Phosphine complexes of group 4 metals. Synthesis, structure, and fluxional behavior of zirconium and hafnium butadiene derivatives

Article abstract of DOI:10.1021/om00109a024

The reaction of magnesium butadiene (Mg·C₄H₆·2THF)_n with the group 4 starting materials MCl₃[N-(SiMe₂CH₂PR₂)₂] (M = Zr, Hf; R = Me, Prⁱ) generates good yields of butadiene complexes of the formula M(η⁴-C₄H₆)Cl[N(SiMe₂CH ₂PR₂)₂]. The remaining chloride of those derivatives having R = Me can be metathesized with alkyllithium reagents to generate hydrocarbyl complexes M(η⁴-C₄H₆)R′[N-(SiMe ₂CH₂PMe₂)₂] (M = Zr, Hf; R′ = Ph, CH₂CMe₃). The single-crystal, X-ray structures of Zr(η⁴-C₄H₆)Ph[N(SiMe₂CH ₂PMe₂)₂] (monoclinic, space group P2₁/c, a = 16.483 (1) A?, b = 11.521 (1) A?, c = 14.168 (2) A?, β = 104.309 (7)° Z = 4, R = R_w = 0.041 for 2349 reflections with I ≥ 3σ(I)) and Hf(η⁴-C₄H₆)Ph-[N(SiMe₂CH ₂PMe₂)₂] (monoclinic, space group P2₁/c, a = 16.323 (1) A?, b = 11.5063 (9) A?, c = 14.214 (2) A?, β = 104.450 (6)°, Z = 4, R = 0.033, and R_w = 0.034 for 3235 reflections with I ≥ 3σ(I)) are reported. In solution, the spectroscopic data are consistent with the 1,3-butadiene moiety undergoing a diene rotation and not the envelope-flipping mechanism common to early metal diene complexes. It is proposed that the phosphine donors of the ancillary ligand help stabilize a M(II) contribution, thereby inducing substantial π-character in the bonding of the diene unit.