Trapping Unstable Terminal Ta−O Multiple Bonds of Monocyclopentadienyl Tantalum Complexes with a Lewis Acid

Abstract

Hydrolysis of Ta-Cl or Ta-C bonds with the water-coordinated adduct [H 2 O‚B(C 6 F 5 ) 3 ] allowed the synthesis of borane-stabilized complexes [TaCp*R 2 {O‚ B(C 6 F 5 ) 3 }] (R ) Cl, CH 2 Ph, Me) with a tantalum-oxo multiple bond. The chloro derivative in the presence of pyridine releases the adduct [py‚B(C 6 F 5 ) 3 ] with formation of the oxo-bridged compound [TaCp*Cl 2 (µ-O)] 2 . DFT calculations have been carried out to determine the electronic properties of the Ta-O and O-B bonds.

η2‐Iminoacyl and η2‐Acyl Monocyclopentadienyl Tantalum Complexes Bearing Oxo and Oxo‐Borane Ligands

“…All the values of the bond lengths and angles of compound 2d are very close to the corresponding bond lengths and angles found for the parent compound [TaCp*Cl{η 2 -C(Me)=NAr}(O)] [10] except for the Ta [ [21][22][23][24][25][26][27][28][29][30][31] The Ta-O bond in 2d is longer than that in the oxo-borane compound [TaCp*Cl 2 {O·B(C 6 F 5 ) 3 }] [21] [1.784(2) Å]. This bond length is similar to the lower end of the range of Ta-O bond lengths for compounds with Ta-O-Ta bridges (1.82-2.10 Å) [32][33][34][35] and with terminal Ta-OH bonds (1.85-1.97 Å).…”

“…NMR spectra were recorded at 300. 13 [42] [TaCp*(CH 2 Ph) 2 {O·B(C 6 F 5 ) 3 }], [21] [TaCp*Me 2 -{O·B(C 6 F 5 ) 3 }], [21] [TaCp*Cl{η 2 -C(Me)=NAr}(O)] [10] and B-(C 6 F 5 ) 3 [43] were prepared by literature methods, and H 2 O·B-(C 6 F 5 ) 3 [44] was prepared from H 2 O and B(C 6 F 5 ) 3 in toluene at room temperature and used in situ without further purification.…”

“…[10,11] The versatility and potential applications of all these results determined by the R and X substituents of the imido complexes [TaCp*MeX(NR)] led us to extend our studies to similar insertion reactions of CNR and CO into the Taalkyl bonds of the related oxo-borane compounds [TaCp*X 2 {O·B(C 6 F 5 ) 3 }] that have recently been isolated. [21] Results and Discussion [21][22][23][24][25][26][27][28][29][30][31] and the 1 H NMR spectra with the monosubstitution of only one of the alkyl ligands. These pale yellow complexes are air and thermally stable in solution.…”

“…The Ta have values that are normally seen for these types of compounds. [21][22][23][24][25][26][27][28][29][30][31] The whole set of angles and bond lengths of the [Ta-(η 2 -acyl)] group is in line with compounds of this type [1] and is similar to those found in the other two tantalum-acyl complexes for which X-ray structures are known, [TaCp*Me{η 2 -C(CH 2 CMe 2 Ph)=O}{N(2,6-Me 2 C 6 H 3 )}] [39] and [TaCp*Cl 3 {η 2 -C(CH 2 CMe 3 )=O}]. [40] However, in the particular case of the isostructural imido derivative [TaCp*Me{η The insertion of a second CNAr or CO molecule into these new acyl and iminoacyl oxo-borane complexes was not observed, in contrast with the behaviour observed for the analogous tert-butyl imido complexes.…”

Synthesis and Reactivity of Oxametallacyclic Niobium Compounds by Using α,β‐Unsaturated Carbonyl Ligands

“…Complexes 1-3 present three nucleophilic centers that can react with protic acids: the Nb-Cl, [21][22][23][24] the Nb-C [24] , and the oxametallacyclic Nb-O [19] bonds. It would be reasonable to expect that the Nb-C bond should be the most reactive one toward protonolysis due to its lower bond energy, the higher energy of the resulting C-H bond, and the higher nucleophilic character of the niobium-bonded alkyl carbon atom.…”