Herbert David E, Tanabe Makoto, Bourke Sara C, Lough Alan J, Manners Ian
School of Chemistry, University of Bristol, Bristol, England, BS8 1TS.
J Am Chem Soc. 2008 Mar 26;130(12):4166-76. doi: 10.1021/ja077334+. Epub 2008 Mar 4.
Cyclopentadienyl (Cp) ligands in moderately strained [1]- and [2]ferrocenophanes [Fe{(eta5-C5H4)2(ERx)y}: Fe{(eta5-C5H4)2SiMe2} (1), Fe{(eta5-C5H4)CH2}2 (10)] and highly strained [2]ruthenocenophanes [Ru{(eta5-C5H4)CR2}2 {R = H (15), Me (16)}] are susceptible to partial substitution by P donors and form mixed-hapticity metallocycles-[M(L2){(eta5-C5H4)(ERx)y(eta1-C5H4)}]: [Fe(dppe){(eta5-C5H4)SiMe2(eta1-C5H4)}] (5), [Fe(dmpe){(eta5-C5H4)SiMe2(eta1-C5H4)}] (6), [Fe(dmpe){(eta5-C5H4)(CH2)2(eta1-C5H4)}] (11), [Ru(dmpe){(eta5-C5H4)(CH2)2(eta1-C5H4)}] (17), [Ru(dmpe){(eta5-C5H4)(CMe2)2(eta1-C5H4)}] (18), and [Ru(PMe3)2{(eta5-C5H4)(CH2)2(eta1-C5H4)}] (19)-through haptotropic reduction of one eta5-, pi-bound Cp to eta1, sigma-coordination. These reactions are strain-controlled, as highly ring-tilted [2]ruthenocenophanes 15 and 16 [tilt angles (alpha) approximately 29-31 degrees ] react without irradiation to form thermodynamically stable products, while moderately strained [n]ferrocenophanes 1 and 10 (alpha approximately 19-22 degrees ) require photoactivation. The iron-containing photoproducts 5 and 11 are metastable and thermally retroconvert to their strained precursors and free phosphines at 70 degrees C. In contrast, the unprecedented ring-opening polymerization (ROP) of the essentially ring-strain-free adduct 6 to afford poly(ferrocenyldimethylsilane) [Fe(eta5-C5H4)2SiMe2]n (Mw approximately 5000 Da) was initiated by the thermal liberation of small amounts of P donor. Unlike reactions with bidentate analogues, monodentate phosphines promoted photolytic ROP of ferrocenophanes 1 and 10. MALDI-TOF analysis suggested a cyclic structure for the soluble poly(ferrocenyldimethylsilane), 8-cyclic, produced from 1 in this manner. While the polymer likewise produced from 10 was insoluble, the initiation step in the ROP process was modeled by isolation of a tris(phosphine)-substituted ring-opened ferrocenophane [Fe(PMe3)3{(eta5-C5H4)(CH2)2(C5H5)}][OCH2CH3] (13[OCH2CH3]) generated by irradiation of 10 and PMe3 in a protic solvent (EtOH). Studies of the cation 13 revealed that the Fe center reacts with a Cp- anion with loss of the phosphines to form [Fe(eta5-C5H5){(eta5-C5H4)(CH2)2(C5H5)}] (14) under conditions identical to those of the ROP experiments, confirming the likelihood of "back-biting" reactions to yield cyclic structures or macrocondensation to produce longer chains.
在适度应变的[1] - 和[2] - 二茂铁衍生物[Fe{(η⁵ - C₅H₄)₂(ERₓ)y}：Fe{(η⁵ - C₅H₄)₂SiMe₂} (1)，Fe{(η⁵ - C₅H₄)CH₂}₂ (10)]以及高度应变的[2] - 钌茂衍生物[Ru{(η⁵ - C₅H₄)CR₂}₂ {R = H (15)，Me (16)}]中的环戊二烯基（Cp）配体易被P供体部分取代，并通过将一个η⁵ - 、π键合的Cp向η¹ - 、σ配位的迁移氢化反应形成混合配体金属环 - [M(L₂){(η⁵ - C₅H₄)(ERₓ)y(η¹ - C₅H₄)}]：[Fe(dppe){(η⁵ - C₅H₄)SiMe₂(η¹ - C₅H₄)}] (5)，[Fe(dmpe){(η⁵ - C₅H₄)SiMe₂(η¹ - C₅H₄)}] (6)，[Fe(dmpe){(η⁵ - C₅H₄)(CH₂)₂(η¹ - C₅H₄)}] (11)，[Ru(dmpe){(η⁵ - C₅H₄)(CH₂)₂(η¹ - C₅H₄)}] (17)，[Ru(dmpe){(η⁵ - C₅H₄)(CMe₂)₂(η¹ - C₅H₄)}] (18)，以及[Ru(PMe₃)₂{(η⁵ - C₅H₄)(CH₂)₂(η¹ - C₅H₄)}] (19)。这些反应受应变控制，因为高度环倾斜的[2] - 钌茂衍生物15和16 [倾斜角（α）约为29 - 31度]在无光照的情况下反应形成热力学稳定产物，而适度应变的[n] - 二茂铁衍生物1和10（α约为19 - 22度）需要光活化。含铁的光产物5和11是亚稳态的，在70℃下热逆转为其应变前体和游离膦。相比之下，基本无环应变的加合物6发生前所未有的开环聚合（ROP）以得到聚（二茂铁基二甲基硅烷）[Fe(η⁵ - C₅H₄)₂SiMe₂]n（Mw约为5000 Da）是由少量P供体的热释放引发的。与与双齿类似物的反应不同，单齿膦促进二茂铁衍生物1和10的光解ROP。基质辅助激光解吸电离飞行时间（MALDI - TOF）分析表明，以这种方式由1产生的可溶性聚（二茂铁基二甲基硅烷）呈8 - 环状结构。虽然由10同样产生的聚合物不溶，但ROP过程中的引发步骤通过在质子溶剂（乙醇）中照射10和PMe₃分离得到的三（膦）取代的开环二茂铁衍生物[Fe(PMe₃)₃{(η⁵ - C₅H₄)(CH₂)₂(C₅H₅)}][OCH₂CH₃] (13[OCH₂CH₃])进行模拟。对阳离子13的研究表明，在与ROP实验相同的条件下，Fe中心与一个Cp⁻阴离子反应并失去膦以形成[Fe(η⁵ - C₅H₅){(η⁵ - C₅H₄)(CH₂)₂(C₅H₅)}] (14)，证实了发生“回咬”反应以产生环状结构或宏观缩合以产生更长链的可能性。
