Multiple Established Forms of Palladium Acetate Binding to the Four N-atom Donor 2,3-Dicyano-5,6-di(2-pyridyl)-pyrazine, [(CN)2dpp]

The reaction of the ligand 2,3-dicyano-5,6-di(2-pyridyl)-1,4-pyrazine, [(CN) 2 dpp], with Pd(OAc) 2 , in CH 3 CN leads to the formation of three novel complexes which were characterized by thermogravimetric analysis, single crystal and powder X-ray measurements, MALDI-TOF mass spectra, IR and UV-visible spectroscopy as well as electrochemistry. As established by crystallographic work, the complex of formula [(CN)2 dppPd(OAc)2 ].H 2 O (molar ratio ligand/Pd(II) 1:1; species 3) shows a single Pd(OAc) 2 unit coordinated to each nitrogen of the two pyridyl (py) groups of [(CN) 2 dpp]. i.e. the “py-py” mode of coordination previously established for the analogs [(CN) 2 dppMCl 2 ] (M = Pd(II) or Pt(II)). The second isolated species was a highly insoluble dinuclear Pd(II) complex of formula [(CN) 2 dpp{Pd(OAc 2}2 ].5H 2 O (molar ratio ligand/Pd(II) 1:2; species 1), where the two Pd(OAc) 2 units were each coordinated to one pyrazine nitrogen and one N atom of the pyridyl group on [(CN) 2 dpp] (“py-pyz” binding). Based on crystallographic work, the third isolated species is assigned the formula [(CN)(CONH)dppPd(OAc)] (molar ratio ligand/Pd(II) 1:1; species 2), which was formed by hydrolysis of a CN substituent on [(CN) 2 dpp] giving a - CONH - group and a product with an unprecedented “py-pyz” type of coordination. Electrochemical and spectroelectrochemical data of complexes 1, 2, and 3 in DMF and DMSO were used to assign the sites of electron transfer.