Synthesis and Reactivity of Tantalum Complexes Supported by the Pincer Ligand 2,6-Pyridinedicarboxylate. Preparation of an Unprecedented Water-Soluble Iminoacyl Complex

The tantalum complex [TaCp*Me(OTf)((OOC)2py-κ3-O,N,O)] (1) has been synthesized by reaction of [TaCp*Me3(OTf)] (Cp* = η5-C5Me5, OTf = trifluoromethylsulfate) with 2,6-pyridinedicarboxylic acid. Complex 1 reacts with HOTf to yield the new tantalum carboxylate derivative [TaCp*(OTf)2((OOC)2py-κ3-O,N,O)] (2) or with MeOH to render the corresponding methoxide compound [TaCp*(OMe)(OTf)((OOC)2py-κ3-O,N,O)] (3). The reaction of 2 with H2O gives the hydroxo complex [TaCp*(OH)(OTf)((OOC)2py-κ3-O,N,O)] (4). Moreover, compound 1 reacts with tBuNC to yield the cationic iminoacyl-containing derivative [TaCp*{C(Me)NtBu-κ2-C,N}((OOC)2py-κ3-O,N,O)](OTf) (5), which is hygroscopic and reacts with water to render the corresponding water-soluble adduct (5·H2O). The reaction of 1 with B(C6F5)3 in a 1:1 or 1:2 molar ratio renders the corresponding adducts [TaCp*Me(OTf){(O(O·B(C6F5)3C))(OOC)py-κ3-O,N,O}] (6) or [TaCp*Me(OTf){(O(O·B(C6F5)3C))2py-κ3-N,O,O}] (7), respectively. The molecular structures of complexes 1·C7H8, 3, 4, 5·H2O, and 6·CH2Cl2 have been established by X-ray diffraction methods.