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

M(NMe 2 ) 4 (M = Zr, 1a; Hf, 1b) and the silyl anion (SiBu t Ph 2 )- (2) in Li(THF) 2 SiBu t Ph 2 (2-Li) were found to undergo a ligand exchange to give [M(NMe 2 ) 3 (SiBu t Ph 2 ) 2 ]- (M = Zr, 3a; Hf, 3b) and [M(NMe 2 ) 5 ] - (M = Zr, 4a; Hf, 4b) in THF. The reaction is reversible, leading to equilibria: 2 1a (or 1b) + 2 2 ↔ 3a (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(SiMe 3 ) 2 ligand in (Me 2 N) 3 Zr-N(SiMe 3 ) 2 (6a) to give 3a and [N(SiMe 3 ) 2 ]- (7) in reversible reaction: 6a + 2 2 ↔ 3a + 7. The following equilibria have also been observed and studied: 2M(NMe 2 ) 4 (1a; 1b) + [Si(SiMe 3 ) 3 ]- (8) - (Me 2 N) 3 M-Si(SiMe 3 ) 3 (M = Zr, 9a; Hf, 9b) + [M(NMe 2 ) 5 ]- (M = Zr, 4a; Hf, 4b); 6a (or 6b) + 8 ↔ 9a (or 9b) + [N(SiMe 3 ) 2 ]- (7). The current study represents rare, direct observations of reversible amide-silyl exchanges and their equilibria. Crystal structures of 5, (Me 2 N) 3 Hf-Si(SiMe 3 ) 3 (9b), and [Hf(NMe 2 ) 4 ] 2 (dimer of 1b), as well as the preparation of (Me 2 N) 3 M-N(SiMe 3 ) 2 (6a; 6b) are also reported.