The reaction of Fe(CO) 2 (η 2 -CS 2 ){P(OPh) 3 } 2 1 with two equivalents of PBu 3 in a minimum volume of a polar solvent such as acetonitrile or dimethylsulfoxide afforded the thiocarbonyl derivative Fe(CO) 2 (CS){P(OPh) 3 } 2 2 in ca. 80% yield whereas reaction in solvents such as dichloromethane or benzene afforded the substitution products Fe(CO) 2 (η 2 -CS 2 ){P(OPh) 3 }(PBu 3 ) and Fe(CO) 2 (η 2 -CS 2 )(PBu 3 ) 2 . Although desulphurization of Fe(CO) 2 (η 2 -CS 2 ){P(OR) 3 } 2 by PBu 3 in polar solvents is not a general route to Fe(CO) 2 (CS){P(OR) 3 } 2 for all R, the new compound Fe(CO) 2 (CS){P(OEt) 3 } 2 has been obtained and characterised spectroscopically. The crystal structures of 2 and Fe(CO) 3 {P(OPh) 3 } 2 were determined and are very similar. Both compounds are trigonal bipyramidal about the Fe atom with trans apical phosphite ligands and a trigonal planar arrangement of CO/CS groups. The CS ligand in 2 was found to be disordered over two sites with occupancies 0.63 and 0.37.