Ring Contraction of a Tungstacyclopentane Supported on Silica: Direct Conversion of Ethylene to Propylene.

The reaction of W(NAr)( 13 C 4 H 8 )(OSiPh 3 ) 2 ( 1 ) (NAr = 2,6-diisopropylphenylimido) with silica partially dehydroxylated at 700 °C (SiO 2-700 ) is highly dependent on the reaction conditions. The primary product of this reaction is W(NAr)( 13 C 4 H 8 )(OSiPh 3 )(OSi(O-) 3 ) ( 2 ) when the reaction is carried out in the dark. Grafting 1 onto SiO 2-700 in ambient lab light results in the formation of 2 , W(NAr)( 13 CH 2 13 CH 2 )(OSiPh 3 )(OSi(O-) 3 ) ( 4 ), and one isomer of square-pyramidal W(NAr)( 13 CH 2 13 CH( 13 Me) 13 CH 2 )(OSiPh 3 )(OSi(O-) 3 ) ( 3 ). Heating 2 to 85 °C for 6 h results in the formation of 3 , 4 , W(NAr)( 13 CH( 13 Me) 13 CH 2 13 CH 2 )(OSiPh 3 )(OSi(O-) 3 ) ( 5 ), and W(NAr)(( 13 CH 2 ) 2 13 CH( 13 Me)( 13 CH 2 ) 2 )(OSiPh 3 )(OSi(O-) 3 ) ( 6 ). Photolysis of 2 with blue LEDs (λ max = 450 nm) produces 4, both isomers of 3, 5 , and free ethylene. In the presence of excess ethylene and blue LED irradiation at 85 °C, 1 /SiO 2-700 catalyzes the direct conversion of ethylene to propylene.