Polymer [Pd(CH2SO2C6H4Me)2]n, a precursor to remarkably stable Pd organometallics

Abstract

A polymer [Pd(CH₂SO₂C₆H₄Me)₂]_n is obtained by thermolysis of cis-[Pd(CH₂SO₂C₆H₄Me)₂(NCMe)₂] to release the MeCN ligands. The corresponding coordination sites are then occupied by weak Pd–O bonds, easier to break than the previous Pd–N bonds. This allows us to produce from the polymer cis complexes containing ligands weaker than NCMe, such as acetone or water. The complexes cis-[Pd(CH₂SO₂C₆H₄Me)₂{OC(CD₃)₂}₂], cis-[Pd(CH₂SO₂C₆H₄Me)₂(OH₂)₂], and cis-[Pd(CH₂SO₂C₆H₄Me)₂(OH₂){OC(CD₃)₂}], and cyclic dimers [Pd(CH₂SO₂C₆H₄Me)₂(OH₂)]₂ with bridging methylsulphone groups are formed. The Pd : PPh₃ : OH₂ 1 : 1 : 1 reaction of the polymer produces cis-[Pd(CH₂SO₂C₆H₄Me)₂(OH₂)(PPh₃)], which isomerizes to trans-[Pd(CH₂SO₂C₆H₄Me)₂(OH₂)(PPh₃)], with water O-coordinated to Pd and making hydrogen bonds to the two SO₂ groups as seen in its X-ray structure. A similar role is played by RNH₂ groups in the structures of trans-[Pd(CH₂SO₂C₆H₄Me)₂(NH₃)(PPh₃)] and the dimer μ-(N₂H₄)(trans-[Pd(CH₂SO₂C₆H₄Me)₂(PPh₃)])₂. In addition to these interesting intramolecular hydrogen bonding properties provided by the SO₂ groups, the structural and ¹H NMR data available suggest that the CH₂SO₂C₆H₄Me group is an interesting kind of strong alkyl σ donor, with high trans influence, and forms very stable Pd complexes extraordinarily resistant to reductive elimination and to hydrolysis by water at room temperature.