ChemInform Abstract: Axially Asymmetric Metal Alkyls. Part 5. Synthesis and Reduction to Zr(III) Species of Group 4 Metallepines (ML(η-C5H5)2) (L: (2-CHRC6H4)2- 2; R: H; M: Ti, Zr, or Hf), Isomers of (ZrL(η-C5H5)2) (R: SiMe3), and meso-(M(1,8-(CHSiMe3)2C10H6)(η-C5H5)2) (M: Zr or Hf); X-Ray Crystal Structures of (TiL(η-C5H5)2) (R: H) and λ- and δ-RS-(ZrL(η-C5H5)2) (R: SiMe3).

ChemInform Abstract

The synthesis of the metallacyclic complexes (III) by two methods is described. A Zr complex (52% yield) containing mono-trimethylsilyl substituted cyclopentadienyl rings is obtained analogously using the Grignard compound (IV) as the reagent. Reaction of (Ib) with the dilithium reagent (V) (conditions are critical) gives a mixture of diastereoisomers of δ-RS- and λ-RS-(VI) and δ-RR- and λ-SS-(VII) which cannot be separated. (VI) is readily converted to (VII) by photolysis. The "strained" metallacycles meso-(IX) are prepared from an intrinsically unstable dilithium reagent, generated in situ in the reaction mixture. Reduction of (III), (VI) and (VII), and (IX) chemically and electrochemically (reversible) shows that the d¹ species, generated by one-electron transfer, are stable at ca. 20 °C except for M: Hf (-78 °C). For (III) the reduction may be associated with the rupture of one carbon-metal bond. The structure of (IIIa) (space group Pnn2, Z=8) and (VI) (space group P2₁/n, Z=4) are established from X-ray diffraction data.