3-Metalla-1,2-dioxolanes and Their Reactivity

The ethene complexes [MI(CH2CH2)]+ (M = Ir, Rh) can be oxygenated by molecular oxygen or air in the solid state, to form isolable unsubstituted 3-metalla-1,2-dioxolanes [MIII(CH2CH2OO-κ2C1,O2)]+. Such selectivity could not be achieved in solution. The stereoselectivity of the oxygenation process is highly dependent on the ligand, the metal and the counterion used. Oxygenation of [(tpa)M(CH2CH2)]PF6 {tpa = tri(2-pyridylmethyl)amine; 4PF6, 7PF6} results in the formation of two isomeric 3-metalladioxolanes, whereas oxygenation of [(tpa)M(CH2CH2)]BPh4 (4BPh4, 7BPh4) only yields one isomer. Furthermore, oxygenation of [(Metpa)Rh(CH2CH2)]PF6 {14PF6, Metpa = [(6-methyl-2-pyridyl)methyl]bis(2-pyridylmethyl)amine} proved to be much slower than that of [(tpa)Rh(CH2CH2)]PF6 (7PF6). The solid propene complex [(tpa)Rh(CH2CHCH3)]BPh4 (23BPh4) loses propene on reaction with molecular oxygen, and selectively forms the peroxo complex [(tpa)Rh(η2-O2)]BPh4 (24BPh4). The obtained 3-metalla-1,2-dioxolanes rearrange, both in the solid state and in solution, to formylmethyl hydroxy complexes on exposure to photons or protons. The isomeric 3-rhoda-1,2-dioxolanes [(tpa)Rh(CH2CH2OO-κ2C1,O2)]+8a+ and 8b+ differ in reactivity. On exposure of a solution of 8aPF6/8bPF6 to glass-filtered daylight, isomer 8b+ rearranges to form the formylmethyl hydroxy complex 9b+. This rearrangement is three times faster than the rearrangement of 8a+ to 9a+. The iridadioxolanes are much more reactive than the corresponding rhodadioxolanes, whereas the iridium formylmethyl hydroxy complexes are less reactive than the corresponding rhodium formylmethyl hydroxy complexes. The tpa formylmethyl hydroxy complexes react reversibly with carbon dioxide to form formylmethyl hydrogen carbonate complexes. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)