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Issue 31, 2012
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Mononuclear, helical binuclear palladium and lithium complexes bearing a new pyrrole-based NNN-pincer ligand: fluxional property

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Abstract

A new pyrrole based NNN-pincer ligand, 2,5-bis(3,5-dimethylpyrazolylmethyl)pyrrole 2, was readily synthesized in two steps from pyrrole in 56% yield. The lithiation of the pincer ligand 2 using n-BuLi led to isolation of the dimeric lithium complex, [Li{μ-C4H2N-2,5-(CH2Me2pz)2-N,N,N}]24, in 23% crystalline yield. The transmetalation reaction of 4 with [Pd(PhCN)2Cl2] afforded the mononuclear Pd(II) complex, [PdCl{C4H2N-2,5-(CH2Me2pz)2-N,N,N}] 5, containing one chloride ion in 45% yield. Alternatively 5 was obtained in an excellent yield of 87% by the reaction of 2 with [Pd(COD)Cl2] in the presence of triethylamine. On the contrary, a 20-membered macrometalacyclic molecule, [Pd2Cl4{μ-C4H3N-2,5-(CH2Me2pz)2-N,N}2] 6, in which two PdCl2 units are bridged by two molecules of 2 to give a helical structure, was synthesized by the reaction of 2 with [Pd(COD)Cl2] in the absence of base. The acetate analogue of complex 5, [Pd(OAc){C4H2N-2,5-(CH2Me2pz)2-N,N,N}] 3, was obtained by the treatment of 2 with [Pd(OAc)2]. The pyrrole twist angle of 5 is higher than that of 3. Complexes 3 and 5 show an AB pattern for their methylene protons at room temperature in CDCl3 as well as in DMSO-d6. The variable temperature NMR studies showed that the acetate and chloride complexes exhibit slightly different coalescence temperatures, which is a solvent dependent phenomenon, and twist angles.

Graphical abstract: Mononuclear, helical binuclear palladium and lithium complexes bearing a new pyrrole-based NNN-pincer ligand: fluxional property

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Publication details

The article was received on 28 Feb 2012, accepted on 29 May 2012 and first published on 31 May 2012


Article type: Paper
DOI: 10.1039/C2DT30816A
Citation: Dalton Trans., 2012,41, 9503-9512
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    Mononuclear, helical binuclear palladium and lithium complexes bearing a new pyrrole-based NNN-pincer ligand: fluxional property

    D. Ghorai, S. Kumar and G. Mani, Dalton Trans., 2012, 41, 9503
    DOI: 10.1039/C2DT30816A

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