Trans-Difluoro Complexes of Palladium(II)

Complexes trans-[(Py)(2)Pd(Ph)(F)] (1; Py = pyridine) and trans-[(t-BuPy)(2)Pd(Ph)(F)] (2; t-BuPy = 4-tert-butylpyridine) have been prepared from the corresponding iodides and AgF. Thermal decomposition of 1 and 2 in anhydrous benzene at 80 degrees C did not result in C-F bond formation, but Pd black and Ph(2) were produced instead, along with novel difluorides trans-[(Py)(2)Pd(F)(2)] (3) and trans-[(t-BuPy)(2)Pd(F)(2)] (4). Both 3 and 4, the first trans-difluoro d(8) square complexes, were independently synthesized from the corresponding diiodides and AgF and fully characterized. Contrary to filled/filled d(pi)-p(pi) repulsion considerations, the Pd-F bond distances in 3 and 4 are unprecedentedly short, being only 1.947(4)-1.958(4) A and shorter than those in 1 and 2 by 0.12-0.13 A. The mechanism of formation of 3 and 4 and bonding in these complexes are discussed.