A systematic first-principles study is performed to investigate the
20-electron transition metal complexes
(CH)TM(EE)
(TM = Cr, Mo, W; EE = CO,
N, BF). The bond dissociation energy (De) based on
(CH)TM(EE)
→
(CH)TM(EE)
+ EE indicates much lower
thermodynamic stability of
(CH)TM(N)
because of poor binding ability of N ligands. For the
thermodynamic stable
(CH)TM(EE)
complexes (TM = Cr, Mo, W; EE = CO,
BF), their 20-electron nature is derived from their occupied nonbonding
molecular orbital mainly donated by ligands. Furthermore, charge
transfer from TMs to the CH ligands is
revealed by the atoms in molecules (AIM) theory, leading to the positive
charges of the TM atoms. On the other hand, the nature of the
TM-E bond has been thoroughly analyzed by the energy
decomposition analysis (EDA) method. The absolute value of interaction
energies (|ΔE|) between
(CH)TM(EE)
and EE has the same trend as the
corresponding bond dissociation energy and Wiberg bond orders of
TM-E bonds, following the order W > Mo
> Cr with same ligands and BF > CO with same
TM. Additionally, the largest contribution to the
ΔE values is the repulsive term
ΔE. Similar contributions from covalent and
electrostatic terms to the TM-E bonds were found, which
can be described as the classic dative bond with nearly same σ and π
contributions. The stronger σ donations and π backdonations in
(CH)TM(BF)
than in
(CH)TM(CO)
indicate much more stability of
(CH)TM(BF).
Theoretical Insight into 20‐Electron Transition‐Metal Complexes (C
5
H
5
)
2
TM(E
1
E
2
)
2
(TM = Cr, Mo, W; E
1
E
2
= CO, N
2
, BF): Stabilities, Electronic Structures, and Bonding Nature
