Electron-Deficient Vanadium Alkyl Complexes: Synthesis and Molecular Structure of the Vanadium(III) Dinitrogen Complex [(Me3CCH2)3V]2(μ-N2)

The vanadium(III) dinitrogen-bridged complex [(Me3CCH2)3V]2(μ-N2) (1), obtained from reaction of VCl3(THF)3 and Me3CCH2Li under nitrogen, is converted to the vanadium(V) oxo complex OV(CH2CMe3)3 (3) by reaction with styrene oxide. Both 1 and 3 decompose at ambient temperature to give neopentane and species which are active in the ring-opening metathesis polymerization of norbornene.

CCDC 124616: Experimental Crystal Structure Determination

Related Article: J.-K.F.Buijink, A.Meetsma, J.H.Teuben, H.Kooijman, A.L.Spek|1995|J.Organomet.Chem.|497|161|doi:10.1016/0022-328X(95)00113-5,An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

CCDC 124617: Experimental Crystal Structure Determination

Related Article: J.-K.F.Buijink, A.Meetsma, J.H.Teuben, H.Kooijman, A.L.Spek|1995|J.Organomet.Chem.|497|161|doi:10.1016/0022-328X(95)00113-5,An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

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One of the trimethylphosphine ligands in CpV(NAr)(PMe3)2 (3; Ar = 2,6-C6H3-i-Pr2), obtained by magnesium reduction of CpV(NAr)Cl2 (2), can be substituted by CO, ethylene, or diphenylacetylene to give the corresponding pi-acceptor (L) complex CpV(NAr)(L)-(PMe3) (L = CO, 4; L = C2H4, 5; L = PhC=Ph, 6). 3 reacts with Ph3P=CHPh to form the first vanadium(V) alkylidene, CpV(NAr)(=CHPh)(PMe3) (7)

Alkylation and reductive dimerization of half-sandwich imido vanadium dichlorides

The vanadium imido complex ArNVCl3 (2) (Ar = 2,6-C6H3-(iPr)2) can be converted to the half-sandwich imido vanadium complex CpV(NAr)Cl2 (3) by reaction with CpSiMe3. Reaction of 3 and of CpV(N-p-tolyl)Cl2 (1) with alkylating reagents did not allow the isolation of the pure dialkyl complexes but showed extensive reduction of vanadium. Reaction of 1 with AlMe3 leads to the formation of a mixture of diamagnetic dimeric, imido-bridged complexes (CpV)2(μ-N-p-tolyl)2MeR (R = Me or Cl), which can be converted to the pure chloro compound [CpV(μ-N-p-tolyl)Cl]2 (4) by reaction with HCl. Dimerization is prevented when the more bulky ArN ligand is used. Alkylation of 4 with MeLi proceeds cleanly to give the methyl compound [CpV(μ-N-p-tolyl)Me]2 (5). The molecular structures of the formally vanadium(IV) complexes 4 and 5 have been obtained, showing a planar cyclovanadazene core with a vanadium-vanadium single bond and V-Cl and V-CMe bond lengths that are characteristic of V(V) compounds. Compound 5 reacts with CO by insertion in the V-C bond, but no reaction is observed with other small unsaturated molecules or Brønsted acids. The 51V NMR chemical shifts of the new complexes are reported and compared with the chemical shifts of known imido vanadium complexes.

Structure and Reactivity of Mono(cyclopentadienyl)vanadium Alkynyl and Aryne Complexes

Starting from CpVCl2(PMe3)2 (1) the paramagnetic mono- and bis(phenylethynyl) complexes CpVCl2-n(C≡CPh)n(PMe3)2 [n = 1 (2), 2 (3)] have been synthesized. Both compounds were characterized by X-ray diffraction and were found to be thermally more stable than other CpVIII hydrocarbyl complexes. The CpVIII bis(phenyl) complex CpVPh2(PMe3)2 (5) decomposes at ambient temperature through β-hydrogen abstraction to give the first isolated vanadium benzyne complex, CpV(η2-C6H4)(PMe3)2 (6). The molecular structure of 6 indicates that this compound can best be described as a high-spin d2 vanadium(III) benzometallacyclopropene. The cyclopropene character is expressed in the reactivity of 6, showing insertion of unsaturated substrates. Insertion of diphenylacetylene gives CpV(η2-PhC=CPhC6H4)(PMe3)2 (7), with a planar vanadaindene structure, whereas terminal alkenes CH2=CRR´ (R = H, Me; R´ = H, Me) insert regioselectively to give β-substituted metallaindanes CpV(η2-CH2CRR´C6H4)PMe3 (R and R´ = H, 8a; R = H, R´ = Me, 8b; R and R´ = Me, 8c), which show a low thermal stability in case one of the β-substituents is a hydrogen. With t-BuCN double insertion followed by rearrangement of the intermediate diazametallacycle gives the isoindolenine-substituted vanadium(III) imido complex CpV[NC(t-Bu)N=C(t-Bu)C6H4](PMe3)2 (9). The benzyne complex 6 reacts with dihydrogen to form the known triple-decker CpV(C6H6)VCp through partial hydrogenation of the benzyne ligand.

α-, β-, and δ-Hydrogen Abstraction in the Thermolysis of Paramagnetic Vanadium(III) Dialkyl Complexes

Electron deficient paramagnetic vanadium(III) diakyls CpV(CH2CMe2R)2(PMe3) (14 electron, R = Me (2), Ph (3)) and CpV[CH(SiMe3)2]2 (12 electron, 4) have been synthesized. At ambient temperature 2 decomposes through α-hydrogen abstraction to produce, in the presence of dmpe (1,2-bis(dimethylphosphino)ethane), the first vanadium alkylidene CpV(CHCMe3)dmpe (6), which has been structurally characterized. In contrast, 3 decomposes in the presence of excess PMe3 through orthometalation of the aryl substituent to give the metallacycle complex CpV(σ2-CH2CMe2C6H4)(PMe3)2 (7). In the absence of excess PMe3 the (μ-alkyl)2(μ-aryl)2 dimer [CpV(μ2-CH2CMe2C6H4)]2 (8) is formed, with a short (2.313(2) Å) metal-metal distance. Reaction of CpV(Me)Cl(PMe3)2 (9) with n-BuLi produces the 1-butene complex CpV(η2-CH=CHEt)(PMe3)2 (10) through β-hydrogen abstraction and reductive elimination. Reactivity of the alkylidene complex 6 includes the formation of the first imido complex of trivalent vanadium, CpV[=NC(CMe3)=C(CMe3)H](dmpe) (12), with V=N = 1.707(2) Å and a Z-configuration around the C-C bond, in the reaction with t-BuCN. Crystallographic data for 6: P21/a, a = 13.699(2) Å, b = 8.966(1) Å, c = 15.386(2) Å, β = 101.87(1)°, Z = 4. For 7: P1, a = 9.671(2) Å, b = 14.261(4) Å, c = 8.528(2) Å, α = 94.89(2)°, β = 100.55(2)°, γ = 77.78(2)°, Z = 2. For 8: P21/c, a = 9.812(9) Å, b = 14.019(10) Å, c = 17.407(10) Å, β = 96.76(6)°, Z = 4. For 12: P1, a = 9.147(1) Å, b = 11.005(1) Å, c = 13.489(1) Å, α = 71.95(1)°, β = 89.70(1)°, γ = 69.56(1)°, Z = 2.