Such a compound has now been synthesized from [Cp*TaCl,] 1 (Cp* = qs-C5Mes) and tris(trimethy1stan-ny1)amine 2 [Eq. (a)]. Evidence for the six-membered cy-
1 2 clic structure of 3 is provided by the 'H NMR spectrum, which indicates the presence of two nonequivalent pentamethylcyclopentadienyl groups (6= 2.08, 2.12) in a ratio of 1 :2. In addition to the molecular ion peak ( m / z loss), the mass spectrum always reveals small amounts of the tetramer [Cp*TaN(Cl)], ( m / z 1460). The IR spectrum exhibits a strong absorption at 960 cm-', which we ascribe to the Ta-N valence vibration.
Crystals of 3 suitable for an X-ray structure analysis (Fig. I)'"] were obtained by recrystallization from toluene/ hexane. The six-membered (TaN)3 ring, containing tetrahedrally coordinated tantalum atoms, is not completely planar in the solid state but instead exists in a kind of boat conformation, with the atoms Ta(2), N(3), Ta(3), and N(2) lying in the same plane (k0.03 pm). Ta(1) lies 13 pm and N(l) 39 pm from this plane. The molecule has a non-crystallographic mirror plane through C1(1), Ta(l), and N(1); two Cp* rings lie below and one lies above the (TaN)3 ring plane, as expected on the basis of the NMR spectrum. The Ta-N bond lengths (average 188(2) pm) are comparable to those in [BrSTaNTaBr5]3Q (185 pmI7]) and lie between the values for Ta=NR (175-178pm) and .l8] IR, 'H NMR, and mass spectra established its identity as 3. Yield: 490 mg (67%).