MONOPROTONATION AND DIPROTONATION OF THE [(ETA-5-C5H5)TI(W5O18)]3- AND [(ETA-5-C5ME5)TI(W5O18)]3- ANIONS

Reaction of [(eta-5-C5H5)Ti(W5O18)][(n-C4H9)4N]3 with trichloroacetic acid in ethanol/dichloromethane followed by crystallization from nitroethane/p-xylene yields [(eta-5-C5H5)Ti(W5O18H)][(n-C4H9)4N]2.0.5[C6H4(CH3)2], which, according to a single-crystal X-ray diffraction study [a = 12.519 (4) angstrom, b = 12.957 (4) angstrom, c = 17.364 (6) angstrom, alpha = 92.95 (3)-degrees, beta = 97.22 (2)-degrees, gamma = 99.28 (2)-degrees, Z = 2, space group P1BAR-C(i)l (No. 2)], contains hydrogen-bonded dimers of [(eta-5-C5H5)Ti(W5O18H)]2- ions protonated at OTiW doubly-bridging oxygens. Diprotonation can be achieved using HCI in CH3CN to obtain the [(eta-5-C5H5)Ti(W5O18H2)]- ion according to an X-ray crystallographic study [a = 12.744 (2) angstrom, b = 12.720 (2) angstrom, c = 16.754 (3) angstrom, alpha = 95.88 (2)-degrees, beta = 99.52 (2)-degrees, gamma = 90.37 (2)-degrees, Z = 2, space group P1BAR-C(i)l (No. 2)] of [(eta-5-C5H5)Ti(W5O18H2)] [(n-C4H9)4N]2Cl. Here, a pair of cis-OTiW oxygens are protonated, and comparison with the [(eta-5-C5H5)Ti(W5O18)][(n-C4H9)4N]3.H2O structure [a = 17.287 (3) angstrom, b = 23.868 (5) angstrom, c = 18.032 (4) angstrom, beta = 91.05 (2)-degrees, Z = 4, space group P2(1)/n (an alternate setting of P2(1)/c, No. 14)] shows an induced pattern of trans bond length alternation throughout the [(eta-5-C5H5)Ti(W5O18H2)]- anion structure. The pentamethylcyclopentadienyl complexes [(eta-C5Me5)Ti(W5O18)]3-, [(eta-5-C5Mes)Ti(W5O18H)]2-, and [eta-C5Me5)Ti(W5O18H2)]- have also been prepared in crystalline form as tetra-n-butylammonium salts. According to infrared spectroscopy, these species have the same metal-oxygen structural framework observed for their unsubstituted cyclopentadienyl analogues.