Stabilization of low-oxidation-state early transition-metal complexes bearing 1,2,4-triphosphacyclopentadienyl ligands:: Structure of [{Sc(P3C2tBu2)2}2];ScII or mixed oxidation state?
Stabilization of low-oxidation-state early transition-metal complexes bearing 1,2,4-triphosphacyclopentadienyl ligands:: Structure of [{Sc(P3C2tBu2)2}2];ScII or mixed oxidation state?
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DOI：
10.1002/anie.200390267
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发表时间：
2003-01-01
影响因子：
16.6
通讯作者：
Nixon, JF
中科院分区：
文献类型：
--
作者：
Clentsmith, GKB;Cloke, FGN;Nixon, JF
稀土元素络合物的三价氧化态的普遍性是众所周知的，并有充分的文献记载。[1]传统上，二价镧系元素化学仅限于EuII，YbII和SmII，[2，3]然而，最近的工作已经详细描述了充分表征的TmII，[4-6] NdII [5]和DyII [7]复合物的合成，并报道了它们对其他非反应性小分子的令人印象深刻和前所未有的反应性。[4，7，8]相比之下，早期的二价化学的平行发展，更大的镧系元素似乎是一个不可能的任务。LnIII/LnII对，已经很高的晚期镧系元素（！2002年。5 V vs. NHE），[3]可能被证明对于较大的早期成员具有过高的幅度。然而，在特殊条件下，例如在金属蒸气合成（MVS）实验中，[9]零，单，[10]和二价[11]金属中心甚至可以接近正电性第3族金属。已证明挥发性和反应性磷杂炔tBuC P是这种MVS反应中的重要原料，因为它能够在MVS反应器中进行环化反应，得到各种能够支持氧化态的杂环配体，这些氧化态对于这些高度路易斯酸性的金属是迄今为止未知的。[12]环中磷原子的存在降低了未占据轨道的能量，并促进了金属的δ回键，从而稳定了还原氧化态的d电子。[13]这里报道的工作描述了芳香族三磷酰基环P3 C2 tBu 2的应用程序的化学最小的第3族金属，即钪，但没有诉诸MVS技术。用1，3-P3 C2 tBu 2阴离子处理ScI 3，作为其无碱钾盐，[14]得到均配的三价络合物[Sc（P3 C2 tBu 2）3]。这被证明是低价钪化学的一个方便的切入点，因为P3 C2 tBu 2环是比Cp* 或Cp“差得多的电子供体（Cp*= C5 Me 5 β，Cp”= 1，3-C5 H3（SiMe 3）2 β），并且能够充当离去基团。在这里的固态和溶液结构的减少，正式二价Sc配合物稳定的1，2，4-triphosphacyclopyrene环，沿着与其父ScIII复杂的细节。此外，我们描述了两个新的Sc配合物，这是在极好的协议与实验结果的DFT计算结果。无碱K [P3 C2 tBu 2]和ScI 3在甲苯或均三甲苯中回流长时间加热产生深红色溶液，在后处理时可从中分离出红色晶体。红色产物的质谱（m/z 738）表明其式为[Sc（P3 C2 tBu 2）3]（1）[Eq.①]。适合于X射线衍射实验的晶体从庚烷生长，并且1的结构呈现在图1中。化合物1的钪原子与两个P3 C2 tBu 2环η5键合，配位通过第三个P3 C2 tBu 2环以η2方式与两个相邻的磷中心键合完成。Sc ± M距离（M=环重心）分别为2.326（9）和2.371（9），且η2键合的磷原子对称配位（Sc ± P4 2.762（3），Sc ± P5 2.792（3））。虽然在文献中没有[M（P3 C2 tBu 2）3]化合物的其他例子，但我们在未发表的工作中合成并结构表征了同源的YIII、TmIII和UIII衍生物，它们都是同构的，但具有更长的Ln/Acrylate M和Ln/Acrylate（η2-P2）键长。[15]相应的Ce、Sm和
The prevalence of the tervalent oxidation state for complexes of the rare-earth elements is both well understood and amply documented.[1] Traditionally, bivalent lanthanide chemistry has been limited to just EuII, YbII, and SmII,[2, 3] however, quite recent work has detailed the syntheses of well-characterized TmII,[4–6] NdII,[5] and DyII [7] complexes and has reported their impressive and unprecedented reactivity towards otherwise unreactive small molecules.[4, 7, 8] Parallel development of bivalent chemistry for the earlier, larger lanthanides might seem an impossible task by comparison. The LnIII/LnII couple, already high for the late series lanthanides (! À2. 5 V versus NHE),[3] might prove to be of prohibitively high magnitude for the larger, earlier members. Nevertheless, under special conditions, for instance those operating in metal vapor synthesis (MVS) experiments,[9] zero-, uni-,[10] and bivalent [11] metal centers can be accessed even for the electropositive Group 3 metals. The volatile and reactive phosphaalkyne, tBuC P, has proved to be an important feedstock in such MVS reactions, as it is able to undergo cyclization reactions in the MVS reactor to give a variety of heterocyclic ligands capable of supporting oxidation states that were hitherto unknown for these highly Lewis-acidic metals.[12] The presence of phosphorus atoms in the ring lowers the energy of the unoccupied orbitals and promotes δ back-bonding from the metal, thus stabilizing the d electrons of reduced oxidation states.[13] The work reported here describes the application of the aromatic triphospholyl ring P3C2tBu2 to the chemistry of the smallest Group 3 metal, namely scandium, but without resort to the MVS technique. Treatment of ScI3 with the 1, 3-P3C2tBu2 anion, as its base-free potassium salt,[14] gives the homoleptic, tervalent complex [Sc (P3C2tBu2) 3]. This proves to be a convenient entry point for subvalent scandium chemistry, as the P3C2tBu2 ring is a much poorer electron donor than either Cp* or Cp’’(Cp*= C5Me5 À, Cp’’= 1, 3-C5H3 (SiMe3) 2 À), and is capable of acting as a leaving group. Here the solidstate and solution structures of a reduced, formally bivalent Sc complex stabilized by the 1, 2, 4-triphosphacyclopentadienyl ring are presented, along with details of its parent ScIII complex. In addition, we describe the results of DFT calculations on both new Sc complexes, which are in excellent agreement with the experimental findings. Prolonged heating of base-free K [P3C2tBu2] and ScI3 in toluene or mesitylene at reflux gives rise to a deep red solution from which red crystals may be isolated upon workup. The mass spectrum of the red product (m/z 738) suggests its formulation as [Sc (P3C2tBu2) 3](1)[Eq.(1)]. Crystals suitable for an X-ray diffraction experiment were grown from heptane and the structure of 1 is presented in Figure 1. The scandium atom of compound 1 is η5-bound to two of the P3C2tBu2 rings and coordination is completed by a third P3C2tBu2 ring bound in an η2 fashion to two adjacent phosphorus centers. The ScÀM distances (M= ring centroid) are 2.326 (9) and 2.371 (9), respectively, and the η2-bound phosphorus atoms are coordinated symmetrically (ScÀP4 2.762 (3), ScÀP5 2.792 (3)). Although there are no other examples of [M (P3C2tBu2) 3] compounds in the literature, we have in unpublished work synthesized and structurally characterized the homologous YIII, TmIII, and UIII derivatives that are all isostructural, but have longer Ln/AcÀM and Ln/AcÀ (η2-P2) bond lengths.[15] The corresponding Ce, Sm, and