Selective tripodal titanium silsesquioxane catalysts for the epoxidation of unactivated olefins

Regiomeric mixture of HMe2Si(CH2)3( i-Bu)6Si7O9(OH)3 ( 6), containing a Si- H group in one of the ligands of the silsesquioxane, was tethered onto a vinyl terminated hyperbranched poly(siloxysilane) polymer via a hydrosilation reaction to generate extremely active catalysts, P1-8 and c-P1-8. The synthesis of 6, in good yield, was accomplished via hydrosilation of CH2=CHCH2( i-Bu)7Si8O12 (1) to generate ClMe2Si(CH2)3(i-Bu) 7Si8O12 (3) followed by the reduction of 3 with LiAlH4 to afford HMe2Si(CH 2)3(i-Bu)7Si8O 12 (4) where the base-catalyzed excision of one framework silicon was employed to generate a regiomeric mixture of 6..;[Ti(NMe2){Et3Si(CH2)3( i-Bu)6Si7O12}] (7), [Ti(NMe2){HMe2Si(CH2)3( i- Bu)6Si7O12}] (8), [Ti(NMe2){(i-C4H9) 7Si7O12}] (9) and [Ti(NMe 2){(c-C6H11)7Si7O 12}] (10) were synthesized via protonolysis of Ti(NMe2)4 with one equivalent of the trisilanol precursor in order to determine if the presence of isomers would be intrinsically different as compared to the uniformly substituted catalysts. Isomers 8 and 9, demonstrated lower activity as compared to the uniformly substituted catalysts 9 and 10, however the isomers still exhibited extremely high catalytic activity for the epoxidation of 1-octene using tert-butyl hydroperoxide (TBHP) relative to titanium catalysts used in industry. Additionally, 9, 10, P1-8 and c-P1- 8 were very selective catalysts for the epoxidation of various olefins such as terminal (1-octene), cyclic (cyclohexene or 1-methylcyclohexene), and more demanding olefins (limonene or alpha-pinene) employing TBHP as the oxidant. Furthermore, P1-8 and c-P1-8 were recyclable with minimal loss of titanium however the catalysts could also be repaired if a loss in activity was observed.;Preliminary epoxidation reactions employing P1-8 and c-P1-8 along with hydrogen peroxide (H2O 2) as the oxidant were also explored using different solvents. P1-8 degraded quickly due to the hydrolysis of the titanium from the large amount of water present in the reaction mixture however c-P1-8 showed activity for the epoxidation of cyclohexene. Finally, regiomeric mixture of Ti(NMe2)(HS(CH2)3)(i-C 4H9)6Si7O12) (13), was tethered onto gold nanoparticles for the conversion of propene to propylene oxide using molecular hydrogen and oxygen. While the catalysts showed low activity under our reaction conditions, numerous improvements can be investigated in order to improve upon the catalysts.