Vinylcyclopropan‐Komplexe und Vinylcyclopropane aus Carben‐Komplexen und 1,3‐Dienen

Vinylcyclopropane Complexes and Vinylcyclopropanes from Benzylidene Complexes and 1,3‐Dienes Benzylidenepentacarbonyl complexes (CO) 5 M[C(C 6 H 4 R‐ p )H] ( 1 ) [M – W:RH ( a ), OMe ( b ); MCr: R – H ( c ), OMe ( d )], react with cyclopentadiene by stereospecific transfer of the benzylidene ligand to one CC bond of the diene and coordination of the resulting endo ;‐6‐arylbicyclo[3.1.0]hex‐2‐ene ( 4 ) to the metal. The [CO] 5 M fragment occupies the exo ‐position. Addition of bromide liberates 4 from the metal. The reaction of 1a with 1,3‐cyclohexadiene gives the corresponding ( endo ;‐7‐phenylbicyclo[4.1.0]hept‐2‐ene)tungsten complex ( 6 ) and, after addition of Br − , the free bicyclic compound. The sequential reaction of 1a with 1,2,3,4,5‐pentamethylcyclopentadiene and Br − affords the endo ;‐6‐phenyl‐ exo ;‐4‐methyl isomer of pentamethylphenylbicyclo[3.1.0]hex‐2‐ene 9 with more than 85% stereoselectivity. The benzylidene transfer from 1a to cis ‐and trans ‐pentadiene, isoprene, and 2‐chloro‐1,3‐butadiene proceeds regiospecifically to the more electron‐rich CC bond to give ( E )‐ and (Z)‐phenylvinylcyclopropanes. The E/Z ratio ranges from 0.52 to 2.2. The structures of the complexes 3d and 6 were established by X‐ray analyses.