REACTION OF SODIUM AMALGAM WITH IS(DICARBONYL-ETA-5-CYCLOPENTADIENYLMOLYBDENUM(I)) AND L)BIS(DICARBONYL-ETA-5-CYCLOPENTADIENYLMOLYBDENUM) TETRAFLUOROBORATE COMPLEXES - CRYSTAL-STRUCTURE OF 5-C5H5)(CO)2)2(MU-HC-EQUIVALENT-TO-CCH(CH2CH3))]2]

The behaviour of mu-enyne complexes [Cp2Mo2(CO)4(mu-HC=CR)][Cp2Mo2(CO) 4 = [Mo(eta5-C5H5)(CO)2]2; R = C(CH3)=CH2 (1); R = CH=CHCH 3 (2); R = C6H9 (3)] and of the corresponding mu-eta2,eta3-allenyl [Cp2Mo2(CO)4(m u-eta2,eta3-HC=CR')[BF4] [R' = C(CH3)2 (4); R'= CHCH2CH3 (5); R'= C6H1 0 (6)] towards Na/Hg has been studied and compared with that of the vi nylacetylene and protonated Vinylacetylene species [Cp2Mo2(CO)4(mu=HC= CCH2)] (11) and [Cp2Mo2(CO)4(mu-eta2,eta3-HC=CCHCH3)]-[BF4] (14), resp ectively. It appears that when the C(gamma) carbon atom of the mu-enyn e bears a hydrogen atom (complexes 2 and 11), dimerization occurs lead ing to tetrametallic species [[{Cp2Mo2(CO)4}(mu-HC=CH2CHCH3)]2] (8) an d [[{Cp2Mo2(CO)4}(mu-HC=CCH2CH2)]2] (12). In the other cases, mu-sigma ,eta3 allylic species such as [Cp2Mo2(CO)4{mu-sigma,eta3-HC-CH-C(CH3)2 )] (7) are formed. Reaction of Na/Hg with most of the mu-eta2, eta3, a llenyl complexes regenerates the parent mu-enyne compounds. When the ' 'C+'' carbon atom bears a hydrogen atom, carbon-carbon coupling leadin g to a dimerization is favoured. The crystal structure of tetrametalli c [[{Cp2Mo2(CO)4}{mu-HC=CCH(CH2CH3))]2] (10) obtained from 5 has been determined.