An Effective Route to Dinuclear Niobium and Tantalum Imido Complexes

Gómez, Manuel; Hernández-Prieto, Cristina; Martı́n, Avelino; Mena, Miguel; Santamarı́a, Cristina

doi:10.1021/acs.inorgchem.7b01652

Cited by 10 publications

(4 citation statements)

References 46 publications

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“…Another strategy is to use inner-sphere reductants that are less prone to over-reduction. In this context, Tsurugi and Mashima have promoted the use of organosilicon reductants, such as 3,6-bis(trimethylsilyl)-1,4-cyclohexadiene 66–68 ( 7 ) and 1,4-bis(trimethylsilyl)-1,4-dihydropyrazine 69–71 derivatives (for example, 8 ), to reduce group 4 and group 5 metal halides (Fig. 2c) for homogeneous catalytic applications.…”

Section: Generation Of Low-valent Complexesmentioning

confidence: 99%

Modern applications of low-valent early transition metals in synthesis and catalysis

et al. 2018

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Low-valent early transition metals are often intrinsically highly reactive as a result of their strong propensity toward oxidation to more stable high-valent states. Harnessing these highly reducing complexes for productive reactivity is potentially powerful for C-C bond construction, organic reductions, small-molecule activation and many other reactions that offer orthogonal chemoselectivity and/or regioselectivity patterns to processes promoted by late transition metals. Recent years have seen many exciting new applications of low-valent metals through building new catalytic and/or multicomponent reaction manifolds out of classical reactivity patterns. In this Review, we survey new methods that employ early transition metals and invoke low-valent precursors or intermediates in order to identify common themes and strategies in synthesis and catalysis.

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Section: Generation Of Low-valent Complexesmentioning

confidence: 99%

Modern applications of low-valent early transition metals in synthesis and catalysis

et al. 2018

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“…Complexes 6 and 7 were obtained as a white crystalline powder and purified via recrystallization from a saturated toluene solution at −30 °C. The reaction between the imido group and water is well known in numerous studies. − Complexes 6 and 7 were characterized by 1 H NMR spectroscopy, EA, FT-IR, and single-crystal X-ray analysis (Tables S1 and S2 and Figures S13–S16 and ). The 1 H NMR spectrum of complex 6 showed only edpa ligand peaks at 0.90 (s, 9H, CC(C H 3 ) 3 ), 1.05 (t, 3H, OCH 2 C H 3 ), and 3.76 ppm (q, 2H, OC H 2 CH 3 ).…”

Section: Resultsmentioning

confidence: 99%

New Volatile Tantalum Imido Precursors with Carboxamide Ligands

et al. 2021

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A series of Ta(V) t Bu-imido/N-alkoxy carboxamide complexes, TaCl2(N t Bu)(pyridine)(edpa) (1), TaCl(N t Bu)(edpa)2 (2), Ta(N t Bu)(edpa)3 (3), TaCl2(N t Bu)(pyridine)(mdpa) (4), and Ta(N t Bu)(mdpa)3 (5), were successfully synthesized by metathesis reactions between Ta(N t Bu)Cl3(py)2 and several equivalents of Na(edpa) (edpaH = N-ethoxy-2,2-dimethylpropanamide) and Na(mdpa) (mdpaH = N-methoxy-2,2-dimethylpropanamide). Furthermore, complexes 3 and 5 were simply transformed to new dimeric structures [Ta(μ2–O)(edpa)3]2 (6) and [Ta(μ2–O)(mdpa)3]2 (7) with the elimination of the N t Bu imido group by air exposure. Compounds 1–7 were characterized by 1H and 13C nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, elemental analysis, thermogravimetric analysis (TGA), and single-crystal X-ray diffraction. Single-crystal X-ray diffraction analysis revealed that complexes 3 and 5 have a distorted pentagonal bipyramidal geometry around the central Ta atom, with three monoanionic bidentate N-alkoxy carboxamide ligands and one t Bu imido ligand saturating the coordination of tantalum ions. TGA revealed that complexes 3 and 5 had superior thermal characteristics and stability. These complexes could potentially be applied as precursors for tantalum oxide thin films.

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“…We then examined the reduction of some imido chloride complexes of group 5 and 6 metals, as low-valent early transition metal complexes bearing an imido ligand have attracted much interest because of their strong electron-donating nature . When ( t BuN)NbCl 3 (py) 2 was treated with 2c in toluene at room temperature, chloride-bridged dinuclear niobium(IV) complex 29 was obtained as a poorly soluble purple precipitate together with 1 equiv of ClSiMe 3 and 0.5 equiv of Me 4 pyrazine . On the other hand, the reaction with non-methylated reductant 2a afforded Nb(V) complex 30 with the formation of 1 equiv of ClSiMe 3 , as summarized in Scheme .…”

Section: Reduction Of Early Transition Metal Complexes With Electron-...mentioning

confidence: 99%

Salt-Free Reduction of Transition Metal Complexes by Bis(trimethylsilyl)cyclohexadiene, -dihydropyrazine, and -4,4′-bipyridinylidene Derivatives

Tsurugi

Mashima

2019

Acc. Chem. Res.

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Conspectus Chemical reduction of transition metals provides the corresponding low-valent transition metal species as a key step for generating catalytically active species in metal-assisted organic transformations and is a fundamental unit reaction for preparing organometallic complexes. A variety of metal-based reductants, such as metal powders and organometallic reagents of alkali and alkaline-earth metals, have been developed to date to access low-valent metal species. During the reduction, however, reductant-derived metal salts are formed as reaction waste, some of which often interact with the reactive low-valent metal center, thereby disrupting the catalytic performance and hampering the isolation of organometallic complexes as a result of salt coordination to the coordinatively unsaturated vacant and active sites and the formation of thermally unstable ate complexes. In this Account, we emphasize the synthetic utility and versatility of organic reductants containing two trimethylsilyl groups, i.e., 1,4-bis(trimethylsilyl)cyclohexa-2,5-diene (1a) and its methyl derivative (1b), 1,4-bis(trimethylsilyl)dihydropyrazine (2a) and its dimethyl (2b) and tetramethyl (2c) derivatives, and 1,1′-bis(trimethylsilyl)-4,4′-bipyridinylidene (3), leading to the reduction of various kinds of metal compounds in a salt-free fashion by release of two electrons together with the coproduction of easily removable (hetero)aromatics and trimethylsilyl derivatives from these organic reductants 1–3. When homoleptic chlorides of group 5 and 6 metals are treated with 1a and 1b, in situ-generated highly reactive low-valent metal species react with redox-active molecules such as ethylene, α-diimines, and α-diketones to produce metallacyclopentane, (ene–diamido)metal, and (ene–diolato)metal complexes, respectively. The advantage of the salt-free protocol is further exemplified in the low-valent titanocene-catalyzed Reformatsky-type reaction when 2c is used as a reductant: the yield of the product using the organosilicon reductant is higher than that when manganese powder is used as the reductant for the catalytic Reformatsky-type reaction of ethyl 2-bromoisobutyrate and its derivatives with various aldehydes. Moreover, when halides, carboxylates, and acetylacetonate compounds of late transition metals and main-group elements are treated with the organosilicon reductant 2c, metal(0) particles are smoothly precipitated under mild conditions. Among them, metallic nickel(0) nanoparticles are applicable to reductive biaryl formation and reductive cross-coupling of aryl halides/aryl aldehydes. In addition, reduction of the heterogeneous catalysts on a solid supporting matrix was also achieved by this salt-free reduction method; volatile byproducts are easily removed from the catalyst surface without suppressing the catalytic performance. Thus, the salt-free reduction strategy is a very powerful synthetic method that can be extended to various metals throughout the periodic table.

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An Effective Route to Dinuclear Niobium and Tantalum Imido Complexes

Cited by 10 publications

References 46 publications

Modern applications of low-valent early transition metals in synthesis and catalysis

Modern applications of low-valent early transition metals in synthesis and catalysis

New Volatile Tantalum Imido Precursors with Carboxamide Ligands

Salt-Free Reduction of Transition Metal Complexes by Bis(trimethylsilyl)cyclohexadiene, -dihydropyrazine, and -4,4′-bipyridinylidene Derivatives

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