Preparation and Reactivity of Mono‐ and Dinuclear Derivatives of Niobium and Tantalum Pentahalides with Alkyl Aryl Ethers

Abstract

The niobium and tantalum pentahalides MX5 (X = F, Cl) react with a series of bifunctional alkyl aryl ethers in a 2:1 ratio, resulting in formation of the dinuclear species (MX5)2[μ‐κ2‐(O–O)] [2a–h, 3a–d; O–O = 1,4‐(OMe)2C6H4, 1,4‐(OMe)2‐2,5‐C6H2F2, 1,3‐(OMe)2C6H4, PhO(CH2)2OPh]. The mononuclear complexes MX5(L) [L = κ1‐1,4‐(OMe)2C6H4, X = F, M = Nb, 4a; L = κ2‐1,3‐(OMe)2C6H4, X = Cl, M = Ta, 4c; L = MeOC6H5, X = F, M = Nb, 4d; L = MeOC6H5, X = Cl, M = Nb, 4e] have been prepared by 1:1 molar reactions of MX5 with the appropriate reactant. Alternatively, NbCl5[κ1‐1,4‐(OMe)2C6H4] (4b) has been obtained upon addition of acetone to (NbCl5)2[μ‐κ2‐1,4‐(OMe)2C6H4] (2b). The aryloxide complexes TaBr4[κ1‐OC6H4(4‐OMe)] (5a), NbCl4[κ1‐OC6H3(Me)(4‐OEt)] (5b) and TaX4[κ2‐OC6H4(2‐OMe)] (X = Cl, 7a; X = Br, 7b) form an admixture with equimolar amounts of alkyl halide by addition of dialkoxyarenes to MX5 (X = Cl, Br), as result of room‐temperature C–O bond cleavage. Differently, the ionic species [MF4(κ2‐O–O)2][M2F11] [O–O = 1,2‐(OMe)2C6H4, M = Nb, 6a; O–O = 1,2‐(OMe)2C6H4, M = Ta, 6b; O–O = 1,2,4‐(OMe)3C6H3, M = Nb, 6c] are produced cleanly by treating ortho‐dimethoxyarenes with MF5 in the opportune stoichiometry. All the products described herein were obtained selectively in good to excellent yields and were characterized by spectroscopic and analytical techniques. Moreover, the molecular structure of 2b was elucidated by an X‐ray diffraction study.

Stable [M2F11]– (M = Nb, Ta) Salts of Protonated 1,3‐Dimethoxybenzene

“…The reactions of 1,3‐dimethoxybenzene with an excess of 1 , carried out in either CH 2 Cl 2 or in CHCl 3 , quickly afforded the coordination adducts (MF 5 ) 2 [κ 2 ‐1,3‐(OMe) 2 C 6 H 4 ] (M = Nb, 2a ; M = Ta, 2b ),8 see Scheme . Compounds 2a and b were identified by means of NMR spectroscopy conducted on CD 2 Cl 2 solutions in strictly anhydrous conditions (see Experimental Section).…”

Long‐Lived Radical Cations of Monocyclic Arenes at Room Temperature Obtained by NbF5 Acting as an Oxidizing Agent and Counterion Precursor

“…Herein, we describe the synthesis and the characterization of long‐lived [Nb 2 F 11 ] − salts at room temperature of radical cations of monocyclic arenes, including benzene. Our discovery started with a serendipitous event: we noticed that a yellow chloroform solution of (NbF 5 ) 2 [μ‐κ 2 ‐1,4‐F 2 ‐2,5‐(OMe) 2 C 6 H 2 ],7 in the presence of excess NbF 5 , turned emerald green on a hot summer day (temperature in the laboratory was ca. 30 °C).…”

Phosphoramidate Tantalum Complexes for Room‐Temperature CH Functionalization: Hydroaminoalkylation Catalysis

“…Halogen substituents are tolerated as shown with product 3 e (entry 5) to give amine building blocks ready for catalyzed coupling protocols 5j. Even chelating catechol derivatives12 can be used (entry 6) to give the expected compound 3 f in good yield (80 %), with extended reaction times. Using the same reaction conditions N , N ′‐dimethyl‐1,4‐phenylenediamine was monoalkylated to give 3 g (entry 7) and unreacted starting material 13.…”