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

A general picture is given of the reactivity of the two Fischer-type alkyl(hydrazino)carbene complexes (CO)5Cr:C(CH3)N(Bn)N(CH3)2 (1) and (CO)4Cr:C(CH3)N(Bn)N(CH3)2 (3). Unlike their org. isolobal hydrazide analogs, they easily yield the corresponding α-anions at -78°, 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 α-position, thus making it possible to introduce a new stereogenic center in the mol.