Control of optically active structure of thioether‐phthalocyanine aggregates by chiral Pd(II)‐BINAP complexes in toluene and at the toluene/water interface

Abstract

The Pd(II)-2,2'-bis(diphenylphosphino)-1,1'-binaphthyl (BINAP)-mediated chiral assembly of thioether-derivatised phthalocyanatomagnesium(II) compounds (MgPc(SR)8, SR is benzylthio (SBz) or benzhydrylthio (Bh)) was formed in toluene and at the toluene/water interface, and investigated by means of UV-Vis absorption and circular dichroism (CD) spectroscopy combined with the centrifugal liquid-membrane (CLM) devise. Interfacial tension measurements indicated that, in the presence of PdSO4 in the aqueous phase, BINAP ligand adsorbed as a monolayer forming Pd(II)BINAP2+ complex at the toluene/water interface. UV-Vis absorption spectrum of MgPc(SR)8 in the Q-band region was blue-shifted in toluene upon addition of [Pd(II)BINAP]Cl2, but red-shifted at the toluene/water interface when Pd(II)BINAP2+ was formed at the interface. These results suggested that MgPc(SR)8-Pd(II)BINAP complex formed H-aggregate (face-to-face type) in toluene solution and J-aggregate (end-to-end type) at the toluene/water interface, respectively. Moreover, the specific bisignate CD spectral pattern in both systems indicated that the aggregates of MgPc(SR)8-Pd(II)BINAP complexes were chirally twisted, well controlled by the chirality of BINAP ligand. Very interestingly, the morphology of MgPc(SBz)8-Pd(II)BINAP and MgPc(SBh)8-Pd(II)BINAP aggregates formed at the toluene/water interface were significantly different as the rodlike and the ribbonlike crystalline structure, respectively, as observed by a scanning electron microscopy (SEM). On the basis of these experimental results, we proposed schematic molecular models of the chiral aggregates of MgPc(SR)8-Pd(II)BINAP complexes and demonstrated the specific role of the toluene/water interface.