New titanatranes and an unexpected reactivity trend in (dialkylamido)titanatranes

The relative rates of displacement of the NR[sub 2] group in (dialkylamido)titanatranes R[sub 2]N[ovr Ti(OCH[sub 2]CH[sub 2])[sub 3]N] by -OH and -SH compounds is in the order NEt[sub 2] [much gt] NMe[sub 2] > N(i-Pr)[sub 2]. This unanticipated order is rationalized on the postulated prior formation of HR[sub 2]N[sup +][ovr Ti(OCH[sub 2]CH[sub 2])[sub 3]N] (A), which facilitates departure of R[sub 2]NH upon subsequent nucleophilic attack. For R = Et and i-Pr, the concentration of A is higher than for R = Me, owing to the basicity order Et[sub 2]N [congruent] (i-Pr)[sub 2]N > Me[sub 2]N. The greater reactivity of A where R = Me relative to R = i-Pr is attributed to the greater steric protection from nucleophilic attack on the metal afforded by the H(i-Pr)[sub 2]N[sup +] group. The faster reactions of CF[sub 3]CH[sub 2]OH and PhOH compared with their sterically similar but more weakly acidic analogues CH[sub 3]CH[sub 2]OH and i-PrOH< respectively, support this hypothesis as do the comparable displacement rates of Et[sub 2] and Me[sub 2]N in the presence of the strong nonnucleophilic base P(MeNCH[sub 2]CH[sub 2])[sub 3]N and the reactions of 4 and 14 with HBF[sub 4] and NH[sub 4]Cl but not with NaBF[sub 4] or Me[sub 4]NCl. New titanatranyl derivatives reported include five arylates, two thioarylates, and four diolates. 21 refs., 2 figs., 5 tabs.