Tetra-2,3-pyrazinoporphyrazines with Externally Appended Pyridine Rings. 8. Central (ZnII, CuII, MgII(H2O), CdII) and Exocyclic (PdII)

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• 作者：Maria Pia Donzello ; Elisa Viola ; Xiaohui Cai ; Luisa Mannina ; Claudio Ercolani ; Karl M. Kadish
• 刊名：Inorganic Chemistry
• 出版年：2010
• 出版时间：March 1, 2010
• 年：2010
• 卷：49
• 期：5
• 页码：2447-2456
• 全文大小：929K
• 年卷期：v.49,no.5(March 1, 2010)
• ISSN：1520-510X

文摘

A series of heteropentametallic porphyrazine macrocycles, represented as [(PdCl₂)₄LM], where L = dianion of tetrakis-2,3-[5,6-di(2-pyridyl)pyrazino]porphyrazine and M = Zn^II, Cu^II Mg^II(H₂O) or Cd^II, were prepared by reaction of the corresponding mononuclear [LM] species, and their behavior was examined by UV−visible and NMR spectroscopy, electrochemistry, and thin layer spectroelectrochemistry in nonaqueous media. The PdCl₂ units in [(PdCl₂)₄LM] are coordinated at the pyridine N atoms of the external dipyridinopyrazine fragments (“py-py” coordination) and are displaced out of the plane of the central pyrazinoporphyrazine macrocycle as verified by ¹H and ¹³C NMR data on [(PdCl₂)₄LZn]. The same arrangement is also strongly suggested by similar NMR data on the Mg^II and Cd^II analogues. The predominant component in the synthesized materials among the four predictable macrocyclic isomers has the four exocyclic N_2(py)PdCl₂ square planar coordination sites on the same side of the central macrocyclic framework (4:0 isomer, C_4v symmetry), and this is accompanied by a minor isomeric component (2:2 cis or trans), in line with previous findings on the pentapalladated species [(PdCl₂)₄LPd]. IR, UV−visible, and NMR spectral data also provide evidence for transmetalation reactions of the type [(PdCl₂)₄LMg(H₂O)] → [(PdCl₂)₄LPd] and [(PdCl₂)₄LCd] → [(PdCl₂)₄LPd], with the amount of [(PdCl₂)₄LPd] formed varying from batch to batch. Dissociation of the four exocyclic PdCl₂ units from [(PdCl₂)₄LM] occurs in pyridine, but the compounds are stable in N,N-dimethylformamide (DMF) or dimethylsulfoxide (DMSO) and can be stepwise reduced via two one-electron reversible or quasi-reversible processes, prior to an irreversible electroreduction of the bound PdCl₂ group at more negative potentials. This metal-centered reduction leads to a [LM]²⁻ product which is then further reduced to [LM]³⁻ and [LM]⁴⁻ at the electrode surface. The first two reductions of the heteropentametallic compounds are easier than those of the monometallic [LM] species but generally more difficult than reduction of the related octacationic [L′M]⁸⁺ derivatives (L′ = the octamethylated free-base dianion) whose redox properties were previously reported. The Cd^II octacation [L′Cd]⁸⁺, isolated as an iodide salt, was also synthesized for the first time in the current study, and its spectroscopic and electrochemical properties are compared to that of the previously examined analogues.