Synthesis and evaluation of the catalytic properties of homo- and hetero-bimetallic complexes containing bridging diphenylphosphido ligands

Article abstract of DOI:10.1016/0022-328X(92)83047-L

The bimetallic complex <(CO)3Ru(μ-PPh2)2Ru(CO)3> (1) has been prepared in 42percent yield by the reaction of with tetraphenyldiphosphine in refluxing THF.Other new heterobimetallic complexes containing bridging diphenylphosphido ligands, e.g., <(CO)3Ru(μ-PPh2)2Fe(CO)3> (2), <(CO)3Ru(μ-PPh2)2M(CO)4> (4: M = Cr; 5: M = Mo; 6: M = W) and <(PPh3)M'(μ-PPh2)2M(CO)4> (7: M' = Pd, M = Cr; 8: M' = Pd, M = Mo; 10: M' = Pt, M = Mo) have been synthesized by the "bridge-assisted" sunthetic method.The X-ray structure of <(PPh3)Pd(μ-Ph2)2Mo(CO)4> (8) is reported.These complexes, along with <(CO)3Fe(μ-PPh2)2Fe(CO)3>, <(PPh3)Pd(μ-PPh2)2W(CO)4>, and <(PPh3)Pt(μ-PPh2)2W(CO)4> have been screened as catalyst precursors for (i) the hydroformylation of styrene (120 deg C, 20 bar, CO/H2 = 1), and (ii) the hydrogenation of cyclohexanone (140 deg C, 40 bar H2).The most efficient precursor for the first catalytic reaction was found to be the RuFe complex 2: a synergistic effect between iron and ruthenium has been observed, the turn-over frequency (TOF) increasing from 0.4 h^-1 for the RuRu complex 1 and 0.9 h^-1 for the FeFe complex 3, to 4.0 h^-1 for the FeRu compound 2.The three complexes were recovered at the end of the catalytic reaction.In the catalytic hydrogenation of cyclohexanone, the most active was found to be the RuMo complex 5 but it was not recovered at the end of the reaction.