Efficient Demetalation of Fischer Alkoxy- and Amino-Biscarbene Complexes of Chromium via CO-Promoted Sulfuration and Selenylation

CO-promoted sulfuration with elemental sulfur and selenylation with elemental selenium of Fischer
biscarbene complexes of chromium have been achieved by means of in-situ-generated SCO and SeCO,
efficiently affording thio- and selenocarboxylates. Intramolecular reactivity inversion of the chromium
carbene carbon bonds (CrC) in an alkoxy−alkoxy biscarbene complex was realized by replacement of
the alkoxy group bonded to the more reactive CrC carbon atom with an amino moiety. A strained
cyclobutenyl ring activates the aminocarbene carbon bond, which thus undergoes oxidation, sulfuration,
and selenylation under mild conditions. Demetalation of alkynyl, alkenyl, and alkyl Fischer monocarbene
complexes was also investigated by the same method, from which selenium- or sulfur-insertion complexes
and seleno- and thiocarboxylates were obtained.