1,4-Phenylene incorporated decaphyrin tetrarhodium(I) complex: Synthesis, structures, and chiroptical properties

1,4-Phenylene-incorporated decaphyrin(1.0.1.0.0.1.0.1.0.0) 1 has been previously synthesized and optically resolved in the free-base form; however, it undergoes racemization at elevated temperature. In this study, we fixed the figure-of-eight conformation by means of rhodium(I) coordination. The resulting tetranuclear Rh(I) complex 1-Rh-4, which is scarcely reported to date, exhibited considerable conformational stability. Accordingly, it could be readily resolved by high-performance liquid chromatography (HPLC) on a chiral stationary phase, and no racemization was observed even at 110 ?. Importantly, the tetranuclear porphyrinoid complex bearing a unique edge-to-edge alignment of the two 1,4-phenylene spacers revealed a relatively large molar circular dichroism (CD) with an absorption dissymmetry factor (g(abs)) of 0.018. While a two-fold larger g(abs) of up to 0.036 was seen for the structural congener 1, wherein the 1,4-phenylene spacers adopt a face-to-face orientation. Thus, it serves to be an attractive basis to explore the structural effect on the chiroptical properties of the expanded porphyrinoid.