Vinyl C−H Activation Reactions of Vinyl Esters Mediated by B(C6F5)3

Tandem dihetero-Diels–Alder and Huisgen cycloaddition reactions. Synthesis, crystal structure and hydrolysis of the novel cage phosphoranes

The reaction of 2-(1-phenylvinyloxy)benzo-1,3,2-dioxaphosphole with activated carbonyl compounds leads to the stereoselective formation of cage phosphoranes.

Oxygen extrusion from amidate ligands to generate terminal Ta=O units under reducing conditions. How to successfully use amidate ligands in dinitrogen coordination chemistry

A series of mixed Cp* amidate tantalum complexes Cp*Ta(RNC(O)R')X(3) (where R = Me(2)C(6)H(3), (i)Pr, R' = (t)Bu, Ph, X = Cl, Me) have been prepared via salt metathesis and their fundamental reactivities under reducing conditions have been explored. Reaction of the tantalum chloro precursors with potassium graphite under N(2) or Ar leads to the stereoselective formation of the terminal tantalum oxo species, Cp*Ta=O(η(2)-RN=CR')Cl. This represents the formal extrusion of oxygen from the amidate ligand to the reduced tantalum center and is accompanied by the formation of the iminoacyl fragment bound to Ta(v). Amidate dinitrogen complexes, [Cp*TaCl(RNC(O)(t)Bu)](2)(μ-N(2)) (where R = Me(2)C(6)H(3), (i)Pr) were synthesized via salt metathesis from the known [Cp*TaCl(2)](2)(μ-N(2)) precursor, establishing that amidate ligands can support dinitrogen complexes, but not the reduction process often necessary for their synthesis.

Trapping unstable terminal M-O multiple bonds of monocyclopentadienyl niobium and tantalum complexes with Lewis acids

Hydrolysis of [NbCp'Cl(4)] (Cp' = η(5)-C(5)H(4)SiMe(3)) with the water adduct H(2)O·B(C(6)F(5))(3) afforded the oxo-borane compound [NbCp'Cl(2){O·B(C(6)F(5))(3)}] (2a). This compound reacted with [MgBz(2)(THF)(2)] giving [NbCp'Bz(2){O·B(C(6)F(5))(3)}] (2b), whereas [NbCp'Me(2){O·B(C(6)F(5))(3)}] (2c) was obtained from the reaction of [NbCp'Me(4)] with H(2)O·B(C(6)F(5))(3). Addition of Al(C(6)F(5))(3) to solutions containing the oxo-borane compounds [MCp(R)X(2){O·B(C(6)F(5))(3)}] (M = Ta, Cp(R) = η(5)-C(5)Me(5) (Cp*), X = Cl 1a, Bz 1b, Me 1c; M = Nb, Cp(R) = Cp', X = Cl 2a) afforded the oxo-alane complexes [MCp(R)X(2){O·Al(C(6)F(5))(3)}] (M = Ta, Cp(R) = Cp*, X = Cl 3a, Bz 3b, Me 3c; M = Nb, Cp(R) = Cp', X = Cl 4a), releasing B(C(6)F(5))(3). Compound 3a was also obtained by addition of Al(C(6)F(5))(3) to the dinuclear μ-oxo compound [TaCp*Cl(2)(μ-O)](2), meanwhile addition of the water adduct H(2)O·Al(C(6)F(5))(3) to [TaCp*Me(4)] gave complex 3c. The structure of 2a and 3a was obtained by X-ray diffraction studies. Density functional theory (DFT) calculations were carried out to further understand these types of oxo compounds.

A new fluorous soluble Lewis acidic borane system

Treatment of trichlorovinylsilane with 3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluoro-1-octanol (3 equiv.) in the presence of excess triethylamine produces the fluorous vinylsilane, 1, which can be isolated in 74% yield as an analytically pure oil. The addition of bis(pentafluorophenyl)borane to 1 produces the fluorous boranes, 2a–2b, as an analytically pure, isomeric mixture of anti-Markovnikov and Markovnikov hydroboration products in 38% isolated yield. Compounds 2a–2b are soluble in both arene solvents and perfluoro(methylcyclohexane). Treatment of 2a–2b with excess trimethylphosphine generates a mixture of products, including the Lewis adduct, 3, which can be isolated as an analytically pure oil in 15% yield. When exposed to either dimethylaminopyridine or piperidine at room temperature, the trimethylphosphine donor in 3 is cleanly displaced, based on in situ 31P NMR studies; under similar conditions, triethylamine does not react with 3. Addition of either dimethylaminopyridine or piperidine to 2a–2b, followed by purification and subsequent treatment with an excess of either hydrogen chloride or p-toluenesulfonic acid, results in cleavage of the Si–O linkages and the regeneration of 3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluoro-1-octanol.Key words: fluorous, borane, silane, Lewis acid.