Morasch Michael, Vilpas Timothy, Patel Neha, Maurer Johannes, Thum Stefan, Schmidt Marcel A, Langer Jens, Harder Sjoerd
Inorganic and Organometallic Chemistry, Universität Erlangen-Nürnberg, Egerlandstrasse 1, 91058, Erlangen, Germany.
Angew Chem Int Ed Engl. 2025 Jul 7;64(28):e202506989. doi: 10.1002/anie.202506989. Epub 2025 May 22.
DFT calculations on β-diketiminate (BDI) complexes with the full series of alkaline-earth (Ae) metals show that (BDI)AeAe(BDI) complexes of the heavier Ae metals (Ca, Sr, Ba) have long weak Ae─Ae bonds that are prone to homolytic bond cleavage. However, isolation of (BDI)Sr(μ-N)Sr(BDI) with a side-on bridging N dianion should thermodynamically be feasible. Attempts to stabilize such a complex with the super bulky BDI* ligand failed (BDI* = HC[(Me)C = N-DIPeP], DIPeP = 2,6-EtCH-phenyl). First, N fixation with a Sr complex was enabled by a heterobimetallic approach. Reduction of (NN)Sr with potassium gave (NN)SrK(N) (6-Sr); NN = N-Si(Me)CHCHSi(Me)-N. A similar Ca product was also isolated (6-Ca). Crystal structures reveal a N anion with side-on bonding to Ae and end-on coordination to K. DFT calculations and Atoms-In-Molecules analyses show mainly ionic bonding. Both 6-Ae complexes are synthons for hitherto unknown (BDI*)AeAe(BDI*) (Ae = Ca, Sr) and react by releasing N and two electrons. Although surprisingly stable in benzene, the reduction of I and H is facile. Fast reaction with Teflon led to formation of crystalline [(NN)SrKF] (7), which is labile and decomposed to KF and (NN)Sr. Latter reactivity underscores potential use of 6-Ae complexes as very strong, hydrocarbon-soluble reducing agents.
对含有全系列碱土金属（Ae）的β-二酮亚胺（BDI）配合物进行的密度泛函理论（DFT）计算表明，较重的Ae金属（Ca、Sr、Ba）的（BDI）AeAe（BDI）配合物具有长的弱Ae─Ae键，易于发生均裂键断裂。然而，从热力学角度来看，分离带有侧桥连N二价阴离子的（BDI）Sr（μ-N）Sr（BDI）应该是可行的。尝试用超庞大的BDI配体（BDI = HC[(Me)C = N-DIPeP]，DIPeP = 2,6-EtCH-苯基）来稳定这种配合物却失败了。首先，通过异双金属方法实现了用Sr配合物固定N。用钾还原（NN）Sr得到（NN）SrK（N）（6-Sr）；NN = N-Si（Me）CHCHSi（Me）-N。还分离出了类似的Ca产物（6-Ca）。晶体结构揭示了一个N阴离子，它以侧键与Ae相连，以端键与K配位。DFT计算和分子中的原子分析表明主要是离子键。两种6-Ae配合物都是迄今未知的（BDI*）AeAe（BDI*）（Ae = Ca、Sr）的合成子，并通过释放N和两个电子进行反应。尽管在苯中出人意料地稳定，但I和H的还原很容易。与聚四氟乙烯快速反应导致形成结晶的[(NN)SrKF]（7），它不稳定，会分解为KF和（NN）Sr。后者的反应活性突出了6-Ae配合物作为非常强的、可溶于烃类的还原剂的潜在用途。
