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Amide−Silyl Ligand Exchanges and Equilibria among Group 4 Amide and Silyl Complexes

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journal contribution
posted on 17.09.2007, 00:00 by Hu Cai, Xianghua Yu, Shujian Chen, He Qiu, Ilia A. Guzei, Zi-Ling Xue
M(NMe2)4 (M = Zr, 1a; Hf, 1b) and the silyl anion (SiButPh2)- (2) in Li(THF)2SiButPh2 (2-Li) were found to undergo a ligand exchange to give [M(NMe2)3(SiButPh2)2]- (M = Zr, 3a; Hf, 3b) and [M(NMe2)5]- (M = Zr, 4a; Hf, 4b) in THF. The reaction is reversible, leading to equilibria:  2 1a (or 1b) + 2 23a (or 3b) + 4a (or 4b). In toluene, the reaction of 1a with 2 yields [(Me2N)3Zr(SiButPh2)2]-[Zr(NMe2)5Li2(THF)4]+ (5) as an ionic pair. The silyl anion 2 selectively attacks the −N(SiMe3)2 ligand in (Me2N)3Zr−N(SiMe3)2 (6a) to give 3a and [N(SiMe3)2]- (7) in reversible reaction:  6a + 2 2 3a + 7. The following equilibria have also been observed and studied:  2M(NMe2)4 (1a; 1b) + [Si(SiMe3)3]- (8) ↔ (Me2N)3M−Si(SiMe3)3 (M = Zr, 9a; Hf, 9b) + [M(NMe2)5]- (M = Zr, 4a; Hf, 4b); 6a (or 6b) + 89a (or 9b) + [N(SiMe3)2]- (7). The current study represents rare, direct observations of reversible amide−silyl exchanges and their equilibria. Crystal structures of 5, (Me2N)3Hf−Si(SiMe3)3 (9b), and [Hf(NMe2)4]2 (dimer of 1b), as well as the preparation of (Me2N)3M−N(SiMe3)2 (6a; 6b) are also reported.