Chiral Tectonics: VCD and ECD Application for Epimerization of a Star-Burst Tetranuclear Complex with a Labile Central Core

The present article reports the application of vibrational circular dichroism (VCD) and temperature-dependent electronic circular dichroism (ECD) methods to reveal the dynamical aspects of a star-burst tetranuclear metal complex with a labile central core in a solution. One-handed chiral inert tecton, ∆- or Λ-[Ru(III)(acac)2(taetH)] (acacH = acetylacetone, taetH2 = tetraacetylethane), was prepared by reacting [Ru(acac)3] with taetH2 in solid at 120 °C. The ∆Λ-pair of pure enantiomers was obtained chromatographically. On adding Al(ClO4)3 to its enantiopure solution, three units of one-handed tecton were assembled spontaneously around an aluminum(III) ion to form a star-burst tetranuclear complex, [{∆- or Λ-Ru(acac)2(taet)}3Al(III)]. The VCD spectrum recorded on the CDCl3 solution of the complex showed that the central chirality around an Al(III) ion took dominantly the absolute configuration antipodal to those of peripheral Ru(III) units at the temperature lower than −10 °C. The complex underwent interconversion between the ∆- and Λ-configurations around a central Al(III) core (or epimerization) in solution. The activation energy barrier was determined from the time courses of ECD spectra in CHCl3 and CH3OH.

Structural study of mono-, di- and tetranuclear complexes of the {Re(CO)3}+ fragment with thiosemicarbazone/thiosemicarbazonate ligands containing benzothiazole or benzoxazole groups

Thiosemicarbazone form mononuclear and dinuclear complexes as bidentate ligands with {Re(CO)3}+ and a tetranuclear complex with unusual bideprotonated thiosemicarbazonate.

Activation of carbon suboxide (C3O2) by U(iii) to form a cyclobutane-1,3-dione ring

[U(η5-C5H4SiMe3)3] reductively couples three C3O2 molecules to form a tetranuclear complex with a central cyclobutane-1,3-dione ring, via an intermediate bridging ketene complex.

Structural diversity of polynuclear Mg x O y cores in magnesium phenoxide complexes

The binuclear complex bis(2,6-di-tert-butyl-4-methylphenolato)-1κO,2κO-(1,2-dimethoxyethane-1κ2 O,O′)bis(μ-phenylmethanolato-1:2κ2 O:O)(tetrahydrofuran-2κO)dimagnesium(II), [Mg2(C7H7O)2(C15H23O)2(C4H8O)(C4H10O2)] or [(BHT)(DME)Mg(μ-OBn)2Mg(THF)(BHT)], (I), was obtained from the complex [(BHT)Mg(μ-OBn)(THF)]2 by substitution of one tetrahydrofuran (THF) molecule with 1,2-dimethoxyethane (DME) in toluene (BHT is O-2,6- t Bu2-4-MeC6H4 and Bn is benzyl). The trinuclear complex bis(2,6-di-tert-butyl-4-methylphenolato)-1κO,3κO-tetrakis(μ-2-methylphenolato)-1:2κ4 O:O;2:3κ4 O:O-bis(tetrahydrofuran)-1κO,3κO-trimagnesium(II), [Mg3(C7H7O)4(C15H23O)2(C4H8O)2] or [(BHT)2(μ-O-2-MeC6H4)4(THF)2Mg3], (II), was formed from a mixture of Bu2Mg, [(BHT)Mg( n Bu)(THF)2] and 2-methylphenol. An unusual tetranuclear complex, bis(μ3-2-aminoethanolato-κ4 O:O:O,N)tetrakis(μ2-2-aminoethanolato-κ3 O:O,N)bis(2,6-di-tert-butyl-4-methylphenolato-κO)tetramagnesium(II), [Mg4(C2H6NO)6(C15H23O)2] or Mg4(BHT)2(OCH2CH2NH2)6, (III), resulted from the reaction between (BHT)2Mg(THF)2 and 2-aminoethanol. A polymerization test demonstrated the ability of (III) to catalyse the ring-opening polymerization of ∊-caprolactone without activation by alcohol. In all three complexes (I)–(III), the BHT ligand demonstrates the terminal κO-coordination mode. Complexes (I), (II) and (III) have binuclear rhomboid Mg2O2, trinuclear chain-like Mg3O4 and bicubic Mg4O6 cores, respectively. A survey of the literature on known polynuclear Mg x O y core types for ArO–Mg complexes is also presented.