Axially asymmetric metal alkyls. Part 5. Synthesis and reduction to ZrIII species of Group 4 metallepines [ML(η-C5H5)2][L =(2-CHRC6H4)22–, 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)

Abstract

Treating [MCl₂(η-C₅H₄R′)₂] with a di-Grignard reagent and/or a dilithium reagent based on (2-CHRC₆H₄)₂^2–(L) yields the metallacycles [ML(η-C₅H₄R′)₂](R = R′= H, M = Ti, Zr, or Hf; R = H, R′= SiMe₃, M = Zr)(5), and a mixture of diastereoisomers of λ-RS- and δ-RS-[ZrL(η-C₅H₅)₂](R = SiMe₃)(6a), and λ-RR-and δ-SS-[ZrL(η-C₅H₅)₂](R = SiMe₃)(6b). Compound (6a) was readily converted to (6b) by photolysis in hexane. The ‘strained’ metallacycles meso-[M{1,8-(CHSiMe₃)₂C₁₀H₆}(η-C₅H₅)₂](M = Zr or Hf)(7) were prepared from an intrinsically unstable dilithium reagent. Reduction of (5),(6a) and (6b), and (7) chemically and electrochemically shows that the generated d¹ species are stable at ca. 20 °C except for M = Hf, and that for (5)[and possibly (6a) and (6b)] reduction is associated with metal–carbon bond rupture. The structures of (5)(M = Ti) and (6a) have been established from single-crystal X-ray diffraction data [Ti–C^α 2.20₇Å, C^α–Ti–C^α 87_·8°, dihedral angle between phenyl groups, φ 62.2°; Zr–C^α 2.33₈Å, C^α–Zr–C^α 98.3(2)°, φ 73.6°].