Site-Selective and Stepwise Complexation of Transition Metal Fragments on Calixarene and Functions of Polynuclear Calixarene Complexes

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In spite of the recent interest in metallocalixarenes little is known for late transition metal complexes of unmodified calixarenes. In this study we have developed the synthetic methods for group 7-10 transition metal derivatives of calixarenes and revealed their unique reactivities. As for the calixarene group 9 metal complexes, the reaction of [(cod)M(Ome)]2 (M = Rh, Ir) with calix[4]arenes (LH4) in the molar ratio of 0.5-0.6: 1 has been found to give the rhodium arene complexes [(cod)M(LH3)], while that in the molar ratio of 1.1-1.5:1(M = Rh) leads to the selective formation of the dinuclear complexes [{(cod)Rh}2(LH2)] in which one of the Rh(cod)+ fragments is coordinated by an aryl group and the other by two phenolic oxygen atoms. The stepwise synthesis of the Rh-Ir heterobimetallic analogue of the latter complex has also been achieved. On the other hand, the anionic dioxorhenium complex [Ph4P][ReO2L] (LH4 = p-tBu-calix[4]arene) is synthesized by treatment of LHLi3 with [Ph4P][ReOCI4] followed by oxidation with Ag2O. [Ph4P][ReO2L] is the first calixarene rhenium complex in which the metal atom is directly bound to the body of calixarene. More importantly, [Ph4P][ReO2L] reacts with solvated cationic species [Pd(C3H5)(Me2CO)x]+ and [Rh(nbd)(Me2CO)x]+ to afford the heterobimetallic complexes [ReO2LPd(C3H5)] and [ReO2LRh(nbd)], respectively. The latter complexes provide the first examples of dinucelar calixarene complexes which possess a heterodinuclear transition metal core inside the cavity of a calixarene ligand.