Nickel(<scp>ii</scp>)-methyl complexes adopting unusual seesaw geometries

Hill, Ethan A.; Zhao, Norman; Filatov, Alexander S.; Anderson, John S.

doi:10.1039/c9cc09249h

Cited by 6 publications

(27 citation statements)

References 35 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Single crystals of 7·PPh 3 and 7·P i Bu 3 were grown from a saturated THF and toluene solutions, respectively. The solid-state structures, depicted in Figure , indicate they are square planar and exhibit characteristic Ni–C bonds (1.929(3) Å for 7·PPh 3 and 1.935(3) Å for 7·P i Bu 3 ), similar to known complexes. ,,− The different steric profiles of phosphine ligands does not have a significant influence on the bond angles, with a N(2)–Ni(1)–C(1) angle of 168.5(1)° for 7·PPh 3 and 166.9(1)° for 7·P i Bu 3 ].…”

Section: Results and Discussionmentioning

confidence: 83%

“…Single-crystal X-ray diffraction provided structural data for 3 , and an ORTEP depiction is shown in Figure . The nickel center adopts a rare seesaw geometry; only a few examples of disphenoidal Ni(II) complexes are known. − There are few relevant structurally characterized examples of complexed 8-AQ ligand moieties where the ligand has not already undergone C–H activation. Previously, phenyl C(sp 2 )–H activated complexes have been isolated as penta-coordinated complexes with one C(sp 2 )–H bond activated for Ni and Co-catalyzed systems. − A single Cu(II) complex in known without activation for bis[ N -(quinolin-8-yl)benzamidato-κ 2 N , N ′]copper(II) …”

Section: Results and Discussionmentioning

confidence: 99%

See 1 more Smart Citation

Mechanism of 8-Aminoquinoline-Directed Ni-Catalyzed C(sp³)–H Functionalization: Paramagnetic Ni(II) Species and the Deleterious Effect of Carbonate as a Base

Liu

Johnson

2021

Organometallics

View full text Add to dashboard Cite

Studies into the mechanism of 8-aminoquinoline-directed nickel-catalyzed C(sp3)–H arylation with iodoarenes were carried out, to determine the catalyst resting state and optimize catalytic performance. Paramagnetic complexes undergo the key C–H activation step. The ubiquitous base Na2CO3 is found to hinder catalysis; replacement of Na2CO3 with NaO t Bu gave improved catalytic turnovers under milder conditions. Deprotonation of the 8-aminoquinoline derivative N-(quinolin-8-yl)pivalamide (1a) at the amide nitrogen using NaH, followed by reaction with NiCl2(PPh3)2 allowed for the isolation of complex Ni([AQpiv]-κN,N)2 (3) with chelating N-donors (where [AQpiv] = C9NH6NCO t Bu). Complex 3 is a four-coordinate disphenoidal high-spin Ni(II) complex, excluding short anagostic Ni-- t Bu hydrogen interactions. Complex 3 reacts with the paddle-wheel [Ph3PNi(μ-CO2 t Bu)2]2 (6·PPh 3 ) or t BuCO2H to give insoluble {[AQpiv]Ni(O2C t Bu)}2 (5). Dissolution of 5 in donor solvents L (L= DMSO and DMF) gave a paramagnetic intermediate assigned by NMR as [AQpiv]Ni(O2C t Bu)L (5·L) and equilibrium reformation of 3 and 6·L. DFT calculations support this equilibrium in solution. Both 3 and 5 undergo C–H activation at temperatures as low as 80 °C and in the presence of PR3 (PR3 = PPh3, P i Bu3) to give Ni(C9NH6NCOCMe2CH2-κN,N,C)PR3 (7·PR 3 ). The C–H functionalization reaction orders with respect to 7·P i Bu 3 , iodoarenes, and phosphines were determined. Hammett analysis using electronically different aryl iodides suggests a concerted oxidative addition mechanism for the C–H functionalization step; DFT calculations were also carried out to support this finding. When Na2CO3 is used as the base, the rate determination step for C–H functionalization appears to be 8-aminoquinoline deprotonation and binding to Ni. The carbonate anion was also observed to provide a deleterious NMR-inactive low-energy off-cycle resting state in catalysis. Replacement of Na2CO3 with NaO t Bu improved catalysis at milder conditions and made carboxylic acid and phosphine additives unnecessary. Complex 3 and its functionalized analogues were observed as the catalyst resting state under these conditions.

show abstract

Section: Results and Discussionmentioning

confidence: 83%

Section: Results and Discussionmentioning

confidence: 99%

Mechanism of 8-Aminoquinoline-Directed Ni-Catalyzed C(sp³)–H Functionalization: Paramagnetic Ni(II) Species and the Deleterious Effect of Carbonate as a Base

Liu

Johnson

2021

Organometallics

View full text Add to dashboard Cite

show abstract

“…Therefore, we decided to pursue a Co IV oxidation state with a bulkier and more donating ligand featuring adamantyl (Ad) groups to support an oxidized metal center, protect the reactive Co−O unit, and inhibit side reactions. 43 Here, we show that the 1 e − oxidation of an Ad-substituted terminal Co III -oxo complex results in a more active oxidant, which activates aliphatic C−H bonds with subsequent rebound. C−H activation proceeds through a transient and highly reactive Co IV -oxo intermediate.…”

Section: ■ Introductionmentioning

confidence: 64%

Enzyme-Like Hydroxylation of Aliphatic C–H Bonds From an Isolable Co-Oxo Complex

et al. 2021

Self Cite

View full text Add to dashboard Cite

The selective hydroxylation of aliphatic C–H bonds remains a challenging but broadly useful transformation. Nature has evolved systems that excel at this reaction, exemplified by cytochrome P450 enzymes, which use an iron-oxo intermediate to activate aliphatic C–H bonds with k 1 > 1400 s–1 at 4 °C. Many synthetic catalysts have been inspired by these enzymes and are similarly proposed to use transition metal-oxo intermediates. However, most examples of well-characterized transition metal-oxo species are not capable of reacting with strong, aliphatic C–H bonds, resulting in a lack of understanding of what factors facilitate this reactivity. Here, we report the isolation and characterization of a new terminal CoIII-oxo complex, PhB(AdIm)3CoIIIO. Upon oxidation, a transient CoIV-oxo intermediate is generated that is capable of hydroxylating aliphatic C–H bonds with an extrapolated k 1 for C–H activation >130 s–1 at 4 °C, comparable to values observed in cytochrome P450 enzymes. Experimental thermodynamic values and DFT analysis demonstrate that, although the initial C–H activation step in this reaction is endergonic, the overall reaction is driven by an extremely exergonic radical rebound step, similar to what has been proposed in cytochrome P450 enzymes. The rapid C–H hydroxylation reactivity displayed in this well-defined system provides insight into how hydroxylation is accomplished by biological systems and similarly potent synthetic oxidants.

show abstract

“…Closer to the explored catalyst structure, four-coordinate Ni(II)−Me complexes with strongly donating tris-carbene borate ligands exhibit the same seesaw geometry observed here in the triplet state, as well as the distorted square-planar geometry of the singlet (Figure 5). 69 Although the carbene system resulted in a more stable singlet state than the triplet, tuning electron density around the metal atom to distort the ligand field could easily alter the preference.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Singlet-to-Triplet Spin Transitions Facilitate Selective 1-Butene Formation during Ethylene Dimerization in Ni(II)-MFU-4l

et al. 2021

View full text Add to dashboard Cite

Catalytic ethylene dimerization is an important chemical reaction that suffers from a lack of selectivity for the desired product, 1-butene. Metal–organic frameworks (MOFs) bearing Ni-based catalytic sites have been shown to yield record selectivity for 1-butene. Early efforts to understand this selectivity revealed that chain propagation and 2-butene formation are competitive with 1-butene, seemingly at odds with experimental evidence that these products are disfavored. Here, we present an alternative mechanism for selective 1-butene formation in the highest performing MOF, Ni(II)-MFU-4l. Our study reveals competing electronic spin configuration pathways that intersect along the reaction coordinate. Intersystem crossing provides an explanation for the selective formation of 1-butene in the MOF. Furthermore, we explore intersystem crossing as a unique design principle for MOF catalyst design and highlight a departure from conventional molecular catalyst design paradigms.

show abstract

Nickel(ii)-methyl complexes adopting unusual seesaw geometries

Abstract: Tris-carbene borate supported nickel methyl complexes adopt unusual seesaw geometries due to competing electronic and chelate effects.

Cited by 6 publications

References 35 publications

Mechanism of 8-Aminoquinoline-Directed Ni-Catalyzed C(sp³)–H Functionalization: Paramagnetic Ni(II) Species and the Deleterious Effect of Carbonate as a Base

Mechanism of 8-Aminoquinoline-Directed Ni-Catalyzed C(sp³)–H Functionalization: Paramagnetic Ni(II) Species and the Deleterious Effect of Carbonate as a Base

Enzyme-Like Hydroxylation of Aliphatic C–H Bonds From an Isolable Co-Oxo Complex

Singlet-to-Triplet Spin Transitions Facilitate Selective 1-Butene Formation during Ethylene Dimerization in Ni(II)-MFU-4l

Contact Info

Product

Resources

About

Nickel(ii)-methyl complexes adopting unusual seesaw geometries

Abstract: Tris-carbene borate supported nickel methyl complexes adopt unusual seesaw geometries due to competing electronic and chelate effects.

Cited by 6 publications

References 35 publications

Mechanism of 8-Aminoquinoline-Directed Ni-Catalyzed C(sp3)–H Functionalization: Paramagnetic Ni(II) Species and the Deleterious Effect of Carbonate as a Base

Mechanism of 8-Aminoquinoline-Directed Ni-Catalyzed C(sp3)–H Functionalization: Paramagnetic Ni(II) Species and the Deleterious Effect of Carbonate as a Base

Enzyme-Like Hydroxylation of Aliphatic C–H Bonds From an Isolable Co-Oxo Complex

Singlet-to-Triplet Spin Transitions Facilitate Selective 1-Butene Formation during Ethylene Dimerization in Ni(II)-MFU-4l

Contact Info

Product

Resources

About

Mechanism of 8-Aminoquinoline-Directed Ni-Catalyzed C(sp³)–H Functionalization: Paramagnetic Ni(II) Species and the Deleterious Effect of Carbonate as a Base

Mechanism of 8-Aminoquinoline-Directed Ni-Catalyzed C(sp³)–H Functionalization: Paramagnetic Ni(II) Species and the Deleterious Effect of Carbonate as a Base