When this was first proposed (and to this day), it was not
clear how reagents such as WCl6 andAlEt2Cl or Mo(CO)6 on
alumina might lead to a metal–carbene complex. Typical Fischer
carbene complexes, such as (CO)5WC(OMe)Ph, involved
low valent metals and had electron donor groups on the carbene
carbon. In addition, the basic reaction of a metal–carbene complex
with an alkene had not yet been observed. Nevertheless,
this mechanistic suggestion appeared very attractive (it has
the look of something so simple that it is probably right) and
energized organometallic chemists to test its implications and
to devise ways to make new types of metal–carbene complexes
as potential catalysts.