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The reactivity of NbCl 5 , NbF 5 and TaCl 5 with a selection of commercial imines was investigated for the first time by using dichloromethane as reaction medium. NbCl 5 reacted with Ph 2 C NH, in 1:2 molar ratio, affording [Ph 2 C NH 2 ][NbCl 5 (N CPh 2 )], 1 , in 55% yield, as result of imine self-protonation. The iminium salt [PhCH NH t Bu][NbCl 6 ], 2 , was isolated in 52% yield from NbCl 5 and PhCH N t Bu (1:1 molar ratio), while a low yield of [ t Bu 2 C NH 2 ][NbCl 6 ], 3 , was identified from NbCl 5 / t Bu 2 C NH. The 1:1 reactions of NbF 5 with Ph 2 C NH and PhCH N t Bu were accompanied by electron interchange and led to the isolation of the salts [Ph 2 C NH 2 ][NbF 6 ], 4 , and [PhCH NH t Bu][NbF 6 ], 5 , respectively, in ca. 50% yields. Few crystals of [Ph 2 C NH 2 ] 2 [Ta 2 Cl 10 O], 6 , were recovered from TaCl 5 /Ph 2 C NH, the anion being probably generated by the action of adventitious water. Compounds 1 – 6 were characterized by elemental analysis, IR and NMR spectroscopy. The structures of 1 , 4 and 6 were ascertained by X-ray diffraction studies. [ABSTRACT FROM AUTHOR]

Abstract: The room temperature reactions of a series of 1,2-dialkoxyalkanes ROCH2CH(R′)OR′′ with MX5 (M=Nb, Ta; X=Br, I) in 1:1 ratio result in single C–O bond cleavage and high-yield formation of the halo-alkoxides MBr4[κ2-OCH2CH(R′)OR′′] or [NbI4{κ1-OCH2CH(R′)OR′′}]2, and equimolar amounts of the corresponding alkyl halides RX. The reaction of NbBr5 with 1,2-dimethoxyethane, dme, proceeds with preliminary formation of the ionic species [NbBr4(κ2-dme)(κ1-dme)][NbBr6], 3b, which has been identified by solution NMR at low temperature and conductivity analyses. The gas-phase structure of 3b has been optimized by DFT calculations, confirming that the dme ligands adopt bidentate and monodentate coordination, respectively. Although the formation of NbOBr3(dme), 4b, 1,4-dioxane and MeBr from NbBr5/dme (ratio 1:2) is an exoergonic process (calculated =−115.96kcalmol−1), it is inhibited at room temperature. High temperature conditions enhance the production of 1,4-dioxane at the expense of selectivity. The dinuclear species NbOBr3(dme)NbBr5 (Nb–O–Nb), 5b, (X-ray) has been isolated in modest yield as byproduct of the room temperature reaction of NbBr5 with dme. In general, the 1:2molar reactions of NbX5 (X=Br, I) with ROCH2CH(R′)OR′′ occur with the exclusion of nearly one equivalent of organic reactant. [Copyright &y& Elsevier]

Abstract: The Group 5 pentahalides MX5 (M=Nb, Ta; X=Cl, Br), 1, react with a variety of epoxides (1,2-epoxybutane, styrene oxide, 2,3-dimethyl-2,3-epoxybutane, epoxycyclohexane, ethylene oxide) in a 1:3 molar ratio to afford the dinuclear dihalide-tris(2-haloalcoholato) complexes [MX2(OR)2(μ-OR)]2 [M=Nb, X=Cl, R=–CH(Et)CH2Cl, 2a; M=Nb, X=Cl, R=–CH2CH(Ph)Cl, 2b; M=Nb, X=Cl, R=–C(Me)2C(Me)2Cl, 2c; M=Nb, X=Br, R=–CH2CH(Ph)Br, 2d; M=Nb, X=Br, R=–C(Me)2C(Me)2Br, 2e; M=Ta, X=Cl, R=–CH(Et)CH2Cl, 2f; M=Ta, X=Cl, ▪, 2g; M=Ta, X=Br, R=–CH2CH2Br, 2h], in moderate to good yields. The products, 2a–h, result from multiple epoxide insertion into metal–halide bonds, and the reactions involving 1,2-epoxybutane and styrene oxide proceed with high regioselectivity. The molecular structure of 2h has been elucidated by X-ray diffraction. Differently, NbF5 adds one equivalent of 2,3-dimethyl-2,3-epoxybutane to give the monomer NbF5[Oce:italic> t )], 3, in high yield, as a result of epoxide to ketone isomerization. The reactions of MF5 (M=Nb, Ta) with other epoxides proceed non-selectively according to various pathways, including formation of C–O and C–F bonds and C–C and C–H cleavages. [Copyright &y& Elsevier]

Abstract: Niobium and tantalum pentahalides, MX5 (1), react with acetic acid and halo-substituted acetic acids, in 1:1 ratio, to give the dinuclear complexes [MX4(μ-OOCMe)]2 [M=Nb, X=Cl, 2a; M=Ta, X=Cl, 2b; Br, 2c] and [MCl4(μ-OOCR)]2 [M=Nb, R=CH2Cl, 4a; CHCl2, 4c; CCl3, 4e; CF3, 4g; CHBr2, 4i; CH2I, 4j; M=Ta, R=CH2Cl, 4b; CHCl2, 4d; CCl3, 4f; CF3, 4h]. The solid state structures of 2b and 4e have been ascertained by X-ray diffraction studies. The reactions of 1 with acetic anhydride and halo-substituted acetic anhydrides result in C–O bond activation and afford 2 and 4, respectively, with concomitant formation of acetyl halides. Moreover, the complexes MCl5[OC(Cl)Me] [M=Nb, 3a; M=Ta, 3b] have been detected in significant amounts within the mixtures of the reactions of MCl5 with acetic anhydride. TaI5 is unreactive, at room temperature, towards both MeCOOH and (MeCO)2O. MF5 react with RCOOH (R=Me, CH2Cl) in 1:1 molar ratio, to afford the ionic compounds [MF4(RCOOH)2][MF6], 5a–d, in high yields. The additions of (RCO)2O (R=Me, CH2Cl) to MF5 give 5, suggesting that anhydride C–H and C–O bonds activation is operative during the course of these reactions. [Copyright &y& Elsevier]