Oxo/imido heterometathesis: From molecular stoichiometric studies to well-defined heterogeneous catalysts

Zhizhko, Pavel A.; Bushkov, Nikolai S.; Pichugov, Andrey V.

doi:10.1016/j.ccr.2021.214112

Cited by 9 publications

(33 citation statements)

References 273 publications

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“…The most important region of the spectrum is the area of the quaternary NCMe 3 resonance (40-80 ppm) as this signal is strongly sensitive to the state of N t Bu group. [1,11] It is well-known that for Ti complexes containing =N t Bu, À NH t Bu and NH 2 t Bu ligands, this resonance usually appears at ca. 70, 60 and 50 ppm respectively (see references given in Ref.…”

Section: Synthesis and Grafting Of Imido Bis-aryloxide Ti(=n T Bu)(oa...mentioning

confidence: 99%

“…The product of sufficient purity can be also obtained as a yellow-orange powder through precipitation from the concentrated toluene solution with pentane and subsequent washing with pentane. 1…”

Section: Generalmentioning

confidence: 99%

“…XRD suitable orange crystals were obtained from a saturated heptane solution at À 15 °C (note however that the solubility of the pure complex in aliphatic solvents is relatively low). 1…”

Section: Ti(=n T Bu)(oar Tbu )(Me 2 Pyr)(py) (3)mentioning

confidence: 99%

“…Oxo/imido heterometathesis [1] is a family of reactions mechanistically related to olefin metathesis. It is mediated by transition metal oxo or imido complexes interconverting through a sequence of [2 + 2] cycloaddition and cycloreversion steps providing catalytic imido-deoxygenation of various oxo substrates (such as aldehydes, ketones, carboxylic acid derivatives, isocyanates, etc.)…”

Section: Introductionmentioning

confidence: 99%

“…It has been welldocumented that the most reactive with respect to oxo/imido exchange M=NR moieties are formed by the transition metals in the left part of the d-block (in particular for group 4). [1][2][3][4][5][6][7][8][9] However the successful application of these highly reactive species as oxo/ imido heterometathesis catalysts only became possible with the development of well-defined silica-supported Ti imido complexes [10,11] prepared through Surface Organometallic Chemistry (SOMC), [12][13][14][15][16][17][18] such as Ti imido pyrrolyl complex 1/SiO 2 (Scheme 1,b) that is currently the most active catalyst for such reactions. [1,10,11,19,20] The efficiency of the supported systems is associated with the stabilization of Ti=O intermediates of the catalytic cycle (that readily dimerize in solution) through a covalent attachment to the surface of the support, thus preventing their bimolecular transformations.…”

Section: Introductionmentioning

confidence: 99%

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Design of 4‐Coordinate Ti Imido Aryloxide on the Surface of Silica for Catalytic Oxo/Imido Heterometathesis

Pichugov

Bushkov

Rumyantsev

et al. 2022

Helvetica Chimica Acta

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We report here the synthesis of 4‐coordinate Ti imido complexes Ti(=NtBu)(OArtBu)2(py) (2) and Ti(=NtBu)(OArtBu)(Me2Pyr)(py) (3) (ArtBu=O‐2,6‐tBu2‐4‐MeC6H2, Me2Pyr=2,5‐dimethylpyrrolyl) and study their grafting onto the surface of partially dehydroxylated silica with the aim to prepare 4‐coordinate Ti imido aryloxide surface species. Study of the resulting materials with IR, solid‐state NMR, elemental and mass balance analyses demonstrates that grafting of bis‐aryloxide complex 2 leads to a predominant formation of silica‐supported Ti amide (≡SiO)Ti(NHtBu)(OArtBu)2(py) resulting from the protonation of the imido ligand with the surface silanols and only a smaller fraction of the desired imido species (≡SiO)Ti(=NtBu)(OArtBu)(py). The use of the tailored complex 3 where one of the aryloxides is replaced with a more reactive pyrrolyl ligand significantly increases the selectivity of grafting leading to the formation of the Ti imido aryloxide (≡SiO)Ti(=NtBu)(OArtBu)(py) as major surface species. The obtained materials show high activity in catalytic oxo/imido heterometathesis supporting the previously proposed hypothesis that electron‐donating environments are favorable for this transformation.

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Section: Synthesis and Grafting Of Imido Bis-aryloxide Ti(=n T Bu)(oa...mentioning

confidence: 99%

Section: Generalmentioning

confidence: 99%

“…XRD suitable orange crystals were obtained from a saturated heptane solution at À 15 °C (note however that the solubility of the pure complex in aliphatic solvents is relatively low). 1…”

Section: Ti(=n T Bu)(oar Tbu )(Me 2 Pyr)(py) (3)mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Design of 4‐Coordinate Ti Imido Aryloxide on the Surface of Silica for Catalytic Oxo/Imido Heterometathesis

Pichugov

Bushkov

Rumyantsev

et al. 2022

Helvetica Chimica Acta

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The Role of L‐Ligands in Silica‐Supported Ti Oxo/Imido Heterometathesis Catalysts

Bushkov,

Rumyantsev,

Pichugov

et al. 2024

Applied Organom Chemis

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We report here the preparation and characterization of new well‐defined silica‐supported Ti imido complexes that present an L‐ligand variation in a structure of currently the most active oxo/imido heterometathesis catalyst (≡SiO)Ti(=NtBu)(Me2Pyr)(py)2 (1s), where py is replaced with stronger electron‐donating 4‐(N,N‐dimethylamino)pyridine (2s) or bidentate 2,2′‐bipyridine (3s). The materials were characterized with elemental and mass balance analyses and IR and solid‐state NMR that confirmed the selective formation of surface Ti species with terminal imido ligand. Evaluation of the catalytic oxo/imido heterometathesis activity of the obtained materials demonstrated that L‐ligands have a pronounced influence on the catalytic performance. In particular, the replacement of pyridine with stronger donating ligands resulted in a significant drop of activity. The catalytic results are discussed in view of the reaction mechanism and implications for further catalyst development.

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Tungsten Oxide Dispersed on Silica as Robust and Readily Available Oxo/Imido Heterometathesis Catalyst

Bushkov,

Rumyantsev,

Zhizhin

et al. 2024

ChemPlusChem

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Continuing our investigation of catalytic oxo/imido heterometathesis as novel water‐free method for C=N bond construction, we report here the application of classical transition metal oxides dispersed on silica (MOx/SiO2, M = V, Mo, W) as cheap, robust and readily available alternative to the catalysts prepared via Surface Organometallic Chemistry (SOMC). The oxide materials demonstrated activity in heterometathetical imidation of ketones, WO3/SiO2 being the most efficient. We also describe a new well‐defined supported W imido complex (≡SiO)W(=NMes)2(Me2Pyr) (Mes = 2,4,6‐Me3C6H2, Me2Pyr = 2,5‐dimethylpyrrolyl) and characterize it with SOMC protocols, which allowed us to identify the position of W on the oxo/imido heterometathesis activity scale (Mo < W < Ta) and showed that W in fact provides an optimal balance between activity and stability. Noteworthy, the performance of WO3/SiO2 was only slightly inferior to that of the SOMC analog enabling the efficient synthesis of a broad range of ketimines hardly accessible by classical methods, in most cases W being a competitive and robust alternative to the most active albeit highly sensitive Ti imido systems. Combined with the availability of the catalyst, this facilitates a more widespread application of heterometathesis methodology in organic synthesis including potential larger scale applications.

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Oxo/imido heterometathesis: From molecular stoichiometric studies to well-defined heterogeneous catalysts

Cited by 9 publications

References 273 publications

Design of 4‐Coordinate Ti Imido Aryloxide on the Surface of Silica for Catalytic Oxo/Imido Heterometathesis

Design of 4‐Coordinate Ti Imido Aryloxide on the Surface of Silica for Catalytic Oxo/Imido Heterometathesis

The Role of L‐Ligands in Silica‐Supported Ti Oxo/Imido Heterometathesis Catalysts

Tungsten Oxide Dispersed on Silica as Robust and Readily Available Oxo/Imido Heterometathesis Catalyst

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