NEW TITANATRANES AND AN UNEXPECTED REACTIVITY TREND IN (DIALKYLAMIDO)TITANATRANES

The relative rates of displacement of the NR2 group in (dialkylamido)titanatranes R2NTi(OCH2CH2)3N by -OH and -SH compounds is in the order NEt2 >> NMe2 > N(i-Pr)2. This unanticipated order is rationalized on the postulated prior formation of HR2N+Ti(OCH2CH2)3N (A), which facilitates departure of R2NH 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 Et2N almost-equal-to (i-Pr)2N > Me2N. 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)2N+ group. The faster reactions of CF3CH2OH and PhOH compared with their sterically similar but more weakly acidic analogues CH3CH20H and i-PrOH, respectively, support this hypothesis as do the comparable displacement rates of Et2N and Me2N in the presence of the strong nonnucleophilic base P(MeNCH2CH2)3N and the reactions of 4 and 14 with HBF4 and NH4Cl but not with NaBF4 or Me4NCl. New titanatranyl derivatives reported include five arylates, two thioarylates, and four diolates. The X-ray parameters for [i-PrSTi(OCH2CH2)3N]2 are as follows: triclinic, space group PI (No. 2), a = 7.434(5) angstrom, b = 12.540 (3) angstrom, c = 7.034(3) angstrom, alpha = 105.72(3)-degrees, 98.87(3)-degrees, gamma = 85.30(4)-degrees, and Z = 1. For [Me2COTi(OCH2CH2)3N]2 these parameters are as follows: monoclinic, space group P2(1)/n (No. 14), a = 6.6590(6) angstrom, b = 17.819(2) angstrom, c = 10.095(1) angstrom, and beta = 107.975(9)-degrees.