Fifty years of oxacalix[3]arenes: A review

• Kevin Cottet,
• Paula M. Marcos and
• Peter J. Cragg

Beilstein J. Org. Chem. 2012, 8, 201–226, doi:10.3762/bjoc.8.22

• diffraction and 51V NMR data it was proposed that the VO group bound within the macrocyclic cavity, by analogy to the Ti(IV) complex, and that these units formed linear aggregates held together by V=O···V=O interactions. Ten years later, Redshaw was able to prove Hampton’s assertion regarding the structure by

Thermodynamic and kinetic stabilization of divanadate in the monovanadate/divanadate equilibrium using a Zn-cyclene derivative: Towards a simple ATP synthase model

• Hanno Sell,
• Anika Gehl,
• Frank D. Sönnichsen and
• Rainer Herges

Beilstein J. Org. Chem. 2012, 8, 81–89, doi:10.3762/bjoc.8.8

• thermodynamically as shown by NMR titration. Moreover, EXSY NMR experiments reveal that the vanadate dimer is also kinetically stabilized with respect to hydrolysis by complexation with Zn-cyclene. Keywords: EXSY NMR; NMR titration; supramolecular chemistry; vanadate condensation; 51V NMR; Zn-cyclene

• ]. For the analysis of the multicomponent system, 1-D 51V NMR titrations of Na3VO4 with ligand 1 were performed at three different pH values at 25 °C (pH ~9.5 CHES buffer (N-cyclohexyl-2-aminoethanesulfonic acid); pH ~8.5 EPPS buffer (3-[4-(2-hydroxyethyl)-1-piperazinyl]propanesulfonic acid); pH ~7.6

• . The 51V NMR titration at pH 9.5 is shown in Figure 3 (for the corresponding spectra recorded at pH 7.6 and 8.5 see Supporting Information File 1). The addition of Zn-benzylcyclene 1 leads to an upfield shift of the monovanadate and the divanadate signal at all pH values that were investigated. This

Kinetics and mechanism of vanadium catalysed asymmetric cyanohydrin synthesis in propylene carbonate

• Michael North and
• Marta Omedes-Pujol

Beilstein J. Org. Chem. 2010, 6, 1043–1055, doi:10.3762/bjoc.6.119

• from 51V NMR spectroscopy suggested that propylene carbonate coordinates to VO(salen)NCS, blocking the free coordination site, thus inhibiting its Lewis acidity and accounting for the reduction in catalytic activity. This explanation was further supported by a Hammett analysis study, which indicated

• came from 51V NMR studies of complex 2 (Figure 5). The spectrum of complex 2 in CDCl3 shows a resonance at −580 ppm (Figure 5a). It is known from X-ray crystallography that the isothiocyanate unit in complex 2 is directly bound to the vanadium ion through the nitrogen atom. Thus, the vanadium ion is

• ), in which the vanadium ion is bound to four oxygen atoms and two nitrogen atoms. When the 51V NMR spectrum of complex 2 is recorded in propylene carbonate, the 51V NMR signal is observed at −571 ppm (Figure 5c), again indicative of formation of a species, such as 5, in which the vanadium ion is bound