Synthesis and reactions of thermally stable platinum(II) carboxylic acids (hydroxycarbonyls) containing bis(tertiary phosphines)

Article abstract of DOI:10.1021/om00120a029

Platinum(II) carboxylic acids (or hydroxycarbonyls) of general formula Pt(CO₂H)(C₆H₉)(P-P) (C₆H₉ = 1-cyclohexenyl; P-P = Ph₂PCH₂CH₂PPh₂ (1), cis-Ph₂PCH=CHPPh₂ (2), Ph₂PCH₂CH₂CH₂PPh₂ (3), and Ph₂PCH₂CH₂CH₂CH₂PPh ₂ (4)) have been prepared by the successive reaction of water and carbon monoxide with the cyclohexyne complexes Pt(C₆H₈)(P-P). Complex 3 readily inserts a second molecule of CO into the platinum(II)-cyclohexenyl bond to give an acylplatinum(II) carboxylic acid, Pt(CO₂H)-(COC₆H₉)(Ph₂PCH ₂CH₂CH₂PPh₂) (5). The complexes, which have been characterized by elemental analysis, IR spectroscopy and ¹H, ¹³C, and ³¹P NMR spectroscopy, are monomeric in dichloromethane but appear to be associated through hydrogen bonds in the solid state. Complexes 1-5 do not decarboxylate in the solid state up to ca. 80°C and do not form carboxylate ions by loss of a proton. These properties probably arise from the presence of nondissociating, strongly electron-donating ligands in the coordination sphere. The platinum(II) carboxylic acids do readily undergo esterification with alcohols, and 3 reacts with dimethylamine or tert-butylamine to give carbamoyl complexes Pt(CONR¹R²)(C₆H₉)(Ph ₂PCH₂CH₂CH₂PPh₂) (R¹ = R² = Me, 6; R¹ = t-Bu, R² = H, 7). These reactions, and the ready exchange of ¹³CO with the Pt-CO₂H group, indicate that the carboxylic acids behave as [Pt(C₆H₉)(CO)(P-P)]OH, although the carbonyl cations could not be detected in solutions of the acids. Treatment of 5 with HBF₄ gives [Pt(COC₆H₉)(CO)-(Ph₂PCH₂CH ₂CH₂PPh₂)]BF₄, as expected, whereas 3 undergoes competitive cleavage of the platinum-(II)-cyclohexenyl bond and consequent β-elimination of CO₂ from the Pt-CO₂H group.