Efficient synthesis of the cyclometalated complex fac-[Rh(ppy)3] (ppy = 2-phenylpyridinato)

A new convenient high-yield synthesis of the tris-cyclometalated complexes fac-[Rh(ppy)3] (4; ppy = 2-phenylpyridinato) was developed. Complex 4 was prepared in a kind of one-pot synthesis starting from in situ prepared [Rh(acac)(coe)2] (2) which was heated in refluxing 2-phenylpyridine for a short time. After purification by filtration over alumina, compound 4 was obtained in yields of 65%. Also [Rh(acac)(ppy)2] (3) was prepared in a similar manner by oxidative addition of Hppy in refluxing toluene in high yields. In contrast to previous findings with the analogous iridium compounds, there was not any hint at the formation of the isomer mer-[Rh(ppy)3] using similar reaction conditions as applied for iridium. Furthermore the compound [{Rh(μ-Cl)(ppy)2}2] (5) was prepared from [{Rh(μ-Cl)(coe)2}2] (1) and Hppy in refluxing toluene in nearly quantitative yield.