The chloro(alkyl)metallocenes [MR*(Cl)(η-C5H5)2] [R* = -CH(SiMe3)C6H4Me-o; M = Zr 1 or Hf 2] have been prepared from [MCl2(η-C5H5)2] and LiR*(tmen) (tmen = N,N,N′,N′-tetramethylethane-1,2-diamine); further alkylation occurred only for M = Zr, affording rac-3a and meso-3b, [ZrR*2(η-C5H5)2]. In contrast, reaction of 2 equivalents of Li[CH(SiMe3)2](tmen) with [ZrCl2(η-C5H5)2] yielded an alkyl elimination product possessing μ-η1:η5-C5H42- ligands. Compound 1 was reversibly reduced (E1/2red = -1.72 V vs. saturated calomel electrode, SCE) whereas 2, 3a or 3b were irreversibly reduced (Ered = -2.12, -2.08, -2.00 V respectively vs. SCE). Thermolysis of 3b in toluene gave 3a (80°C) or 'Zr(C10H8)' (120°C). Photolysis of 3a or 3b at 20°C in tetrahydrofuran (thf) yielded a 1:1 mixture of 3a and 3b; a d1 intermediate has been unambiguously identified as [ZrR*(η-C5H5)2]. Reduction of 1 (Na-Hg), or 3a and 3b (Na[C10H8]), in thf also gave [ZrR*(η-C5H5)2] but this slowly transformed into [ZrR*(η-C5H5)2(thf)], and 1 with Na[C10H8] and PPh3 gave [ZrR*(η-C5H5)2(PPh3)]. Reduction of 1, 3a or 3b, or photolysis of 3a or 3b, in the presence of PMe3 gave [ZrR*(η-C5H5)2(PMe3)]. Crystal structure determinations showed a slightly more crowded metal environment in 2 than in 1, consistent with the view that dialkylation in 2 is limited on steric grounds; M-σ-C 2.359(4) (1), 2.322(8) (2), metal-centroid 2.22 (1), 2.21 (2), M-Cl 2.444(1) (1), 2.418(3) (2) Å. The structure of 3a confirms the rac assignment, M-σ-C 2.374 Å, metal-centroid 2.23, 2.24 Å.
|Number of pages||8|
|Journal||Journal of the Chemical Society - Dalton Transactions|
|Publication status||Published - 7 Sep 1997|