| Abstract
| - Depending on the steric bulk of their silyl groups, disilazane reagents HN(SiMe3)2 and HN(SiHMe2)2 selectively yield bis- and tetrakis-silylated calix[4]arene derivatives. Similar to its reactivity on silica surfaces, the yttrium silylamide Y[N(SiHMe2)2]3(THF)2 forms aryloxide bond-linked and silylated moieties on the lower-rim calix[4]arene surface, while the SiH group acts as a versatile spectroscopic probe.
- The synthesis and the spectroscopic and structural characterization of lower-rim-silylated and rare-earth-metalatedcalix[4]arenes are presented. Hexamethyldisilazane, HN(SiMe3)2, reacted in a selective manner with [p-tert-butylcalix[4]arene]H4 (1) in refluxing mesitylene to give the 1,3-silylated product [p-tert-butylcalix[4]arene(SiMe3)2]H2 (2) in high yield. The molecular structure of compound 2, as revealed by X-ray crystallography, shows thepinched cone conformation of the calixarene bowl, featuring hydrogen bonding between the phenylsilyl ether andphenolic oxygen atoms (O···O, 2.838 Å). From the reaction of the sterically more crowded tetraphenyldimethyldisilazane, HN(SiMePh2)2, only starting material could be recovered. In contrast, tetramethyldisilazane, HN(SiHMe2)2, afforded the tetrakis-silylated product [p-tert-butylcalix[4]arene(SiHMe2)4] (3) in hexane solution atambient temperature. A single-crystal X-ray diffraction study of compound 3 established the 1,2-alternateconformation, which is also present in solution, as indicated by 1H NMR spectroscopy. The yttrium complexY[N(SiHMe2)2]3(THF)2 (4) exchanged all of its silylamide ligands when treated with an equimolar amount of 1in toluene at ambient temperature to yield compound 5, as indicated by IR and NMR spectroscopy. The molecularstructure of 5 revealed a centrosymmetric dimer of composition [Y{p-tert-butylcalix[4]arene(SiHMe2)}(THF)]2.Three of the deprotonated phenolic oxygen atoms of the calixarene bowl bind to the metal center, two as terminalligands and one in a bridging mode, while the fourth undergoes in situ silylation (ν(SiH) 2127 cm-1). The distorted-trigonal-bipyramidal coordination geometry is completed by a THF molecule. Bis-silylated 2 reacted with 4 toform the heteroleptic complex {Y[p-tert-butylcalix[4]arene(SiMe3)2][N(SiHMe2)2]} (6). Crystal data: C50H72O4Si2 (2), triclinic, P1̄, a = 12.8914(3) Å, b = 14.9270(5) Å, c = 15.1652(4) Å, α = 77.293(2)°, β = 65.019(2)°,γ = 72.234(2)°, Z = 2; C52H80O4Si4 (3), triclinic, P1̄, a = 10.1774(2) Å, b = 14.1680(2) Å, c = 18.7206(2) Å,α = 95.8195(8)°, β = 95.5294(8)°, γ = 98.1098(7)°, Z = 2; C100H132O10Si2Y2, 2(C6H6) (5), triclinic, P1̄, a =13.2625(4) Å, b = 14.5894(3) Å, c = 17.0458(5) Å, α = 65.0986(14)°, β = 77.8786(8)°, γ = 85.5125(13)°,Z = 1.
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