Synthesis of Novel Titanasiloxanes with Ring and Cage Structures Using Sterically Demanding Substituents

Abstract

Novel oligomeric titanasiloxanes have been synthesized in good yields by reaction of sterically demanding organosilanetriols with titanium alkoxides. The silanetriols tBu2(Me3Si)FlSi(OH)3 (5), (Me3Si)FlSi(OH)3 (6), and MeFlSi(OH)3 (7) and the titanium alkoxides Ti(OEt)4, Ti(OiPr)4, and Ti(OiPr)2(acac)2 have been used as starting materials (Fl = fluorenyl). Quite different structures are obtained by only small modifications of the organic substituents of the substrates. Thus, the condensation reactions result in the formation of the polyhedral titanasiloxanes [tBu2(Me3Si)FlSi]4O12[TiOEt]4 (8), [(Me3Si)FlSi]2O5[Ti(OEt)]4[μ2-OEt]6[μ4-O] (9), ([tBu2(Me3Si)FlSi]3O10[Ti(OiPr)]4[μ2-OiPr]2[μ3-O]Ti)2O (10), and [MeFlSi]2O8[Ti(OiPr)]6[μ2-OiPr]4[μ3-O]2[PhNH2]2 (11) and the cyclic titanasiloxane [MeFlSi(OiPr)]2O4[Ti(acac)2]2 (12). A 1:1 stoichiometry of the starting materials leads to 8 and 12 in quantitative yield, while 9−11 are isolated in minor quantities. If the appropriate substrate ratio is used, the latter compounds can also be obtained in high yields. All titanasiloxanes have been characterized by X-ray crystallography, NMR, IR, and elemental analysis.

Recent Developments in the Chemistry of Molecular Titanosiloxanes and Titanophosphonates

“…These titanosiloxanes serve as model compounds for Ti incorporated zeolites which are well known for their exceptional catalytic properties. Later, we and others (Murugavel et al, 2003;Voigt et al, 1996;Lindemann et al, 2002;Nolte et al, 2003) have reported the synthesis of a number of cubic titanosiloxanes, [RSiO 3 TiR 0 ] 4 , from the reaction of TiR 0 4 with RSi(OH) 3 , in high yields.…”

“…Reaction of equimolar amounts of (Me 3 Si)FluorenylSi(OH) 3 and Ti(OEt) 4 in hexane led to a mixture of products (Nolte et al, 2003 (54) (Scheme 18) could be isolated in good yield by the reaction in the appropriate stoichiometry (1 equiv of silanetriol and 2 equiv of Ti(OEt) 4 ). Compound 54 can be described as consisting of a rather symmetrical framework of two silicon and four titanium atoms, which is completely wrapped by organic groups, i.e., by fluorenyl substituents at silicon and by ethoxy substituents at titanium.…”

“…The reaction of tBu 2 (Me 3 Si)FluorenylSi(OH) 3 and Ti ( (Nolte et al, 2003). Compound 55 was obtained as a colorless solid, which is highly soluble in polar and nonpolar solvents.…”

“…The reaction of MeFluorenySi(OH) 3 and Ti(OiPr) 4 in a 1 : 1 stoichiometry and small amounts of aniline led to a mixture of products (Nolte et al, 2003 alkoxide, water, and aniline were used. The structure of 56 can be described on the basis of a cubic core unit, possessing two silicon and six titanium atoms in corner positions.…”

“…The reaction of MeFluorenylSi(OH) 3 and Ti(OiPr) 2 (acac) 2 in a 1 : 1 stoichiometry led to the cyclic titanosiloxane [MeFluorenylSi(OiPr)] 2 O 4 [Ti(acac) 2 ] 2 (57) in good yields (Scheme 21) (Nolte et al, 2003). The centrosymmetric structure of 57 can be described as an eight-membered Si 2 O 4 Ti 2 ring.…”