ORGANIC SYNTHESES VIA TRANSITION-METAL COMPLEXES .83. CIS-1-METALLA-1,3,5-HEXATRIENES (BUTADIENYLCARBENE COMPLEXES) OF TUNGSTEN VIA RING-OPENING OF PYRANYLIDENE COMPLEXES

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 prim ary amines RNH(2) (4a-d)(R = allyl, n-Bu, CH(2)Ph, i-Pr) to 3 at -15 d egrees C yields salt-type (3Z)-6-amino-1-tungsta-1,2,5-hexatrienes 5a- d by reversible ring opening of the pyranylidene ring. Addition of 4a- c at 20 degrees C affords (3Z)-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, py rrolidine] 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. Th ermolysis of 6a in THF/pyridine affords the captodative 1-amino-1,3-he xadien-5-one 12. 2H-Pyran-2-ylidene complex 3, C19H12O7W, was characte rized by X-ray diffraction.