Fischer-type alkyl(hydrazino)carbene complexes: new synthetic potential in comparision with aminocarbene complexes.

A general picture is given of the reactivity of the two Fischer-type alkyl(hydrazino)carbene complexes (CO)5CrC(CH3)- N(Bn)N(CH3)2 (1) and (CO)4CrC(CH3)N(Bn)N ¸¹¹¹¹¹¹¹¹¹º (CH3)2 (3). Unlike their organic isolobal hydrazide analogues, they easily yield the corresponding a-anions at 78°C, which react with various electrophiles. Furthermore, the tetracarbonyl chelate 3 (easily generated from 1) has greater synthetic potential than aminocarbenes: for example, it can be alkylated stepwise twice in the a-position, thus making it possible to introduce a new stereogenic centre in the molecule.