Softening the Donor-Set: From [Cu(P^P)(N^N)][PF6] to [Cu(P^P)(N^S)][PF6]

We report the synthesis and characterization of [Cu(P^P)(N^S)][PF6] complexes with P^P = bis(2-(diphenylphosphino)phenyl) ether (POP) or 4,5-bis(diphenylphosphino)-9,9- dimethylxanthene (xantphos) and N^S = 2-(iso-propylthio)pyridine (iPrSpy) or 2-(tert-butylthio)pyridine (tBuSpy). The single crystal structures of [Cu(POP)(iPrSPy)][PF6] and [Cu(POP)(tBuSPy)][PF6] have been determined and confirm a distorted tetrahedral copper(I) centre and chelating P^P and N^S ligands in each complex. Variable temperature (VT) 1H and 31P{1H} NMR spectroscopy reveals dynamic behavior with motion of the POP backbone in [Cu(POP)(iPrSPy)][PF6] and [Cu(POP)(tBuSPy)][PF6] frozen out at 238 K. VT NMR spectroscopic data including EXSY peaks in the ROESY spectrum of [Cu(xantphos)(tBuSPy)][PF6] at 198 K reveal that two conformers exist in an approximate ratio of 5:1. Replacing bpy by the N^S ligands shifts the Cu+/Cu2+ oxidation to a higher potential. The copper(I) compounds are weak emitters in the solid state with PLQY values of <2%. These values are similar to those for [Cu(POP)(bpy)][PF6] and [Cu(xantphos)(bpy)][PF6] in the solid state.

Structure elucidation of β-cyclodextrin–xylazine complex by a combination of quantitative 1H–1H ROESY and molecular dynamics studies

The complexation of xylazine with β-cyclodextrin was studied in aqueous medium. 1H NMR titrations confirmed the formation of a 1:1 inclusion complex. A ROESY spectrum was recorded with long mixing time which contained TOCSY artifacts. It only confirmed the presence of xylazine aromatic ring in the β-cyclodextrin cavity. No information regarding the mode of penetration, from the wide or narrow side, could be obtained. We calculated the peak intensity ratio from the inter-proton distances for the most stable conformations obtained by molecular dynamics studies in vacuum. The results show that highly accurate structural information can be deduced efficiently by the combined use of quantitative ROESY and molecular dynamics analysis. On the other hand, a ROESY spectrum with no spin diffusion can only compliment an averaged ensemble conformation obtained by molecular dynamics which is generally considered ambiguous.

Structural Elucidation of a Novel Scalarane Derivative by Using High-Field (14.1T) N.M.R. Spectroscopy

A novel scalarane derivative (2) has been isolated from the marine sponge Carteriospongia foliascens. A complete assignment of the 1H and 13C n.m.r. spectra of (2) was achieved by using cosy-90, 1H-detected 1H/13C correlation (HMQC sequence) and 1H-detected long-range 1H/13C correlation (HMBC sequence) experiments, all measured at 600 MHz. The assignment of stereochemistry at C4 was supported by a ROESY spectrum.