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. 2025 Jul 17;31(40):e202501543.
doi: 10.1002/chem.202501543. Epub 2025 Jul 2.

C,N-Chelated Organogermanium(II) Hydride as Catalyst for Esterification of Aldehydes

Dominik Vítek  1 , Jiří Tydlitát  2 , Libor Dostál  1 , Milan Erben  1 , Štěpán Podzimek  3 , Zdeňka Růžičková  1 , Jaromír Vinklárek  1 , Roman Jambor  1
Affiliations

C,N-Chelated Organogermanium(II) Hydride as Catalyst for Esterification of Aldehydes

Dominik Vítek et al. Chemistry. .

Abstract

The reactions of the monomeric C,N-chelated organogermanium(II) hydride L(H)Ge·BH3 (1) with potassium alkoxides KOR provided potassium hydrido-alkoxo-germanato-borates {K(THF)2[BH3·Ge(L)(H)(OR)]}2 (R = tBu (2), C(CH3)2CH2CH3 (3)) as products of KOR addition. Compounds 2 and 3 react with benzaldehyde under formation of alkyl esters of benzoic acid along with elimination of a neutral complex L(H)Ge·BH3 (1). Thus complex 1 was tested as a useful catalyst for esterification of aldehydes by KOtBu. The GC-MS analysis revealed formation of t-butyl esters of appropriated carboxylic acids. The mechanistic studies for the esterification of benzaldehyde with KOtBu catalyzed by 1 were also performed either theoretically (DFT calculations), or experimentally (NMR and IR spectroscopy).

Keywords: IR spectroscopy; NMR spectroscopy; esterification; germylene; hydride.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Scheme 1
Scheme 1
Synthesis of {K(THF)2[BH3·Ge(L)(H)(OR)]}2 (R =  t Bu (2), C(CH3)2CH3CH3 (3).
Figure 1
Figure 1
Molecular structures of 2 and 3. Hydrogen atoms (except of the GeH) and coordinated molecules of THF are omitted. Selected bond distances (Å) and angels (°): For 2: Ge1─O1 1.8428(17), Ge1─B1 2.053(3), K1─O1 2.700(2), Ge1─H1 1.49(4), O1─Ge1─C1 105.99(9), O1─Ge1─B1 105.36(10). For 3: Ge1─O1 1.845(2), Ge1─B1 2.050(4), K1─O1 2.706(2), Ge1─H1 1.48(4), O1─Ge1─C1 106.70(11), O1─Ge1─B1 106.04(13).
Scheme 2
Scheme 2
Stoichiometric reaction of 2 and 3 with benzaldehyde.
Scheme 3
Scheme 3
Esterification reaction of benzaldehyde with KO t Bu catalyzed by 1.
Figure 2
Figure 2
The courses of stoichiometric (A, B) and catalytic (C) reactions monitored by time‐resolved FTIR spectroscopy. Experimental conditions: A) benzaldehyde + KO t Bu + 1, B) benzaldehyde + 2, C) benzaldehyde + KO t Bu + 10 mol% of 1.
Scheme 4
Scheme 4
Catalytic cycle for the esterification of benzaldehyde with KO t Bu catalyzed by 1 proposed by DFT calculations (optimalization of 2, Int1, and ΔG) in the combination with the experimental studies (NMR and IR spectroscopy).
Figure 3
Figure 3
Optimized geometries of 2 and 2‐mon and relative Gibbs free energies (in kcal mol−1; calculated in n‐hexane at the M06/cc‐pVTZ(‐PP) level).
Figure 4
Figure 4
Energetical profile for the reaction of 2 with 2 eq. of benzaldehyde to give Int1 (in kcal mol−1; calculated in n‐hexane at the M06/cc‐pVTZ(‐PP) level).
Scheme 5
Scheme 5
Esterification of substituted aldehydes by KO t Bu catalyzed by 1.
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