Structural and reaction chemistry of the open chromocene bis(2,4-dimethylpentadienyl)chromium

Article abstract of DOI:10.1021/om00154a026

The reactivity of the open chromocene Cr(2,4-C₇H₁₁)₂ (C₇H₁₁ = dimethylpentadienyl) has been investigated and found to parallel that of metal allyl complexes, such as Ni(C₃H₅)₂. Thus, exposure to an excess of dmpe (Me₂PC₂H₄PMe₂) or t-C₄H₉NC brings about naked chromium reactions , leading to the formation of Cr(dmpe)₃ and Cr(CN(t-C₄H₉))₆, respectively, in good yields. With amine hydrochlorides and dmpe, one pentadienyl ligand may be removed, leading to the paramagnetic, 16-electron complex Cr(2,4-C₇H₁₁)(Cl)(dmpe), which could also be prepared from CrCl₂(dmpe)₂ and 1 equiv of K(2,4-C₇H₁₁). Reaction of the monochloride complex with LiCH₃ leads to the formation of the analogous methyl complex. Structural determinations are reported for Cr(2,4-C₂H₁₁)₂ and Cr(2,4-C₇H₁₁)(Cl)(dmpe). For Cr(2,4-C₇H₁₁)₂, an open-sandwich structure was found, with the average Cr-C bond distance being 2.163 (3) ?, comparable to the value of 2.169 (4) ? for chromocene. The structure has been refined to agreement indices of R = 0.040 and R_w = 0.053 in space group D₄⁴-P4₃2₁2 (No. 96) with a = b = 8.090 (1) ? and c = 20.847 (3) ? for Z = 4. For Cr(2,4-C₇H₁₁)(Cl)(dmpe), an unsymmetric piano-stool geometry was observed, in which one phosphorus atom is located under the open edge of the pentadienyl ligand, while the chlorine atom and other phosphorus atom are located under the formally uncharged C(2) and C(4) atoms of the pentadienyl ligand. The structure has been refined to agreement indices of R = 0.063 and R_w = 0.056 in space group D_2h¹⁵-Pbca (No. 61) with a = 12.578 (2) ?, b = 12.117 (2) ?, and c = 23.094 (5) ? for Z = 8.