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. 2019 Feb 18;10(16):4402-4411.
doi: 10.1039/c8sc05380d. eCollection 2019 Apr 28.

Donor-acceptor-stabilised germanium analogues of acid chloride, ester, and acyl pyrrole compounds: synthesis and reactivity

Mahendra Kumar Sharma  1 , Soumen Sinhababu  1 , Pritam Mahawar  1 , Goutam Mukherjee  1 , Bhawana Pandey  2 , Gopalan Rajaraman  2 , Selvarajan Nagendran  1
Affiliations

Donor-acceptor-stabilised germanium analogues of acid chloride, ester, and acyl pyrrole compounds: synthesis and reactivity

Mahendra Kumar Sharma et al. Chem Sci. .

Abstract

Germaacid chloride, germaester, and N-germaacyl pyrrole compounds were not known previously. Therefore, donor-acceptor-stabilised germaacid chloride (i-Bu)2ATIGe(O)(Cl) → B(C6F5)3 (1), germaester (i-Bu)2ATIGe(O)(OSiPh3) → B(C6F5)3 (2), and N-germaacyl pyrrole (i-Bu)2ATIGe(O)(NC4H4) → B(C6F5)3 (3) compounds, with Cl-Ge[double bond, length as m-dash]O, Ph3SiO-Ge[double bond, length as m-dash]O, and C4H4N-Ge[double bond, length as m-dash]O moieties, respectively, are reported here. Germaacid chloride 1 reacts with PhCCLi, KOt-Bu, and RLi (R = Ph, Me) to afford donor-acceptor-stabilised germaynone (i-Bu)2ATIGe(O)(CCPh) → B(C6F5)3 (4), germaester (i-Bu)2ATIGe(O)(Ot-Bu) → B(C6F5)3 (5), and germanone (i-Bu)2ATIGe(O)(R) → B(C6F5)3 (R = Ph 6, Me 7) compounds, respectively. Interconversion between a germaester and a germaacid chloride is achieved; reaction of germaesters 2 and 5 with TMSCl gave germaacid chloride 1, and 1 reacted with Ph3SiOLi and KOt-Bu to produce germaesters 2 and 5. Reaction of N-germaacyl pyrrole 3 with thiophenol produced a donor-acceptor-stabilised germaacyl thioester (i-Bu)2ATIGe(O)(SPh) → B(C6F5)3 (10). Furthermore, the attempted syntheses of germaamides and germacarboxylic acids are also discussed.

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Figures

Chart 1
Chart 1. Silicon analogues of an acid chloride I, aldehyde II, and ester III.
Scheme 1
Scheme 1. Synthesis of donor–acceptor-stabilised germaacid chloride 1. Notes: (a) in the alphanumerical numbering pattern, G denotes germylene, and D denotes germanium μ-oxo dimer, and (b) products with a GeO → B(C6F5)3/Ge-OTMS → B(C6F5)3 moiety are given a linear/arbitrary numerical numbering pattern (starting from 1).
Scheme 2
Scheme 2. Synthesis of donor–acceptor-stabilised germaester 2.
Scheme 3
Scheme 3. Attempted synthesis of donor–acceptor-stabilised germaamides that resulted in amine → borane adducts.
Scheme 4
Scheme 4. Synthesis of donor–acceptor-stabilised N-germaacyl pyrrole 3.
Scheme 5
Scheme 5. Reactions of germaacid chloride 1 with various lithium/potassium salts.
Scheme 6
Scheme 6. Reaction of germaacid chloride 1 with lithium bis(trimethylsilyl)amide.
Scheme 7
Scheme 7. Interconversion between germaesters 2/5 and germaacid chloride 1.
Scheme 8
Scheme 8. Reaction of N-germaacyl pyrrole 3 with thiophenol.
Fig. 1
Fig. 1. UV-vis spectra of compounds 1, 2, and 10 (30 μM solution) in toluene.
Fig. 2
Fig. 2. Molecular structure of germaacid chloride 1 with thermal ellipsoids at the 50% probability level. All hydrogen atoms and a solvent molecule (dichloromethane) are omitted for clarity. Selected bond lengths (Å) and angles (deg): Ge1–O1 1.698(2), O1–B1 1.493(5), Ge1–Cl1 2.117(1), Ge1–N1 1.831(3), Ge1–N2 1.846(3); O1–Ge1–N1 111.60(1), O1–Ge1–N2 116.79(1), O1–Ge1–Cl1 112.25(9), B1–O1–Ge1 134.6(2), N2–Ge1–N1 87.46(1), N1–Ge1–Cl1 116.19(1), N2–Ge1–Cl1 110.52(1). Data collection temperature: 100 K.
Fig. 3
Fig. 3. Molecular structure of germaynone 4 with thermal ellipsoids at the 50% probability level. All hydrogen atoms and a solvent molecule (dichloromethane) are omitted for clarity. Selected bond lengths (Å) and angles (deg): Ge1–O1 1.708(2), O1–B1 1.489(4), Ge1–C16 1.856(3), Ge1–N1 1.860(2), Ge1–N2 1.845(2); O1–Ge1–N1 114.10(1), O1–Ge1–N2 110.17(1), O1–Ge1–C16 113.63(12), B1–O1–Ge1 131.46(2), N2–Ge1–N1 86.91(1), N1–Ge1–C16 112.42(2), N2–Ge1–C16 116.98(1). Data collection temperature: 100 K.
Fig. 4
Fig. 4. Molecular structure of germaacyl thioester 10 with thermal ellipsoids at the 50% probability level. All hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and angles (deg): Ge1–O1 1.698(3), O1–B1 1.501(5), Ge1–S1 2.199(2), Ge1–N1 1.864(4), Ge1–N2 1.866(4); O1–Ge1–S1 116.19(1), B1–O1–Ge1 144.0(3), N2–Ge1–N1 85.72(2). Data collection temperature: 100 K.
Fig. 5
Fig. 5. NBO calculated Ge–O σ-bond in germaacid chloride 1, N-germaacyl pyrrole 3, and germaacyl thioester 10. The hybridisations of the germanium and oxygen orbitals involved in the overlap are mentioned along with the percentage contributions of the constituent atoms to the Ge–O bond.
Fig. 6
Fig. 6. Pictorial view of NBO donor–acceptor interactions between p or spx (x = 3.82, 0.29) orbitals of oxygen and the σ* orbital of the Ge–Cl bond/π* orbitals of the Ge–NATI bonds in compound 1 (a–e), s or p orbitals of oxygen and s or p orbitals of germanium in compound 2 (f–h), p or spx (x = 0.32, 4.59) orbitals of oxygen and s or p orbitals of germanium in compound 3 (i–l), s or p orbitals of oxygen and p or sp1.45 orbitals of germanium in compound 10 (m–p), and p orbital of oxygen and σ* orbital of Ge–S bond in compound 10 (q). Energy values are given in kcal mol–1. Hydrogen atoms are omitted for clarity. The cut–off interaction energies for LP → LP* and LP → BD* are ≥30 kcal mol–1 and 20 kcal mol–1, respectively.
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