A new gold catalyst: Formation of gold(I) carbonyl, [Au(CO)(n)](+) (n=1,2) in sulfuric acid and its application to carbonylation of olefins

A new gold catalyst, [Au(CO)n](+) (n = 1, 2), was synthesized by using a facile method from commercial gold(III) oxide, Au2O3, in concentrated H2SO4, which exhibits high catalytic activity for carbonylation of olefins. The gold monocarbonyl [Au(CO)](+) (1) and dicarbonyl [Au(CO)(2)](+) (2) cations coexist in H2SO4 solution, the former of which is much more stable than the latter. Both of the carbonyls show LR spectra of v(CO) (2194, 2208 cm(-1)) higher than that of free CO (2143 cm(-1)), indicating nonclassical (sigma-only) gold-CO bonding. The gold carbonyl complexes coexisting in the coned H2SO4 solution exhibit a single resonance in the C-13 NMR spectrum at 171 ppm at; ambient temperature and pressure, reflecting rapid CO exchange between 1 (164 ppm) and 2 (175 ppm), The nonclassical gold(I) carbonyl solution worked as an excellent catalyst, with which olefins reacted with CO to give tert-carboxylic acids in good yields at room temperature and atmospheric pressure. The gold(I) dicarbonyl cation 2 was found to function as an active species for the carbonylation. An olefin-gold(I)-carbonyl complex was proposed as a possible intermediate in the metal carbonyl-catalyzed carbonylation in the strongly acidic medium.