AN UNUSUAL DICARBENIUM FULVALENE COMPLEX, [FVMO(2)(CO)4(MU-ETA(3)ETA(3)-CH2C-CCH2)][BF4](2) (FV=FULVALENE), WHICH EXHIBITS REACTIVITY TOWARD WEAK NUCLEOPHILES

The title compound was prepared and characterized by spectroscopic met hods. The complex Mo(2)-(CO)(4)(mu-eta(3):eta(3)-CH2C=CCH2)][BF4](2) ( 3) exhibits reactivity toward weak nucleophiles such as MeOH, H2O, and PhOMe, affording the monocarbenium ions (2)-(Co)(4)(mu-eta(2):eta(3)- MeOCH(2)C=CCH2)][BF4] (4), vMo(2)(CO)(4)-(mu-eta(2):eta(3)-HOCH2C=CCH2 )][BF4] (5), and (4)(mu-eta(2):eta(3)-CH2C=CCH(2)C(6)H(4)OMe)][BF4] (6 a, b; para:ortho 55:45), respectively. When 3 was treated with strong nucleophiles such as pyridine and triphenylphosphine, double nucleophi lic attack occurred, yielding the )(mu-eta(2):eta(3)-C5H5NCH2C=CCH2NC5 H5))]-[BF4](2) (7) and u-eta(2):eta(3)-PPh(3)CH(2)C=CCH2-PPh(3))][BF4] (2) (8), respectively. The reactivity of the fulvalenyl-bridged dimoly bdenum propargyl dication complex 3 is compared to that of the related cyclopentadienyl system and discussed.