Reactions of DI-η 5-cyclopentadienyltricarbonyltriphenylphosphinediiron; an improved synthesis of the cyclopentadienylcarbonyliron tetramer

Abstract

The compound (C 5H 5) 2Fe 2(CO) 3PPh 3, previously obtained by the photolysis of (C 5H 5) 2Fe 2(CO) 4 with PPh 3, may also be obtained by reflluxing these same reactants in benzene. The compound was isolated in pure form by means of low temperature column chromatography. It is unstable in solution in the absence of added PPh 3. Solid samples also are unstable over long periods of time. Decomposition in solution is complete within one hour at 80° yielding a mixture of (C 5H 5) 2Fe 2(CO) 4 and (C 5H 5) 4Fe 4(CO) 4. This reaction is suppressed by excess PPh 3. Heating a mixture of (C 5H 5) 2Fe 2(CO) 3PPh 3 and P(OEt) 3 gives a nearly quantitative yield of (C 5H 5) 2Fe 2(CO) 3P(OEt) 3. Refluxing a xylene solution of (C 5H 5) 2Fe 2(CO) 4 containing a slight molarr excess of PPh 3 for 7 h results in the isolation of (C 5H 5) 4Fe 4(CO) 4 in 56% yield, making this reaction by far the most convenient method for the preparation, in gram quantities, of this transition metal cluster.