Mechanism of 8-Aminoquinoline Directed Ni-Catalyzed C(sp3)-H Functionalization: Paramagnetic Ni(II) Species, and the Deleterious Effect of Na2CO3 as a Base

<p>Studies into the mechanism of 8-aminoquinoline-directed nickel-catalyzed C(sp³)–H arylation with iodoarenes are described, in an attempt to determine the catalyst resting state and optimize catalytic performance. Paramagnetic complexes are identified that are undergo the key C–H activation step. Hammett analysis using electronically different aryl iodides suggests a concerted oxidative addition mechanism for the C–H functionalization step; DFT calculations were also performed 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<i>^t</i>Bu not only improved catalysis at milder conditions but also eliminated the need for carboxylic acid and phosphine additives.</p>

Mechanism of 8-Aminoquinoline Directed Ni-Catalyzed C(sp3)-H Functionalization: Paramagnetic Ni(II) Species, and the Deleterious Effect of Na2CO3 as a Base

<p>Studies into the mechanism of 8-aminoquinoline-directed nickel-catalyzed C(sp³)–H arylation with iodoarenes are described, in an attempt to determine the catalyst resting state and optimize catalytic performance. Paramagnetic complexes are identified that are undergo the key C–H activation step. Hammett analysis using electronically different aryl iodides suggests a concerted oxidative addition mechanism for the C–H functionalization step; DFT calculations were also performed 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<i>^t</i>Bu not only improved catalysis at milder conditions but also eliminated the need for carboxylic acid and phosphine additives.</p>

Mechanism of 8-Aminoquinoline Directed Ni-Catalyzed C(sp3)-H Functionalization: Paramagnetic Ni(II) Species, and the Deleterious Effect of Na2CO3 as a Base

<p>Studies into the mechanism of 8-aminoquinoline-directed nickel-catalyzed C(sp³)–H arylation with iodoarenes are described, in attempts to determine the catalyst resting state and optimize catalytic performance. Paramagnetic complexes are identified that are undergo the key C–H activation step. Hammett analysis using electronically different aryl iodides suggests a concerted oxidative addition mechanism for the C–H functionalization step; DFT calculations were also performed 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<i>^t</i>Bu not only improved catalysis at milder conditions but also eliminated the need for carboxylic acid and phosphine additives.</p>

Analysis of reduced paramagnetic shifts as an effective tool in NMR spectroscopy

A recently introduced concept of reduced paramagnetic shifts (RPS) in NMR spectroscopy is applied here to a series of paramagnetic complexes with different metal ions, such as iron(II), iron(III) and...

A Paramagnetic NMR Spectroscopy Toolbox for the Characterisation of Paramagnetic/Spin-Crossover Coordination Complexes and Metal-Organic Cages

<div> <p>The large paramagnetic shifts and short relaxation times resulting from the presence of a paramagnetic centre complicate NMR data acquisition and interpretation in solution. In contrast to the large number of standard NMR methods for diamagnetic compounds, the number of paramagnetic NMR methods is limited and spectral assignment often relies on theoretical models. We report a toolbox of 1D (¹H, proton-coupled ¹³C, selective ¹H‑decoupling ¹³C, steady-state NOE) and 2D (COSY, NOESY, HMQC) paramagnetic NMR methods for the straightforward structural characterisation of paramagnetic complexes in solution and demonstrate its general applicability for fields from coordination chemistry to spin‑crossover complexes and supramolecular chemistry through the characterisation of Co^II and high-spin Fe^II mononuclear complexes as well as a Co₄L₆ cage. The toolbox takes advantage of the reduced signal overlap, decreased instrument time and greater sensitivity from the presence of the paramagnetic centre while overcoming the loss of structural information from the wide chemical shift dispersion and broad signals. In some circumstances, more structural information was revealed in the COSY spectra than would be observable for a diamagnetic analogue; as well as the expected through-bond cross-peaks, through-space and exchange cross-peaks were also observed for mononuclear complexes with multiple ligand environments and fast ligand exchange. With this toolbox, the standard characterisation of paramagnetic complexes and cages is now possible using NMR spectroscopic methods. </p> </div> <br>

A Paramagnetic NMR Spectroscopy Toolbox for the Characterisation of Paramagnetic/Spin-Crossover Coordination Complexes and Metal-Organic Cages

<div> <p>The large paramagnetic shifts and short relaxation times resulting from the presence of a paramagnetic centre complicate NMR data acquisition and interpretation in solution. In contrast to the large number of standard NMR methods for diamagnetic compounds, the number of paramagnetic NMR methods is limited and spectral assignment often relies on theoretical models. We report a toolbox of 1D (¹H, proton-coupled ¹³C, selective ¹H‑decoupling ¹³C, steady-state NOE) and 2D (COSY, NOESY, HMQC) paramagnetic NMR methods for the straightforward structural characterisation of paramagnetic complexes in solution and demonstrate its general applicability for fields from coordination chemistry to spin‑crossover complexes and supramolecular chemistry through the characterisation of Co^II and high-spin Fe^II mononuclear complexes as well as a Co₄L₆ cage. The toolbox takes advantage of the reduced signal overlap, decreased instrument time and greater sensitivity from the presence of the paramagnetic centre while overcoming the loss of structural information from the wide chemical shift dispersion and broad signals. In some circumstances, more structural information was revealed in the COSY spectra than would be observable for a diamagnetic analogue; as well as the expected through-bond cross-peaks, through-space and exchange cross-peaks were also observed for mononuclear complexes with multiple ligand environments and fast ligand exchange. With this toolbox, the standard characterisation of paramagnetic complexes and cages is now possible using NMR spectroscopic methods. </p> </div> <br>