775322-79-7Relevant academic research and scientific papers
Nonchelated d0 zirconium-alkoxide-alkene complexes
Stoebenau III, Edward J.,Jordan, Richard F.
, p. 8162 - 8175 (2007/10/03)
The reaction of Cp′2Zr(OtBu)Me (Cp′ = C5H4Me) and [Ph3C][B(C6F 5)4] yields the base-free complex [Cp′ 2Zr(OtBu)][B(C6F5)4] (6), which exists as Cp′2Zr(OtBu)(CIR)+ halocarbon adducts in CD2Cl2 or C6D 5Cl solution. Addition of alkenes to 6 in CD2Cl 2 solution at low temperature gives equilibrium mixtures of Cp′2- Zr(OtBu)(alkene)+ (12a-l), 6, and free alkene. The NMR data for 12a-l are consistent with unsymmetrical alkene bonding and polarization of the alkene C=C bond with positive charge buildup at Cint and negative charge buildup at Cterm. These features arise due to the lack of d-π* back-bonding. Equilibrium constants for alkene coordination to 6 in CD2Cl2 at -89 °C, K eq = [12][6]-1[alkene]-1, vary in the order: vinylferrocene (4800 M-1) ? ethylene (7.0) ≈ α-olefins > cis-2-butene (2.2) > trans-2-butene (a CD2Cl2 molecule, and rapid rotation of the alkene around the metal-(alkene centroid) axis.
Alkyne and alkene complexes of a d0 zirconocene aryl cation
Stoebenau III, Edward J.,Jordan, Richard F.
, p. 11170 - 11171 (2007/10/03)
The generation and properties of nonchelated Zr-aryl-alkyne and Zr-aryl-alkene complexes that are stabilized by the presence of β-Si-substituents in the alkyne and alkene ligands and fluorination of the aryl ligand are described. Reaction of [Cp′2Zr(OtBu)(ClCD2Cl)][B(C6F5)4] (1, Cp′ = C5H4Me) with alkyne and alkene substrates (L) generates Cp′2Zr(OtBu)(L)+ adducts (L = HC≡CCH2SiMe3 (2); H2C=CHCH2SiMe3 (3); HC≡CMe (4); H2C=CHCH2CMe3 (5)). Equilibrium constants for substrate binding (Keq = [Zr-L][1]-1[L]-1; CD2Cl2, -89 °C) are much larger for the β-Si-substituted compounds 2 (1.0(2) × 105 M-1) and 3 (1.7(4) × 103 M-1) than for hydrocarbon analogues 4 (3.6(7) × 102 M-1) and 5 (1.9(1) M-1), which is ascribed to β-Si stabilization of the partial positive charge on Cint of the bound substrate. [Cp2Zr(C6F5)][B(C6F5)4] (7, Cp = C5H5) was generated by the reaction of Cp2Zr(C6F5)Me with [Ph3C][B(C6F5)4] in C6D5Cl. Reaction of 7 with alkyne and alkene substrates (L) generates Cp2Zr(C6F5)(L)+ adducts (L = HC≡CCH2SiMe3 (8); H2=CCHCH2SiMe3 (10)). No insertion of the substrate into the Zr-C6F5 bond is observed in 8 (at -38 °C) or 10 (up to 22 °C). The allyltrimethylsilane ligand in 10 undergoes nondissociative alkene face exchange ( alkene flipping , i.e., exchange of the Cp2Zr(C6F5)+ unit between the two alkene enantiofaces without alkene dissociation), with a first-order rate constant kflip = 23(1) s-1 (C6D5Cl, -38 °C). 10 also undergoes slower reversible decomplexation of the alkene (kdissoc = 5.0(8) s-1; C6D5Cl, -38 °C). Copyright
