Gyroscope-Like Complexes Based on Dibridgehead Diphosphine Cages That Are Accessed by Three-Fold Intramolecular Ring Closing Metatheses and Encase Fe(CO)3, Fe(CO)2(NO)+, and Fe(CO)3(H)+ Rotators

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• 作者：Georgette M. Lang ; Takanori Shima ; Leyong Wang ; Kyle J. Cluff ; Katrin Skopek ; Frank Hampel ; Janet Blümel ; John A. Gladysz
• 刊名：Journal of the American Chemical Society
• 出版年：2016
• 出版时间：June 22, 2016
• 年：2016
• 卷：138
• 期：24
• 页码：7649-7663
• 全文大小：928K
• 年卷期：0
• ISSN：1520-5126

文摘

Reactions of trans-Fe(CO)₃(P((CH₂)_mCH═CH₂)₃)₂ (m = a/4; b/5, c/6, e/8) and Grubbs’ catalyst (12–24 mol %, CH₂Cl₂, reflux) give the cage-like trienes trans-Fe(CO)₃(P((CH₂)_mCH═CH(CH₂)_m)₃P) (3a–c,e, 60–81%). Hydrogenations (ClRh(PPh₃)₃, 60–80 °C) yield the title compounds trans-Fe(CO)₃(P((CH₂)_n)₃P) (4a–c,e, 74–86%; n = 2m + 2), which have idealized D_3h symmetry. A crystal structure of 4c suggests enough van der Waals clearance for the Fe(CO)₃ moiety to rotate within the three P(CH₂)₁₄P linkages; structures of E,E,E-3a show rotation to be blocked by the shorter P(CH₂)₄CH═CH(CH₂)₄P linkages. Additions of NO⁺BF₄^– give the isoelectronic and isosteric cations [Fe(CO)₂(NO)(P((CH₂)_n)₃P)]⁺BF₄^– (5a–c⁺BF₄^–; 81–98%). Additions of [H(OEt₂)₂]⁺BAr_f^– (BAr_f = B(3,5-C₆H₃(CF₃)₂)₄) afford the metal hydride complexes mer,trans-[Fe(CO)₃(H)(P((CH₂)_n)₃P)]⁺BAr_f^– (6a–c,e⁺BAr_f^–; 98–99%). The behavior of the rotators in the preceding complexes is probed by VT NMR. At ambient temperature in solution, 5a,b⁺BF₄^– and 6a⁺BAr_f^– show two sets of P(CH₂)_n/2 ¹³C NMR signals (2:1), whereas 5c⁺BF₄^– and 6b,c⁺BAr_f^– show only one. At higher temperatures, the signals of 5b⁺BF₄^– coalesce; at lower temperatures, those of 5c⁺BF₄^– and 6b⁺BAr_f^– decoalesce. These data give ΔH^⧧/ΔS^⧧ values (kcal/mol and eu) of 8.3/–28.4 and 9.5/–6.5 for Fe(CO)₂(NO)⁺ rotation (5b,c⁺) and 6.1/–23.5 for Fe(CO)₃(H)⁺ rotation (6b⁺). ¹³C CP/MAS NMR spectra show that the Fe(CO)₃ moiety in polycrystalline 4c (but not 4a) undergoes rapid rotation between −60 and 95 °C. Approaches to minimizing these barriers and developing molecular gyroscopes are discussed.