Yttrium calix[4]arene complexes. Silylation and silylamine elimination reactions on model oxo surfaces

The synthesis and the spectroscopic and structural characterization of lower-rim-silylated and rare-earth-metalated calix[4]arenes are presented. Hexamethyldisilazane, HN(SiMe3)(2), reacted in a selective manner with [p-tert-butylcalix[4]arene]H-4 (1) in refluxing mesitylene to give the 1,3-silylated product [p-tert-butylcalix[4]arene(SiMe3)(2)]H-2 (2) in high yield. The molecular structure of compound 2, as revealed by X-ray crystallography, shows the pinched cone conformation of the calixarene bowl, featuring hydrogen bonding between the phenylsilyl ether and phenolic oxygen atoms (O . . .O, 2.838 Angstrom). 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 at ambient temperature. A single-crystal X-ray diffraction study of compound 3 established the I,2-alternate conformation, which is also present in solution, as indicated by H-1 NMR spectroscopy. The yttrium complex Y[N(SiHMe2)(2)](3)(THF)(2) (4) exchanged all of its silylamide ligands when treated with an equimolar amount of 1 in toluene at ambient temperature to yield compound 5, as indicated by IR and NMR spectroscopy. The molecular structure 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 terminal ligands and one in a bridging mode, while the fourth undergoes in situ silylation (v(SiH) 2127 cm(-1)). The distorted-trigonal-bipyramidal coordination geometry is completed by a THF molecule. Bis-silylated 2 reacted with 4 to form the heteroleptic complex {Y[p-tert-butylcalix[4]arene(SiMe3)(2)][N(SiHMe2)(2)]} (6). Crystal data: C50H72O4Si2 (2), triclinic, P (1) over bar, a = 12.8914(3) Angstrom, b = 14.9270(5) Angstrom, c = 15.1652(4) Angstrom, alpha = 77.293(2)degrees, beta = 65.019(2)degrees, gamma = 72.234(2)degrees, Z = 2; C52H80O4Si4 (3), triclinic, P (1) over bar, a = 10.1774(2) Angstrom, b = 14.1680(2) Angstrom, c = 18.7206(2) Angstrom, alpha = 95.8195(8)degrees, beta = 95.5294(8)degrees, gamma = 98.1098(7)degrees, Z = 2; C100H132O10Si2Y2, 2(C6H6) (5), triclinic, P (1) over bar, a = 13.2625(4) Angstrom, b = 14.5894(3) Angstrom, c = 17.0458(5) Angstrom, alpha = 65.0986(14)degrees, beta = 77.8786(8)degrees, gamma = 85.5125(13)degrees, Z = 1.