Aldehydes condense on the germaniumphosphorus bond of diethyl(triethylgermyl)phosphine with opening of the CO double bond and formation of phosphorus alkoxygermanes of the structure GeOCHP. The insertion derivatives of chloral and bromal are unstable and decompose via a β-elimination process. The addition of dialkylketones is far more difficult and only the ketones with a little hindered carbonyl group, such as cyclopentanone, or those activated by electron-attracting groups, such as hexafluoro-, hexachloroacetone, 1,1,3,3-tetrafluoro-1,3-dichloro- or 1,3,3-trifluoro-1,1,3-trichloropropanone lead to insertion derivatives which are not very stable [with the exception of (CF 3) 2CO], which have been characterized by their transposition, decomposition, oxidation or hydrolysis products. α-Ethylenic aldehydes and ketones such as crotonaldehyde, cinnamaldehyde and 2-cyclopentene- 1 -one give 1,4-dipolar additions on their conjugated system, with formation of phosphorus enoxygermanes; hydrolysis of these derivatives leads to γ-phosphorus aldehydes or ketones. An addition mechanism involving an ionic cleavage of the germaniumphosphorus bond is considered. Ketenes insert in the germaniumphosphorus bond through an exclusive opening of the carbonyl group. Hydrolysis of the phosphorus enoxygermanes which are thus formed leads to “α-phosphoryl-ketones” which are also isolated by the action of germylphosphines on acid anhydrides.