New Complexes of Niobium( V ) and Tantalum( V ) with Monoanionic NNO Heteroscorpionate Ligands

A new synthetic route based on bis(3,5‐dimethylpyrazol‐1‐yl)acetic acid (Hbdmpza) ( 1 ) has afforded the alcohol 2,2‐bis(3,5‐dimethylpyrazol‐1‐yl)ethanol (Hbdmpze) in good yield. This alcohol and the related lithium compound [{Li(bdmpza)(H 2 O)} 4 ] are excellent precursors for introducing these scorpionate ligands into transition metal complexes. For example, the lithium compound and Hbdmpze (the latter after prior addition of n BuLi) react with a solution of MCl 5 (M = Nb, Ta) in THF to give, after stirring for 12 h at −70 °C, a solution from which the complexes [MCl 4 (κ 3 ‐bdmpzx)] ( x = a , M = Nb 2 , Ta 3 ; x = e , M = Nb 4 , Ta 5 ) have been isolated. When solutions of 2 − 5 in THF were stirred at ca. 20 °C for 48 h, the oxo complexes [MCl 2 (O)(κ 3 ‐bdmpzx)] ( x = a , M = Nb 6 , Ta 7 ; x = e , M = Nb 8 , Ta 9 ) were isolated. The structures of these complexes have been determined by spectroscopic methods and the X‐ray crystal structure of 8 has been established. Finally, a new class of heteroscorpionate‐metal complexes containing an alkoxide ligand has been prepared. Direct reaction of the complexes [MCl 4 (κ 3 ‐bdmpza)] (M = Nb 2 , Ta 3 ) with several alcohols gave the complexes [MCl 3 (κ 3 ‐bdmpza)(OR)] (M = Nb, R = Me 10 , Et 11 , i Pr 12 , t Bu 13 ; M = Ta, R = Me 14 , Et 15 , i Pr 16 , t Bu 17 ) after the appropriate workup. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)