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

Abstract

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The versatility of pyrazole/pyrazolate as ligands has allowed the synthesis and the structural characterization of four diferent types of new orthometalated palladium compounds, for hich DFT calculations have een 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 ith exo-bidentate pyrazolatos are the first paddlewheel dinuclear palladium(II) compound ith pyrazolato ridging 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 een 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) ith pyrazoles as monodentate ligands have also een obtained, in hich, according to the QTAIM analysis, additional Br•••HNpz 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 ecause 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) ere also synthesized y oxidation of compounds 2 with PhICl2. DFT calculations highlighted their greater stability compared to that of similar compounds ith N,N-donor ligands, such as formamidinatos and triazenidos