REACTION OF SODIUM AMALGAM WITH (MU-ENYNE)BIS(DICARBONYL-ETA-5-CYCLOPENTADIENYLMOLYBDENUM(I)) AND (MU-ETA-2,ETA-3-ALLENYL)BIS(DICARBONYL-ETA-5-CYCLOPENTADIENYLMOLYBDENUM) TETRAFLUOROBORATE COMPLEXES - CRYSTAL-STRUCTURE OF [[(MO(ETA-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(mu-eta2,eta3-HC=CR')[BF4] [R' = C(CH3)2 (4); R'= CHCH2CH3 (5); R'= C6H10 (6)] towards Na/Hg has been studied and compared with that of the vinylacetylene and protonated Vinylacetylene species [Cp2Mo2(CO)4(mu=HC=CCH2)] (11) and [Cp2Mo2(CO)4(mu-eta2,eta3-HC=CCHCH3)]-[BF4] (14), respectively. It appears that when the C(gamma) carbon atom of the mu-enyne bears a hydrogen atom (complexes 2 and 11), dimerization occurs leading to tetrametallic species [[{Cp2Mo2(CO)4}(mu-HC=CH2CHCH3)]2] (8) and [[{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, allenyl complexes regenerates the parent mu-enyne compounds. When the ''C+'' carbon atom bears a hydrogen atom, carbon-carbon coupling leading to a dimerization is favoured. The crystal structure of tetrametallic [[{Cp2Mo2(CO)4}{mu-HC=CCH(CH2CH3))]2] (10) obtained from 5 has been determined.