The Reactivity of Phosphagermaallene Mes*P═C═Ge(t-Bu)Tip toward Aldehydes and Ketones: an Experimental and Theoretical Study

Phosphagermaallene Mes*P=C=Ge(t-Bu)Tip 1 (Tip = 2,4,6- triisopropylphenyl, Mes* = 2,4,6-tri-tert-butylphenyl) has been obtained by an improved synthesis in relation to the previously reported preparation starting from t-BuGeCl3. Very short Ge=C (1.761(2) A) and P=C (1.625(2) A) double bond lengths, trigonal planar geometry around the Ge atom, and GeCP bond angle of 166.57° are indicative of an heteroallenic structure for 1. Its reactions with crotonaldehyde and cinnamaldehyde lead to 1-oxa-2-germacyclobutanes by a [2 + 2] cycloaddition between the Ge=C and C=O double bonds; with methyl vinyl ketone, both a [2 + 4] cycloaddition between the Ge=C and the O=C-C=C moieties and an ene-reaction are observed leading to a 1-oxa-2-germacyclohex-5-ene and a germyl(butadienyl)ether, respectively. With acetophenone, an ene-reaction occurs to afford exclusively a germyl(vinyl)ether. DFT calculations have been performed to explain the regiochemistry observed. © 2010 American Chemical Society.