“Metalloazine” Complexes of Molybdenum and Zirconium

A series of “metalloazines” of molybdenum and zirconium was prepared. Molybdenum metalloazines are obtained by reaction between diazo compounds and a molybdenum(IV) complex, OMo(DTC)2 (DTC = a dialkyldithiocarbamate), by oxidative addition. These species are electrophilic at the terminal carbon and add nucleophiles, including ylides. Zirconium metalloazines can be prepared by reaction between zirconium(II) phosphine complexes and diazo compounds, but they are better prepared by metathesis between Cp2ZrCl2 and hydrazone derivatives. These species behave as nucleophiles at carbon and condense with aldehydes or ketones to yield olefins. Several mechanistic studies were performed concerning olefination using zirconium metalloazines; these suggest that olefins are formed by a process of antiperiplanar approach of the carbonyl containing substrate to the metalloazine, giving preferentially the Z olefin isomer. (A similar antiperiplanar approach is suggested for reaction between molybdenum metalloazines and ylides, given that Z olefins predominate in this process, too.).