Synthesis, Molecular Structure, and Reactivity of a Half-Sandwich Vanadium(III) Imido Complex: The First Vanadium(V) Alkylidene

Buijink, Jan-Karel F.; Teuben, Jan H.; Kooijman, Huub; Spek, Anthony L.

doi:10.1021/om00020a003

Cited by 102 publications

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“…In the reaction of 2 with I 2 , we also detect, by 11 B NMR spectroscopy, the formation of BPh 3 as a side product. This observation suggests that I 2 might be also oxidizing the BÀC(phenyl) bond of the BPh 4 À counter anion to afford 4. Magnetic susceptibility measurements (Evans, m eff = 1.94 m B ), single-crystal X-ray diffraction study, and solution EPR (g iso = 1.976, A iso = 64 10 À4 cm À1 , 51 V, I = 7/2, 99.6 %, Figure 2) spectra are consistent with the d 1 vanadium(iv) complex 4 containing a terminal alkylidene functionality.…”

Section: )]mentioning

confidence: 99%

“…[4] Since there are only a handful of vanadium-alkylidene complexes known, [3][4][5][6] we report the synthesis of the first cationic and neutral four-coordinate vanadium(iv)-neopentylidene complexes [(Nacnac)V=CH-tBu(thf)](BPh 4 ) and [(Nacnac)V = CHtBu(I)] (Nacnac À = [Ar]NC(Me)CHC(Me)N[Ar], Ar = 2,6-(CHMe 2 ) 2 C 6 H 3 ), and subsequent thermolysis of each system. These d 1 paramagnetic species reported herein are kinetically stable, and contain the shortest V=C bonds reported so far.…”

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Cationic and Neutral Four‐Coordinate Alkylidene Complexes of Vanadium(IV) Containing Short VC Bonds

Basuli

Kilgore

et al. 2004

Angew Chem Int Ed

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High-oxidation state transition-metal alkylidenes have received considerable attention in the past few years since these systems are capable of catalyzing important processes such as olefin metathesis, alkyne polymerization, and Wittigtype reactions. [1,2] Although transition-metal alkylidene complexes of the nucleophilic "Schrock-type" have been extensively studied for the 4d and 5d metals of Group 5, the chemistry for 3d vanadium systems has been far less explored. The first example of a vanadium(iii)-alkylidene complex, [CpV(CHtBu)(dmpe)](dmpe = bis(dimethylphosphanyl)-ethane), was reported by Hessen, Teuben, and co-workers and involved a-hydrogen abstraction of the bis(alkyl) precursor.[3] In contrast to the heavier d 0 alkylidene congeners, which are prepared by a-hydrogen abstraction, the synthesis of the first(Ar = 2,6-(CHMe 2 ) 2 C 6 H 3 ) involved a two-electron oxidation of the precursor [CpV(NAr)(PMe 3 ) 2 ] with the Wittig reagent Ph 3 P = CHPh by alkylidene transfer. [4] Since there are only a handful of vanadium-alkylidene complexes known, [3][4][5][6] we report the synthesis of the first cationic and neutral four-coordinate vanadium(iv)-neopentylidene complexes [(Nacnac)V=CH-tBu(thf)](BPh 4 ) and [(Nacnac)V = CHtBu(I)] (Nacnac À = [Ar]NC(Me)CHC(Me)N[Ar], Ar = 2,6-(CHMe 2 ) 2 C 6 H 3 ), and subsequent thermolysis of each system. These d 1 paramagnetic species reported herein are kinetically stable, and contain the shortest V=C bonds reported so far.Our recent strategy to prepare the first four-coordinate titanium-neopentylidene complex by an oxidatively induced a-hydrogen abstraction reaction [7] motivated us to pursue other 3d transition metals containing this reactive motif.Unlike titanium, vanadium displays more diverse redox chemistry, hence oxidation states ranging from + 2 to + 5 can occur. Using the precursor [(Nacnac)VCl 2 ][8] developed by Budzelaar and co-workers and two equivalents of LiCH 2 -tBu, [1g] we prepared the corresponding bis(neopentyl) complex [(Nacnac)V(CH 2 tBu) 2 ] (1) in 80 % yield as dark brown needles (Scheme 1). Attempts to obtain crystals suitable for a single-crystal X-ray structure determination were unsuccessful, but elemental analysis, magnetic susceptibility measurements (m eff = 2.96 m B ), and reactivity (vide infra) are in agreement with the formation of 1.[9] Complex 1 is a close analogue of the nBu derivative prepared by Budzelaar and co-workers, differing only by the lack of b-hydrogen atoms. (2) in 74 % yield (Scheme 1). Complex 2 is stable in the solid state, but its solutions (Et 2 O, C 6 H 6 , THF) gradually decompose over several hours at room temperature.Dark brown single crystals of 2 were grown from THF solutions of the complex layered with Et 2 O at À35 8C. The structure of 2 (Figure 1) reveals a cationic and four-coordinate vanadium center with pseudotetrahedral geometry, a very short V = C bond length (V(1)ÀC(33) 1.795(3) ), and an obtuse V(1)-C(33)-C(34) angle of 159.8(4)8. [9,10] The highly distorted neopentylidene ligand suggests that there is ...

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Cationic and Neutral Four‐Coordinate Alkylidene Complexes of Vanadium(IV) Containing Short VC Bonds

Basuli

Kilgore

et al. 2004

Angew Chem Int Ed

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“…Figure 4 shows V K-edge XANES spectra of toluene solution containing 1 in the presence of MAO and Al i Bu3 (10.0 equiv). The spectra of (imido)vanadium(V) trichloride, V(N-2,6-Me2C6H3)Cl3 41) , and (imido) vanadium(IV) dichloride, V(NAd)Cl2(NMe2H)2 (Ad 1-adamantyl) 39) , are also shown for comparison 42) .…”

Section: Analysis Of Catalyst Solution Consisting Of V(n-26-me2c6h3)mentioning

confidence: 99%

Effect of Al Cocatalyst in Ethylene and Ethylene/Norbornene (Co)polymerization by (Imido)vanadium Dichloride Complexes Containing Anionic <i>N</i>-Heterocyclic Carbenes Having Weakly Coordinating Borate Moiety

Nagai

Mitsudome

Tsutsumi

et al. 2017

J. Jpn. Petrol. Inst.

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Bu3 catalyst possessed uniform molecular weight distributions and compositions. Formation of vanadium(III) species could be assumed upon presence of Al i Bu3, especially on the basis of both NMR and ESR spectra (silent) and certain significant changes in the V K-edge XANES (pre-edge and edge region) spectrum, whereas no significant changes in the XANES spectrum were observed from the toluene solution containing 1 upon addition of MAO. It is thus suggested that a difference in the catalyst performances between in the presence of MAO and Al i Bu3 should be due to a formation of different catalytically active species with different oxidation states.

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A Transient V^III–Alkylidene Complex: Oxidation Chemistry Including the Activation of N₂ to Afford a Highly Porous Honeycomb‐Like Framework

et al. 2008

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Terminal vanadium alkylidenes [1][2][3][4] still constitute a rare class of complexes, and this type of functional group, when combined with this metal, has been far less explored than its heavier congeners niobium [5,6] and tantalum. [6] Part of this limitation revolves around the ability of vanadium to populate low-valent oxidation states, especially the + 3 state. As a result, alkylation reactions stemming from the high-valent metal complex often lead to reduction as opposed to the more prototypical transmetalation/a-hydrogen abstraction processes encountered in Nb V and Ta V alkylidenes.[6] Out of the few terminal vanadium alkylidene complexes known (e.g. V III ,[1] V IV , [3] and V V[4] ), only the high-valent system appears to be highly reactive for ring-opening metathesis polymerization (ROMP).[4] Therefore, an entry to the V V alkylidene group directly from a V III precursor would represent an attractive synthetic strategy for this metal given the vast quantity of low-valent vanadium halide precursors available. In general, heat, photolysis, Lewis bases, or Brønsted bases can incite a-hydrogen abstraction to form Schrock-like MÀC multiple bonds. [6,7] More recently, a one-electron oxidation step has been also shown to promote a-hydrogen abstraction. [7] When the metal is in a highoxidation state, powerful Lewis acids such as Al(CH 3 ) 3 can also instigate a-hydrogen abstraction as well as trap the MÀC multiple bond.[ [8][9][10] Although a handful of vanadium alkylidenes have been generated by treatment of a bis-alkyl precursor with PR 3 , [1] the concept of using two-electron oxidants to promote a-hydrogen abstraction, to the extent of providing a facile entry to the V V alkylidene unit, has not been realized.Herein we demonstrate that p acids or two-electron oxidants can ultimately lead to a-hydrogen abstraction when the metal in question is a low-valent V III bis-neopentyl species. As a result, a transient, four-coordinate V III neopentylidene can be generated and trapped with a series of two-electron oxidants to afford a family of V V alkylidenes. In the case where the p acid promoting the a-hydrogen abstraction is sterically crowded, N 2 becomes the substrate of choice to afford the first vanadium bridging end-on dinitrogenalkylidene species. The solid state packing diagram for this complex displays a highly "porous" honeycomb-like framework along the activated N 2 unit. During the course of our investigation, we also discovered that the elusive V III alkylidene generated in these set of reactions can be trapped with a chelate p acid such as 2,2'-bipyridine (bpy).When the bis-alkyl precursor, readily prepared from a one-pot reaction of Li(PNP) and [VCl 3 (thf) 3 ] followed by alkylation with the appropriate stoichiometry of LiCH 2 tBu, [11] was treated with N 2 CPh 2 in diethyl ether, a gradual reaction ensued over a period of 12 h to afford the V V alkylidenediphenylmethylene hydrazido [12] complex [(PNP)V( = CHtBu)(N 2 CPh 2 )] (2) in 62 % yield after workup of the reaction mixture (Scheme 1). Li...

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Synthesis, Molecular Structure, and Reactivity of a Half-Sandwich Vanadium(III) Imido Complex: The First Vanadium(V) Alkylidene

Cited by 102 publications

References 0 publications

Cationic and Neutral Four‐Coordinate Alkylidene Complexes of Vanadium(IV) Containing Short VC Bonds

Cationic and Neutral Four‐Coordinate Alkylidene Complexes of Vanadium(IV) Containing Short VC Bonds

Effect of Al Cocatalyst in Ethylene and Ethylene/Norbornene (Co)polymerization by (Imido)vanadium Dichloride Complexes Containing Anionic <i>N</i>-Heterocyclic Carbenes Having Weakly Coordinating Borate Moiety

A Transient V^III–Alkylidene Complex: Oxidation Chemistry Including the Activation of N₂ to Afford a Highly Porous Honeycomb‐Like Framework

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Synthesis, Molecular Structure, and Reactivity of a Half-Sandwich Vanadium(III) Imido Complex: The First Vanadium(V) Alkylidene

Cited by 102 publications

References 0 publications

Cationic and Neutral Four‐Coordinate Alkylidene Complexes of Vanadium(IV) Containing Short VC Bonds

Cationic and Neutral Four‐Coordinate Alkylidene Complexes of Vanadium(IV) Containing Short VC Bonds

Effect of Al Cocatalyst in Ethylene and Ethylene/Norbornene (Co)polymerization by (Imido)vanadium Dichloride Complexes Containing Anionic <i>N</i>-Heterocyclic Carbenes Having Weakly Coordinating Borate Moiety

A Transient VIII–Alkylidene Complex: Oxidation Chemistry Including the Activation of N2 to Afford a Highly Porous Honeycomb‐Like Framework

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A Transient V^III–Alkylidene Complex: Oxidation Chemistry Including the Activation of N₂ to Afford a Highly Porous Honeycomb‐Like Framework