摘要:
                                A study of the reactions of the titanium imido methyl cation [Ti((NBu)-Bu-t)(Me-3[9]aneN(3))X](+) (5(+), X = Me) and key analogues (6(+), X = CH2SiMe3; 7(+), X = Cl) with a range of unsaturated substrates provides a comprehensive evaluation of reaction site selectivity in transition-metal cations which contain both Ti=NR and Ti-R ' functional groups as potential sites for 2 pi + 2 pi cycloaddition and migratory insertion, respectively. Cations 5+ and 6(+) reacted with MeCN to form Ti-R ' insertion products. Insertion reactions were also exclusively observed in their reactions with N,N '-disubstituted carbodiimides or tert-butyl isocyanate. In contrast, reaction of the chloride cation 7+ with diisopropylcarbodiimide or tert-butyl isocyanate afforded the unusual a adducts [Ti((NBu)-Bu-t)(Me-3[9]aneN(3))(L)Cl](+) (L = (PrNCNi)-Pr-i Pr, (BuNCO)-Bu-t), which slowly underwent 2,7 + 2 pi cycloaddition. Reaction of 5+ with the internal alkynes PhCCR (R = Ph, SiMe3) also showed exclusive preference for insertion into the Ti-Me bond. In contrast, reaction with terminal alkynes RCCH (R = Ph, SiMe3) yielded only the azametallacyclic products via 2-pi + 2 pi cycloaddition reactions. The chloride cation 7+ also underwent a 2 pi + 2 pi cycloaddition with PhCCH but was unreactive toward PhCCPh, ethylene, styrene, or 1-hexene.