REACTIONS OF (CO)5WCHC6H5 WITH ALKENES

Addition of CF3CO2H to a CH2CI2 solution of N(CH2CH3)4+(CO)5WCH(OCH3)C6H5- (5) at -78 °C produces a red solution of (CO)5WCHC6H5 (4), which was characterized by low-temperature 1H NMR and by reaction with P(n-Bu3) to give (CO)5WCH[P(n-Bu)3]C5H5 (6). Thermal decomposition of 4 at -56 °C occurs with a half-life of 24 min. The reaction of 4 with alkenes occurs rapidly at -78 °C to give phenylcyclopropanes; no metathesis-like products were observed. The relative reactivity of alkenes toward 4 was in the order CH2=C(CH3)2 > CH2=CHCH3 ≫> CH2=C2, indicating that the reaction involved electrophilic attack of the carbene complex on the alkene. The stereochemistry of cyclopropane formation could not be explained in terms of formation of the most stable intermediate metallacyclobutane. The stereochemistry of cyclopropane formation is explained in terms of transition state 25 which involved formation of a bond from the carbene carbon atom of 4 to the less substituted end of an alkene and interaction of the positively polarized, more substituted end of the alkene with the ipso carbon atom of the phenyl group of 4. © 1979, American Chemical Society. All rights reserved.