Aminolysis of the 2H-pyran-2-ylidenetungsten
complex 3 affords amino-1-tungsta-1,3,5-hexatrienes with different structures, depending on the reaction
temperature and the type
of amine involved. Addition of primary amines RNH2
(4a
−
d) (R = allyl,
n-Bu, CH2Ph, i-Pr)
to 3 at −15 °C yields salt-type
(3Z)-6-amino-1-tungsta-1,3,5-hexatrienes
5a
−
d by reversible
ring opening of the pyranylidene ring. Addition of
4a
−
c at 20 °C affords
(3Z)-2-amino-1-tungsta-1,3,5-hexatrienes 6a
−
c by an
irreversible ring opening of the pyranylidene ring.
Secondary amines RR1NH
8a
−
c [RR1N =
Me2N, 2-(hydroxymethyl)pyrrolidine,
pyrrolidine]
undergo an irreversible ring opening to
2-amino-1-tungsta-1,3,5-hexatrienes
9a
−
c. Aminolysis of 3 in the presence of
Me3SiCl/Et3N affords acetimino
pyranylidene complexes 10,
from which (3Z)-2,6-diamino-1-tungsta-1,3,5-hexatrienes
11 are derived upon aminolysis.
Thermolysis of 6a in THF/pyridine affords the
captodative 1-amino-1,3-hexadien-5-one 12.
2H-Pyran-2-ylidene complex 3,
C19H12O7W, was characterized by
X-ray diffraction.