Labile carbonyl groups

The discovery that additions of catalytic amounts of CoCl2, activated carbon, or metals on metal oxide or carbon supports are extremely effective in labilizing carbonyl groups in Fe(CO)5 is thus particularly noteworthy. Stepwise substitution products Fe(CO)5 x(CNR)x (x = 1-5) have been obtained in high yield with short reaction times using these catalysts (see Table III) (759). 

The labile carbonyl groups in iron pentacarbonyl can be replaced by chloride to give a different metal carbonyl. These reactions are characterized by low yield, which can be improved using high pressure. 

Unlike ethynylation, in which acetylene adds across a carbonyl group and the triple bond is retained, in vinylation a labile hydrogen compound adds to acetylene, forming a double bond. 

Kuhn and Low149 (see also, Ref. 150) were the first to recognize that glycosidic linkages that are) to a carbonyl group are alkali-labile, and are... 

Ketones react with hydroperoxides with formation a series of labile peroxides. This addition is performed reversibily across the carbonyl group of the ketone with the formation of a new peroxide. 

Another probable reaction of homolytic decomposition of ester hydroperoxide is the intramolecular interaction of the hydroperoxide group with the carbonyl group of ester with the formation of labile hydroxyperoxide succeeded the splitting of the weak O—O bond (see decomposition of hydroperoxides in oxidized ketones in Chapter 8). 

The crystal structures of both (PPN)[M(CO)6] derivatives have been determined.717 The coordination polyhedron is octahedral (Nb—C 2.098(5) A CNbC 89.2(2)°). The PPN moiety is constrained to be centrosymmetric, and thus linear. These compounds correspond to the lowest oxidation state of niobium and tantalum for which structural data are available. A single v(CO) is found in the IR (1854 and 1852 cm-1 for Nb and Ta respectively). Comparable spectra are observed for Na[M(CO)6] in pyridine, but in solvents of lower dielectric constants such as tetrahydrofuran, additional bands attributed to distortion of the anion by the countercation are observed. [Nb(CO)6] appears to be the most labile carbonyl of the group VA analogs. 

The synthesis of chromones by the Kostanecki-Robinson method frequently yields a 3-acetylchromone. This acetyl group forms a 1,3-diketone with the pyran carbonyl group and is therefore labile in an alkaline medium. Treatment with aqueous carbonate or other base removes such groups but has no effect on other acyl substituents, for example the 6-acetyl of 3,6-diacetyl-2-methylnaphtho[l,2- ]pyran-4-one (516). 

---