Ghisolfi Alessio, Waldvogel Audrey, Routaboul Lucie, Braunstein Pierre
Laboratoire de Chimie de Coordination, Institut de Chimie (UMR 7177 CNRS), Université de Strasbourg , 4 rue Blaise Pascal, F-67081 Strasbourg Cedex, France.
Inorg Chem. 2014 Jun 2;53(11):5515-26. doi: 10.1021/ic500194y. Epub 2014 May 12.
The coordination chemistry of a new functional quinonoid zwitterion (E)-3-oxo-4-((2-(pyridin-2-yl)ethyl)amino)-6-((2-(pyridin-2-yl)ethyl)iminio)cyclohexa-1,4-dienolate (2, H2L), in which a CH2CH2 spacer connects the N substituents of the quinonoid core with a pyridine group, was explored in Pd(II) chemistry. Different coordination modes have been observed, depending on the experimental conditions and the reagents. The reaction of H2L with [Pd(μ-Cl)(dmba)]2 (dmba = o-C6H4CH2NMe2-C,N) afforded the dinuclear complex [{PdCl(dmba)}2(H2L)] (3) in which H2L acts as a NPy,NPy bidentate ligand. Deprotonation of this complex with NaH resulted in the formation of the dinuclear complex [{Pd(dmba)}2(μ-L)] (4) in which a shift of the Pd(II) centers from the NPy sites to the N,O donor sites of the zwitterion core has occurred, resulting in a N2O2 tetradentate behavior of ligand L. Reaction of 4 with HCl regenerates 3 quantitatively. Chloride abstraction from 3 with AgOTf (OTf = trifluoromethanesulfonate) resulted in loss of one of the two dmba ligands and formation of an unusual tetranuclear Pd(II) complex, [{Pd(dmba)}(μ-L)Pd]2(OTf)2 (5), in which two dinuclear entities have dimerized, one pyridine donor group from each dimer forming a bridge with the other dinuclear entity. This results in a N2, O2, NPy, NPy hexadentate behavior for the ligand L. Complexes 3 and 4 constitute an unprecedented reversible, switchable system where deprotonation or protonation promotes the reversible migration of the Pd(dmba) moieties, from the NPy sites in 3, to the N,O donor sites of the quinonoid core in 4, respectively. This switch modifies the extent of π-delocalization involving the potentially antiaromatic quinonoid moiety and is accompanied by a significant color change, from red in 3 to green in 4. The presence of uncoordinated pyridine donor groups in 4 allowed the use of this complex for the preparation of the neutral tetranuclear complex [{Pd(dmba)}2(μ-L){PdCl(dmba)}2] (6) in which 4 acts as a NPy,NPy-bidentate metalloligand toward two PdCl(dmba) moieties. Halide abstraction from 6 afforded the monocationic, tetranuclear complex [{Pd(dmba)}2(μ-L){Pd(dmba)}2(μ-Cl)]PF6 (7) in which the two Pd(dmba) moieties are connected by ligand L and a bridging chloride. By Cl/PF6 anion metathesis, it was possible to switch quantitatively from complex 6 to 7 and vice versa. All new compounds were unambiguously characterized by IR, NMR, and mass spectroscopy. Single-crystal X-ray diffraction is also available for molecules 2-5 and 7.
研究了一种新型功能性醌类两性离子（E）-3-氧代-4-（（2-（吡啶-2-基）乙基）氨基）-6-（（2-（吡啶-2-基）乙基）亚氨基）环己-1,4-二烯醇盐（2，H₂L）的配位化学，其中一个CH₂CH₂间隔基将醌类核心的N取代基与一个吡啶基团相连。根据实验条件和试剂的不同，观察到了不同的配位模式。H₂L与[Pd(μ-Cl)(dmba)]₂（dmba = o-C₆H₄CH₂NMe₂-C,N）反应得到双核配合物[{PdCl(dmba)}₂(H₂L)]（3），其中H₂L作为NPy,NPy双齿配体。用NaH使该配合物去质子化，导致形成双核配合物[{Pd(dmba)}₂(μ-L)]（4），其中Pd(II)中心从NPy位点转移到两性离子核心的N,O供体位点，导致配体L呈现N₂O₂四齿配位行为。4与HCl反应定量再生3。用AgOTf（OTf = 三氟甲磺酸盐）从3中脱去氯离子，导致两个dmba配体之一丢失，并形成一种不寻常的四核Pd(II)配合物[{Pd(dmba)}(μ-L)Pd]₂(OTf)₂（5），其中两个双核实体二聚化，每个二聚体中的一个吡啶供体基团与另一个双核实体形成桥连。这导致配体L呈现N₂、O₂、NPy、NPy六齿配位行为。配合物3和4构成了一个前所未有的可逆、可切换体系，其中去质子化或质子化分别促进了[Pd(dmba)]⁺部分从3中的NPy位点到4中醌类核心的N,O供体位点的可逆迁移。这种切换改变了涉及潜在反芳香性醌类部分的π离域程度，并伴随着显著的颜色变化，从3中的红色变为4中的绿色。4中未配位的吡啶供体基团的存在使得该配合物可用于制备中性四核配合物[{Pd(dmba)}₂(μ-L){PdCl(dmba)}₂]（6），其中4作为NPy,NPy双齿金属配体与两个PdCl(dmba)部分配位。从6中脱去卤离子得到单核阳离子四核配合物[{Pd(dmba)}₂(μ-L){Pd(dmba)}₂(μ-Cl)]PF₆（7），其中两个Pd(dmba)部分通过配体L和一个桥连氯离子相连。通过Cl/PF₆阴离子复分解反应，可以定量地从配合物6切换到7，反之亦然。所有新化合物均通过红外光谱、核磁共振光谱和质谱进行了明确表征。分子2 - 5和7也有单晶X射线衍射数据。
