Complexes of tantalum with triaryloxides: Ligand and solvent effects on formation of hydride derivatives

A family of tantalum compounds supported by the triaryloxide [R-L](3-) ligands are reported [H-3(R-L) = 2,6-bis(4-methyl-6-R-salicyl)-4-tert-butylphenol, where R = Me or 'Bu]. The reaction of H-3[Me-L] with TaCl5 in toluene gave [(Me-L)TaCl2](2) (1). The ['Bu-L] analogue [('Bu-L)TaCl2](2) (2) was synthesized via treatment of TaCl5 with Li-3['Bu-L]. A THF solution of LiBHEt3 was added to 1 in toluene to provide [(Me-L)TaCl(THF)](2) (3), while treatment of 2 with 2 equiv of LiBHEt3 or potassium in toluene followed by recrystallization from DME resulted in formation of [M(DME)(3)][{('Bu-L)TaCl)(2)(mu-Cl)] [M = Li (4a), K (4b)]. When the amount of MBHEt3 (M = Li, Na, K) was increased to 5 equiv, the analogous reactions in toluene afforded [ (bit-'Bu-L)Ta}(2) (mu-H)(3)M] [M = Li(THF)(2) (5a), Na(DME)(2) (5b), K(DME)(2) (5c)]. During the course of the reaction, the methylene CH activation of the ligand took place. Dissolution of 5a in DME produced [{(bit-'Bu-L)Ta}(2)(mu-H)(3)Li(DME)(2)] (6), indicating that the coordinated THF molecules are labile. When the 2/LiBHEt3 reaction was carried out in THF, the ring opening of THF occurred to yield [('Bu-L)Ta(OBu '')(2)](2) (7) along with a trace arnount of [Li(THF)(4)][{('Bu-L)TaCl}(2)(mu-OBu '')] (8). Treatment of 2 with potassium hydride in DME yielded [ ('Bu-L)TaCl2K(DME)(2)}(2)(mu-OCH2CH2O)] (9), in which the ethane-1,2-diolate ligand arose from partial C-O bond rupture of DME. The X-ray crystal structures of 2, 3, 4, 5a, 6, 7, and 9 are described. (c) 2005 Published by Elsevier B.V.