The Group 5 pentahalides MX 5 (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 [MX 2(OR) 2(μ-OR)] 2 [M = Nb, X = Cl, R = –CH(Et)CH 2Cl, 2a; M = Nb, X = Cl, R = –CH 2CH(Ph)Cl, 2b; M = Nb, X = Cl, R = –C(Me) 2C(Me) 2Cl, 2c; M = Nb, X = Br, R = –CH 2CH(Ph)Br, 2d; M = Nb, X = Br, R = –C(Me) 2C(Me) 2Br, 2e; M = Ta, X = Cl, R = –CH(Et)CH 2Cl, 2f; M = Ta, X = Cl, ▪, 2g; M = Ta, X = Br, R = –CH 2CH 2Br, 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, NbF 5 adds one equivalent of 2,3-dimethyl-2,3-epoxybutane to give the monomer NbF 5[O C(Me)(Bu t )], 3, in high yield, as a result of epoxide to ketone isomerization. The reactions of MF 5 (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.