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The zirconocene complexes Cp2Zr(L)(η2‐Me3SiC2SiMe3) (1a: L = THF; 1b: L = pyridine) and the ethylene bis(tetrahydroindenyl) complex rac‐(ebthi)Zr(η2‐Me3SiC2SiMe3) (2) react with 2,3,5,6‐tetrafluoropyridine with C–H bond activation to produce the 4‐substituted pyridyl complexes with agostic alkenyl groups Cp'2Zr(4‐C5NF4)[–C(SiMe3)=CH(SiMe3)] (Cp'2 = Cp2) (3) and (Cp'2 = ebthi) (4). With 2,3,4,6‐tetrafluoropyridine, after C–H bond activation, complex 2 yields two isomers of the 5‐substituted pyridyl complex rac‐(ebthi)Zr(3‐C5NF4)[–C(SiMe3)=CH(SiMe3)] with agostic alkenyl groups, 5a and 5b. With pentafluoropyridine complex 1b gives, after dissociation of the bis(trimethylsilyl)acetylene (btmsa), C–F bond activation at the 4‐position and formation of Cp2Zr(4‐C5NF4)F (6). Complex 1b reacts with 3‐chloro‐2,4,5,6‐tetrafluoropyridine by means of a preferred C–Cl activation to give Cp2Zr(3‐C5NF4)Cl (7). These results are in contrast to the reactions of the titanium complex Cp2Ti(η2‐Me3SiC2SiMe3) which, with 2,3,5,6‐tetrafluoropyridine, gaveC–F activation in preference to C–H activation. With pentafluoropyridine, C–F bond activation at the 2‐position was found rather than at the 4‐position. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

The reduction of certain group 4 metallocene dichlorides by magnesium or lithium in the presence or absence of Me 3 SiC 2 SiMe 3 in THF or toluene was investigated, giving in the case of titanium the dinuclear Ti(III) complex [rac-(ebthi)Ti(µ-Cl)] 2 (1). For zirconium the 1-oxa-2-zirconacyclohexane 2 was formed by ring-opening reaction of rac-(ebthi)Zr(η 2 -Me 3 SiC 2 SiMe 3 ) with THF. As a byproduct from the synthesis of Cp* 2 Zr(η 2 -Me 3 SiC 2 SiMe 3 ) starting from Cp* 2 ZrCl 2 another 1-oxa-2-zirconacyclohexane (3) was obtained by ring-opening reaction of THF via the dinuclear complex Cp* 2 Zr(Cl)-(CH 2 ) 4 O-Zr(Cl)Cp* 2 (4). In the case of hafnium the analogous dinuclear complex Cp* 2 Hf(Cl)-(CH 2 ) 4 O-Hf(Cl)Cp* 2 (5) and 1-oxa-2-hafnacyclohexane (6) were the main products of the reaction, inhibiting the synthesis of Cp* 2 -Hf(η 2 -Me 3 SiC 2 SiMe 3 ) (7). The tendency for ring opening of THF initiated by metallocenes increases in the series Ti, Zr, Hf, thus leading to consequences for the synthesis of metallocene complexes.

Not a catalyst killer: In the reaction of 2 with B(C6F5)3, a nucleophilic aromatic substitution with CF bond cleavage leads to the unexpected difluoride 1. Although the formation of ZrF species during olefin polymerization by [Cp′2ZrR]+[RB(C6F5)3]− (Cp′=substituted or unsubstituted η5‐cyclopentadienyl; R=Me, H) catalysts is often described as a deactivation, the catalyst precursor 2 can be regenerated from 1 through treatment with iBu2AlH.

The novel branched oligosilyltriflates of formula [TfO(Me 3 Si) 2 Si] 2 E (2a-d) [E ¼ 0 (2a), SiMe 2 (2b), GeMe 2 (2c), SiMe 2 -SiMe 2 (2d)] and [TfO(Me 3 Si) 2 SiSiMe 2 ] 3 SiMe (9) have been prepared by the protodesilylation of [Ph(Me 3 Si) 2 Si] 2 E (1a-c), [H(Me 3 Si) 2 Si] 2 E (5d) and [Ph(Me 3 Si) 2 SiSiMe 2 ] 3 SiMe (8) using TfOH (CF 3 SO 3 H) as reagent in almost quantitative yields. The crystal structure of 2b is reported.w Electronic supplementary information (ESI) available: experimental details. See