Preparation of the Alkyl Complex Ta(=NSiMe3)[N(SiMe3)2](CH2But)2. Preferential Oxygen Insertion in Its Reaction with O2 and a Ligand Exchange in the Alkoxide Ta(=NSiMe3)[N(SiMe3)2](OCH2But)2

The alkyl amide imide complex Ta(=NSiMe3)[N(SiMe3)(2)](CH2But)(2) (2) has been prepared from the reaction of {Ta(mu-Cl)Cl(=NSiMe3)[N(SiMe3)(2)]}(2) (1) with LiCH2But. Reaction of 2 with O-2 leads to the preferential insertion of oxygen into the two Ta-alkyl bonds, yielding an alkoxy complex, Ta(=NSiMe3)[N(SiMe3)(2)](OCH2But)(2) (3). 3 undergoes a ligand exchange to give Ta-2(mu-NSiMe3)(2)-(OCH2But)(6) (4) and Ta(=NSiMe3)[N(SiMe3)(2)](2)(OCH2But) (5). The exchange reaches an equilibrium: 2 3 = 1/24 + 5; K-eq = 2.10(11) x 10(-4) at 296 K; Delta G degrees(296K) = 4.98(3) kcal. 3 and Shave also been prepared from the reactions of 1 with LiOCH2But, and LiN(SiMe3)(2) and LiOCH2But, respectively. 2 and 4 have been characterized by single-crystal X-ray diffraction.