1P094
Theoretical Study of Mononuclear Nickel(I), Nickel(0), Copper(I), andCobalt(I) Dioxygen Complexes: New Insight into Differences andSimilarities in Geometry and Bonding Nature(Kyoto Univ. Fukui Institute for Fundamental Chemistry)[Introduction]

Yue Chen, Shigeyoshi Sakaki

Activation of dioxygen molecule by the first row transition metals plays crucial roles

in biological oxidation. However, the nickel-dioxygen interaction and the role of the nickel center inthe relevant dioxygen complexes have been much less investigated than those of copper-dioxygen
complexes despite the importance in nickel superoxide dismutase. It is of considerable importance toknow how much and why the electronic structure and the bonding interaction of the nickel(I) dioxygen
complex are different from and/or similar to those of the copper dioxygen complex. In this work,
geometries, bonding nature, and electronic structures of (N^N)Ni(O2) (N^N = β-diketiminate), itscobalt(I) and copper(I) analogues, and (Ph3P)2Ni(O2) were investigated by DFT and MS-RASPT2
methods.
[Results and Discussion](N^N)Cu(O2) and (Me3P)2Ni(O2) take a singlet ground state with a C2V

symmetrical structure and (N^N)Co(O2) takes a890

1.8(1.8 4621)

1.

90
1 .861.84 1)
2(1 .8takes a CS symmetrical structure (Figure 1). In56
7 1 .84
1.8 8 0 )4(1.8structure. Interestingly, however, the (N^N)Ni(O2)1.861.7(1.8 9417 )

triplet ground state with a C2V symmetrical

1.347(1.347)1.393(1.392)(N^N)Ni(O2) (CS)(N^N)Cu(O2) (C2V)(N^N)Ni(O2) with a C2V symmetry, the first and

1.800

1.433

1 .886 .886
100
1.8

is that both of the ground and24

other complexes are much larger. More important

1.8ground state (Figure 2), whereas the energy gap in

1.824

the second excited states exist slightly above the1.405(Me3P)2Ni(O2) (C2V)(N^N)Co(O2) (C2V)

Figure 1. The optimized structures by TPSSTPSS

the first excited states in(N^N)Ni(O2) belong to A”
irreducible

representation

under CS symmetry, while they
belong to different irreducible
representations

inothercomplexes.

Therefore,

thesymmetry

loweringoccurs

through the pseudo-Jahn-Teller
effect in (N^N)Ni(O2) but does
not in other complexes.

Figure2. MS-RASPT2-calculated potential energy surface.

The population of π∗z orbital of the O2 moiety inthese complexes is found between 0.96 and 1.14. The

1.84

complexes exhibit a considerable superoxo naturecorrect(Me3P)2Ni(O2). It is likely concluded that theseRM-O (Å)

total d orbital population is about 7 in (N^N)Co(O2),
8 in the Ni analogue, 9 in the Cu analogue, and 9 in

(Me3P)2Ni(O2)1.86(N^N)Co(O2)

1.82
1.80

(N^N)Ni(O2)1.78rather than a peroxo nature from the viewpoint of

1.76

electron distribution. However, little spin density is

1.74(N^N)Cu(O2)
-3.8

-3.6

-3.4

-3.2

-3.0

-2.8

-2.6

-2.4

-2.2

found on the O2 moiety in these complexes, while thecomplex

possesses

one-1

unpaired electron on the O2 moiety.

(A)
Binding or Interaction Energy (kcalmol )ɳ1-superoxousualWe introduced a new parameter of M-O distance(RcorrectM−O ) in which the difference of ionic radiusamong Ni(0), Ni(I), Co(I), and Cu(I) was considered.
As shown in Figure 3A, the Rcorrect
linearly
M−Ocorrelates to 𝑑𝑦𝑧 orbital energy (𝜀𝑑𝑦𝑧 ) in the valence
state. Also, we found that the interaction energy(EINT ) of the O2 with the metal moiety linearlycorrelates to the 𝜀𝑑𝑦𝑧 (Figure 3B). Hence, the O2

180

EINT160

EBE(Me3P)2Ni(O2)140120(N^N)Co(O2)100(N^N)Ni(O2)8060(N^N)Cu(O2)40-4.0 -3.8 -3.6 -3.4 -3.2 -3.0 -2.8 -2.6 -2.4 -2.2

binding energy (EBE ) largely depends on the dyz
orbital energy and the promotion energy (Eprom ) tothe valence state; see Figure 3B.

(B)

Figure 3. The correlations of (A) Rcorrect
vs.
M−O

The calculated Gibbs energy barriers (∆𝐺 ≠ )εdyz and (B) EBE and EINT vs. ε𝑑𝑦𝑧of hydrogen abstraction from phenol suggest that

Energy (kcal/mol)(N^N)Ni(O2) and (N^N)Co(O2) are reactive(Me3P)2Ni(O2)032

G r30G0‡computational28results

alsosuggest

that(N^N)Cu(O2) is reactive toward phenol with

26

Gibbs energy barriers of 17.1 kcal/mol.

24(N^N)Co(O2)2220Interestingly, we found the linear relationships
between the ∆𝐺 ‡ of hydrogen abstraction and(N^N)Ni(O2)1816

toward phenol but (Me3P)2Ni(O2) is not. Our

the 𝜀𝑑𝑦𝑧 and between Gibbs reaction energy(N^N)Cu(O2)-4.0-3.8-3.6(∆𝐺𝑟 ) and the 𝜀𝑑𝑦𝑧 (Figure 4). These results-3.4-3.2-3.0-2.8-2.6-2.4-2.2

Figure 4. The correlations of ∆𝐺𝑟 vs. ε𝑑𝑦𝑧 , and∆𝐺 ‡ vs. ε𝑑𝑦𝑧 .

[Reference]indicate that higher 𝜀𝑑𝑦𝑧 leads to a stronger
interaction between O2 and ML, which is notfavorable for the reactivity of the dioxygen
complex.

Yao, S.; Bill, E.; Milsmann, C.; Wieghardt, K.; Driess, M., Angew. Chem. Int. Ed. 2008, 47, 7110.