252007-00-4Relevant articles and documents
Photoinduced generation of catalytic complexes from substituted-titanocene-bis(trimethylsilyl)ethyne complexes: Contribution to the mechanism of the catalytic head-to-tail dimerization of terminal alkynes
?těpni?ka, Petr,Gyepes, Róbert,Císa?ová, Ivana,Horá?ek, Michal,Kubi?ta, Ji?í,Mach, Karel
, p. 4869 - 4880 (1999)
A number of substituted-titanocene-alkynyl-alkenyl complexes, [(η5-C5Me4R1) 2Ti(η1-C≡ CR2)(η1-(E)-CH=CHR2)] (R1 = H, Me Ph, Bz; R2 = CMe3, SiMe3, ferrocenyl; A type complexes), were obtained by reacting the corresponding bis(trimethylsilyl)ethyne complexes [(η5-C5Me4R1) 2Ti(η2-Me3SiC≡CSiMe3)] with 1-alkynes R2C≡CH in the dark at 60°C. The complexes undergo a coupling of the carbyl ligands upon exposure to sunlight to give titanocene complexes with 1,4-disubstituted but-1-en-3-ynes, [(η5-C5Me4R1) 2Ti(3,4-η-R2C≡ CCH=CHR2)] (B type complexes). In contrast to A type complexes that do not react further with an excess of tert-butylethyne and (trimethylsilyl)ethyne in the dark, B type complexes induce rapid dimerization of these terminal alkynes to 2,4-disubstituted but-1-en-3-ynes (head-to-tail dimers). This implies that the known dimerization of 1-alkynes in the presence of [(η5-C5Me4R1) 2Ti(η2-Me3SiC≡CSiMe3)] (R1 = H, Me) performed in diffuse daylight is initiated by the B type complexes originating from photoinduced conversion of the initially formed A type products. Titanocene complexes with 2,4-disubstituted but-1-en-3-ynes, [(η5-C5Me4R1) 2Ti(3,4-η-R2C≡CC(R2)=CH2)] (R1 = H, Me, Ph; R2 = SiMe3), were also prepared and their participation in the catalytic cycle was demonstrated.
