Aryl−Oxygen Bond Cleavage by a Trihydride-Bridging Ditantalum Complex

We have described the synthesis of the cyclometalated trihydride ditantalum(V) complexes supported by the aryloxide tridentate ligand. According to variable-temperature NMR studies, these dimers could provide a masked form of Ta(IV)−Ta(IV) and/or Ta(III)−Ta(III). In addition, these complexes were found to undergo hydrodeoxygenation of the aryloxide ligand

Synthesis and Structures of Niobium(V) Complexes Stabilized by Linear-Linked Aryloxide Trimers

The preparation and characterization of a series of niobium(V) complexes that incorporate the linear-linked aryloxide trimers 2,6-bis(4,6-dimethylsalicyl)-4-tert-butylphenol [H3(Me-L)] and 2,6-bis(4-methyl-6-tert-butylsalicyl)-4-tert-butylphenol [H3(tBu-L)] are described. The chloride complex [Nb(Me-L)Cl2]2 (1) was prepared in high yield by reaction of NbCl5 with H3(Me-L) in toluene. In contrast, the analogous reaction with H3(tBu-L) gave a mixture of [Nb(tBu-L)Cl2]2 (2) and [Nb(de-tBu-L)Cl2]2 (3a). During the formation of 3a, one of tert-butyl groups at the ortho position in the tBu-L ligand was lost. When the NbCl5/H3(tBu-L) reaction was carried out in acetonitrile, Nb[H(tBu-L)]Cl3(NCMe) (4) was obtained. Heating a solution of 4 in toluene generated 2 and 3a. The isolated complex 4 underwent ligand redistribution in acetonitrile to produce Nb[H(tBu-L)]2Cl(NCMe) (5). Treatment of NbCl5 with Li3(tBu-L) in toluene afforded 2. The chloride ligands in 1 and 2 smoothly reacted with 4 equiv of MeMgI and LiStBu, resulting in [Nb(R-L)Me2]2 [R = Me (6), tBu (7)] and Nb(Me-L)(StBu)2 (8), respectively. A number of the above complexes have been characterized by X-ray crystallography. In the structures of 1, 2, and 6, the R-L ligand is bound to the metal center with a U-coordination mode, while an alternative S-conformation is adopted for 3a and 8. Complexes 4 and 5 contain a bidentate H(tBu-L) diphenoxide−monophenol ligand

Anisole−Diphenoxide Ligands and Their Zirconium Dichloride and Dialkyl Complexes

Linear triphenol H3[RO3] (2,6-bis(3-tert-butyl-5-methyl-2-hydroxybenzyl)-4-R-phenol; R = Me, tBu) was found to undergo selective mono-deprotonation and mono-O-methylation. Deprotonation of H3[RO3] with 1 equiv of nBuLi resulted in the formation of Li{H2[RO3]}(Et2O)2 (R = Me (1a), tBu (1b)), in which the central phenol unit was lithiated. Treatment of H3[RO3] with methyl p-toluenesulfonate in the presence of K2CO3 in CH3CN gave the corresponding anisol-diphenol H2[RO2O] (2,6-bis(3-tert-butyl-5-methyl-2-hydroxybenzyl)-4-R-anisole; R = Me (2a), tBu (2b)). Reaction of H2[RO2O] with 2 equiv of nBuLi gave the dilithiated derivatives Li2[RO2O]. The lithium salts were reacted with ZrCl4 in toluene/THF to obtain the dichloride complex [RO2O]ZrCl2(thf) (R = Me (3a), tBu (3b)). 3b underwent dimerization along with a loss of THF to generate {[tBuO2O]ZrCl2}2 (4), whereas 4 was dissolved in THF to regenerate the monomer 3b. Alkylation of 3 with MeMgBr, PhCH2MgCl, and Me3SiCH2MgCl gave [MeO2O]ZrMe2(thf) (5), [RO2O]Zr(CH2Ph)2 (R = Me (6a), tBu (6b)), and [tBuO2O]Zr(CH2SiMe3)2 (7), respectively. Reaction of 3b with LiBHEt3 produced the hydride-bridged dimer [Li2(thf)4Cl]{[tBuO3]Zr}2(μ−H)3} (8), in which demethylation of the dianionic [tBuO2O] ligand took place to give the trianionic [tBuO3] ligand. The X-ray crystal structures of 1b, 2a, 3a, 4, 6a, and 7 were reported

Deprotonation Attempts on Imidazolium Salt Tethered by Substituted Phenol and Construction of Its Magnesium Complex by Transmetalation

Several attempts to deprotonate the imidizolium salt 1-methyl-3-(4,6-di-tert-butyl-2-hydroxybenzyl)imidazolium bromide, H2[CO]Br (4), tethered by substituted phenol to yield anonic carbene species M[CO] (M = Li, Na) resulted in the formation of {Na[ON](THF)}2 (5) and {Li[ON](THF)}2 (6) (1-methyl-2-(4,6-di-tert-butyl-2-hydroxybenzyl)imidazole, H[ON]) after warming to room temperature from −78 °C due to 1,2-aryloxy migration. Treatment of in-situ-generated M[CO] with 1.0 equiv of MesMgBr (Mes = 2,4,6-Me3C6H2) produced a rare magnesium NHC complex, {Mg[OC](Mes)}2 (8). Both 5 and 8 have been characterized by an X-ray diffraction study

Aryl−Oxygen Bond Cleavage by a Trihydride-Bridging Ditantalum Complex

We have described the synthesis of the cyclometalated trihydride ditantalum(V) complexes supported by the aryloxide tridentate ligand. According to variable-temperature NMR studies, these dimers could provide a masked form of Ta(IV)−Ta(IV) and/or Ta(III)−Ta(III). In addition, these complexes were found to undergo hydrodeoxygenation of the aryloxide ligand

Anisole−Diphenoxide Ligands and Their Zirconium Dichloride and Dialkyl Complexes

Linear triphenol H3[RO3] (2,6-bis(3-tert-butyl-5-methyl-2-hydroxybenzyl)-4-R-phenol; R = Me, tBu) was found to undergo selective mono-deprotonation and mono-O-methylation. Deprotonation of H3[RO3] with 1 equiv of nBuLi resulted in the formation of Li{H2[RO3]}(Et2O)2 (R = Me (1a), tBu (1b)), in which the central phenol unit was lithiated. Treatment of H3[RO3] with methyl p-toluenesulfonate in the presence of K2CO3 in CH3CN gave the corresponding anisol-diphenol H2[RO2O] (2,6-bis(3-tert-butyl-5-methyl-2-hydroxybenzyl)-4-R-anisole; R = Me (2a), tBu (2b)). Reaction of H2[RO2O] with 2 equiv of nBuLi gave the dilithiated derivatives Li2[RO2O]. The lithium salts were reacted with ZrCl4 in toluene/THF to obtain the dichloride complex [RO2O]ZrCl2(thf) (R = Me (3a), tBu (3b)). 3b underwent dimerization along with a loss of THF to generate {[tBuO2O]ZrCl2}2 (4), whereas 4 was dissolved in THF to regenerate the monomer 3b. Alkylation of 3 with MeMgBr, PhCH2MgCl, and Me3SiCH2MgCl gave [MeO2O]ZrMe2(thf) (5), [RO2O]Zr(CH2Ph)2 (R = Me (6a), tBu (6b)), and [tBuO2O]Zr(CH2SiMe3)2 (7), respectively. Reaction of 3b with LiBHEt3 produced the hydride-bridged dimer [Li2(thf)4Cl]{[tBuO3]Zr}2(μ−H)3} (8), in which demethylation of the dianionic [tBuO2O] ligand took place to give the trianionic [tBuO3] ligand. The X-ray crystal structures of 1b, 2a, 3a, 4, 6a, and 7 were reported

A Synthetic Cycle for H₂/CO Activation and Allene Synthesis Using Recyclable Zirconium Complexes

The zirconium complexes supported by the anisole-bridged bis(phenoxide) ligands serve as an easily recycled auxiliary for converting H2 and CO into allene and hexamethyldisiloxane under mild conditions. Hydrogenolysis of the zirconium benzyl complexes followed by treatment with CO led to formation of oxo-bridged complexes and allene. Deoxygenation of the resulting oxo-bridged complexes with trimethylsilyltrifluoromethanesulfonate and trimethylsilyl chloride and subsequent treatment with benzylmagnesium chloride re-formed the starting benzyl complexes

Nitrogen Atom Transfer from a Dinitrogen-Derived Vanadium Nitride Complex to Carbon Monoxide and Isocyanide

Reduction of [(ONO)­V­(THF)] with KH under an N2 atmosphere cleaves the NN bond to afford a bis­(μ-nitride) V­(IV) dimer. This complex is oxidized to generate a V­(V) nitride. The reactions of the V­(V) nitride with carbon monoxide and isocyanide led to formation of cyanate and carbodiimide complexes. Following treatment of the cyanate complex with alkyne produces an alkyne adduct along with the release of potassium cyanate. Dissolution of the alkyne adduct in THF regenerates the starting complex [(ONO)­V­(THF)], thereby closing a synthetic cycle for conversion of N2 and CO into [NCO]−

Triple-Hydrogen-Bridged Dititanium(III) and Dizirconium(IV) Aryloxide Complexes

The triple-hydrogen-bridged dititanium(III) complex was prepared by the reaction of the titanium(IV) aryloxide complex with LiBHEt3, while a similar reaction using the zirconium aryloxide complex gave the triple-hydrogen-bridged dizirconium(IV) complex. The titanium(III) dimer was found to be diamagnetic, and its dynamic behavior in solution was revealed by NMR studies

Synthesis of (Pentamethylcyclopentadienyl)tantalum Sulfido Complexes via C−S Bond Cleavage of Triphenylmethanethiolate and Formation of a Novel Trithioborato Ligand

Treatment of Cp*TaCl4 with triphenylmethanethiol via C−S bond cleavage gave rise to Cp*TaCl(S)(SCPh3) (1), which was treated with LiSR, Li2S, and NaBH4 to afford Cp*TaS(SR)(SCPh3) (R = CPh3 (2), CMe3 (3)), [Cp*Ta(S)3Li2(THF)2]2 (4), and Cp*3Ta3(S)3(S3BH) (5), respectively. The crystal structures of 1 and 5 were determined by X-ray diffraction