Induced Fitting and Polarization of a Bromine Molecule in an Electrophilic Inorganic Molecular Cavity and Its Bromination Reactivity

Abstract

Dodecavanadate, [V12O32]4− (V12), possesses a 4.4 Å cavity entrance, and the cavity shows unique electrophilicity. Owing to the high polarizability, Br2 was inserted into V12, inducing the inversion of one of the VO5 square pyramids to form [V12O32(Br2)]4− (V12(Br2)). The inserted Br2 molecule was polarized and showed a peak at 185 cm−1 in the IR spectrum. The reaction of V12(Br2) and toluene yielded bromination of toluene at the ring, showing the electrophilicity of the inserted Br2 molecule. Compound V12(Br2) also reacted with propane, n‐butane, and n‐pentane to give brominated alkanes. Bromination with V12(Br2) showed high selectivity for 3‐bromopentane (64 %) among the monobromopentane products and preferred threo isomer among 2‐,3‐dibromobutane and 2,3‐dibromopenane. The unique inorganic cavity traps Br2 leading the polarization of the diatomic molecule. Owing to its new reaction field, the trapped Br2 shows selective functionalization of alkanes.

Isolation of a Nitromethane Anion in the Calix-Shaped Inorganic Cage

“…Thus, V12 can be categorized as one of the guest-responsible Supramolecular Association-Dissociation Switches [3]. In the case of Br 2 , Br 2 inserted into V12 is polarized due to the unique charge distribution of the inside of V12, and the peak of the Br−Br vibration is detected in IR at 185 cm −1 [29]. Furthermore, the stabilization of several kinds of anions in V12 has been reported [25][26][27].…”

“…The distance between the central anion and its nearest neighbor vanadium is far from bonding distances, showing that the central anion is floating in the container. Among polyoxometalates composed of VO 5 square pyramids, a 'calix'-shaped dodecavanadate [V 12 O 32 ] 4− (V12) is known [19][20][21][22][23][24][25][26][27][28][29][30]. The broader upper rim consists of eight edge-shared VO 5 pyramids, with a 4.4 Å cavity entrance and a narrow lower rim consisting of four vertex-shared VO 5 pyramids ( Figure 1).…”

“…In the initial stage of the V12 chemistry, the utility is limited to the guest exchange among nitriles because of the strong affinity between the nitrile group and the V12 container [20][21][22]. Recently, we have developed the host-guest chemistry of V12 [23][24][25][26][27][28][29]. By avoiding the usage of the nitrile group in the synthetic procedure by controlling the oxidation state of the vanadium sources, V12 with guest-exchangeability to various electron-rich groups can be prepared [25].…”

Induced Fitting and Polarization of a Bromine Molecule in an Electrophilic Inorganic Molecular Cavity and Its Bromination Reactivity

“…Fortunately, the crystallinity remains high after the disappearance of the brown color of Br 2 , and the product is suitable for single-crystal X-ray analysis (Figure 1; Supporting Information, Table S1). [28] The V12 crystal structure is maintained and one DCE is inserted into the V12 bowl as a guest molecule. The arrangement of tetra-n-butyl ammonium cations are almost the same as that in the original single crystals.…”

“…Anion structures of a) V12-free and b) V12(DCE) with adsorbed Br 2 based on X-ray crystallographic analysis. [28]…”