Palladium complexes electron count

The types of compounds formed by gold(I) and gold(III) often differ from those of other metals due to the constraints imposed by coordination number and electron count at the metal. Thus, for example, whereas 7r-bonded cyclopentadienyl complexes of palladium and platinum are numerous (336), and a copper(I) species of this type is known (337), cyclopentadienyl complexes of univalent (94, 96, 97) and trivalent (228) gold have invariably been found to be fluxional behavior, similar to that in dicyclopentadienylmercury, was involved (228). 

The complex [(CgHg)Pd (PPh3) (CgH )]+ has recently been reported. Assuming the existence of four Pd-Pd single bonds, show that for each palladium a 16-electron count is satisfied. 

The useful complex (MeCN)2PdCl2 has palladium in the +2 oxidation state because of its tw chlorine atoms and the number of electrons is 8 for the Pd(II) oxidation state and another two eac from the four ligands making 16 in all. This complex does not fulfil the 18-electron rule and reactive. You would have got the same answer if you had counted ten for the palladium, two each fc the nitriles, and one each for the chlorines, but this is not so realistic. 

You can represent the palladium it-allyl cation complex in two ways. Either you draw a neutral ally) group complexed to Pd+ or you draw an aliyl cation complexed to neutral Pd. Though the counting is different (Pd+ has only 9 electrons the neutral aliyl has 3 but the aliyl cation only 2), both come out as it316-electron species, which isjustasweil as they are different ways of drawing the same thing. 

All characterized Pd(I) compounds have Pd-Pd or Pd-M bonds. Accordingly, the paramagnetic behavior anticipated for a d configuration is not found in these multinuclear diamagnetic complexes as the expected unpaired electron is in fact involved in the formation of a metal-metal bond. There are some palladium clusters in formal oxidation states ranging from 0 to -1-1 (metal-metal bonds do not count in the assignment of oxidation states) that will be considered here. 

Counting electrons in most complexes is simple using the table of ligand characteristics above in conjunction with the table on p. 1070. Take tetrakistriphenylphosphine palladiumfO) each neutral phosphine donates two electrons, making a total of eight, and palladium still has its full complement of 10 valence electrons as it is in the zero oxidation state. Overall, the complex has a total of 18 electrons and is a stable complex— in fact too stable it has to lose a PPh3 Ugand before it can enter into reactions. 

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