Synthesis, characterization and catalytic activity in the carbonylation of ethene of cis-[Pd(H2O)2(PPh3)2]X2.nH2O (X=p-CH3C6H4SO3, n=2; X=CH3SO3, n=0). X-ray structure of cis-[Pd(H2O)2(PPh3)2](p-CH3C6H4SO3)2.2H2O and of cis-[Pd(H2O)2(PPh3)2](CH3SO3)2.2CH2Cl2

The complexes cis-[Pd(H2O)2(PPh3)2]X2 · nH2O (Ia: X=p-CH3C6H4SO3, n=2; IIa: X=CH3SO3, n=0) have been synthesized by reacting Pd(OAc)2, PPh3 and HX in acetone in the presence of H2O. They have been characterized by IR, 1H and 31P NMR spectroscopy and TA analysis. By re-crystallization of these complexes, crystals of Ia and IIa · 2CH2Cl2 suitable for the X-ray analysis have been obtained. The solid-state investigation of Ia reveals that the two p-toluenesulfonato units act as counter anions of a dicationic complex, in which the metal atom is surrounded in a square planar environment realized by two water molecules and two PPh3 moieties that are cis to each other. The X-ray investigation of IIa · 2CH2Cl2 shows that also in this case the two PPh3 are cis to each other and that in the acentric triclinic cell there are two independent [Pd(H2O)2(PPh3)2]2+ units, together with two methanesulfonato counter anions and two crystallization molecules of CH2Cl2. The cationic complexes Ia and IIa are easily inter-converted with the neutral species trans-[Pd(p-CH3C6H4SO3)2(PPh3)2] (Ib) and trans-[Pd(CH3SO3)2(PPh3)2] (IIb), respectively, depending on temperature and solvent. In chloroform at r.t., complex Ia catalyzes the carbonylation of ethene to a polyketone; at higher temperature in methanol it catalyzes the hydroesterification of ethene. In both cases catalysis is accompanied by CO2 evolution. These results suggest that catalysis occurs via initial formation of a Pd(II)–H species by interaction of H2O with CO on the metal center though a reaction closely related to that of the water gas-shift.