Organische Synthesen mit Übergangsmetall‐Komplexen, 57. 4,5‐Homotropilidene durch intramolekulare Cyclopropanierung von (Cycloheptatrienylmethyl)carbenchrom‐ oder ‐wolfram‐Komplexen

Organic Syntheses via Transition Metal Complexes, 57 [1] . — 4,5‐Homotropilidenes by Intramolecular Cyclopropanation of (Cycloheptatrienylmethyl)carbenechromium or ‐tungsten Complexes (Cycloheptatrienylmethyl)carbene complexes L n M=C(OEt)‐CH 2 C 7 H 7 [ 3 : L n M=Cr(CO) 5 ( a ), W(CO) 5 ( b )] are obtained in yields of 80% by the reaction of the corresponding methylcarbene complexes L n M=C(OEt)CH 3 1 with tropylium tetrafluoroborate ( 2 ) in THF/Et 3 N. Alkylation of 3 with 2 gives [bis(cycloheptatrienyl)methyl]carbene complexes L n M=C(OEt)CH(C 7 H 7 ) 2 [ 4 : L n M=Cr(CO) 5 ( a ), W(CO) 5 ( b )]. Thermolysis of 3 leads to the formation of an equilibrium mixture of the 4,5‐homotropilidenes 5 and 6 . According to NMR measurements and AM1 calculations the formation of 6 is strongly favored. An equilibrium between 4,5‐homotropilidene complexes is significantly different from that of the metal‐free ligands. By the reaction of 5/6 with bis(ethylene)rhodium 1,3‐pentanedionate ( 8 ) the complexes 9 and 10 of both 4,5‐homotropilidenes 5 and 6 are obtained in a 1:3 ratio. The (1,5‐diene)rhodium(I) complexes 9 and 10 are nonfluxional and configurationally moderately stable at 20°C. The reaction of 5/6 with Fe 2 (CO) 9 gives the π‐allyl,σ complexes 11 and 12 in a 10:3 ratio, both of which may be derived from the minor 4,5‐homotropilidene isomer 5 . In 11 a vinylcyclopropane unit of 5 serves as a four‐electron donor for a Fe(CO) 3 group. In 12 the 4,5‐homotropilidene unit is coordinated as a six‐electron donor to a Fe 2 (CO) 6 unit.