Computational Details
All DFT and MP2[8] geometry optimizations and
vibrational calculations were carried out using the Gaussian 09 program
package.[9] As reported
previously,[6c] both complexes 1 and2 were calculated to be the singlet ground state. Therefore,
only singlet state was considered for the complexes involved in this
system. The 6-31G* basis set was used for C, H, N and
S atoms, and Fe atoms were treated by 6-311G* basis
set. Each optimized structure was analyzed by harmonic
vibrational
frequencies obtained at the same level and characterized as a minimum
(Nimag = 0) or a transition state (Nimag= 1). The transition state structures were shown to connect the reactant
and product on either side via intrinsic reaction coordinate (IRC)
following. Some relaxed potential energy scans of 18 functionals were
performed with only the scanned N−N distance from 0.500 Å to 2.500 Å
with stepsize 0.050 Å. The most reliable available levels, the
domain-based local pair natural orbital coupled cluster method with
single and double excitations and
perturbative
triple corrections
(DLPNO-CCSD(T)[10,11]/6-311G*(Fe)/6-31G*(C, H, N,
S) in conjunction with the correlation fitting auxiliary basis set TZV/C
for the single-point energy calculations were performed for the species
at the MP2 optimized geometries in ORCA
Program[12] as the benchmark data. Considered the
calculation of DLPNO-CCSD(T), the model compounds
CpFe(μ -SMe)2(μ -NHNH3)FeCp
(Cp = η 5-C5H5,1m ) and CpFe(μ -SMe)2(μ -NH)FeCp
(2m ) (Figure 1) were adopted in this systems. The ONIOM
calculations[13] were carried out for 1and 2 to validate the rationality of simplified model (in
Supporting Information).