Unusual reductive coupling of alkynes and ketones: Reactivity of titanacycles supported by dimethylsilylcalix[4]arene (DMSC) ligands

Reaction of [(DMSC)Ti{1,2,4-(Me3Si)(3)C6H3}] (1) With 1 equiv of bipyridine (bpy) or 4,4'-dimethyl-2,2'-dipyridyl (dmbpy) and a slight excess of RC=CH quantitatively produced [(DMSC)Ti(eta (2)-RC=CH)(L-2)] (L-2 = bpy or dmbpy ) (5-16). (DMSC)TiPh2 (17) reacted with greater than or equal to2 equiv of bpy or dmbpy to give (DMSC)Ti(bpy)(2) (18) and (DMSC)Ti(dmbpy)(2) (19), res pectively. Both H-1 and C-13 NMR data, as well as X-ray crystallography in the case of [(DMSC)Ti(eta (2)-HC=CBut)(bpy)] (7), support exe-orientation o f the alkyne's non-H substituent in 5-16. Reaction of [(DMSC)Ti{1,2,4-(Me3S i)(3)C6H3}] (1) With a mixture of RC=CH and R2CO did not give the expected 5-oxa-1-titana-2-cyclopentene products but instead produced 2,7-dioxa-1-tit ana-4-cycloheptenes (20-25). The latter result may be understood in terms o f the unique directing influence of the DMSC ligand.