1-Triflato-3,5,7-trimethyl-1,3,5,7-tetrasilaadamantane and 1,3-bis-triflato-5,7-dimethyl-1,3,5,7-tetrasilaadamantane; synthesis, complexation study and X-ray structure of 1-hydroxy-3,5,7-trimethyl-1,3,5,7-tetrasilaadamantane

The symmetrical 1,3,5,7-tetramethyl-1,3,5,7-tetrasilaadamantane (1) reacts with 1.5 molar equivalents of ICl–AgOTf at room temperature to furnish the hitherto unknown 1-triflato-3,5,7-trimethyl-1,3,5,7-tetrasilaadamantane (9) chemoselectively, in near quantitative yields. The treatment of 9 with 2 mol equivalents of ICl–AgOTf affords the bis-triflate 10 in high yields. Control experiments showed that reaction of 1 with ICl (1 mol equivalents)–CCl4 is sluggish, giving 18% conversion to 1-chloro-3,5,7-trimethyl-1,3,5,7-tetrasilaadamantane (2) after 23 h at room temperature. Addition of AlBr3 catalyzes the process, allowing 73% conversion after 21 h at room temperature. The ICl–AgOTf reagent eliminates the need to prepare and isolate 2 as an intermediate for the synthesis of 9. In silicon NMR spectra, the 29Si SiOTf resonance of 10 is slightly upfield compared with that of 9. Treatment of 9 with a saturated solution of B(C6F5)3 in CH2Cl2 at room temperature shows only minor deshielding at silicon as determined by 29Si-NMR spectroscopy. Attempts to generate donor–acceptor complexes by treatment of 9 with Al(OTf)3–CD3CN and with liquid BCl3 gave no notable changes in the SiOTf NMR chemical shift. In attempts to grow crystals from 9 and 10, white crystals suitable for X-ray analysis were obtained from a sample of 9, the molecular structure of which was shown to be 1-hydroxy-3,5,7-trimethyl-1,3,5,7-tetra-silaadamantane (11), generated by hydrolysis of the SiOTf bond.