Synthesis, Characterization, and Catalytic Activities of Palladium Complexes with Phenylene-Bridged Bis(thione) Ligands

The
neutral phenylene-bridged bis­(thione) compounds, 1,3-bis­(3′-ethylimidazolyl-2′-thione)­benzene
(Betb), 1,3-bis­(3′-butylimidazolyl-2′-thione)­benzene
(Bbtb), and 1,3-bis­(3′-allylimidazolyl-2′-thione)­benzene
(Batb), have been synthesized and characterized. Reactions
of palladium precursor PdCl2(CH3CN)2 with phenylene-bridged bis­(thione) ligands in 1:2 ratio resulted
in the formation of the complexes: PdCl2(L)2 (L = Betb, 3a; L = Bbtb, 3b; L = Batb, 3c, respectively).
In contrast, treatment of the ligands with PdCl2(CH3CN)2 in 1:1 ratio gave cyclometalation palladium
complexes Pd2+Cl­(L–) (L = Betb-H, 4a; L = Bbtb-H, 4b; L
= Batb-H, 4c) through the metal-induced
C–H activation. Complexes 4a–c can also be obtained by the reaction of bis­(thione) ligands and
PdCl2 in 1:1 ratio. The reaction of 3a–c with additional PdCl2(CH3CN)2 also afforded complexes 4a–c. All
ligands and palladium complexes were fully characterized by one-/two-dimensional
NMR spectra, mass spectrometry, and infrared spectrometry. And the
molecular structures of 3a–c, 4a, and 4c have been determined by the single-crystal
X-ray diffraction method. Furthermore, the detailed spectroscopic
properties and catalytic activities of the complexes for the reduction
of nitro compounds were discussed in terms of the modification of
the coordination ligands to the center metal.