Cyclobutenes metalla

Cycloaddition of the carbene chromium complexes 97 with CO incorporation provides a versatile method for naphthol synthesis, in which the metallacy-clic intermediates 99 are involved [47]. An alternative entry to 101 is achieved by metal carbonyl-catalyzed rearrangement of the cyclopropenes 98 via the same metalla-cyclobutenes 99 and vinylketene complexes 100 [52], Mo(CO)6 shows a higher activity than Cr(CO)6 and W(CO)6. The vinylketene complex 103 is formed by the regioselective ring cleavage of 1,3,3-trimethylcyelopropene 102 with an excess of Fe2(CO)9 [53]. (Scheme 35 and 36)... 

Some of the bicyclo[3.1.0]hexene zirconocene derivatives, especially those containing a phenyl group, rearrange quantitatively to the corresponding 4-vinyl-l-metalla-2-cyclobutene derivatives when heated in toluene to 60-80 °C for several hours (equation 131). The 6,6-dimethyl-2,3-diphenyl-2-zirconabicyclo[3.1.0]hex-3-ene derivative prefers ring-opening to the isomeric j/. -allylic complex upon thermolysis. 

Scheme 1 gives a postulated reaction pathway for all these metathesis like reactions. The heteroallenes or the heteroalkenes are supposed to react in a 2 + 2 cycloaddition reaction with Cl3(dme)WCtBu to form metalla cyclobutene derivatives. Electrocyclic ringopening reactions of these (not isolated) metallacycles yield tungsten imido or 0X0 complexes with sigma bonded vinyl, iminyl, ketenyl or keteniminyl ligands. 

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