Competing Pathways in the Reaction of Bis(pentafluorophenyl)borane with Bis(η⁵‐cyclopentadienyl)dimethylzirconium: Methane Elimination versus Methyl–Hydride Exchange and an Example of Pentacoordinate Carbon

Abstract

Filipin complex was obtained from Sigma (F-9765) as a crude mixture containing about 50% filipin 111 or from Upjohn (Lot 2923-DEV-39) containing about about 8 % filipin 111. It can be purified by reversed-phase preparative HPLC. The location of the C1' acetates in 3 and 4 were determined by their cross-peak in the COSY spectra with the readily identifiable C2 proton. The C15 acetate in 3 was identified by the simplicity of its coupling pattern. The location of the C7 acetate in 4 is less secure, and was assigned from the COSY spectrum. The second acetate in 4 must be at either at C7 or C11, and its location does not affect the stereochemical analysis. The assignments for these protons are listed in Fable 1.

Catalytic Systems Based on Cp2ZrX2 (X = Cl, H), Organoaluminum Compounds and Perfluorophenylboranes: Role of Zr,Zr- and Zr,Al-Hydride Intermediates in Alkene Dimerization and Oligomerization

“…A number of Zr borohydride complexes were prepared by Piers et al by the reaction of alkylzirconocenes with HB(C 6 F 5 ) 2 [29][30][31]. The complexes were found to be active in ethylene polymerization provided that additional alkylation with MAO takes place [30].…”

“…Additionally, hydride complexes [Cp′4Zr2H3][B(C6F4R)4] (R = F, SiPr i 3), highly active initiators for the isobutene homopolymerization and isobutene-isoprene copolymerization, were described [28]. A number of Zr borohydride complexes were prepared by Piers et al by the reaction of alkylzirconocenes with HB(C6F5)2 [29][30][31]. The complexes were found to be active in ethylene polymerization provided that additional alkylation with МАО takes place [30].…”

Nucleophilicity of Neutral versus Cationic Magnesium Silyl Compounds

“…For comparison, a bis­(dihydroborate) adduct Cp 2 Zr­{(μ-H) 2 B­(C 6 F 5 ) 2 } 2 is prepared from Cp 2 ZrMe 2 and 4 equiv of HB­(C 6 F 5 ) 2 . Interestingly, the 11 B NMR shift in 7-tmeda is 15.6 ppm upfield from the signal for Cp 2 Zr­{(μ-H) 2 B­(C 6 F 5 ) 2 } 2 (−12.9 ppm, 1 J BH = 64 Hz) …”

Butterfly Methanes: Designing a Novel Class of anti‐van′t Hoff Carbons

“…In 1995, researchers have synthesized a zirconium complex (Cp 2 Zr[CH 2 (HB{C 6 F 5 } 2 ) 2 ]), which is the first mononuclear organometallic compound having a pentacoordinate carbon atom, in which the À CH 2 carbon is in the Hp conformation. [7] In 1996, Radius et al [1] have done a detailed theoretical study of a series of zirconium complexes and explored the effect of substituents, X (À H, À CH 3 ,À OH, À CN, À BH 3 À ) for axial hydrogens in the Hp methane. The results showed that the substitution of two axial hydrogen atoms by À BH 3 À reduces the energy barrier for the deformation from Td to the Hp structure.…”

“…In these complexes, a methylene carbon or alkyl group is bridging a binuclear metal centre (3c–2e bond) with lithium counter ions in the carbon ligand sphere. In 1995, researchers have synthesized a zirconium complex (Cp 2 Zr[CH 2 (HB{C 6 F 5 } 2 ) 2 ]), which is the first mononuclear organometallic compound having a pentacoordinate carbon atom, in which the −CH 2 carbon is in the Hp conformation . In 1996, Radius et al .…”