Carbonyl Olefination Using Readily Prepared Tungsten Metallacycles

Treating the bis(imido) W(NAr)2Cl2(DME) with 2 equiv of cyclooctyne in pentane results in precipitation of a yellow complex containing a 6-membered metallacycle, W(C8H12C8H12NAr)(NAr)Cl2 (1). This easily accessible compound was tested for its ability to effect carbonyl olefination/ring-closing metathesis (CO/RCM) with two substrates. One ketone was tested, 1-acetyl-1-(3-butenyl)cyclopentane, which generates 1-methylspiro[4.4]non-1-ene on CO/RCM. An ester, 4-benzoyloxybut-1-ene, was also test with 1 for CO/RCM. The dichloride 1 was found to be inactive; consequently, several derivatives were prepared, fully characterized including X-ray diffraction, and tested: W(C8H12C8H12NAr)(NAr)(OEt)2 (2), W(C8H12C8H12NAr)(NAr)(OC6H4-p-OMe)2 (3), W(C8H12C8H12NAr)(NAr)(OC6F5)2 (4), and W(C8H12C8H12NAr)(NAr)(Cl)(OTf) (5). In addition, synthesis of cationic complexes was attempted using 1 with Na[B(ArF)4] or AlCl3. We were unsuccessful in fully characterizing the cations; however, these cations generated in situ show very high activity for CO/RCM with these substrates.