1P098

Oxidative Addition of Anhydride to Nickel(0) Species: Reactivity andRegioselectivity(Fukui Institute for Fundamental Chemistry, Kyoto University) ○ Wei Guan,Shigeyoshi Sakaki*[Introduction]
Ni-catalyzed intermolecular deScheme 1. Nickel-Catalyzed Decarboxylative Carboamicarboxylative cycloaddition providnation of Alkynes with Isatoic Anhydrides
es an efficient method for thesynthesis of heterocyclic compounds, which plays a vital role in life
processes due to their biologicalactivities. Recently, Kurahashi andMatsubara et al. successfully
developed a new nickel-catalyzed decarboxylative [4 + 2]
Scheme 2. Regioselectivity of thecycloaddition of isatoic anhydrides with alkynes to provide
Oxidative Aadditionquinolones (Scheme 1).1 The catalytic cycle of the present
reaction consists of four elementary processes: (1)oxidative addition, (2) decarboxylation, (3) alkyne
insertion, and (4) reductive elimination. The first oxidative
addition process is the rate-determining step of thecatalytic cycle, which determines what product is obtained.
Hence, one important task is to understand the reactivity
and regioselectivity of the oxidative
addition; the experimentally reported
product is obtained only when theC2−O2 bond rather than the other C−O,
C−C, and C−N bonds undergoes theoxidative addition (Scheme 2).
[Computational methods]
Geometries were optimized with theM06 hybrid functional, where solvent
effect of toluene was taken into
consideration by the CPCM method.
Two kinds of basis set system wereemployed here. In basis set I (BS-I), theLos Alamos relativistic ECPs wereemployed for the core electrons of Ni
and the (541/541/311/1) basis set wasused for its valence electrons. The 631G(d) basis sets were employed forother main group elements. A better
basis set system was employed for theevaluation of energy changes. In BS-II,(311111/22111/411/11) basis set wasemployed for Ni with the ECPs of the
Stuttgart−Dresden−Bonn group. The 6311+G(2d,p) basis sets were employedfor other elements. All calculations werecarried out by the Gaussian 09 program.
[Results and Discussion]
The oxidative addition step is theapproach of a bis-ligated Ni(0) catalyst

Figure 1. Energy
Oxidative Addition.

Profiles(ΔG°353.15)

fortheNi(PMe3)(alkyne) Ni2 to isatoic anhydride R1, leading to the formation of five kinds of adduct,
where the C=O bond, the C=C bond in the phenyl ring, the O atom, and the C−N bond in theheterocyclic ring participate in coordination. Among them, η2-complexes 1e is the most stable; seeFigure 1. From the above initial intermediates, five kinds of TS for bond activation are optimized
here; TS1a for the C2−O2 bond activation, TS1b for the C3−N bond activation, TS1c for theC1−C2 bond activation, TS1d for the C3−O2 bond activation, and TS1e for the C4−N bondactivation. All products of the oxidative addition are pseudo-square-planar four-coordinated Ni(II)complexes. TS1a is the most stable among all TSs, indicating the anhydride C2−O2 bond ispreferentially activated. Although 2d is much stable, the strong C‒CO2 bond obstructs the next
decarboxylation.
For the most favorable pathway, R1 approaches Ni2 to form a η2-adduct 1a, as shown in Figure
2, in which the carbonyl group coordinates with the Ni center. Transition state TS1a takes athree-membered-ring. In TS1a, the Ni−C2 and Ni−O2 distances become shorter from 1.97 and2.81 to 1.87 and 2.14 Å, respectively, while the C2−O2 bond is elongated to 1.79 Å from 1.43 Å in
1a, suggesting that the C2−O2 bond breaking is in progress. The immediate 2a is a pseudosquare-planar four-coordinated Ni(II) complex. The ΔG°⧧ and ΔG° values of this process are 14.3
and 6.1 kcal/mol, respectively.

Figure 2. Optimized Structures and Selected Geometrical Parameters (Bond Length in Angstrom
Unit and Bond Angle in Degree) of 1a, TS1a, and 2a.
In the oxidative addition process, Ni2 considerably donates 3dπ electrons of Ni to the low-lying
unoccupied π* anti-bonding orbital of R1. As shown in Scheme 3(A), the LUMO of R1 mainly
consists of the π*C‒C anti-bonding orbitals in the phenyl moiety into which the π*C‒O anti-bonding
orbital of the heterocyclic ring mixes in a bonding way. The HOMO of Ni2 mainly consists of the3dπ of Ni orbital, which overlaps with the pπ‒pπ anti-bonding overlap between C2 and O2 atoms.
Hence, this CT leads to the C2−O2
Scheme 3. LUMO of R1 and Important Kohn-Sham MOs
bond breaking and Ni−acyl andand Their Electron Populations of each MO of R1 andNi−carboxylate bond formations.
Ni2 Moieties in TS1aThe pπ‒pπ anti-bonding overlap is
not found in the other C3−O2,
C3−N, and C4−N pairs. Thus, theCT to the LUMO of R1 explains
the reason why the anhydride
C2−O2 bond is preferentially
activated by Ni2; in other words,
thisCTdetermines
theregioselectivity. The use of strong
electron-donating ligand such as
PCy3 enhances the CT accordingly
to promote the anhydride C(=O)−Obond cleavage.
[Reference]
1. Yoshino, Y.; Kurahashi, T.; Matsubara, S. J. Am. Chem. Soc. 2009, 131, 7494.