64625-61-2Relevant academic research and scientific papers
Flexibly bridged binuclear rhodium and iridium complexes of p-xylylenebis(3-(2,4-pentanedione))
Whitmore, Bryan C.,Eisenberg, Richard
, p. 1697 - 1703 (2008/10/08)
Binuclear complexes of Rh and Ir containing a flexibly bridging bis(2,4-pentanedionato)ligand have been synthesized and characterized. The reaction of [M(μ-Cl)(1,5-COD)]2 (M = Rh, Ir) with p-xylylenebis(3-(2,4-pentanedione)), xyl(Hacac)2, and 2 equiv of KOH results in the formation of the binuclear compounds (M(COD))2(xyl(acac)2). The cyclooctadiene ligand in these complexes is readily displaced from the metal centers by either CO or PPh3, leading to the formation of (M(CO)2)2(xyl(acac)2) and (M(PPh3)2)2(xyl(acac)2), respectively. The (M(CO)2)2(xyl(acac)2) complexes react with excess triphenylphosphine, leading to the displacement of one CO from each metal center and the formation of (M(CO)-(PPh3))2(xyl(acac)2). The rhodium complex (Rh(CO)2)2(xyl(acac)2) also reacts with triphenyl phosphite to produce the phosphite derivative, (Rh(P(OPh)3)2)2(xyl(acac)2), which is found to act as a catalyst precursor for propylene hydrogenation. At 24°C and under 320 torr of H2 + C3H6 (2.5:1), propane forms at the rate of 8 mol of product (mol of catalyst)-1 h-1 in the presence of a 7.4 × 10-4 M solution of the phosphite derivative in toluene. The binuclear iridium complex (Ir-(CO)(PPh3))2(xyl(acac)2) undergoes oxidative-addition reactions with allyl bromide or benzyl bromide, producing the iridium(III) species (IrR(CO)(PPh3)Br)2(xyl(acac)2) where R = σ-allyl and benzyl, respectively. The mononuclear iridium complex Ir(PPh3)2(acac) has also been synthesized and characterized. The reaction of this complex with H2 results in the formation of IrH2(PPh3)2(acac), whereas the reaction of Ir(COD)(acac) with H2 in the presence of 2 equiv of PPh3 leads to the formation of mer- and fac-IrH3(PPh3)3 as determined by 1H NMR spectroscopy. The significance of these reactions in terms of the stability of rhodium and iridium acac complexes in catalytic systems is discussed.
