Metallocene derivatives of early transition metals. Part 4. Chemistry of the complexes [M(η-C5H5)2RR′][M = Ti, Zr, or Hf; R = CH2M′Me3(M′= C, Si, Ge, or Sn) or CH(SiMe3)2; R′= Cl or alkyl] and the X-ray structures of [Zr(η-C5H5)2(CH2M′Me3)2](M′= C or Si)

Abstract

The metallocene(IV) halogeno-alkyls [M(η-C₅H₅)₂RX][type (i) R = CH₂SnMe₃, X = Cl or Br, M = Ti (also X = I), Zr, or Hf; type (ii) R = CH₂SiMe₃, X = Cl or Br, M = Ti, Zr, or Hf; type (iii) R = CH₂GeMe₃, X = Cl, M = Ti] have been prepared either by interaction of the appropriate Grignard reagent and [M(η-C₅H₅)₂Cl₂] or from [M(η-C₅H₅)₂RCl] and Mg(CH₂SnMe₃)X (Cl–X exchange). Metallocene(IV) dialkyls [M(η-C₅H₅)₂RR′][type (iv) R = CH₂SnMe₃= R′, M = Ti, Zr, or Hf; type (v) R = CH₂SnMe₃, R′= CH₂SiMe₃, M = Ti, Zr, or Hf; type (vi) R = CH₂CMe₃= R′, M = Ti or Zr; type (vii) R = CH₂SnMe₃; R′= CH₂CMe₃, CH₂GeMe₃, or Me; M = Ti; type(viii) R = CH₂SiMe₃, R′= CH₂GeMe₃, M = Ti; type (ix) R = CH(SiMe₃)₂; R′= Me, Et, Prⁿ, CH₂SiMe₃, or Ph; M = Zr] have been synthesised by reaction of (a)[for type (v)][M(η-C₅H₅)₂] with 2Mg(CH₂SnMe₃)X (X = Cl or Br) or (b)[M(η-C₅H₅)₂RX] with LiR′. Also obtained are [Ti(η-C₅H₅)₂Cl(OCH₂SiMe₃)] and [{Zr(η-C₅H₅)₂[CH(SiMe₃)₂]H}₂], the latter from [Zr(η-C₅H₅)₂{CH(SiMe₃)₂}Cl] and Li[AlH₄] or [Zr(η-C₅H₅)₂Cl₂] and successively Li[AlH(OBu^t)₃] and Li[CH(SiMe₃)₂]. The reaction of an equimolar portion of HCl in OEt₂ and [Ti(C₅H₅)₂(CH₂SnMe₃)Cl] gives predominantly the products of CH₂–SnMe₃, rather than Ti–CH₂, scission. By contrast, the dialkyls [M(η-C₅H₅)₂RR′], containing one or two CH₂SnMe₃ ligands, give largely RH or R′H and [M(η-C₅H₅)₂Cl (R′ or R)]; the relative ability of R as a leaving group decreases in the sequence CH₂SnMe₃ > CH₂CMe₃ > CH₂SiMe₃ CH₂GeMe₃ > CH₃, the distinctions being more marked for Ti than Zr or Hf. The dialkyls are generally stable when heated at 80 °C in PhMe, except for the titanium complexes; [Ti(η-C₅H₅)₂(CH₂M′Me₃)₂](M′= Si or Ge) gives M′Me₄ as the sole volatile product, with t_½ 110 (M′= Si) or 140 min (M′= Sn). Treatment of [Zr(η-C₅H₅)₂RX][type (ix)] in C₆H₆ with CO under ambient conditions affords the appropriate η²-acyl [Zr(η-C₅H₅)₂(η²-COR)X][type (x), R = CH₂CMe₃ or CH₂SiMe₃, X = Cl or R; or type (xi), R = CH(SiMe₃)₂, X = Me]; the formation of type (xi), rather than the isomer resulting from CO insertion into the less hindered Zr–Me bond, is noteworthy. A single-crystal X-ray diffraction study has been carried out on [Zr(η-C₅H₅)₂(CH₂M′Me₃)₂][M′= C, (28) or Si, (42)]. Crystals of complex (28) are tetragonal, space group I, with a= 9.142(4), b= 9.142(4), c= 23.326(9)Å, β= 90°, and Z= 4. Crystals of (42) are monoclinic, space group P2₁/n, a= 13.745(6), b= 7.048(3), c= 22.057(9)Å, β= 95.65(4)°, and Z= 4. For complex (28), 487 reflections have been considered and the data refined to R= 0.029, R′= 0.032; for complex (42), 2 688 independent reflections led to R= 0.029, R′= 0.033. The slightly larger steric requirement of the neopentyl ligand compared with ^–CH₂SiMe₃ manifests itself in a larger Zr–cyclopentadienyl approach but the Zr–CH₂ bond length is indistinguishable, 2.51 (2)Å for (28) and 2.52(2)Å for (42).