Reactions of complex ligands: Part 91. Application of ring closing metathesis to Fischer-type carbene complexes: synthesis and structure of medium-sized chromium oxacycloalkenylidenes

Six- and seven-membered pentacarbonyl(2-oxacycloalkenylidene) chromium complexes 17 and 6 have been synthesized in moderate to good yields from alkenyloxy(methyl)carbene complex precursors applying an α-alkylation/ruthenium based ring closing metathesis sequence. The ring-closure is hampered for β-alkylated vinylcarbene complexes which may undergo competing intermolecular cross metathesis at the alkenyloxy terminus in low yield.