Titanium(IV) Trifluoromethyl Complexes: New Perspectives on Bonding from Organometallic Fluorocarbon Chemistry

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• 作者：Felicia L. Taw ; Aurora E. Clark ; Alexander H. Mueller ; Michael T. Janicke ; Thibault Cantat ; Brian L. Scott ; P. Jeffrey Hay ; Russell P. Hughes ; Jaqueline L. Kiplinger
• 刊名：Organometallics
• 出版年：2012
• 出版时间：February 27, 2012
• 年：2012
• 卷：31
• 期：4
• 页码：1484-1499
• 全文大小：575K
• 年卷期：v.31,no.4(February 27, 2012)
• ISSN：1520-6041

文摘

Trifluoromethyltrimethylsilane, (CH₃)₃SiCF₃, in the presence of CsF serves as an excellent CF₃ group-transfer reagent, and reaction with Cp₂TiF₂ in THF gives the titanocene trifluoromethyl fluoride complex Cp₂Ti(CF₃)(F) (1; Cp = C₅H₅) in 60% isolated yield. Reaction of complex 1 with the trimethylsilyl reagents, (CH₃)₃SiX (X = OTf = OSO₂CF₃, Cl, Br, I, N₃, and OSO₂Ph), in a tetrahydrofuran or toluene solution affords the corresponding Ti鈥揅F₃ derivatives Cp₂Ti(CF₃)(X) (X = OTf (2), Cl (12), Br (13), I (14), N₃ (15), and OSO₂Ph (16)) in good isolated yields of 67鈥?4%. These compounds have been characterized by a combination of reactivity studies, IR and ¹H/¹³C{¹H}/¹⁹F NMR spectroscopies, and single-crystal X-ray diffraction. The Ti鈥揅F₃ linkage in these complexes is remarkably robust, and although the 伪-C鈥揊 bonds are elongated, there is no evidence of an 伪-fluoride (Ti路路路F鈥揅F₂) between the electrophilic Ti(IV) metal center and any of the C鈥揊 bonds in the trifluoromethyl group in the solid-state or in solution. In the solid-state, these complexes are shock-sensitive; energetic decomposition of Cp₂Ti(CF₃)(F) (1) produces uniform spherical nanoparticles ranging from 70 to 120 nm in size and porous fluorinated oligomers and polymers containing both 鈭?CF₂鈥揅F₂)鈥?and 鈭?CF₂鈥揅FH)鈥?units, as determined by a combination of SEM, XRD, XRF, XPS, and ¹⁹F MAS NMR. Density functional theory results show good agreement with experimental structural data obtained for Cp₂Ti(CF₃)(X) (X = F (1), OTf (2), Cl (12), N₃ (15)) and accurately predicts longer Ti鈥揅F₃ distances than for each specific CH₃ analogue, and the trend extends to structurally related Zr and Hf analogues. Simpler model compounds from groups 4 and 8 (M(CH₃)₄, M(CH₃)₃(CF₃), M(CH₃)₃(CCl₃), and M(CH₃)₃(CF₂CF₂CF₂CF₃); M = Ti, Zr, Hf, Fe, Ru, Os)) were also examined and show that, for group 4 complexes, 蟺-bonding is a significant factor in shortening the strongly ionic M鈥揅H₃ relative to M鈥揅F₃, whereas for the predominantly covalent group 8 analogues, 蟺-back-bonding helps to shorten the predominantly covalent M鈥揅F₃ relative to M鈥揅H₃. The bonding analysis suggests that the significant elongation of C鈥揊 bonds 伪 to metals is mainly a consequence of the electropositivity of the group 4 metal centers, with minor, if any, contributions from 蟺-effects; the bond-lengthening effect is most pronounced at the 伪-position and decays rapidly on moving away from the metal.