A novel facet of carbonyliron-diene photochemistry: The η4-s-trans isomer of the classical Fe(CO)3(η4-s-cis-1,3-butadiene) discovered by time-resolved IR spectroscopy and theoretically examined by density functional methods
A novel facet of carbonyliron-diene photochemistry: The η4-s-trans isomer of the classical Fe(CO)3(η4-s-cis-1,3-butadiene) discovered by time-resolved IR spectroscopy and theoretically examined by density functional methods
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DOI：
10.1021/om020785c
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发表时间：
2003-04-14
期刊：
影响因子：
2.8
通讯作者：
Schaffner, K
中科院分区：
文献类型：
--
作者：
Bachler, V;Grevels, FW;Schaffner, K
本文用ν（CO）区的时间分辨红外光谱重新研究了Fe（CO）_3（η_4-s-cis-1，3-butadiene）（1）和Fe（CO）_4（η_2 - 1，3-butadiene）（2）在室温环己烷溶液中的光解。2的闪光光解（λexc= 308 nm）产生Fe（CO）3（η4-s-trans-1，3-butadiene）（5）作为瞬态产物，其然后重排以形成经典的η4-s-cis-1，3-butadiene络合物1。之前称为配位不饱和Fe（CO）3（η2- 1，3-丁二烯）（3）的物种5也是由1光生的，在这种情况下沿着的是非常短寿命的CO损失碎片Fe（CO）2（η4- 1，3-丁二烯）（在CO气氛下τ < 4 μs）。它的衰变符合温度依赖性一级动力学（25 °C时τ = 13 ms; ΔH ε = 17.3 kcal·mol-1），1.根据BP 86理论水平的密度泛函计算，5存在于一个明显的能量最低点，高于1 20.3 kcal·mol-1，与之相隔15.0 kcal·mol-1的势垒。其计算结构涉及129°的二烯二面角。相比之下，物种3（具有-150.1 °的二烯二面角）被预测存在于一个相当平坦的最小值中，这使得它的寿命太短，无法用我们的仪器检测到。Fe（CO）5的闪光光解除了产生熟悉的Fe（CO）4（solv）碎片外，还产生寿命极短（<1 μs）的双不饱和Fe（CO）3（solv）物种（τ = 10−15 μs），在不存在除CO以外的潜在捕集剂的情况下，Fe 2（CO）9是最终产物。故意用水污染系统会导致Fe（CO）4（H2O）的形成。作为更长寿命的瞬态（ca. 1ms）。在1，3-丁二烯存在下，2和5几乎同时出现。后者衰变，再次在毫秒的时间范围内，与1的形成，从而提供了明确的证据，从Fe（CO）5的单光子路线1除了建立双光子序列通过单取代配合物2。
The photolysis of Fe(CO)3(η4-s-cis-1,3-butadiene) (1) and Fe(CO)4(η2-1,3-butadiene) (2), formerly studied in low-temperature matrixes, is reexamined in cyclohexane solution at ambient temperature using time-resolved IR spectroscopy in the ν(CO) region. Flash photolysis of2(λexc= 308 nm) generates Fe(CO)3(η4-s-trans-1,3-butadiene) (5) as a transient product, which then rearranges to form the classical η4-s-cis-1,3-butadiene complex1. Species5, previously addressed as the coordinately unsaturated Fe(CO)3(η2-1,3-butadiene) (3), is also photogenerated from1, in this case along with the very short-lived CO loss fragment Fe(CO)2(η4-1,3-butadiene) (τ < 4 μs under CO atmosphere). It decays by temperature-dependent first-order kinetics (τ = 13 ms at 25 °C; ΔH⧧= 17.3 kcal·mol-1) with nearly complete recovery of1. According to density functional calculations at the BP86 level of theory,5resides in a distinct energy minimum, 20.3 kcal·mol-1above1and separated from it by a barrier of 15.0 kcal·mol-1. Its computed structure involves a diene dihedral angle of 129°. Species3(with a diene dihedral angle of −150.1°), by contrast, is predicted to exist in a rather flat minimum, which makes it too short-lived for detection with our instrumentation. Flash photolysis of Fe(CO)5generates the very short-lived (<1 μs) doubly unsaturated Fe(CO)3(solv) species in addition to the familiar Fe(CO)4(solv) fragment (τ = 10−15 μs), Fe2(CO)9being the ultimate product in the absence of potential trapping agents other than CO. Deliberate contamination of the system with water gives rise to the formation of Fe(CO)4(H2O) as a longer lived transient (ca. 1 ms). In the presence of 1,3-butadiene, both2and5appear almost instantaneously. The latter decays, again in the millisecond time range, with formation of1, thus providing clear evidence of a single-photon route from Fe(CO)5to1in addition to the established two-photon sequence via the monosubstituted complex2.