CONVERSION OF METALLACYCLIC ZIRCONOXYCARBENE COMPLEXES YIELDING CONVENTIONAL FISCHER-TYPE CARBENE COMPLEXES OR METAL-FREE ORGANIC-PRODUCTS

Reaction of (butadiene)zirconocene with hexacarbonyltungsten yields the metallacyclic (ττ-allyl)-zirconoxycarbene complex Cp2ZrOC[=W(CO)5]C4H6 (2). Subsequent coupling with pinacolone gives the nine-membered metallacycle irarcs-Cp2ZrOC[=W(CO)5]CH2CH=CHCH2CMe(CMe3)0 (3). Both compounds 2 and 3 show a very low Fischer carbene complex reactivity. Hydrolytic removal of the zirconocene moiety transforms the rather unreactive zirconoxycarbene complexes into conventional heteroatom-stabilized transition-metal carbene complexes. Thus, treatment of 3 with water in tetrahydrofuran generates a hydroxycarbene tungsten complex in situ, which is efficiently trapped by added excess diazomethane to yield the enol ether H2C=C(OCH3)CH2CH=CHCH2CMe(CMe3)OH as the major reaction product. Similarly, controlled hydrolysis of 3 in the presence of pyridine N-oxide gives HOOCCH2CH= CHCH2CMe(CMe3)OH. The reaction of 3 with tetra-n-butylammonium fluoride trihydrate in tetrahydrofuran cleaves the metallacycle to give a zirconium-free acylmetallate anion (Bu4N+ counterion) which is readily O-alkylated by using Meerwein's reagent to produce H5C2OC[=W(CO)5]CH2CH= CHCH2CMe(CMe3)OH (11, ca. 70% overall yield). Similarly, the zirconoxycarbene complex 2 yields H6C2OC[=W(CO)5]CH2CH=CHCH3 upon treatment with Bu4NF(H20)3 followed by alkylation with (H5C2)3OBF4-. © 1990, American Chemical Society. All rights reserved.