1P091
Theoretical Study of Ketone Insertion into Ge(II)-H Bond:
Comparison with that into Rh(I)-H Bond
(FIFC, Kyoto Univ.) Nozomi Takagi, Shigeyoshi Sakaki
INTRODUCTION
Activation of small molecules is one of the fundamental characteristics of transition
metal complexes, which is very important as the initial step of various catalytic
reactions. The partially occupied valence d orbitals of a transition metal which areusually very close in energy play a key role in such reactions. On the other hand, it has
been believed that main-group elements cannot play such a role and cannot be a catalyst
in general. This is because their valence s and p orbitals are far apart in energy.
However, successful synthesis and isolation of novel heavier main-group compounds,
for instance heavier homologues of ethylene, acetylene, benzene, ketone or carbene,
opened a new area of chemistry. The recent experiments report that some of suchheavier homologues exhibit reactivity toward dihydrogen and some small molecules
containing C=O, C≡C, N=N, and C=N bonds without any external catalysts.
In this work, we focus on activation of ketone by the Ge(II) hydride 1 producing therelevant germylene alcoxide 2 (Scheme 1a).1 It is noted that this reaction resembles well
the initial step of the hydrogenation reaction of ketone by the Rh(I) hydride 3 (Scheme1b). We wish to disclose the mechanism of these reactions, discuss the essential
similarity/dissimilarity between Ge(II) and Rh(I), and assess the potential for activatingsmall molecules with a main-group-based catalyst.
MeArNGeHNMeAr

Ar = 2,6-diisopropylphenylMe1F3CCArGeOPhNMeRhOC

CF3PhCHOH + 1Ph(a)

Ar

R3SiH

2PPh3Ph3P

H2F3C HN

CF3PhCHOSiR3 + 1H

PPh3

H23H3CCO(PPh3)3RhOCHPhCH3CH3PhCHOH + 3(b)PhScheme 1

COMPUTATIONAL DETAILSAll geometries were optimized by the DFT method with B3PW91 functional. For

the energy evaluation and the analysis of the electronic structure, a triple-ζ basis set
with 2d and 1f polarization functions was employed for Ge with the ECPs ofStuttgart-Dresden-Bonn group. A triple-ζ basis set with 2f polarization functions wasemployed for Rh with the same ECPs. The 6-311G(d) basis sets were employed for theother elements, where a diffuse function was added to O and one p polarization function
was added to H of hydride, dihydrogen, and silane. The Gibbs energy in solvent wascalculated incorporating with the polarized continuum model (PCM), where thetranslational entropy was corrected with the method developed by Whitesides et al. The
relative energy was evaluated up to the MP4(SDTQ) and CCSD(T) levels for the modelmolecules and the MP2 and SCS-MP2 levels for the real molecules.
RESULTS AND DISCUSSION
The theoretical calculations show that the reaction of 1 with CF3PhC=O occurs in
one-step process via four-membered transition state TS1,2, where the Ge-H σ-bonding
MO of 1 interacts with the C=O π*-antibonding MO of ketone (Figure 1). The
experimental fact that (CH3)2C=O and Ph2C=O cannot react with 1 is explained in termsof their higher-lying C=O π*-antibonding MO. To construct catalytic cycle withmain-group-based catalyst, the regeneration process of 1 is investigated with severalsubstrates. When silane is employed as the second reagent, 1 is regenerated withformation of silylether. However, further reaction is very difficult, when dihydrogen isemployed.
The characteristic features of heavy main-group-based catalyst as well as themechanism of the hydrogenetion reaction of 3 will be presented in the symposium.
[kcal/mol]+11.0 / +36.3

TS1,20.0

1.864
1 .2
76+5.7 / +34.9

F

Si8GeOF

F1.843CF FF

9H(590.0i cm-1)

H212.6

Ge0.0SiMe3H

88.3

1.518

1SiH4OC

1.431
FFSiF3H
288.8(76.7i cm-1)

F-20.0

1.870
FO04
1 .4

-30.0

91.3

22.3

2.400

CF3PhCO
+10.0

-10.0

+17.5 / +52.1+16.7 / +30.3+20.0

Ge114.6

FC

H-16.1 / -1.6

CF3PhCHOH-16.4 / +14.1-26.9 / -7.2

-27.5 / -14.3-34.1 / -19.6

F-40.0-36.7 / -22.1

CF3PhCHOSiH3
CF3PhCHOSiMe3
CF3PhCHOSiF3

Figure 1. Optimized structures and relative energy (ΔE0 / ΔG0sol) for the reaction shown in Scheme 1a.
Energies, distances, and angles are in kcal/mol, Å, and degree, respectively.
1S. K. Mandal, H. W. Roesky, Acc. Chem. Res., 2012, 45, 298.