Synthesis of Bismuth and Antimony Complexes of the?Larger? Calix[n]arenes (n = 6, 8); from Mononuclear to Tetranuclear Complexes.

A series of calix[n]arene (n = 6?8) bismuth and antimony complexes were synthesized and fully characterized by NMR, X-ray, IR, UV-Vis and elemental analysis. The monobismuth calix[6]arene complex [Bi{tBuC6(H)3}]21 was prepared by the reaction of para-tert-butylcalix[6]arene (tBuC6(H)6) with one equivalent of Bi[N(SiMe3)2]3. Complex 1 featured a Bi2(?-O)2 central core similar to other bismuth calixarene complexes prepared by our group. Reaction of calix[6]arene (HC6(H)6) with two equivalents of Bi(OtBu)3 yielded different outcomes depending on the reaction solvent. If THF was used, complex [Bi{HC6(H)3}] 2 was obtained in 72% yield; however, when toluene was used, complexes 2 and [Bi2{HC6}] 3 were isolated in 23 and 57% yields, respectively. Mononuclear complexes 1 and 2 displayed dimeric structures in the solid state with cone-like conformations for the calixarene ligands. The 1H NMR spectrum of complex 2 displays patterns for an asymmetric structure with two signals in a 2?:?1 ratio for the unreacted OH groups. Treatment of calix[6]arenes RC6(H)6 (R = H, tBu) with two equivalents of SbR3 (R = OtBu, NMe2) produced dinuclear complexes [Sb2{HC6}] 4, and [Sb2{tBuC6}] 5, respectively. The 1H NMR spectra for the dinuclear complexes 3, 4, and 5 showed the characteristic calixarene pattern for a 1,2,3-alternate conformer. In the process of recrystallization of complex 4 an unexpected trimetallic complex with composition [Sb3O2{HC6(H)}] 4a was obtained in low yield. Treatment of para-tert-butylcalix[7]arene (tBuC7(H)7) with two equivalents of Bi(OtBu)3 produced the bimetallic complex [Bi2O{tBuC7(H)3}]26. Complex 6 contains an overall Bi4O2(OAr)8 core system with a structural resemblance to other bimetallic bismuth calixarene complexes reported by our group. The larger para-benzylcalix[8]arene (BnC8(H)8) and calix[8]arene (HC8(H)8) reacted with excess Bi(OtBu)3 to produce the tetranuclear complexes [Bi4O2{HC8}] 7 and [Bi4O2{BnC8}] 8, respectively. The solid state structure of complex 8 featured a dimeric unit with the calixarene ligands in pinched-cone conformation and displaying an overall Bi8O4(OAr)16H2O core. No metal ?-arene interactions were observed.