]M(C2H4) follow the trend expected based on covalent radii of M(I) ions. The calculated ethylene–M interaction energy of κ2-[MeB(6-(CF3)Py)3]M(C2H4) indicated that the gold(I) forms the strongest interaction with ethylene. A comparison to the related poly(pyrazolyl)borates is also presented.

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Synthesis and Characterization of Dimethylbis(2-pyridyl)borate Nickel(II) Complexes: Unimolecular Square-Planar to Square-Planar Rotation around Nickel(II)

Cited by 9 publications

References 70 publications

Direct Observation of β-Chloride Elimination from an Isolable β-Chloroalkyl Complex of Square-Planar Nickel

Direct Observation of β-Chloride Elimination from an Isolable β-Chloroalkyl Complex of Square-Planar Nickel

Mechanism of Ni N-heterocyclic carbene catalyst for C–O bond hydrogenolysis of diphenyl ether: a density functional study

Copper(I), Silver(I), and Gold(I) Ethylene Complexes of Fluorinated and Boron-Methylated Bis- and Tris(pyridyl)borate Chelators

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