Synthesis and Reactivity of Monocyclopentadienyl Tantalum Complexes with Pincer Dialkoxide Ligands

The new tantalum dialkoxide complexes Cp*TaCl2(OCH2)2py (1), trans-Cp*TaMe2(OCH2)2py (2), and cis-Cp*TaMe2(OCH2)2py (3) (Cp* = η5-C5Me5; (OCH2)2py = 2,6-pyridinedimethoxide) have been synthesized. The molecular structures of complexes 1 and 2 have been studied by X-ray diffraction methods. The reaction of complex 3 with carbon monoxide renders Cp*Ta(η2-Me2CO)(OCH2)2py (4), while with isocyanides yields the respective azatantalacyclopropanes Cp*Ta(η2-Me2CNxylyl)(OCH2)2py (6) (xylyl = 2,6-dimethylphenyl) and Cp*Ta(η2-Me2CNtBu)(OCH2)2py (7). The molecular structure of complex 4 has been established by X-ray diffraction. The coordinated ketone in 4 can be reduced to 2-propanol in the presence of water. On the other hand, compound 3 reacts with triflic acid (HOTf) to render the corresponding cationic derivative [Cp*TaMe(OCH2)2py]OTf (8).