to determine the influence of the nature of the phosphane on the first ligand
substitution step. It is possible, however, to compare the results of reactions conducted
near room temperature, that is the formation of the early detectable products.
In THF, the reaction of K+[HFe(CO)4]− with phosphanes allows the isolation
of the monosubstituted hydridocarbonylferrate [HFe(CO)3P]− in four cases
(Table 2). As may be seen, the Tolman cone angle of the phosphane is an important
parameter, as evidenced by the difference in reactivity between PPh3 and P(OMe)3,
which have similar pKa values [57]. However, the basicity of the phosphane also
plays an important role since P(OPh)3 (pKa=−1.20) and PPh2OMe (pKa=2.69)
react much more rapidly than P(n-Bu)3 and even PMe2Ph which exhibit cone angles
in the same range, but much higher pKa values (Table 2).