ADDITION AND CYCLOADDITION REACTIONS OF THE CHIRAL AND HIGHLY NUCLEOPHILIC ALKYNYL COMPLEX [(ETA-5-C5H4ME)(CO)(PPH3)MNCCME]-

The anionic alkynyl complex [Cp'(CO)(PPh3)MnC=CCH3]- (3) can be generated in situ by the addition of 2 equiv of n-BuLi to a solution of the carbene complex Cp'(CO)(PPh3)Mn=C(OMe)CH2CH3 (2). Complex 3 adds electrophiles such as H2O, MEI, MeOSO2CF3, [Et3O] [BF4], EtI, Bu(t)I, and RC{O}Cl (R = Me, Ph) to form vinylidene complexes Cp'(CO)(PPh3)Mn=C=CMe(R) (R = H, Me, Et, Bu(t)(5c), C{O}Me (6a), and C{O}Ph). Alkylation of 6a with MeOTf affords the vinyl carbyne complex [Cp'(CO)(PPh3)Mn=CC(Me)=C(OMe)Me]+CF3SO3-. The beta-carbon of the propynyl ligand of 3 also adds to the central carbon atom of the heterocumulenes TolNCO, Ph2CCO, and CO2 to form, after protonation or alkylation, the vinylidene complexes Cp'(CO)(PPh3)Mn=C=CMe(C{O}R) (R = NHTol, CHPh2, OMe), and 3 undergoes conjugate addition with trans-4-phenyl-3-buten-2-one to give, after protonation, the vinylidene complex Cp'(CO)(PPh3)Mn=C=CMe(CH(Ph)CH2C{O}Me), 13. In the presence of BF3.Et2O, complex 3 undergoes [2 + 3] cycloaddition of the C=C bond of the propynyl ligand across the epoxide linkage of isobutylene oxide and cyclohexene oxide to form new cyclic carbene complexes 14 and 17. A similar [2 + 4] cycloaddition occurs with 3,3-dimethyloxetane to give carbene complex 20. These latter reactions are highly stereospecific due to the chiral nature of 3, and they give a single pair of enantiomers of 14 and 20. The mechanisms of these reactions are discussed, and complexes 2, 5c, 13' (the Cp analogue of 13), 14, and 20 have been crystallographically characterized.