SYNTHESIS AND STRUCTURE OF BINUCLEAR CYCL OPENTADIENYLTRICARBONYLMANGANESE COMPLEXES OF THE TYPE (CO) 3MN[(ETA-5-C5H4)-X-(ETA-5-C5H4)]MN(CO)3

The synthesis of various members of the family of title compounds (CO) 3Mn[(eta5-C5H4)-X-(eta5-C5H4)]Mn(CO)3 has been achieved by a variety o f methods: the mononuclear bridging groups X = S (1a) and X = Si(C6H5) 2 (1b) have been introduced by standard methods via (eta5-C5H4Li)Mn(CO )3. The dicarbon bridging entities -MeC=CMe- and -MeC(OH)-(OH)CMe- hav e been formed by reductive coupling of the corresponding ring acetylat ed complexes. Reductive coupling of [eta5-alpha-C5H3CH3(COCH3)]Mn(CO)3 (2a) under mild conditions with TiCl3/LiAlH4 leads to the correspondi ng vicinal diol C(OH)(CH3)-C(OH)(CH3)[eta5-C5H3(alpha-CH3)]Mn(CO)3 (3) . Under less mild conditions the McMurry type reduction leads to the c orresponding olefin ha-CH3)]C(CH3)=C(CH3)[eta5-C5H3(alpha-CH3)]Mn(CO)3 (4a). The olefin is obtained as a mixture of Z/E- and R/S-isomers; th e corresponding four diastereomeric forms of 4a are separable by capil lar gas chromatography. Using the same approach the beta-isomer [eta5- beta-C5H3CH3(COCH3)]Mn(CO)3 (2b) yields a mixture of the four isomers of eta-CH3)]C(CH3)=C(CH3)[eta5-C5H3(beta-CH3)]Mn(CO)3 (4b). In an anal ogous way (eta5-C5H4-COCH3)Mn(CO)3 (5) is coupled to give the Z- (6a) and E-isomers (6b) of (CO)3Mn[eta5-C5H4]C(CH3)=C(CH3)[eta5-C5H4]Mn(CO) 3. The isomers are easily separated by column chromatography. As a bin uclear species closely related to the title compounds, eta5-C5H3CH3[be ta-COCH2(eta6-C6H5)Cr(CO)3]}Mn(CO)3 (8) is obtained by Cr(CO)3-complex ation of {eta5-C5H3CH3[beta-COCH2(C6H5)]}Mn(CO)3 (7). All the compound s have been characterised by the usual spectroscopic and analytical te chniques. In addition the compounds 1a, 1b, 2a, the meso-form of 3, 3a , 6a, 6b and 8 have been characterised by X-ray analyses.