775322-87-7Relevant academic research and scientific papers
Nonchelated alkene and alkyne complexes of d0 zirconocene pentafluorophenyl cations
Stoebenau III, Edward J.,Jordan, Richard F.
, p. 8638 - 8650 (2007/10/03)
This paper describes the generation and properties of nonchelated d 0 zirconocene-aryl-alkene and alkyne adducts that are stabilized by the presence of β-SiMe3 substituents on the substrates and the weak nucleophilicity of the -C6F5 ligand. The cationic complexes [(C5H4R)2Zr(C6F 5)][B(C6F5)4] (4a: R = H, 4b: R = Me) were generated by methide abstraction from (C5H 4R)2Zr(C6F5)Me by Ph 3C+. NMR studies show that 4a,b contain an o-CF...Zr dative interaction and probably coordinate a PhCl molecule in PhCl solution. Addition of allyltrimethylsilane (ATMS) to 4a,b in C6D5Cl solution at low temperature produces an equilibrium mixture of (C 5H4R)2Zr(C6F5)(H 2C=CHCH2SiMe3)+ (7a,b), 4a,b, and free ATMS. Similarly, addition of propargyltrimethylsilane (PTMS) to 4a produces an equilibrium mixture of Cp2Zr(C6F5)(HC= CCH2SiMe3)+ (8a), 4a, and free PTMS. The NMR data for 7a,b,and 8a are consistent with highly unsymmetrical substrate coordination and substantial polarization of the substrate multiple bond with significant positive charge buildup at Cint and negative charge buildup at Cterm. PTMS binds to 4a more strongly than ATMS does. The ATMS adducts undergo nondissociative alkene face exchange ("alkene flipping"), i.e., exchange of the (C5H4R) 2Zr(C6F5)+ unit between the two alkene enantiofaces without decomplexation of the alkene, on the NMR time scale.
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
