SYNTHESIS, STRUCTURE, AND REACTIONS OF THE CLUSTERS (ETA-C5H5)2(CHEL)RH3(CO)(CF3C2CF3) - THE 1ST 46-ELECTRON ALKYNE-M3 CLUSTERS WITH A PARALLEL ATTACHMENT OF THE ALKYNE

Treatment of the binuclear complex (eta-C5H5)2Rh2(mu-CO)(mu-eta-2-CF3C2CF3) with chelate complexes of the type (chel)Rh(CO)2 gives the trinuclear clusters (eta-C5H5)2(chel)Rh3(CO)(CF3C2CF3). Clusters have been prepared with chel = acetylacetonato and other substituted beta-diketonates, 8-hydroxyquinolate, N-p-tolylsalicylaldimine, and other Schiff bases. The structure of the complex (eta-C5H5)2(thd)Rh3(CO)(CF3C2CF3), where thd is 2,2,6,6-tetramethyl-3,5-heptanedionate, has been determined by X-ray crystallography. Crystal data: C26H29F6O3Rh3, M(r) 812.2, triclinic, P1BAR, a = 10.905 (2) angstrom, b = 11.170 (2) angstrom, c = 13.3869 (15) angstrom, Z = 2, final R = 0.050 for 6588 ''observed'' reflections. The molecular structure establishes that the hexafluorobut-2-yne adopts a parallel bonding mode rather than the perpendicular attachment normally observed for 46-electron alkyne-M3 clusters. It also reveals a very unsymmetrical attachment of the face-bridging carbonyl. Spectroscopic results show that two isomers coexist in acetone solution, with the major isomer exhibiting fluxional behavior. In chlorinated solvents (CHCl3, CH2Cl2), only one isomer is present. Various addition reactions have been investigated. Cluster fragmentation occurs in the reactions with CO, CN-t-Bu, PhC = CH, and PHPh2. New complexes isolated from these reactions include (eta-C5H5)2Rh2(CN-t-Bu)2(mu-eta-1-CF3C2CF3) and (eta-C5H5)2Rh2(mu-PPh2)[mu-eta-1,eta-2-C(CF3)C(CF3)H]. Cluster retention is observed in the reactions with SO2 and tri-p-tolyphosphine; the cluster derivatives isolated from these additions are (eta-C5H5)2(acac)Rh3(CO)(mu-SO2)(CF3C2CF3) and (eta-C5H5)2(acac)Rh3(mu-CO)[P(p-tolyl)3](CF3C2CF3). There is chelate ligand exchange in the reaction with 1,10-phenanthroline to give the cationic cluster [(eta-C5H5)2(phen)Rh3(CO)(CF3C2CF3)]+. Removal of the acac ligand from (eta-C5H5)2(acac)Rh3(CO)(CF3C2CF3) by treatment with Si(CH3)3Cl in the presence of other ligands has given the cluster products (eta-C5H5)2Rh3(CO)(CF3C2CF3)(dppm-H) and (eta-C5H5)2Rh3(CO)(CF3C2CF3)[P(p-tolyl)3]Cl.