19559-06-9Relevant academic research and scientific papers
Non-Oxido-Vanadium(IV) Metalloradical Complexes with Bidentate 1,2-Dithienylethene Ligands: Observation of Reversible Cyclization of the Ligand Scaffold in Solution
Fugel, Malte,Grabowsky, Simon,Harmer, Jeffrey R.,Kleemiss, Florian,Lork, Enno,Schlüter, Dirk,Sugimoto, Kunihisa,Vogt, Matthias
, p. 1335 - 1343 (2020/02/04)
Derivatives of 1,2-dithienylethene (DTE) have superb photochromic properties due to an efficient reversible photocyclization reaction of their hexatriene structure and, thus, have application potential in materials for optoelectronics and (multi-responsive) molecular switches. Transition-metal complexes bearing switchable DTE motifs commonly incorporate their coordination site rather distant from the hexatriene system. In this work the redox active ligand 1,2-bis(2,5-dimethylthiophen-3-yl)ethane-1,2-dione is described, which reacts with [V(TMEDA)2Cl2] to give a rare non-oxido vanadium(IV) species 3(M,M/P,P). This blue complex has two bidentate en-diolato ligands which chelate the VIV center and give rise to two five-membered metallacycles with the adjacent hexatriene DTE backbone bearing axial chirality. Upon irradiation with UVA light or prolonged heating in solution, the blue compound 3(M,M/P,P) converts into the purple atropisomer 4(para,M/para,P). Both complexes were isolated and structurally characterized by single-crystal X-ray diffraction analysis (using lab source and synchrotron radiation). The antiparallel configuration (M or P helicity) present in both 3(M,M/P,P) and 4(para,M/para,P) is a prerequisite for (reversible) 6π cyclization reactions. A CW EPR spectroscopic study reveals the metalloradical character for 3(M,M/P,P) and 4(para,M/para,P) and indicates dynamic reversible cyclization of the DTE backbone in complex 3(M,M/P,P) at ambient temperature in solution.
Investigations of the Magnetic and Spectroscopic Properties of V(III) and V(IV) Complexes
Van Stappen, Casey,Maganas, Dimitrios,Debeer, Serena,Bill, Eckhard,Neese, Frank
supporting information, p. 6421 - 6438 (2018/06/14)
Herein, we utilize a variety of physical methods including magnetometry (SQUID), electron paramagnetic resonance (EPR), and magnetic circular dichroism (MCD), in conjunction with high-level ab initio theory to probe both the ground and ligand-field excited electronic states of a series of V(IV) (S = 1/2) and V(III) (S = 1) molecular complexes. The ligand fields of the central metal ions are analyzed with the aid of ab initio ligand-field theory (AILFT), which allows for a chemically meaningful interpretation of multireference electronic structure calculations at the level of the complete-active-space self-consistent field with second-order N-electron valence perturbation theory. Our calculations are in good agreement with all experimentally investigated observables (magnetic properties, EPR, and MCD), making our extracted ligand-field theory parameters realistic. The ligand fields predicted by AILFT are further analyzed with conventional angular overlap parametrization, allowing the ligand field to be decomposed into individual σ- and π-donor contributions from individual ligands. The results demonstrate in VO2+ complexes that while the axial vanadium-oxo interaction dominates both the ground- and excited-state properties of vanadyl complexes, proximal coordination can significantly modulate the vanadyl bond covalency. Similarly, the electronic properties of V(III) complexes are particularly sensitive to the available σ and π interactions with the surrounding ligands. The results of this study demonstrate the power of AILFT-based analysis and provide the groundwork for the future analysis of vanadium centers in homogeneous and heterogeneous catalysts.
Reductive transformation of V(iii) precursors into vanadium(ii) oxide nanowires
Ojelere, Olusola,Graf, David,Ludwig, Tim,Vogt, Nicholas,Klein, Axel,Mathur, Sanjay
, p. 6842 - 6849 (2018/06/01)
Vanadium(ii) oxide nanostructures are promising materials for supercapacitors and electrocatalysis because of their excellent electrochemical properties and high surface area. In this study, new homoleptic vanadium(iii) complexes with bi-dentate O,N-chelating heteroarylalkenol ligands (DmoxCHCOCF3, PyCHCOCF3 and PyNCOCF3) were synthesized and successfully transformed by reductive conversion into VO nanowires. The chemical identity of V(iii) complexes and their redox behaviour were unambiguously established by single crystal X-ray diffraction studies, cyclic voltammetry, spectrometric studies and DFT calculations. Transformation into the metastable VO phase was verified by powder X-ray diffraction and thermo-gravimetry. Transmission electron microscopy and X-ray photoelectron spectroscopy data confirmed the morphology and chemical composition of VO nanostructures, respectively.
Novel vanadium complexes supported by a bulky tris(pyrazolyl)borate ligand
Petrov, Pavel A.,Smolentsev, Anton I.,Bogomyakov, Artem S.,Konchenko, Sergey N.
, p. 60 - 64 (2017/04/10)
The V(III) complex [V(TptBu2)Cl2] (1, TptBu2?=?hydrotris(3,5-di-tert-butylpyrazolyl)borate) was synthesized by the reaction of [VCl3(THF)3] (prepared in situ) and K(TptBu2). Reduction of 1 with potassium mirror afforded the V(II) complex [V(TptBu2)Cl] (2). Both complexes were characterized by means of a single crystal X-ray diffraction. 1 represents the first example of pentacoordinated vanadium tris(pyrazolyl)borate (Tp) complexes. The V(III) ion environment is a distorted trigonal bipyramid. 2 is the first V(II) Tp-complex. The V(II) ion has tetrahedral environment, and the Cl atom is deviated from the B–V axis (∠B(1)–V(1)–Cl(1)?=?157.8°). Magnetic susceptibility measurements showed reasonable μeff values at 300?K: 2.80 (1) and 3.78 (2) μB, those prove the oxidation states of V: +3 (1) and +2 (2).
A Carbene Catalysis Strategy for the Synthesis of Protoilludane Natural Products
Hovey, M. Todd,Cohen, Daniel T.,Walden, Daniel M.,Cheong, Paul H.-Y.,Scheidt, Karl A.
supporting information, p. 9864 - 9867 (2017/08/08)
The Armillaria and Lactarius genera of fungi produce the antimicrobial and cytotoxic mellolide, protoilludane, and marasmane sesquiterpenoids. We report a unified synthetic strategy to access the protoilludane, mellolide, and marasmane families of natural products. The key features of these syntheses are 1) the organocatalytic, enantioselective construction of key chiral intermediates from a simple achiral precursor, 2) the utility of a key 1,2-cyclobutanediol intermediate to serve as a precursor to each natural product class, and 3) a direct chemical conversion of a protoilludane to a marasmane through serendipitous ring contraction, which provides experimental support for their proposed biosynthetic relationships.
Neutral and cationic vanadium (III) Alkyl and allyl complexes with a cyclopentadienyl-amine ancillary ligand
Liu, Guohua,Beetstra, Dirk J.,Meetsma, Auke,Hessen, Bart
, p. 3914 - 3920 (2008/10/09)
The (N,N-dimethylaminoethyl)cyclopentadienyl vanadium(III) complex [η5,η1-C5H4(CH 2)2-NMe2]VCl2(PMe3) (1), in which the pendant amine is coordinated to the metal center, was prepared by the reaction of VCl3(PMe3)2 with Li[C 5H4(CH2)2NMe2] in THF. Reaction of 1 with 2 equiv of MeLi yields [η5-C5H 4(CH2)2NMe2]VMe2(PMe 3)2 (2), in which the amine is released in favor of the binding of a second phosphine. Compound 2 reacts with [PhNMe2H]- [BPh4] to form the ionic complex {[η5, η2-C5H4(CH2)2N(Me) CH2]V(PMe3)2}[BPh4] (3), in which a methyl group of the pendant NMe2 functionality is metalated, and 2 equiv of methane. Reaction of 1 with allylmagnesium chloride yields [η5-C5H4(CH2) 2NMe2]V(η3-C3H 5)Cl(PMe3) (4), in which the amine is released in favor of the η3-bonding of the allyl ligand. Methylation of 4 to yield thermally labile [η5-C5H4(CH 2)2NMe2]V(η3-C3H 5)Me(PMe3) (5), followed by reaction with [PhNMe 2H][BPh4], gives protonation exclusively at the methyl group to yield the ionic allyl complex {[η5,η1- C5H4(CH2)2NMe2] V(η3-C3H5)(PMe3)}[BPh 4] (6) without concomitant NMe2 maetalation.
Structural studies of complexes of vanadium(III) and titanium(IV) with N,N-dimethylaminoniethylferrocenyl
Hitchcock, Peter B.,Hughes, David L.,Leigh, G. Jeffery,Sanders, J. Roger,De Souza, Jaisa S.
, p. 1161 - 1173 (2007/10/03)
Vanadium(III) and titanium(IV) complexes containing 12-16 valence-shell electrons have been synthesised by treatment of cyclopentadienylmetal halides with the lithium salt of N,N-dimethylaminomethylferrocene, Li(FcN). The structurally characterized products were [(η5-C5H5)2Ti(η 1-FcN)Cl] 1, [(η5-C5H5)Ti(FcN)xCl3 -x)] (x = 1, complex 2; x = 2, complex 3; and x = 3, complex 4) and [V(FcN)2Cl] 6. They contain FcN bound either monodentate, through the aromatic 2-carbon atom, or bidentate, through that carbon and the amine nitrogen. Despite employing a variety of spectroscopic techniques, we were unable to distinguish the mode of binding in any way other than a crystal structure analysis. Compound 4 changes spontaneously at room temperature into the structurally characterised [(η5-C5H5)Ti(FcN)(FcN′)] 5. The ligand FcN′ arises by metallation of one methyl group of one FcN in 4 with elimination of H(FcN). This kind of metallation has not been recognised hitherto in titanium or vanadium FcN chemistry, and it may explain why yields of required products are sometimes very low. The synthetic and structural versatility of the ligand FcN have been clearly demonstrated.
Preparation of New Vanadium(II) Iodides and Crystal Structure of Hexakis(acetonitrile)vanadium(II) (Tetraiodide)
Hitchcock, Peter B.,Hughes, David L.,Leigh, G. Jeffery,Sanders, J. Roger,Souza, Jaisa de,et al.
, p. 3683 - 3688 (2007/10/02)
The reaction of with SiMe3I in acetonitrile under reflux yielded a vanadium(II) cation (2+) with a counter ion I4(2-).The latter is not symmetrical, though linear, and the reasons are discussed.The new compound diiodotetrakis(tetrahydrofuran)vanadium(II) is shown to be a versatile precursor for vanadium diiodides, such as , the structure of which has also been determined.
Chemistry of carbon monoxide free cyclopentadienylvanadium(I) alkene and alkyne complexes
Hessen, Bart,Meetsma, Auke,Van Bolhuis, Fré,Teuben, Jan H.,Helgesson, G?ran,Jagner, Susan
, p. 1925 - 1936 (2008/10/08)
The compounds CpV(L)(PMe3)2 (L = η2-ethene (2), η2-alkyne) form a new class of highly reactive CO-free LpVI complexes. Paramagnetic 2 was prepared from CpVCl(PMe3)2 and 0.5 mol of BrMg(CH2)4MgBr. An X-ray structure determination shows a relatively short ethene C=C distance of 1.365 (5) A?. The η2-alkyne complexes are readily available by Mg reduction of CpVCl2(PMe3)2 in the presence of the alkyne. The X-ray structure of CpV(η2-PhC=CPh)(PMe3)2 (4) shows the alkyne ligand to be asymmetrically oriented relative to the other ligands in the complex. The ethene ligand in 2 is readily replaced by CO or PhC≡CPh. 2,2′-Bipyndine displaces a phosphine as well to produce the paramagnetic CpV(η2-bpy)PMe3 (5). C,C coupling is observed in the reaction of 2 with CO2 to form the vanadalactone CpV[CH2CH2C(O)O]PMe3 (6). PhSSPh oxidatively adds to 2 to form [CpV(μ-SPh)2]2. 1-Hexene is slowly catalytically dimerized by 2. The alkyne complex 4 reacts with various hydrocarbon substrates through initial phosphine loss and subsequent C,C coupling. With 1,3-butadiene the hexadienediyl complex CpV(η1,η3-C2Ph2C 4H6)PMe3 (9) is formed. With ethene 2:1 cotrimerization with the alkyne ligand occurs to produce an η4-diphenylhexadiene complex, CpV[η4-CH2=CHC(Ph)=C(Ph)Et]PMe3 (10), which was characterized by X-ray diffraction. With 2-butyne, 4 reacts to give CpV(η2-MeC≡CMe)(η2-PhC≡CPh)PMe 3 (13), which subsequently forms the metallacycle CpV(C4Me2Ph2)PMe3 (14). An X-ray structure determination shows 14 to have a bent metallacyclopenta-1,3 5-triene structure (formally an V(V) dicarbene) with V=C bond distances of 1.891 (3) and 1.893 (3) A?. Analogous bicyclic products are formed through reduction of CpVCl2(PMe3)2 in the presence of diynes. A summary of the crystal data is as follows: for 2, Pbca, a = 12.351 (3) A?, b = 15.526 (4) A?, c = 16.948 (3) A? (130 K), Z = 8; for 4, P21/n, a = 8.249 (2) A?, b = 17.619 (2) A?, c = 16.278 (2) A?, β = 100.61 (2)° (130 K), Z = 4; for 10, P1, a = 8.875 (3) A?, b = 9.589 (2) A?, c = 15.081 (6) A?, α = 90.95 (3)° β = 91.54 (3)°, γ = 117.44 (2)° (130 K), Z = 2; for 14, P212121, a = 12.957 (3) A?, b = 19.205 (5) A?, c = 9.155 (2) A? (170 K), Z = 4.
Bimetallic halides. Crystal structure of and ethylene polymerization by VCl2·ZnCl2·4THF
Smith, Paul D.,Martin, Joel L.,Huffman, John C.,Bansemer, Rick L.,Caulton, Kenneth G.
, p. 2997 - 3002 (2008/10/08)
The title compound is prepared either by the zinc reduction of VCl4(THF)2 in refluxing THF or by the reaction of [V2(μ-Cl)3-(THF)6]2Zn 2Cl6 with ZnCl2(THF)2 in THF at 90°C. The crystal structure indicates discrete molecules of (THF)4V(μ-Cl)2ZnCl2. The six-coordinate environment of vanadium approximates octahedral geometry whereas the four-coordinate zinc geometry is virtually tetrahedral. The octahedron and tetrahedron are linked by two chloride bridges. Crystals belong to the monoclinic space group P21/c with cell dimensions (-158°C) a = 14.732 (5) A?, b = 9.680 (3) A?, c = 16.207 (6) A?, and β = 94.12 (2)° and Z = 4. High catalytic activity was found for ethylene polymerization by the title compound as well as for several other related V/Zn/Cl/THF compounds whose structures have been established. Catalyst activity is greatly enhanced by added halocarbons. Activity of V(II) compounds equals or exceeds that of V(III) compounds, which tends to deny a previous suggestion that the halocarbon functions to keep vanadium in oxidation state +3. Moreover, the V(II) compounds fail to be oxidized to V(III) even by neat CH2Cl2.
