Niob- und Tantal-Komplexe des N-metallierten Hexamethylimidophosphorsäuretriamids und des Tris-tert-butyliminophosphorans

Weber, Klaus; Korn, Klaus; Schulz, Michael; Korth, Karsten

doi:10.1002/(sici)1521-3749(199908)625:8<1315::aid-zaac1315>3.0.co;2-b

“…They differ from siloxides in their degree of zwitterionic character and the energy and radial extent of the donor atom (N 2p vs O 2p; Scheme A). In contrast to the few previous studies of imidophosphorane chemistry employing alkyl or aryl substituents, − dialkylamide substituents (piperidine in this case) amplify this zwitterionic character by stabilizing the P cationic character and terminal nitrogen N 2– character (Scheme A). Spectroscopic, reactivity, and theoretical studies of homoleptic trivalent and tetravalent complexes of cerium supported by the tris(piperidinyl)imidophosphorane ligand, [NP(pip) 3 ] − [pip = piperidinyl, a six-membered ring, N(C 5 H 10 )], indicate that covalent interactions between the metal and ligand govern the most significant stabilization of tetravalent cerium observed to date. , The binding of a potassium ion in the inner coordination sphere of the trivalent complex contributes significantly to the thermodynamic driving force for complex oxidation.…”

Section: Introductionmentioning

confidence: 72%

Homoleptic Imidophosphorane Stabilization of Tetravalent Cerium

Rice¹,

Su

²

,

Gompa³

et al. 2019

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The homoleptic complexes of cerium with the tris(piperidinyl)imidophosphorane ligand, [NP(pip)3]−, present the most negative Ce3+/4+ redox couple known (<−2.64 V vs Fc/Fc+). This dramatic stabilization of the cerium tetravalent oxidation state [>4.0 V shift from the Ce3+/4+ couple in 1 M HClO4(aq)] is established through reactivity studies. Spectroscopic studies (UV–vis, electron paramagnetic resonance, and Ce L3-edge X-ray absorption spectroscopy), in conjunction with density functional theory studies, reveal the dominant covalent metal–ligand interactions underlying the observed redox chemistry and the dependence of the redox potential on the binding of potassium in the inner coordination sphere.

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Niobium & Tantalum: Inorganic & Coordination Chemistry

Hubert‐Pfalzgraf¹

2005

Encyclopedia of Inorganic Chemistry

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The chemistry of niobium and tantalum ranges from oxidation states +V to −III with no species of oxidation state −II known so far. The chemistry of those oxophilic metals is dominated by their highest oxidation states, V and IV. Pentahalides especially chlorides are the most usual starting material. They form numerous complexes especially with hard donors and are used for access not only to pentavalent metal alkoxides, amides, thiolates, and so on but also to most molecular species in lower oxidation states. Oxo species are formed quite easily by O‐donor abstraction reactions or adventitious hydrolysis. Pentavalent alkoxides are active in various catalytic processes and are useful precursors for access to oxide ceramics such as ferroelectrics via the formation of heterometallic species. The most relevant results in organometallic chemistry of Nb and Ta have been obtained with ancillary, bulky aryloxide or siloxide ligands. Niobium is more prone to reduction than tantalum. Chalcogenides and chalcogenohalides are often one–dimensional solids and display a rich structural and synthetic chemistry. Numerous trispyrazolylborate derivatives of Nb and Ta have been reported for oxidation states V to I. The development of the nonaqueous chemistry of those elements in intermediate oxidation states has become an active and fruitful area. Species based on MM or MM multiple bonds, the latter especially for Nb, have been characterized. The NbNb triple bond (2.20 Å) is much shorter than the MM distance in the metal. Tri‐ or divalent species are able to promote CE (E = O, S, N) cleavage and thus to generate novel ligands because of the trend of Nb and Ta to form multiple ME bonds and attain their highest oxidation states. CC coupling reactions are observed with unsaturated ligands (alkynes, nitriles, etc.). M III η 2 ‐alkyne complexes have a metallocyclopropene character; they can react with unsaturated organic molecules via stoichiometric reactions. The reservoir of electrons of the MM bond is also of interest for activation of small molecules such as N 2 , H 2 , CO, and so on. Tri or tetradentate N,N; N,P; or N,O ligands have been used to stabilize dimeric dia or paramagnetic dinitrogen complexes. The bridging, highly activate N 2 ligand is amenable to functionalization in some cases, and cleavage into nitrides has been observed. The chemistry of reduced Nb and Ta halides is rich in clusters with nonintegral oxidation states (between III and I). Hexanuclear clusters dominate the aqueous chemistry for these oxidation states. One of their potential applications could be their use as contrasting agents. The species in the lowest oxidation states are essentially based on carbonyl ligands.

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Niobium & Tantalum: Inorganic & Coordination Chemistry

Hubert‐Pfalzgraf

¹

2005

Encyclopedia of Inorganic and Bioinorganic Chemistry

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The chemistry of niobium and tantalum ranges from oxidation states +V to −III with no species of oxidation state −II known so far. The chemistry of those oxophilic metals is dominated by their highest oxidation states, V and IV. Pentahalides especially chlorides are the most usual starting material. They form numerous complexes especially with hard donors and are used for access not only to pentavalent metal alkoxides, amides, thiolates, and so on but also to most molecular species in lower oxidation states. Oxo species are formed quite easily by O‐donor abstraction reactions or adventitious hydrolysis. Pentavalent alkoxides are active in various catalytic processes and are useful precursors for access to oxide ceramics such as ferroelectrics via the formation of heterometallic species. The most relevant results in organometallic chemistry of Nb and Ta have been obtained with ancillary, bulky aryloxide or siloxide ligands. Niobium is more prone to reduction than tantalum. Chalcogenides and chalcogenohalides are often one–dimensional solids and display a rich structural and synthetic chemistry. Numerous trispyrazolylborate derivatives of Nb and Ta have been reported for oxidation states V to I. The development of the nonaqueous chemistry of those elements in intermediate oxidation states has become an active and fruitful area. Species based on MM or MM multiple bonds, the latter especially for Nb, have been characterized. The NbNb triple bond (2.20 Å) is much shorter than the MM distance in the metal. Tri‐ or divalent species are able to promote CE (E = O, S, N) cleavage and thus to generate novel ligands because of the trend of Nb and Ta to form multiple ME bonds and attain their highest oxidation states. CC coupling reactions are observed with unsaturated ligands (alkynes, nitriles, etc.). M III η 2 ‐alkyne complexes have a metallocyclopropene character; they can react with unsaturated organic molecules via stoichiometric reactions. The reservoir of electrons of the MM bond is also of interest for activation of small molecules such as N 2 , H 2 , CO, and so on. Tri or tetradentate N,N; N,P; or N,O ligands have been used to stabilize dimeric dia or paramagnetic dinitrogen complexes. The bridging, highly activate N 2 ligand is amenable to functionalization in some cases, and cleavage into nitrides has been observed. The chemistry of reduced Nb and Ta halides is rich in clusters with nonintegral oxidation states (between III and I). Hexanuclear clusters dominate the aqueous chemistry for these oxidation states. One of their potential applications could be their use as contrasting agents. The species in the lowest oxidation states are essentially based on carbonyl ligands.

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Niob- und Tantal-Komplexe des N-metallierten Hexamethylimidophosphorsäuretriamids und des Tris-tert-butyliminophosphorans

Cited by 8 publications

References 11 publications

Homoleptic Imidophosphorane Stabilization of Tetravalent Cerium

Homoleptic Imidophosphorane Stabilization of Tetravalent Cerium

Niobium & Tantalum: Inorganic & Coordination Chemistry

Niobium & Tantalum: Inorganic & Coordination Chemistry

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