Organic Syntheses via Transition Metal Complexes. 83.1 cis-1-Metalla-1,3,5-hexatrienes (Butadienylcarbene Complexes) of Tungsten via Ring Opening of Pyranylidene Complexes

Aminolysis of the 2 H -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 RNH 2 ( 4a − d ) (R = allyl, n- Bu, CH 2 Ph, i- Pr) to 3 at −15 °C yields salt-type (3 Z )-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 (3 Z )-2-amino-1-tungsta-1,3,5-hexatrienes 6a − c by an irreversible ring opening of the pyranylidene ring. Secondary amines RR 1 NH 8a − c [RR 1 N = Me 2 N, 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 Me 3 SiCl/Et 3 N 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 . 2 H -Pyran-2-ylidene complex 3, C 19 H 12 O 7 W, was characterized by X-ray diffraction.