The substitution reaction of (CNC)Fe(-)2N(2) with CO
The substitution mechanism of two N-2 ligands in (CNC)Fe(-)2N(2) replaced by CO was studied theoretically at the B3LYP/LACVP* level. Both S(N)1 and S(N)2 mechanisms were considered. The calculated results for the gas phase suggested that: 1) in S(N)1 mechanism, N-2 elimination, which involves S-0-T-1 PESs crossing, is the rate control step for both substitution stages. The barrier heights are 9.7 kcal mol(-1) and 13.05 kcal mol(-1), respectively. 2) In S(N)2 mechanism, the calculated barrier heights on LS PES are respectively 13.7 and 19.83 kcal mol(-1) for the two substitution steps, but S-0-T-1 PESs crossing lowers the two barriers to 10.7 and 15.7 kcal mol(-1), respectively. 3) Inclusion of solvation effect of THF by PCM model, the relative energies of all the key species (including minima, transition states and S-0-T-1 crossing points) do not have great difference from their gas phase relative energies. Considering that for each substitution step, S(N)1 barrier heights is slightly smaller than S(N)2 barrier, S(N)1 mechanism seems to be slightly preferable to S(N)2 mechanism.
co n-2 ligands s(n)2 mechanism s-0-t-1 pess crossing barrier heights (cnc) fe-2n(2)