TITANATRANES AND AZATITANATRANES - NUCLEOPHILIC-SUBSTITUTION REACTIONS ON THE AXIAL POSITION

The titanatrane Me2N activated Ti(OCH2CH2)3N (8) is shown to be labile to substitution of the axial NMe2 group by a variety of OR groups in reactions with the corresponding ROH reagent to give Z activated Ti(OCH2CH2)3N in better than 90% yield where Z is O-i-Pr (1), OSiPh3 (4), O-t-Bu (5), OPh (6), and OCMe2Et (9). RSH compounds also cleanly react with 8 to give analogous products, in better than 85% in most cases, wherein Z is SEt (10), S-i-Pr (11), SCMe2Et (12), SPh (13), and S-allyl (14). The lability of 8 to nucleophilic substitution is related in part to its unique oxygen-bridged centrosymmetric dimeric structure which in contrast to 1 features each monodentate axial substituent trans to an oxygen rather than to the tertiary nitrogen. Crystallographic parameters for 8 are space group P2(1)/c, a = 11.154 (5) angstrom, b = 10.942 (2) angstrom, c = 9.708 (5) angstrom, alpha = 90.0-degrees, beta = 115.4 (2)-degrees, gamma = 90.0-degrees, and Z = 2. In contrast, the new azatitanatrane Me2N activated Ti(MeNCH2CH2)3N (15) does not display susceptibility to nucleophilic displacement of its axial Me2N group, decomposing instead. The compound t-BuO activated Ti(MeNCH2CH2)3N was synthesized in 54% yield, however, by reacting Ti(NMe2)4 with 1 equiv of t-BuOH followed by 1 equiv of (MeNHCH2CH2)3N.