Synthesis of Phosphine Trans-Substituted Derivatives of Iron Pentacarbonyl

The synthesis of trans-Fe (CO)3(PR3)2 (PR3 = PPh3, PPh2Me, PPh2CHCH2, P(c-C6H11)3, P(n-C4H9)3, PPh2H) can be achieved by refluxing iron pentacarbonyl under reducing conditions in the presence of ligand in 1-butanol. Addition of iron pentacarbonyl to a 1-butanol solution of sodium borohydride at room temperature results in a quantitative conversion of the iron carbonyl complex to the corresponding mononuclear formyl complex. Upon heating the initially formed formyl species decomposes to form the tetracarbonylhydridoferrate(0) anion . This hydride is believed to undergo reaction with the phosphine ligand to yield the isolated trans-substituted iron complex. Even though traces of monosubstituted product were detected in the crude reaction mixture by infrared spectroscopy, uncontaminated trans-substituted complexes were isolated after crystallization from dichloromethane/methanol. All complexes have been found to be sensitive to oxygen if in solution, with the rate of decomposition depending on the kind of ligand. However, if they are dry and under vacuum no apparent decomposition takes place. All synthesized complexes have been characterized by IR spectroscopy, 31P NMR, and by their melting points. The value of the presented synthesis is based on its high selectivity, extremely short reaction time, good to very good yields, and its simplicity