Peralkylcyclopentadienyl tungsten polyhydride complexes

Article abstract of DOI:10.1021/om00139a028

[WCp*H₄]₂ (Cp* = η⁵-C₅Me₅) has been prepared by the reaction of [WCp*Cl₄]₂ with LiAlH₄ followed by treatment with methanol. Analogous η⁵-C₅Me₄Et, η⁵-C₅Me₄-n-Pr, η⁵-C₅Me₄-t-Bu, η⁵-C₅Et₅, and η⁵-C₅Et₄-t-Bu complexes have been prepared similarly. Reaction of [WCp*H₄]₂ (Cp* = η⁵-C₅Me₅) with CO under pressure gives the known dinuclear hydrido carbonyl complex [WCp*H(CO)₂]₂, whereas with PMe₃ a hydrido phosphine complex W₂Cp*₂H₆(PMe₃) is formed. The dimeric unit is retained when [WCp*H₄]₂ is mixed with [W(η⁵-C₅Me₄-t-Bu)H₄]₂ and during the reaction of this mixture with CO or PMe₃. A trimeric trihydride complex, [WCp*H₃]₃, forms together with a small amount of [WCp*H₄]₂ upon high-pressure hydrogenation of WCp*Me₄. Reaction of WCp*Cl₄(PMe₃) with LiAlH₄ gives the monomeric phosphine hydride complex WCp*H₅(PMe₃). [WCp*H₄]₂ can be protonated cleanly by HBF₄ to give [W₂Cp*₂H₉]BF₄. With use of analogous methodology several hydride complexes containing the two-carbon-linked cyclopentadienyl ligand η⁵,η⁵-Et₄C₅CH ₂CH₂C₅Et₄ have been prepared. The octahydride complex [WH₄]₂-(η⁵,η⁵-Et ₄C₅CH₂CH₂C₅Et ₄) crystallizes as a toluene solvate in the triclinic space group P1 with a = 14.828 (3) A?, b = 15.963 (5) A?, c = 7.854 (3) A?, α = 93.03 (3)°, β = 98.04 (2)°, γ = 110.91 (2)°, and Z = 2. Diffraction data (Mo Κα) were collected at -50°C with a CAD4F-11 diffractometer, and the structure was refined to R₁ = 4.3% and R₂ = 4.7% for 4595 absorption corrected reflections having 3° ≤ 2θ ≤ 50° and F_o > 4σ(F_o). The complex shows a dinuclear structure with a W-W distance of 2.591 (1) A? and slightly distorted bridging ligand system. The hydride ligands could not be located, even using a data set collected at -180°C. An interesting difference in the reactivity of [WCp*H₄]₂ and [WH₄]₂(η⁵,η⁵-Et ₄C₅CH₂CH₂C₅Et ₄) is that the latter does not react readily with CO. ¹H NMR data for all neutral hydride complexes show intramolecular hydride exchange to be rapid on the NMR time scale under most conditions, while the exchange of terminal and bridging hydrides in [W₂Cp*₂H₉]⁺ is slow at -30°C (400 MHz).