Molybdenum and Tungsten Alkylidene and Metallacyclobutane Complexes That Contain a Dianionic Biphenolate Pincer Ligand

Molybdenum imido alkylidene and tungsten
oxo alkylidene complexes
that contain a tridentate “pincer” [ONO]2– ligand have been prepared and treated with ethylene to give unsubstituted
metallacyclobutane complexes that have a 16e count. Both Mo and W
metallacyclobutane complexes exchange C2D4 into
the metallacyclobutane ring at 22 °C at a rate that is first
order in metal and zero order in C2D4. These
metallacycles lose ethylene at least 104–105 times slower than reported 14e unsubstituted Mo and W metallacyclobutane
complexes that have been explored in the literature that have a TBP
geometry with the metallacyclobutane ring bound in the equatorial
positions. Our studies suggest that breaking up the metallacyclobutane
ring in these 16e d0 Mo or W complexes is slow because
a 14e TBP metallacyclobutane complex cannot be accessed readily.