Pyrazole and Pyrazolate as Ligands in the Synthesis and Stabilization of New Palladium(II) and (III) Compounds

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• 作者：Francisco Estevan ; Pipsa Hirva ; Albert Ofori ; Mercedes Sanaú ; Tanja Špec ; MaAngeles Úbeda
• 刊名：Inorganic Chemistry
• 出版年：2016
• 出版时间：March 7, 2016
• 年：2016
• 卷：55
• 期：5
• 页码：2101-2113
• 全文大小：653K
• ISSN：1520-510X

文摘

The versatility of pyrazole/pyrazolate as ligands has allowed the synthesis and the structural characterization of four different types of new orthometalated palladium compounds, for which DFT calculations have been performed in order to investigate their relative stabilities. [Pd₂{μ-(C₆H₄)PPh₂}₂{μ-(R,R′₂pz)}₂] (R = R′ = H, 2a; R = Br, R′ = H, 2b; R = CH₃, R′ = H, 2c; R = H, R′ = CH₃, 2d; R = Br, R′ = CH₃, 2e) compounds with exo-bidentate pyrazolatos are the first paddlewheel dinuclear palladium(II) compounds with pyrazolato bridging ligands described and characterized in the literature. In the process of the synthesis of 2a, a new tetranuclear intermediate compound, [Pd₄{μ-(C₆H₄)PPh₂}₄(μ-pz)₂(μ–OH)₂] (3a), has been isolated and structurally characterized. Compounds of the general formula [Pd₂{μ-(C₆H₄)PPh₂}₂Br₂(R,R′₂pzH)₂] (R = R′ = H, 4a; R = Br; R′ = H, 4b; R = CH₃; R′ = H, 4c; R = H; R′ = CH₃, 4d; R = Br; R′ = CH₃, 4e) with pyrazoles as monodentate ligands have also been obtained, in which, according to the QTAIM analysis, additional Br···HN_pz weak interactions stabilize their structure. The tetranuclear Pd₂Ag₂ compounds, [Pd₂{μ-(C₆H₄)PPh₂}₂{μ-(R,R′₂pz-Ag-R,R′₂pz)}₂] (R = R′ = H, 5a; R = Br; R′ = H, 5b; R = CH₃, R′ = H, 5c), showed a distorted tetrahedron disposition of the metal atoms. The QTAIM analysis revealed an enhanced stability because of additional metal–metal interactions. New palladium(III) compounds, [Pd₂{μ-(C₆H₄)PPh₂}₂{μ-(R,R′₂pz)}₂Cl₂] (R = R′ = H, 6a; R = Br, R′ = H, 6b) were also synthesized by oxidation of compounds 2 with PhICl₂. DFT calculations highlighted their greater stability compared to that of similar compounds with N,N-donor ligands, such as formamidinatos and triazenidos.