Molybdenum and tungsten oxo 2-adamantylidene
(Adene) complexes
that contain two nonafluoro-tert-butoxide (ORF9) ligands have been prepared through addition of 2-methylene-
or 2-ethylideneadamantane to neophylidene or neopentylidene complexes.
The isolated oxo complexes include W(O)(Adene)(ORF9)2(PPh2Me) (1
W
), W(O)(Adene)(ORF9)2 (2
W
), W(O)(Adene)(2,5-dimethylpyrrolide)2 (3
W
), W(O)(Adene)(2,5-dimethylpyrrolide)(2,6-dimesitylphenoxide)
(4
W
), Mo(O)(Adene)(ORF9)2(PPhMe2) (1
Mo
), and Mo(O)(Adene)(ORF9)2 (2
Mo
). Compound 2
W
is a dimer that contains unsymmetrically bridging oxo ligands;
it dissociates readily and reversibly into monomers, especially in
the presence of a donor such as THF. In contrast, 2
Mo
is a monomer. Both 2
W
and 2
Mo
are remarkably
stable thermally. The pale-blue complexes Mo(Adene)(ORF9)2Cl2 (5
Mo
) and W(Adene)(ORF9)2Cl2 (5
W
) are formed upon addition of PCl5 to 2
Mo
and 2
W
, respectively. The oxo complexes are reactive
olefin metathesis initiators, while 5
Mo
and 5
W
are relatively poor initiators. We ascribe the thermal stability of 2
Mo
and 2
W
to resistance of the 2-adamantylidene ligands to couple bimolecularly,
to the absence of an α-hydrogen in the alkylidene, or both.