2,5‐Norbornadiene C–C Coupling Reactions Mediated by Iridium Complexes

Betoré, M. Pilar; Garcı́a-Orduña, Pilar; Lahoz, Fernando J.; Polo, Víctor; Oro, Luis A.

doi:10.1002/ejic.201600336

Cited by 4 publications

(5 citation statements)

References 77 publications

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“…The resonance is much less shielded in this iridium(III) complex than when ammonia is bound to other iridium centers. 12 In complex 4, the NH 2 protons of the aniline ligand appear as two distinct AB doublets at 7.39 and 7.27 ppm ( 2 J HH = 10 Hz), a direct consequence of the chirality at iridium. In the 13 C{ 1 H} NMR spectra, the iridium-bound C trz nucleus appears at d C = 153.5 for complex 3 and 155.9 ppm for 4, well within the range of triazolylidene resonances of similar compounds.…”

Section: Resultsmentioning

confidence: 99%

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Unveiling the role of ancillary ligands in acceptorless benzyl alcohol dehydrogenation and etherification mediated by mesoionic carbene iridium complexes

et al. 2018

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We synthesized a set of triazolylidene iridium(iii) complexes [IrCp*(C^N)L] (Cp* = pentamethylcyclopentadienyl, C^N = C,N-bidentate coordinating pyridyl-triazolylidene) containing different neutral or anionic ancillary ligands L and evaluated their impact on the catalytic activity in alcohol conversion. We demonstrate that these ancillary ligands have a strong influence on the catalytic selectivity and direct whether the iridium center preferentially catalyzes either the dehydrogenation or the dehydration of benzyl alcohol. Ligand exchange experiments provide a direct correlation of ligand lability with catalytic activity and selectivity. These results underline the relevance of ancillary ligands and provide a rational approach to tailor the catalytic activity of the iridium center towards aldehyde formation (loss of H) or etherification (elimination of HO).

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Section: Resultsmentioning

confidence: 99%

“…As discussed above, this ratio erodes with increasing reaction time and converges to about 2 at higher conversions. The aniline complex 4 does not show any change of ratio throughout the reaction and forms the ether and the aldehyde in equal amounts (entries [10][11][12].…”

Section: Catalytic Acceptorless Oxidation and Ether Formation Iridiumentioning

confidence: 99%

Unveiling the role of ancillary ligands in acceptorless benzyl alcohol dehydrogenation and etherification mediated by mesoionic carbene iridium complexes

et al. 2018

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“…In there, the iridacycle is also nonplanar, being folded with one carbon atom displaced 0.24 Å out of the plane of the ring atoms. Recently, Oro and co-workers also synthesized iridium complexes containing this structural motif . All are octahedral iridium complexes with five-membered, nonplanar iridacycles.…”

Section: Resultsmentioning

confidence: 99%

Low-Valence Anionic α-Diimine Iron Complexes: Synthesis, Characterization, and Catalytic Hydroboration Studies

et al. 2020

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The synthesis of rare anionic heteroleptic and homoleptic α-diimine iron complexes is described. Heteroleptic BIAN (bis(aryl)iminoacenaphthene) complexes 1-[K([18]c-6)-(thf) 0.5 ] and 2-[K([18]c-6)(thf) 2 ] were synthesized by reduction of the [(BIAN)FeBr 2 ] precursor complex using stoichiometric amounts of potassium graphite in the presence of the corresponding olefin. The electronic structure of these paramagnetic species was investigated by numerous spectroscopic analyses (NMR, EPR, 57 Fe Mossbauer, UV−vis), magnetic measurements (Evans NMR method, SQUID), and theoretical techniques (DFT, CASSCF). Whereas anion 1 is a low-spin complex, anion 2 consists of an intermediate-spin Fe(III) center. Both complexes are efficient precatalysts for the hydroboration of carbonyl compounds under mild reaction conditions. The reaction of bis(anthracene) ferrate(1−) gave the homoleptic BIAN complex 3-[K([18]c-6)(thf)], which is less catalytically active. The electronic structure was elucidated with the same techniques as described for complexes 1-[K([18]c-6)(thf) 0.5 ] and 2-[K([18]c-6)(thf) 2 ] and revealed an Fe(II) species in a quartet ground state.

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“…One illustrative example is the reaction between [Ir(cod)Cl] 2 and 2 equiv of norbornadiene to yield an Ir(III) metallacyclopentane. 36 The ( i-Pr NDI)Ni 2 (C 6 H 6 ) complex (1) undergoes a stoichiometric reaction with norbornadiene to generate oxidative addition product 12 (Figure 3C). 2 The intermediate diene adduct is not detectable even at partial conversions, indicating that the ligand substitution step is slower than C−C activation.…”

Section: Dinuclear Oxidative Additionmentioning

confidence: 99%

“…Second, the alkenes of norbornadiene are sufficiently activated by ring strain such that addition or coupling reactions of the π bonds occur in preference to cleavage of the σ bonds. One illustrative example is the reaction between [Ir(cod)Cl] 2 and 2 equiv of norbornadiene to yield an Ir(III) metallacyclopentane …”

Section: Stoichiometric Reactivity and Catalysismentioning

confidence: 99%

Dinickel Active Sites Supported by Redox-Active Ligands

Uyeda

Farley

2021

Acc. Chem. Res.

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Conspectus Redox reactions that take place in enzymes and on the surfaces of heterogeneous catalysts often require active sites that contain multiple metals. By contrast, there are very few homogeneous catalysts with multinuclear active sites, and the field of organometallic chemistry continues to be dominated by the study of single metal systems. Multinuclear catalysts have the potential to display unique properties owing to their ability to cooperatively engage substrates. Furthermore, direct metal-to-metal covalent bonding can give rise to new electronic configurations that dramatically impact substrate binding and reactivity. In order to effectively capitalize on these features, it is necessary to consider strategies to avoid the dissociation of fragile metal–metal bonds in the course of a catalytic cycle. This Account describes one approach to accomplishing this goal using binucleating redox-active ligands. In 2006, Chirik showed that pyridine–diimines (PDI) have sufficiently low-lying π* levels that they can be redox-noninnocent in low-valent iron complexes. Extending this concept, we investigated a series of dinickel complexes supported by naphthyridine–diimine (NDI) ligands. These complexes can promote a broad range of two-electron redox processes in which the NDI ligand manages electron equivalents while the metals remain in a Ni(I)–Ni(I) state. Using (NDI)Ni2 catalysts, we have uncovered cases where having two metals in the active site addresses a problem in catalysis that had not been adequately solved using single-metal systems. For example, mononickel complexes are capable of stoichiometrically dimerizing aryl azides to form azoarenes but do not turn over due to strong product inhibition. By contrast, dinickel complexes are effective catalysts for this reaction and avoid this thermodynamic sink by binding to azoarenes in their higher-energy cis form. Dinickel complexes can also activate strong bonds through the cooperative action of both metals. Norbornadiene has a ring-strain energy that is similar to that of cyclopropane but is not prone to undergoing C–C oxidative addition with monometallic complexes. Using an (NDI)Ni2 complex, norbornadiene undergoes rapid ring opening by the oxidative addition of the vinyl and bridgehead carbons. An inspection of the resulting metallacycle reveals that it is stabilized through a network of secondary Ni−π interactions. This reactivity enabled the development of a catalytic carbonylative rearrangement to form fused bicyclic dienones. These vignettes and others described in this Account highlight some of the implications of metal–metal bonding in promoting a challenging step in a catalytic cycle or adjusting the thermodynamic landscape of key intermediates. Given that our studies have focused nearly exclusively on the (NDI)Ni2 system, we anticipate that many more such cases are left to be discovered as other transition-metal combinations and ligand classes are explored.

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2,5‐Norbornadiene C–C Coupling Reactions Mediated by Iridium Complexes

Cited by 4 publications

References 77 publications

Unveiling the role of ancillary ligands in acceptorless benzyl alcohol dehydrogenation and etherification mediated by mesoionic carbene iridium complexes

Unveiling the role of ancillary ligands in acceptorless benzyl alcohol dehydrogenation and etherification mediated by mesoionic carbene iridium complexes

Low-Valence Anionic α-Diimine Iron Complexes: Synthesis, Characterization, and Catalytic Hydroboration Studies

Dinickel Active Sites Supported by Redox-Active Ligands

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