Preparation and characterization of mono-cyclopentadienylvanadium dihalide bis-phosphine complexes; crystal structure of (η5-C5H5)VCL2(PMe3)2

Syntheses and crystal structures of new naphthalene– and anthracene–vanadate salts and an unprecedented dimetallabis(anthracene) sandwich complex: [Na(tetrahydrofuran)3][V2(anthracene)2]

Reduction of bis(naphthalene)vanadium(0) by potassium naphthalene (KNp) in tetrahydrofuran (THF) provides a highly reactive, thermolabile, and so far unisolable brown substance, which affords the first reported derivatives of bis(naphthalene)vanadates. From these solutions, thermally stable (298 K) and structurally characterized compounds have been obtained, including dark-red rods of catena-poly[bis(μ3-η4:η6:η4-naphthalene)tetrakis(tetrahydrofuran)dipotassiumvanadium], [K2V(C4H8O)4(C10H8)2] n or [K(THF)2]2[V(C10H8)2] (3), and red plates of (4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane)potassium [1,2-bis(dimethylphosphanyl)ethane]bis(η4-naphthalene)vanadium tetrahydrofuran monosolvate, [K(C18H36N2O6)][V(C10H8)2(C6H16P2)]·C4H8O or [K([2.2.2]cryptand)][V(C10H8)2(dmpe)]·THF [dmpe is 1,2-bis(dimethylphosphanyl)ethane] (4b). Notably, [V(C10H8)2]2− is the only example of a structurally authenticated homoleptic bis(arene)metallate dianion and was obtained by further reduction of the brown material by KNp in THF, in the presence of trimethylphosphane (PMe3). Addition of anthracene (An) to the brown material in THF afforded deep-violet and paramagnetic crystalline (1,4,7,10,13,16-hexaoxacyclooctadecane)bis(tetrahydrofuran)potassium [(η4-anthracene)(tetrahydrofuran)vanadium]-μ-η4:η2-anthracene-[(1,4,7,10,13,16-hexaoxacyclooctadecane)potassium]-μ-η2:η4-anthracene-[(η4-anthracene)(tetrahydrofuran)vanadium] tetrahydrofuran disolvate, [K(C12H24O6)(C4H8O)2][KV2(C12H24O6)(C4H8O)2(C14H10)4]·2C4H8O or [K(18-crown-6)][K(18-crown-6)(THF)2][V(C14H10)2(THF)]2·2(THF) (5), which readily reacted with PMe3 and dmpe to give new vanadate salts. These were structurally characterized as (1,4,7,10,13,16-hexaoxacyclooctadecane)bis(tetrahydrofuran)potassium bis(η4-anthracene)(trimethylphosphane)vanadium tetrahydrofuran monosolvate, [K(C12H24O6)(C4H8O)2][V(C14H10)2(C3H9P)]·C4H8O or [K(18-crown-6)(THF)2][V(C14H10)2(PMe3)]·THF (6), and tetrakis(1,2-dimethoxyethane)potassium bis(η4-anthracene)[1,2-bis(dimethylphosphanyl)ethane]vanadium, [K(C4H10O2)4][V(C14H10)2(C6H16P2)] or [K(DME)4][V(C14H10)2(dmpe)] (DME is 1,2-dimethoxyethane) (7b). The last three structures contain the first known bis(anthracene)vanadates and are thereby derivatives of the unknown bis(anthracene)vanadium(0). Attempts to obtain the sodium salt analog of 5 in THF resulted instead in the formation of a unique substance, (μ3-η6:η6:η6-anthracene)(μ2-η6:η6-anthracene)tris(tetrahydrofuran)sodiumdivanadium, [NaV2(C14H10)2(C4H8O)3] or [Na(THF)3][V2(C14H10)2] (8), containing the first reported dimetallabis(anthracene) sandwich compound.

Homo- and Copolymerization of Ethylene with Norbornene Catalyzed by Vanadium(III) Phosphine Complexes

Herein, we report the homo- and co-polymerization of ethylene (E) with norbornene (NB) catalyzed by vanadium(III) phosphine complexes of the type VCl₃(PMe_nPh_3-n)₂ [n = 2 (1a), 1 (1b)] and VCl₃(PR₃)₂ [R = phenyl (Ph, 1c), cyclohexyl (Cy, 1d), tert-butyl (tBu, 1e)]. In the presence of Et₂AlCl and Cl₃CCOOEt (ETA), 1a-1e exhibit good activities for the polymerization of ethylene, affording linear, semicrystalline PEs with a melting temperature of approximately 130 °C. Mainly alternating copolymers with high comonomer incorporation were obtained in the E/NB copolymerization. A relationship was found between the electronic and steric properties of the phosphine ligands and the catalytic performance. Overall, the presence of electron-withdrawing ligand substituents increases the productivity, complexes with aryl phosphine (weaker σ-donor character) exhibiting a higher (co)polymerization initiation rate than those with alkyl phosphines (stronger σ-donor character). Steric effects also seem to play a key role since 1d and 1e, having large size phosphines (PCy₃ θ = 170° and PtBu₃ θ = 182°, respectively) are more active than 1a (PMe₂Ph θ = 122°). In this case, the larger size of PtBu₃ and PCy₃ likely compensates for their higher donor strength compared to PMe₂Ph.

Non-Innocent Behaviour of Imido Ligands in the Reactions of Silanes with Half-Sandwich Imido Complexes of Nb and V: A Silane/Imido Coupling Route to Compounds with Nonclassical SiH Interactions

Reactions of imido complexes [M(Cp)(=NR')(PR''3)2] (M=V, Nb) with silanes afford a plethora of products, depending on the nature of the metal, substitution at silicon and nitrogen and the steric properties of the phosphine. The main products are [M(Cp)(=NR')(PR3)(H)(SiRnCl3-n)] (M=V, Nb; R'=2,6-diisopropylphenyl (Ar), 2,6-dimethylphenyl (Ar')), [Nb(Cp)(=NR')(PR''3)(H)(SiPhR2)] (R2=MeH, H2), [Nb(Cp)(==NR')(PR''3)(Cl)(SiHRnCl2-n)] and [Nb(Cp)(eta 3-N(R)SiR2--H...)(PR''3)(Cl)]. Complexes with the smaller Ar' substituent at nitrogen react faster, as do more acidic silanes. Bulkier groups at silicon and phosphorus slow down the reaction substantially. Kinetic NMR experiments supported by DFT calculations reveal an associative mechanism going via an intermediate N-silane adduct [Nb(Cp){=N(-->SiHClR2)R'}(PR''3)2] bearing a penta-coordinate silicon centre, which then rearranges into the final products through a Si--H or Si--Cl bond activation process. DFT calculations show that this imido-silane adduct is additionally stabilized by a Si--HM agostic interaction. Si--H activation is kinetically preferred even when Si--Cl activation affords thermodynamically more stable products. The niobium complexes [NbCp(=NAr)(PMe3)(H)(SiR2Cl)] (R=Ph, Cl) are classical according to X-ray studies, but DFT calculations suggest the presence of interligand hypervalent interactions (IHI) in the model complex [Nb(Cp) (==NMe)(PMe3)(H)(SiMe2Cl)]. The extent of Si--H activation in the beta-Si--HM agostic complexes [Cp{eta 3-N(R')SiR2--H}M(PR''3)(Cl)] (R''=PMe3, PMe2Ph) primarily depends on the identity of the ligand trans to the Si--H bond. A trans phosphine leads to a stronger Si--H bond, manifested by a larger J(Si--H) coupling constant. The Si--H activation diminishes slightly when a less basic phosphine is employed, consistent with decreased back-donation from the metal.

Naked (C5Me5)2M Cations (M = Sc, Ti, and V) and Their Fluoroarene Complexes

The ionic metallocene complexes [Cp*(2)M][BPh(4)] (Cp* = C(5)Me(5)) of the trivalent 3d metals Sc, Ti, and V were synthesized and structurally characterized. For M = Sc, the anion interacts weakly with the metal center through one of the phenyl groups, but for M = Ti and V, the cations are naked. They each contain one strongly distorted Cp* ligand, with one (V) or two (Ti) agostic C-H...M interactions involving the Cp*Me groups. For Sc and Ti, these Lewis acidic species react with fluorobenzene and 1,2-difluorobenzene to yield [Cp*(2)M(kappaF-FC(6)H(5))(n)][BPh(4)] (M = Sc, n = 2; M = Ti, n = 1) and [Cp*(2)M(kappa(2)F-1,2-F(2)C(6)H(4))][BPh(4)], the first examples of kappaF-fluorobenzene and kappa(2)F-1,2-difluorobenzene adducts of transition metals. With the perfluorinated anion [B(C(6)F(5))(4)](-), both Sc and Ti form [Cp*(2)M(kappa(2)F-C(6)F(5))B(C(6)F(5))(3)] contact ion pairs. The nature of the metal-fluoroarene interaction was studied by density functional theory (DFT) calculations and by comparison with the corresponding tetrahydrofuran (THF) adducts and was found to be predominantly electrostatic for all metals studied.