OPTICALLY-ACTIVE PENTANUCLEAR WING-TIP BUTTERFLY HETETOTRIMETALLIC CLUSTERS

The pentanuclear heterotrimetallic clusters of formula Fe3MC(CO)(12)M' L {M = Co, M' = Au, L = PPh3 (XIV); M = Co, M' = Pd, L = eta(3)-C3H5 ( XV); M = Co, M' = Pd, L = eta(3)-beta-pinenyl, C10H15 (I); M = Rh, M' = Au, L = PPh3 (XVI); M = Rh, M' = Pd, L = eta(3)-C3H5 (XVII); M = Rh, M' = Pd, L = eta(3)-C10H15 (II)} have been obtained by the addition o f corresponding M'L fragments to heterometallic butterfly [Fe3MC(CO)(1 2)](-), where M = Co (XI) or Rh (X); the butterfly XI has been isolate d in reductive degradation of Go-containing clusters [Fe3Co3C(CO)(15)] (-) or [Fe4CoC(CO)(14)](-). The X-ray crystal structures of XIV and XV have been determined. Both structures have approximately the same pen tanuclear heterotrimetallic cluster cores with M'L groups in bridging position linking wing tips. According to the refinement data, the Co a toms in XIV and XV are placed in the basal position of the butterfly. EXAFS data for XV suggest a structural flexibility of the metal core i n solution. Absorption (AB) and circular dichroism (CD) spectra of two optically active clusters I and II with the same 'wing-tip' butterfly structure were investigated and compared with those for the starting [Pd(eta(3)-beta-C10H15)Cl](2) chiral complex. The noticeable Cotton ef fects (CE) in the CD spectra induced in electron transitions of cluste r metallochromophores demonstrate a strong manifestation of the vicina l optical activity. (C) 1997 Elsevier Science S.A.