Unusual equilibria involving group 4 amides, silyl complexes, and silyl anions via ligand exchange reactions.

Unusual equilibria involving group 4 amides, silyl complexes, and silyl anions via ligand exchange reactions. Research Abstract Details 

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Unusual equilibria involving group 4 amides, silyl complexes, and silyl anions via ligand exchange reactions. Abstract Text:

Xianghua Yu,Hu Cai,Ilia A Guzei,Ziling Xue,

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).

Unusual equilibria involving group 4 amides, silyl complexes, and silyl anions via ligand exchange reactions. Publishing Authors By Initials

X Yu,H Cai,IA Guzei,Z Xue,

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Unusual equilibria involving group 4 amides, silyl complexes, and silyl anions via ligand exchange reactions. Journal Published:

PUBLICATION TYPE: Journal Article

Journal: Journal of the American Chemical Society

VOLUME: 126

Page Numbers: 4472-3

Journal Abbreviation: J. Am. Chem. Soc.

ISSN: 0002-7863

DAY: 14

MONTH: Apr

YEAR: 2004

Unusual equilibria involving group 4 amides, silyl complexes, and silyl anions via ligand exchange reactions. Information

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LANGUAGE: eng

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Grant and Affiliation Information for Unusual equilibria involving group 4 amides, silyl complexes, and silyl anions via ligand exchange reactions.

AFFILIATION: Department of Chemistry, The University of Tennessee, Knoxville, Tennessee 37996-1600, USA.

Country: United States

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MEDLINETA: J Am Chem Soc

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