Two organometallic fragments inclusioned in a 1,3-alternate calix[4]arene tetraphosphane: evidence for transition metal-arene interaction through the cavity

The preparation of an 1,3-alternate calix4]arene tetraphosphane ligand, 25,26,27,28-tetrakis{2-(diphenylphosphino)ethoxy}calix4]arene (4), is described. Ligand 4 is obtained in four steps in 17% overall yield. Reaction of 4 with AgBF4 produced the encapsulated two silver complex Ag2{(P,P,P,P)-tetraphencalix4]arene}](BF4)2. The solid-state structure shows that the encapsulated silver undergoes a substantial pi-interaction by two opposite arene rings. Rhodation of 4 employing Rh(cot)2]BF4 yielded the encapsulated complex with a bent coordination mode. Two organometallic fragments inclusioned inside a 1,3-alternate calix4]arene tetraphosphane was also achieved by the reaction of 4 with PtH(PPh3)2 (thf)]+. Full characterization includes X-ray structural studies of compounds 4-6.