2.2.2. Nature of the solvent (protic or aprotic)
In protic solvents, K+[HFe(CO)3P]− derivatives are readily protonated to generate
the dihydrides H2Fe(CO)3P which, depending on the reaction temperature, either
(i) evolve by loss of H2 to generate the coordinatively unsaturated ‘‘Fe(CO)3P’’
species which react further with an excess ligand to give the disubstituted
Fe(CO)3P2 derivatives, or (ii) evolve by loss of CO to generate the coordinatively
unsaturated H2Fe(CO)2P which react with an excess ligand to give the corresponding
dihydrides H2Fe(CO)2P2. In most cases the dihydrides H2Fe(CO)2P2 may react
further if an excess of P is present to yield the corresponding trisubstituted
Fe(CO)2P3 derivatives. A generalized reaction pathway has been established
(Scheme 4).
In an aprotic solvent, the K+[HFe(CO)3P]− derivatives can be isolated from
reactions at room temperature when P is a phosphite or a phosphinite. In contrast,
when P is a phosphine, this complex is basic enough to deprotonate [HFe(CO)4]−,
thus generating K2Fe(CO)4 and the dihydride H2Fe(CO)3P which evolves as in a
protic medium (Scheme 5).
Solutions of K+[HFe(CO)4]− in THF exhibit the same interaction
(nCO=1856 cm−1) as noted before for Na+[HFe(CO)4]− whereas solutions in methanol
do not. Thus, it could be expected that CO substitution on K+[HFe(CO)4]−