Synthesis and structure of [Zr(R)Cl(η-C5H5)2][R = chiral, highly hindered alkyl: HSiMe3C5H4-2, HSiMe3C6H4Ph2-o, or HSiMe3(C14H9-9)]; influence of the functional group on the nature and stability of their d1 reduction products

Abstract

Reaction of [ZrCl₂(η-C₅H₅)₂] with organolithium reagents Li(tmen)(Rⁿ)[Rⁿ= a highly hindered alkyl, HSiMe₃C₅H₄N-2 (R¹), HSiMe₃C₆H₄PPh₂-o(R²), HSiMe₃(C₁₄H₉-9)(R³)(C₁₄H₉= anthryl), or HSiMe₃(C₆H₄Me-p)(R₄); tmen = Me₂NCH₂CH₂NMe₂] in tetrahydrofuran (thf) yields [Zr(Rⁿ)Cl(η-C₅H₅)₂], compounds (2), (4), (6), and (8), respectively. Electrochemical reduction of (6) is reversible (10 < t_½≲ 50s) whereas for (2), (4), and (8) it is irreversible. Reduction of (2) and (4) yields chloride-free persistent d¹ species, respectively [Zr(R¹)(η-C₅H₅)₂], with R¹ chelating or η³-aza-allyl, and [Z[graphic omitted]Ph₂-o)(η-C₅H₅)₂](³¹P coupling) either in thf (Na[C₁₀H₈]) or toluene (Na/Hg). Reduced (2), (4), (6), and (8) react with PMe₃ yielding d¹[Zr(Rⁿ)(PMe₃)(η-C₅H₅)₂]. Variable-temperature ¹H n.m.r. investigation of (2) in toluene shows an equilibrium between four- and five-co-ordinate complexes; in the solid the latter prevails with a Zr–N distance of 2.34₁Å, and an exceptionally long Zr–Cl distance (2.56₃Å). In (4) the functional group is not bound to the metal centre [Zr–Cl 2.438(1), Zr–C 2.350(4)Å] and in (6) the potentially ambidentate alkyl R³ is bound through the benzylic carbon [Zr–C 2.349(4), Zr–Cl 2.454(1)Å].