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Abstract: The new methyl-tris(pyrazolyl)borate reagents Li[MeTpPh] (1) [MeTpPh]− = MeB(3-Ph-pyrazolyl)3 −) and Tl[MeTpPh] (2) react with TiCl4 to afford (MeTpPh)TiCl3 (3) in 77% and 81% yield respectively. 2 reacts with ZrCl4 and HfCl4 to yield mixtures of products. The reaction of 1 with TiCl3(THF)3 proceeds with B–N bond cleavage to afford TiCl3(3-Ph-pyrazole)(THF)2 as the major product (30%). The reaction of 3 with MeLi (3 equiv) yields 1 (60%) and reduced Ti species, via apparent displacement of [MeTpPh]− and generation of unstable TiCl4Me4−x species. Under MAO activation conditions (MAO = methylalumoxane), 3 polymerizes ethylene to linear polyethylene. 3/MAO is significantly more active in ethylene polymerization than the hydrido-tris(pyrazolyl)borate analogue {HB(3-Ph-pyrazolyl)3}TiCl3/MAO. [ABSTRACT FROM AUTHOR]

Abstract: The generation and properties of the Cp2Zr{CH(SiMe3)2}+ cation are described. An X-ray crystallographic analysis shows that the carborane salt [Cp2Zr{CH(SiMe3)2}][HCB11Me5Br6] contains an agostic Zr–μ-Me–Si interaction in the solid state. Low temperature NMR spectra of the borate salt [Cp2Zr{CH(SiMe3)2}][B(C6F5)4] show that this interaction is retained in solution. Variable temperature NMR spectra establish that the SiMe2(μ-Me) and unbound SiMe3 units of Cp2Zr{CH(SiMe3)2}+ exchange by a “pivot” process involving partial rotation around the Zr–CH(SiMe3)2 bond, with a barrier of ΔG ‡ =9.2(1)kcal/mol at −89°C. Cp2Zr{CH(SiMe3)2}+ does not coordinate alkenes or alkynes. [Copyright &y& Elsevier]

This paper describes the generation and properties of nonchelated d0zirconocene-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(C6F5)][B(C6F5)4] (4a: R = H, 4b: R = Me) were generated by methide abstraction from (C5H4R)2Zr(C6F5)Me by Ph3C+. 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 C6D5CI solution at low temperature produces an equilibrium mixture of (C5H4R)2Zr(C6F5)(H2C=CHCH2SiMe3)+ (7a,b), 4a,b, and free ATMS. Similarly, addition of propargyltrimethylsilane (PTMS) to 4a produces an equilibrium mixture of Cp2Zr(C6F5) (HC≡ CCH2SiMe3Y (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. [ABSTRACT FROM AUTHOR]

The reaction of Cp′2Zr(OtBu)Me (Cp′ = C5H4Me) and [Ph3C][B(C6F5)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 C6D5Cl solution. Addition of alkenes to 6 in CD2Cl2 solution at low temperature gives equilibrium mixtures of Cp′2Zr(OtBu)(alkene)+ (12aI), 6, and free alkene. The NMR data for 12aI 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, Keq = [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 (<0.1). Alkene coordination is inhibited by sterically bulky substituents on the alkene but is greatly enhanced by electron-donating groups and the β-Si effect. Compounds 12aI undergo two dynamic processes: reversible alkene decomplexation via associative substitution of a CD2Cl2 molecule, and rapid rotation of the alkene around the metal-(alkene centroid) axis. [ABSTRACT FROM AUTHOR]

The crystal structure of hexa-μ-hydroxo-do­deca­methylocta-μ3-oxo-do­deca­gallium(III) bis­[tetra­kis­(penta­fluoro­phenyl)­borate(III)] chloro­benzene disolvate dihydrate, [Ga12(CH3)12(μ3-O)8(μ-OH)6](C24F20B)2·2C6H5Cl·2H2O, is reported. The gallium-oxo-hydroxide dication is located on an inversion center and adopts a cage structure composed of 12 fused Ga3O3 rings and is associated with the hydrate mol­ecules and the [B(C6F5)4]− anions through hydrogen bonds and one O-H⃛π-ring interaction. Disordered chloro­benzene solvent mol­ecules are also present in the crystal structure. [ABSTRACT FROM AUTHOR]

The crystal structure of the title compound, [AlCl(CH3)-(C15H13N2)]­[Li(C24BF20)]2­·C6H6, is reported. The unusual coordination features of the lithium(I) cation, including Li-atom coordination to six organohalogen atoms and the shortest Li-F(C) distances so far observed, are discussed. [ABSTRACT FROM AUTHOR]

Reports on the facile insertion reaction of a cationic iminoacyl species with alkynes and alkenes which offer an efficient method for the regioselective acetylation of these substrates. Reactions with nonpolar unsaturated substrates; Effort to develop synthetic applications of Cp2Zr(R)(L)+ complexes; Indication of isomer interconversion.