Department of Chemistry, Texas A&M University , PO Box 30012, College Station, Texas 77843-3012, United States.
Institut für Organische Chemie and Interdisciplinary Center for Molecular Materials, Friedrich-Alexander-Universität Erlangen-Nürnberg , Henkestraße 42, 91054 Erlangen, Germany.
J Am Chem Soc. 2016 Jun 22;138(24):7649-63. doi: 10.1021/jacs.6b03178. Epub 2016 Jun 8.
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)3 P) (3a-c,e, 60-81%). Hydrogenations (ClRh(PPh3)3, 60-80 °C) yield the title compounds trans- Fe(CO)3(P((CH2)n)3 P) (4a-c,e, 74-86%; n = 2m + 2), which have idealized D3h 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)3 P)BF4(-) (5a-c(+)BF4(-); 81-98%). Additions of H(OEt2)2BArf(-) (BArf = B(3,5-C6H3(CF3)2)4) afford the metal hydride complexes mer,trans- Fe(CO)3(H)(P((CH2)n)3 P)BArf(-) (6a-c,e(+)BArf(-); 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(+)BArf(-) show two sets of P(CH2)n/2 (13)C NMR signals (2:1), whereas 5c(+)BF4(-) and 6b,c(+)BArf(-) show only one. At higher temperatures, the signals of 5b(+)BF4(-) coalesce; at lower temperatures, those of 5c(+)BF4(-) and 6b(+)BArf(-) 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(+)). (13)C 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.
反式-Fe(CO)3(P((CH2)mCH═CH2)3)2(m=a/4; b/5, c/6, e/8) 和 Grubbs 催化剂(12-24 mol %, CH2Cl2, 回流)反应生成笼状三烯反式-Fe(CO)3(P((CH2)mCH═CH(CH2)m)3 P)(3a-c,e, 60-81%)。氢化反应(ClRh(PPh3)3, 60-80 °C)生成标题化合物反式-Fe(CO)3(P((CH2)n)3 P)(4a-c,e, 74-86%; n=2m+2), 它们具有理想的 D3h 对称性。4c 的晶体结构表明，Fe(CO)3 部分有足够的范德华间隙可以在三个 P(CH2)14P 键之间旋转；E,E,E-3a 的结构表明旋转被较短的 P(CH2)4CH═CH(CH2)4P 键所阻挡。加入 NO(+)BF4(-)得到等电子等原子的阳离子Fe(CO)2(NO)(P((CH2)n)3 P)BF4(-)(5a-c(+)BF4(-); 81-98%)。加入H(OEt2)2BArf(-)(BArf=B(3,5-C6H3(CF3)2)4)可得到金属氢化物配合物 mer,trans-Fe(CO)3(H)(P((CH2)n)3 P)BArf(-)(6a-c,e(+)BArf(-); 98-99%)。通过 VT NMR 研究了前序配合物中旋转体的行为。在室温下的溶液中，5a,b(+)BF4(-)和 6a(+)BArf(-)显示两组 P(CH2)n/2(13)C NMR 信号(2:1)，而 5c(+)BF4(-)和 6b,c(+)BArf(-)只显示一组。在较高温度下，5b(+)BF4(-)的信号发生了简并；在较低温度下，5c(+)BF4(-)和 6b(+)BArf(-)的信号发生了去简并。这些数据给出了 Fe(CO)2(NO)(+)旋转(5b,c(+))和 Fe(CO)3(H)(+)旋转(6b(+))的 ΔH(⧧)/ΔS(⧧)值(千卡/摩尔和 eu)分别为 8.3/-28.4 和 9.5/-6.5。(13)C CP/MAS NMR 谱表明，多晶态 4c 中的 Fe(CO)3 部分(-60 至 95 °C)在快速旋转。讨论了降低这些能垒和开发分子陀螺仪的方法。
