Synthesis and reactivity towards DIBAL-H of cyclo-siloxanes cyclo-[R2SiOSi(Ot-Bu)2O]2, cyclo-(t-BuO)2Si(OSIR2)2O, and cyclo-R2Si[OSi(Ot-Bu)2]2O (R = Me, Ph)

The six-, eight- and twelve-membered cyclo-siloxanes, cyclo-[R 2 SiOSi(Ot-Bu) 2 O] 2 (R = Me (1), Ph (2)), cyclo-(t-BuO) 2 -Si(OSiR 2 ) 2 O (R = Me (3), Ph (4)), cyclo-R 2 Si[OSi(Ot-Bu) 2 ] 2 O (R = Me (5), Ph (6)) and cyclo-[(t-BuO) 2 Si(OSiMe 2 ) 2 O] 2 (3a) were synthesized in high yields by the reaction of (t-BuO) 2 Si(OH) 2 and [(t-BuO) 2 SiOH] 2 O with R 2 SiCl 2 and (R 2 SiCl) 2 O (R = Me, Ph). Compounds 1-6 were characterized by solution and solid-state 29 Si NMR spectroscopy, electrospray mass spectrometry and osmometric molecular weight determination. The molecular structure of 4 has been determined by single crystal X-ray diffraction and features a six-membered cyclo-siloxane ring that is essentially planar. The reduction of 1-6 with i-Bu 2 AlH (DIBAL-H) led to the formation of the metastable aluminosiloxane (t-BuO) 2 Si(OAli-Bu 2 ) 2 (7) along with Me 2 SiH 2 and Ph 2 SiH 2 .