Yu Xianghua, Cai Hu, Guzei Ilia A, Xue Ziling
Department of Chemistry, The University of Tennessee, Knoxville, Tennessee 37996-1600, USA.
J Am Chem Soc. 2004 Apr 14;126(14):4472-3. doi: 10.1021/ja031899y.
Silyl anion SiButPh2- (2) was found to substitute an amide ligand in Zr(NMe2)4 (3) to give the disilyl complex Zr(NMe2)3(SiButPh2)2- (1a) and Zr(NMe2)5- (1b) in THF. The reaction is reversible, and nucleophilic amide NMe2- attacks the Zr-SiButPh2 bonds in 1a or Zr(NMe2)3(SiButPh2) in the reverse reaction, leading to an unusual ligand exchange equilibrium 2 3 + 2 2 right harpoon over left harpoon 1a + 1b (eq 1). The silyl anion 2 selectively attacks the -N(SiMe3)2 ligand in Zr(NMe2)3[N(SiMe3)2] (6) to give 1a and N(SiMe3)2- (7). Reversible reaction occurs as well, where 7 selectively substitutes the silyl ligand in Zr(NMe2)3(SiButPh2)2- (1a) or Zr(NMe2)3(SiButPh2), giving the equilibrium 6 + 2 2 right harpoon over left harpoon 1a + 7 (eq 3). The thermodynamics of these equilibria has been studied: For eq 1, DeltaH degrees = -8.3(0.2) kcal/mol, DeltaS degrees = -23.3(0.9) eu, and DeltaG degrees 298K = -1.4(0.5) kcal/mol at 298 K; for eq 3, DeltaH degrees = -1.61(0.12) kcal/mol, DeltaS degrees = -2.6(0.5) eu, and DeltaG degrees 298K = -0.8(0.3) kcal/mol. In both equilibria, the enthalpy changes for the forward reactions outweigh the entropy changes, and therefore the substitutions of amide ligands in Zr(NMe2)4 (3) and Zr(NMe2)3[N(SiMe3)2] (6) to afford the disilyl complex 1a are thermodynamically favored. The following equilibria were also observed and studied: Zr(NMe2)3[N(SiMe3)2] (6) + Si(SiMe3)3- (9) right harpoon over left harpoon Zr(NMe2)3[Si(SiMe3)3] (10) + N(SiMe3)2- (7) and Zr(NMe2)4 (3) + 9 right harpoon over left harpoon 10 + Zr(NMe2)5- (1b).
发现硅烷基阴离子SiButPh2-（2）能取代Zr（NMe2）4（3）中的一个酰胺配体，在四氢呋喃中生成二硅烷基配合物Zr（NMe2）3（SiButPh2）2-（1a）和Zr（NMe2）5-（1b）。该反应是可逆的，在逆反应中亲核酰胺NMe2-会攻击1a中的Zr-SiButPh2键或Zr（NMe2）3（SiButPh2），导致一个不寻常的配体交换平衡2 3 + 2 2 ⇌ 1a + 1b（式1）。硅烷基阴离子2能选择性地攻击Zr（NMe2）3[N（SiMe3）2]（6）中的-N（SiMe3）2配体，生成1a和N（SiMe3）2-（7）。同样也会发生可逆反应，其中7会选择性地取代Zr（NMe2）3（SiButPh2）2-（1a）或Zr（NMe2）3（SiButPh2）中的硅烷基配体，得到平衡6 + 2 2 ⇌ 1a + 7（式3）。已对这些平衡的热力学进行了研究：对于式1，在298K时，ΔH° = -8.3(0.2) kcal/mol，ΔS° = -23.3(0.9) eu，ΔG°298K = -1.4(0.5) kcal/mol；对于式3，ΔH° = -1.61(0.12) kcal/mol，ΔS° = -2.6(0.5) eu，ΔG°298K = -0.8(0.3) kcal/mol。在这两个平衡中，正向反应的焓变超过熵变，因此用Zr（NMe2）4（3）和Zr（NMe2）3[N（SiMe3）2]（6）中的酰胺配体取代生成二硅烷基配合物1a在热力学上是有利的。还观察并研究了以下平衡：Zr（NMe2）3[N（SiMe3）2]（6） + Si（SiMe3）3-（9） ⇌ Zr（NMe2）3[Si（SiMe3）3]（10） + N（SiMe3）2-（7）以及Zr（NMe2）4（3） + 9 ⇌ 10 + Zr（NMe2）5-（1b）。
