Controlled Formation of Mixed-Metal Macrocycles Using Dynamic Exchange Processes and Steric Constraints

The exchange reaction of the trinuclear macrocycles [(C6H3iPr3)Ru(C5H3NO2)]3 (AAA) and [(cymene)Ru(C5H3NO2)]3 (BBB) has been studied. It was found that the equilibration proceeds in two steps and that the final mixture is completely dominated by the mixed-metal macrocycles [{(C6H3iPr3)Ru}2{(cymene)Ru}(C5H3NO2)3] (AAB) and [{(C6H3iPr3)Ru}{(cymene)Ru}2(C5H3NO2)3] (ABB). The results are rationalized by assuming unfavorable steric interactions between adjacent (C6H3iPr3)Ru fragments. It is shown that interactions of this kind can be used to bias scramblingprocesses in such a way that mixed-metal macrocycles are obtained in over 80 % yield. The structures of [{(C6Me6)Ru}{(C6H6)Ru}2(C5H3NO2)3] and [(Cp*Rh){(C6H6)Ru}2-(C5H3NO2)3] have been determined by single-crystal X-ray analysis.