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

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Sinhababu, P. Mahawar, G. Mukherjee, B. Pandey, G. Rajaraman and N. Selvarajan, Chem. Sci., 2019, DOI:

10.1039/C8SC05380D.

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DOI: 10.1039/C8SC05380D

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ARTICLE

Donor-Acceptor-Stabilised Germanium Analogues of Acid

Chloride, Ester, and Acyl Pyrrole Compounds: Synthesis and

Reactivity

Received 00th January 20xx,

Accepted 00th January 20xx

Mahendra Kumar Sharma,^aSoumen Sinhababu,^aPritam Mahawar,^aGoutam Mukherjee,^aBhawana

DOI: 10.1039/x0xx00000x

Pandey,^bGopalan Rajaraman^band Selvarajan Nagendran^a*

www.rsc.org/

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=O, Ph₃SiO-Ge=O, and C₄H₄N-Ge=O

t

moieties, respectively, are reported here. Germaacid chloride 1 reacts with PhCCLi, BuOK, 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)(O^tBu)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 KO^tBu 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.

bonds, respectively, were successfully isolated, and the variety

of silanones exceeds that of the germanones.^7-11In addition to

silanones, silicon analogues of aldehyde, ester, amide, formyl

chloride, carboxylic acid, and acid anhydride compounds were

also synthesised via various methods by the groups of Driess

and Roesky.¹²Very recently, Aldridge and co-workers reported

the generation of a silicon analogue of an acid chloride [(N-

nacnac)^ArSi(Cl)=O (I)] through the reaction of the silylene (N-

nacnac)^ArSiCl with N₂O (Chart 1). The metathesis reactions of I

Introduction

The carbonyl group (C=O) in organic compounds such as

ketones [RC(O)R], aldehydes [RC(O)H], acid halides [RC(O)X],

esters [RC(O)OR], amides [RC(O)NR₂], carboxylic acids

[RC(O)OH], and acid anhydrides [RC(O)OC(O)R] is of great

importance in organic chemistry (R = alkyl/aryl group; X =

halogen). The significance of these carbon compounds

provides inspiration for the synthesis of their heavier

analogues,¹⁻³but the synthetic efforts are typically hampered

by the lability of the M=O bond (M = Si, Ge, Sn, Pb). The

instability of this bond stems from the -bond polarisation and

poor -type overlap between M and O atoms, which usually

leads to oligomerisation/polymerisation of compounds

containing such M=O bonds.⁴⁻⁶Strategies that utilise tailor-

made ligands and/or provide donor-acceptor stabilisation to

M/O atoms have been applied to address the aforementioned

problems and have yielded various stable compounds

containing M=O bonds.^7-11Thus, silanones (silaketones) and

germanones (germaketones) with formal Si=O and Ge=O

with K[Et₃BH] and KO^tBu afforded

nacnac)^ArSi(H)=O→BEt₃

(II)] and

nacnac)^ArSi(O^tBu)=O (III)], respectively [(N-nacnac)^Ar

a silaaldehyde [(N-

a

silaester

[(N-

=

HC{(Me₂N)C(Ar)N}₂] (Chart 1).^12aSurprisingly, such analogues

of germanium [L”Ge(O)Y] [L” = a monoanionic ligand; Y = H

(germaaldehyde), Cl (germaacid chloride), OR (germaester),

NR₂(germaamide), OH (germacarboxylic acid), and (OGe(O)L”)

germaacid anhydride] are not yet known, perhaps due to the

difficulty in adding an electron-withdrawing Y atom/group to

the germanium atom in light of the already heavily polarised

Ge=O bond. Owing to our continued interest in the chemistry

of germanium, we were able to isolate the Lewis acid (LA)

complexes L^#Ge=OLA (LA = B(C₆F₅)₃(IV), ZnCl₂(V), SnCl₂(VI),

and GeCl₂(VII)) of a germanone¹⁰starting from a germanium-

-oxo dimer [L^#= aminotroponiminate (ATI), a monoanionic

bidentate ligand]. We now understand that this synthetic

protocol is exploitable for the synthesis of hitherto unknown

germaacid chlorides and germaesters. Consequently, we

report in this article the isolation and reactivity of the first

examples of a donor-acceptor-stabilised germaacid chloride (i-

^a.Department of Chemistry, Indian Institute of Technology Delhi, Hauz Khas, New

Delhi 110 016, India. E-mail: sisn@chemistry.iitd.ac.in

^b.Department of Chemistry, Indian Institute of Technology Bombay, Powai,

Mumbai 400076, India

†Experimental section, UV-vis spectra of compounds 1-2 and 10; molecular

structure determination of compounds D1, D3-D5, 1-7, and 9-10; computational

details (PDF). CIFs for compounds D1, D3-D5, 1-7, and 9-10, are deposited with

the Cambridge Structural Database (CSD); CCDC 1564828−1564834, 1564836, and

1851011−1851015. These data can be obtained free of cost from the CCDC using

the link https://www.ccdc.cam.ac.uk/. See DOI: 10.1039/x0xx00000x

This journal is © The Royal Society of Chemistry 20xx

J. Name., 2013, 00, 1-3 | 1

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germylene s_Vil_ieo_wx_Aid_rte_ic¹_le⁵_Onli(_ni_e-

Bu)₂ATIGe(O)(Cl)B(C₆F₅)₃

(1),

germaester

(i- synthesise

a

germaester,

a

Bu)₂ATIGe(O)(OSiPh₃)B(C₆F₅)₃(2), and N-germaacyl pyrrole Bu)₂ATIGeOSiPh₃(G2) was reacted with

^{DOI: 10.1039/C8}N^SC₂O⁰⁵³⁸⁰i^Dn

was tetrahydrofuran at 60 °C for 2 h to obtain the germanium µ-

(i-Bu)₂ATIGe(O)(NC₄H₄)B(C₆F₅)₃(3). Compound

3

obtained during our search for stable germaamides.

oxo dimer {(i-Bu)₂ATIGe(OSiPh₃)(µ-O)}₂(D2). The reaction of µ-

oxo dimer D2 containing Ge-OSiPh₃bonds with two

equivalents of B(C₆F₅)₃in toluene at room temperature

afforded the first example of a donor-acceptor-stabilised

germaester, namely, (i-Bu)₂ATIGe(O)(OSiPh₃)B(C₆F₅)₃(2)

(Scheme 2), and demonstrated the suitability of the

germanium µ-oxo dimer route for the preparation of

germaesters.

Me₂N

Ar

Me₂N

Ar

Si

Me₂N

Ar

N

O

H

BR'₃

N

O

N

O

Si

O^tBu

Cl

Me₂N

Ar

Me₂N

Ar

Me₂N

Ar

III

II

Ar = 2,6-iPr₂C₆H₃

I

i-Bu

Chart 1. Silicon analogues of an acid chloride I, aldehyde II, and ester III.

OSiPh

³N

N₂O, THF

60 °C

- N₂

N

O

To synthesise

a germaacid chloride, oxidation of the

Ge

1/2

O

germylene monochloride^13a(i-Bu)₂ATIGeCl (G1) with N₂O was

carried out in tetrahydrofuran at room temperature. However,

germylene G1 did not react with N₂O at room temperature,

and therefore, this reaction was performed at higher

temperatures. Germylene G1 reacted with N₂O at 60 °C in

tetrahydrofuran and afforded the germanium µ-oxo dimer {(i-

Bu)₂ATIGe(Cl)(µ-O)}₂(D1) after 2 h as a yellow solid in 60%

yield (Scheme 1).^5,14

N

OSiPh₃

i-Bu

G2

D2

B(C₆F₅)₃, rt

toluene, 2 h

i-Bu

N

O

B(C₆F₅)₃

Ge

N

OSiPh₃

i-Bu

2

Scheme 2. Synthesis of donor-acceptor-stabilised germaester 2.

Cl

N

N₂O, THF

60 °C

- N₂

N

O

Ge

1/2

N

Cl

N

To extend this route for the synthesis of germaamides, a

germanium µ-oxo dimer with Ge-NR₂moieties is required. Two

such germanium µ-oxo dimers, {(i-Bu)₂ATIGeN(H)Ph(µ-O)}₂

(D3) and {(i-Bu)₂ATIGeN(Me)Ph(µ-O)}₂(D4), were obtained

through the reaction of the amidogermylenes (i-

Bu)₂ATIGeN(H)Ph (G3) and (i-Bu)₂ATIGeN(Me)Ph (G4) with N₂O

at 60 °C for 2 h in tetrahydrofuran (Scheme 3). However, the

reaction of µ-oxo dimers D3 and D4 with two equivalents of

B(C₆F₅)₃resulted in the amineborane adducts

PhNH₂B(C₆F₅)₃and Ph(Me)NHB(C₆F₅)₃, respectively, along

Cl

i-Bu

G1

D1

B(C₆F₅)₃, rt

toluene, 2 h

i-Bu

N

O

B(C₆F₅)₃

Ge

N

Cl

i-Bu

1

Scheme 1. Synthesis of donor-acceptor-stabilised germaacid chloride 1. Notes: (a) in with an unidentified oily material instead of the expected

the alphanumerical numbering pattern,

germanium -oxo dimer, and (b) products with a Ge=OB(C₆F₅)₃/Ge-OTMSB(C₆F₅)₃

moiety are given a linear/arbitrary numerical numbering pattern (starting from 1).

G denotes germylene, and D denotes

germaamides (Scheme 3). These reactions suggest that the

synthetic route discussed above is not suitable for the isolation

of donor-acceptor-stabilised germaamides.

i-Bu

N(R)Ph

i-Bu

It appears that 60 C is the optimum temperature for this

N₂O, THF

60 °C

N

O

reaction; higher temperatures afforded the ATI ligand salt

Ge

1/2

- N₂

O

[ATIH]⁺(Cl)^(ATI

=

aminotroponiminate), and lower

N

N(R)Ph

temperatures resulted in lower yields of µ-oxo dimer D1.

Based on the successful conversion of a germanium -oxo

dimer {(i-Bu)₂ATIGe(ⁱPr)(µ-O)}₂(D) containing Ge-C bonds into

donor-acceptor-stabilised germanones IV-VII through the

reaction of D with Lewis acids, we planned to react germanium

-oxo dimer D1 containing Ge-Cl bonds with B(C₆F₅)₃. To our

surprise, treatment of -oxo dimer D1 with two equivalents of

B(C₆F₅)₃in toluene for 2 h at room temperature yielded the

i-Bu

R = H G3, Me G4

i-Bu

R = H D3, Me D4

B(C₆F₅)₃, rt

toluene, 2 h

Unidentified

oily material

B(C₆F₅)₃

PhNH₂

/ PhN(Me)H

B(C₆F₅)₃

Scheme 3. Attempted synthesis of donor-acceptor-stabilised germaamides that

resulted in amineborane adducts.

first example of

a donor-acceptor-stabilised germaacid

On the basis of the products obtained, it was thought that the

lone pairs of electrons on the nitrogen atoms of the NR₂

moieties in D3 and D4 interfered with the expected reaction of

these compounds (D3 and D4) with B(C₆F₅)₃. To confirm this

hypothesis, a germanium µ-oxo dimer containing amino

chloride (i-Bu)₂ATIGe(O)(Cl)B(C₆F₅)₃(1) in quantitative yield

(Scheme 1). This accomplishment inspired us to determine

whether hitherto unknown germaesters and germaamides

could also be isolated using this synthetic strategy of reacting

suitable germanium -oxo dimers with Lewis acids. Thus, to

2 | J. Name., 2012, 00, 1-3

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functional groups with nitrogen atoms that cannot donate lone analogue of acid halides, exhibits reactivity similar t_Vo_iewth_Aa_rt_tico_lef_Oa_nc_linid_e

pairs of electrons to Lewis acids was synthesised and used. As halides and silaacid chloride^12a; therefore, ^Dth^Oi^Is^{: 1}r⁰e^.1a⁰c³ti⁹v^/i^Cty^8So^Cf⁰1⁵³⁸w⁰a^Ds

a pyrrole substituent (Py; NC₄H₄) can satisfy the required further exploited. The lithium and potassium salts of

criterion, the germanium µ-oxo dimer {(i-Bu)₂ATIGe(NC₄H₄)(µ- triphenylsilanol and t-butanol reacted with

1 to result in

O)}₂(D5) with two Ge-NC₄H₄moieties was synthesised in germaesters 2 and (i-Bu)₂ATIGe(O)(O^tBu)B(C₆F₅)₃(5), respectively

quantitative yield by the reaction of the N-germylene pyrrole (Scheme 5), which is another route for the isolation of germaesters

(i-Bu)₂ATIGe(NC₄H₄) (G5) with N₂O in tetrahydrofuran at 60 C in addition to that shown in Scheme 2.

for 2 h (Scheme 4).¹⁶Treatment of µ-oxo dimer D5 with two

i-Bu

equivalents of B(C₆F₅)₃in toluene at room temperature

resulted in the first donor-acceptor-stabilised N-germaacyl

pyrrole, (i-Bu)₂ATIGe(O)(NC₄H₄)→B(C₆F₅)₃(3) in quantitative

yield (Scheme 4). The feasibility of isolating N-germaacyl

pyrrole 3 as a stable species proves that the aforementioned

hypothesis of the interference of lone pairs of electrons on the

nitrogen atoms of the NR₂moieties in µ-oxo dimers D3 and D4

is factually valid.

N

MX, toluene

0 °C - rt, 12 h

- MCl

N

O

B(C₆F₅)₃

O

B(C₆F₅)₃

Ge

Cl

X

N

i-Bu

MX = LiCCPh for 4, KO^tBu for 5

PhLi for 6, MeLi for 7

LiOSiPh₃for 2, LiNC₄H₄for 3

1

X = CCPh (4), O^tBu (5), Ph (6)

= Me (7), OSiPh₃(2), NC₄H₄(3)

Scheme 5. Reactions of germaacid chloride 1 with various lithium/potassium salts.

i-Bu

NC₄H₄

N

N₂O, THF

60 °C

- N₂

N

O

In a similar fashion, alternate synthetic protocols can be

suggested for N-germaacyl pyrrole 3 and germanones. For

Ge

1/2

O

NC₄H₄

N

NC₄H₄

example, treatment of

phenyl/methyl lithium yielded N-germaacyl pyrrole 3 and the

germanones (i-Bu)₂ATIGe(O)(Ph)B(C₆F₅)₃(6)/(i-

1 with lithium pyrrol-1-ide and

i-Bu

G5

D5

B(C₆F₅)₃, rt

toluene, 2 h

Bu)₂ATIGe(O)(Me)B(C₆F₅)₃(7) as products, respectively

(Scheme 5). Thus, from germaacid chloride 1, germaesters, N-

germaacyl pyrrole, and germanones can be derived without

the need to isolate the corresponding germanium--oxo

dimers. This route was also attempted for the possible

isolation of germaamides, and the reactions of germaacid

chloride 1 with the lithium salts PhN(H)Li and PhN(Me)Li were

carried out. However, these reactions faced the same fate as

that of the abovementioned reactions carried out for the

isolation of germaamides (shown in Scheme 3) by yielding

amineborane adducts only.

i-Bu

N

O

B(C₆F₅)₃

Ge

N

NC₄H₄

i-Bu

3

Scheme 4. Synthesis of donor-acceptor-stabilised N-germaacyl pyrrole 3.

In all the reactions, germanium µ-oxo dimers D1-D5 were reacted

with the Lewis acid B(C₆F₅)₃. To understand the utility of other Lewis

acids for the successful conversion of germanium µ-oxo dimers D1,

D2, and D5 to the corresponding donor-acceptor-stabilised

germaacid chloride, germaester, and N-germaacyl pyrrole, a range

of Lewis acids (such as BF₃, GeCl₂, and SnCl₂) were screened.

However, all of these reactions were typically unsuccessful (see the

Supporting Information (SI) for details). Surprisingly, the

germanium-μ-oxo dimer {(i-Bu)₂ATIGe(ⁱPr)(µ-O)}₂(D) with Ge-ⁱPr

bonds was insensitive to the nature of the Lewis acid used.¹⁰Thus,

it reacted smoothly with B(C₆F₅)₃, ZnCl₂, SnCl₂, and GeCl₂to afford

the donor-acceptor-stabilised germanones IV, V, VI, and VII,

respectively.¹⁰

i-Bu

LiN(TMS)₂

toluene

0 °C - rt, 12 h

N

O

B(C₆F₅)₃

O

B(C₆F₅)₃

N(TMS)₂

Ge

- LiCl

Cl

N

i-Bu

[8] (Not Isolated)

1,3 silyl migration

1

i-Bu

TMS

O

N

B(C₆F₅)₃

As the germanium analogues of acid halides, esters, and amides

were previously unknown, there has been no reactivity study on

them. Therefore, the reactivity of the donor-acceptor-stabilised

germaacid chloride 1, germaester 2, and N-germaacyl pyrrole 3 was

studied with great interest to understand how these compounds

behave chemically. It was found that germaacid chloride 1 can react

with various lithium salts and afford clean products. Thus, through

reaction of 1 with lithium phenylacetylide in toluene for 12 h, a

unique example of a germaynone (i-Bu)₂ATIGe(O)(CCPh)B(C₆F₅)₃

(4) was obtained (Scheme 5). Notably, until now, there has been no

example of a silaynone. Furthermore, this reaction reveals that the

chloride attached to the germaacyl moiety can be replaced with

other functional groups, a reactivity omnipresent among acid

chlorides in organic chemistry. Germaacid chloride 1, a heavier

Ge

N

TMS

i-Bu

9

Scheme 6. Reaction of germaacid chloride 1 with lithium bis(trimethylsilyl)amide.

However, another reaction of germaacid chloride 1 with

lithium bis(trimethylsilyl)amide, which aimed again at

obtaining the elusive germaamide, occurred differently and

resulted

in

the

germaimine

(i-

Bu)₂ATIGe(NTMS)(OTMS)B(C₆F₅)₃(9) in quantitative yield

(Scheme 6). This result reveals that the desired germaamide

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[8] was formed as an intermediate, which then underwent 1,3- Ge=OB(C₆F₅)₃moiety, decompose even in tet_Vra_ieh_wy_Ad_rtir_co_lef_Ou_nr_la_inn_e

DOI: 10.1039/C8SC05380D

silyl migration to form the stable compound 9 (Scheme 6).

Reactivity studies with donor-acceptor-stabilised germaesters [ATIH]⁺[(OH)(B(C₆F₅)₃)]^.

2 and 5 demonstrated that an interconversion between these Compounds D1, D3-D5, 1-7, and 10 were characterised

dried

over

a

potassium

mirror

to

afford

germaesters and germaacid chloride

1

is achievable. through multinuclear NMR spectroscopic (¹H, ¹¹B, ¹³C, ¹⁹F, and

Germaesters 2 and 5 reacted with a slight excess of Me₃SiCl in ²⁹Si) and single-crystal X-ray diffraction studies in the solution

1

toluene at room temperature and offered germaacid chloride and solid states, respectively (see the SI for details). In the H

1 (Scheme 7). As mentioned above (Scheme 5), reactions of NMR spectra of D1 and D5, all the resonances are shifted

germaacid chloride 1 with one equivalent of LiOSiPh₃and slightly downfield in comparison to those of the precursor

KO^tBu in toluene at room temperature generated the molecules, germylene monochloride G1 and N-germylene

germaesters 2 and 5, respectively (Scheme 7). This type of pyrrole G5, respectively. This shifting is due to the attachment

interconversion is not known among the analogous silicon of germanium atoms to electronegative oxygen atoms and the

compounds.

concomitant increase in the formal oxidation state of

germanium atoms from +2 to +4. The resonances of the seven-

membered ring protons in 1-7 and 10 are shifted downfield in

comparison to the corresponding protons in germanium-µ-oxo

dimer D1. Owing to the increased electrophilicity of the

germanium atom in the Ge=OB(C₆F₅)₃moiety (of 1-7 and 10)

in comparison to the germanium atoms in the Ge(-O)₂Ge

moiety of D1, these shifts are expected. In the ¹³C NMR spectra

of D1, D3-D5, 1-7, and 10, the expected numbers of signals

were observed. In the ¹¹B NMR spectra of 1, 2, 3, 4, 5, 6, and

10, singlet resonances at −2.46, −2.61, −2.72, −2.79, −2.44,

−3.12, and −2.73 ppm were observed, respectively (Table 1). In

comparison, B(C₆F₅)₃and the donor-acceptor-stabilised

germanone (i-Bu)₂ATIGe(O)(i-Pr)B(C₆F₅)₃(IV) showed singlet

resonances at -2.30 ppm¹⁸and -4.52 ppm,¹⁰respectively.

These data reveal that the resonances in 1-6 and 10 are in

between the resonances of B(C₆F₅)₃and IV. These results

suggest that the electron donation by the germaacyl oxygen

atom to the boron atom in 1, 2, 3, 4, 5, 6, and 10 is reduced

relative to that in IV due to the electron-withdrawing effect of

the Cl, OSiPh₃, NC₄H₄, CCPh, O^tBu, Ph, and SPh atom/group on

the germanium atom, respectively (IV has an electron-

donating i-Pr group on the germanium atom). This effect is

reasonably seen even in the ¹⁹F NMR spectra of compounds 1

(-130, -157, and -162 ppm) and 2 (-130, -157, and -162 ppm).

Here, the resonances due to fluorine atoms are also between

the corresponding resonances for B(C₆F₅)₃(-127, -143, and -

160 ppm)¹⁹and germanone IV (-134, -161, and -166 ppm).¹⁰

The donor-acceptor-stabilised silaaldehyde LSi(H)=OB(C₆F₅)₃

(VIII),^12gsilaformyl chloride IPr∙SiH(Cl)=OB(C₆F₅)₃(IX),^12c

i-Bu

Me₃SiCl, toluene

- Me₃SiOR

N

O

B(C₆F₅)₃

O

B(C₆F₅)₃

OR

Ge

Cl

LiOSiPh₃or

KO^tBu, - LiCl/KCl

N

i-Bu

1

i-Bu

R = SiPh₃2, R = ^tBu 5

Scheme 7. Interconversion between germaesters 2/5 and germaacid chloride 1.

The reactivity studies on N-germaacyl pyrrole 3 demonstrated

that the thiophenoxide moiety of thiophenol can substitute

the pyrrolide of 3. Accordingly, the reaction of N-germaacyl

pyrrole 3 with thiophenol at room temperature in toluene for

6 h resulted in the first example of a germaacyl thioester (i-

Bu)₂ATIGe(O)(SPh)B(C₆F₅)₃(10) in quantitative yield (Scheme

8).

i-Bu

B(C₆F₅)₃

N

PhSH, toluene

6 h, rt

N

O

B(C₆F₅)₃

O

Ge

- Pyrrole

NC₄H₄

N

SPh

i-Bu

10

3

Scheme 8. Reaction of N-germaacyl pyrrole 3 with thiophenol.

Considering this reaction, the feasibility of substituting the

pyrrolide of 3 with hydroxide from a suitable precursor was

investigated, as this might lead to the first example of a donor-

acceptor-stabilised germacarboxylic acid. However, the

reaction of 3 with water in a 1:1 molar ratio for 2 h in toluene

resulted in [ATIH]⁺[(OH)(B(C₆F₅)₃)]^and not the expected

germacarboxylic acid (Scheme S1; see the SI). The

commonality in all of the abovementioned reactions of donor-

acceptor-stabilised germaacid chloride 1, germaester 2, and N-

silaacid

anhydride

[{PhC(^tBuN)₂}Si{=O∙B(C₆F₅)₃}O−Si(H){=O∙B(C₆F₅)₃}N^tBu)(HN^tBu)C

Ph] (X),^12dmonoalumoxane L*Al=OB(C₆F₅)₃(XI),²⁰and

boraacid chloride IPrB(Cl)(=O)B(C₆F₅)₃(XII)²¹have B(C₆F₅)₃

as the acceptor in the M=OB(C₆F₅)₃moiety (M = Si VIII, IX, X;

Al XI; B XII) [L = HC[CMeN(Ar)]₂(Ar = 2,6-ⁱPr₂C₆H₃); IPr = 1,3-

germaacyl pyrrole

nucleophilic substitution in the presence of suitable substrates

without any damage to the Ge=OB(C₆F₅)₃moiety.

3 is that these reactants undergo

bis(2,6-diisopropylphenyl)imidazol-2-ylidene,

L*

=

Et₂NCH₂CH₂NC(Me)CHC(Me)NCH₂CH₂NEt₂]. It may therefore

be appropriate to compare the boron and fluorine resonances

of these compounds with those of 1-6 and 10 (Table 1). These

resonances in compounds VIII, IX, X, XI, and XII are shifted

upfield with respect to the corresponding resonances of

B(C₆F₅)₃(Table 1), which indicates the shielding of boron and

fluorine atoms due to electron donation by oxygen atoms. This

result is similar to that observed for compounds 1-6 and 10,

The germanium-µ-oxo dimers D1-D5, germaacid chloride 1,

germaesters 2 and 5, N-germaacyl pyrrole 3, germaynone 4,

germanones 6 and 7, and germaacyl thioester 10 are stable at

room temperature in an inert atmosphere of dinitrogen. All

these compounds are freely soluble in common organic

solvents, such as toluene, chloroform, and dichloromethane.

Though the germanium-µ-oxo dimers D1-D5 are also freely

soluble in tetrahydrofuran, products 1-7 and 10, containing a

4 | J. Name., 2012, 00, 1-3

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containing a Ge=OB(C₆F₅)₃moiety (Table 1), but as revealed VIII, IX, X, and XII. In the ²⁹Si NMR spectra of germaester 2 , a

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by the ¹¹B NMR spectral data (Table 1), the magnitude of the signal at -13.62 ppm for the SiPh₃group^Dis^Os^I:h¹i⁰ft^.1e⁰d³⁹d^/Co⁸w^Sn^Cf⁰i⁵e³ld⁸⁰i^Dn

shielding in these compounds is lower than that in compounds comparison to that in μ-oxo dimer D2 (-24.72 ppm).¹⁵

¹¹B NMR

chemical shift

(ppm)

S.

No.

¹⁹F NMR chemical shift O−B bond

Compound

Reference

(ppm)

length (Å)

1

2

3

4

−4.52^a

−4.70^b

−5.28^c

--

(-134, -161, and -166)^a

(-132, -162, and -165)^b

(-134, -163, and -168)^c

(-136, -163, and -167)^b

1.473(4)

1.503(3)

1.492(3)

10

12g

12c

12f

Germanone, (i-Bu)₂ATIGe(O)B(C₆F₅)₃(IV)

Silaaldehyde, LSi(H)=OB(C₆F₅)₃(VIII)

Silaformyl chloride, IPr ∙SiH(Cl)=OB(C₆F₅)₃(IX)

Silacarboxylic acid, LSi(HOdmap)(=OB(C₆F₅)₃) (XIII)

1.493(3),

and

1.488(3)

(−3.99, and

(-134, -135, -164,

Silaacid anhydride, [{PhC(^tBuN)₂}Si{=O∙B(C₆F₅)₃}O−Si(H)

{=O∙B(C₆F₅)₃}N^tBu)(HN^tBu)CPh] (X)

12d

−5.46)^c

-165, -167, and -168)^c

5

6

−2.7^d

−4.83^e

−2.30^a

−2.46^a

−2.61^a

−2.72^a

−2.79^a

−2.44^a

−3.12^a

−2.73^a

(-131, -160, and -165)^d

(-134, -164, and -166)^e

(-127, -143, and -160)^a

(-130, -157, and -162)^a

(-133, -159, and -165)^a

(-133, -161, and -165)^a

(-132, -160, and -165)^a

(-133, -160, and -165)^a

1.444(3)

1.518(3)

--

20

Monoalumoxane, L*Al=OB(C₆F₅) (XI)

Boraacid chloride, IPrB(Cl)(=O)B(C₆F₅) (XII)

B(C₆F₅)₃

7

21

8

19

9

1.493(5)

1.497(3)

1.494(6)

1.489(4)

1.505(3)

1.481(3)

1.501(5)

this work

Germaacid chloride, (i-Bu)₂ATIGe(O)(Cl)B(C₆F₅)₃(1)

Germaester, (i-Bu)₂ATIGe(O)(OSiPh₃)B(C₆F₅)₃(2)

N-Germaacyl pyrrole, (i-Bu)₂ATIGe(O)(NC₄H₄)B(C₆F₅)₃(3)

Germaynone, (i-Bu)₂ATIGe(O)(CCPh)B(C₆F₅)₃(4)

Germaester, (i-Bu)₂ATIGe(O)(O^tBu)B(C₆F₅)₃(5)

Germanone, (i-Bu)₂ATIGe(O)(Ph)B(C₆F₅)₃(6)

Germaacyl thioester, (i-Bu)₂ATIGe(O)(SPh)B(C₆F₅)₃(10)

10

11

12

13

14

15

^aIn CDCl₃, ^bin CD₂Cl₂, ^cin THF-d₈, ^din C₆D₆, ^ein C₆D₆/THF-d₈.

Table 1: Comparison of the ¹¹B and ¹⁹F NMR spectral resonances of boron and fluorine atoms and the O−B bond distances in

compounds 1-6 and 10 with B(C₆F₅)₃and other related compounds of group 13-14 elements with an M=OB(C₆F₅)₃moiety(s) (M

= Ge, Si, Al, B).

In a preliminary study of optical properties, the UV-vis spectra LUMO [π^*_(ATI)] transition. Most likely, a different Lewis acid in

of compounds 1, 2, and 10 were recorded in toluene at room compound VII altered the composition of the HOMO.

temperature. Compounds 1, 2, and 10 showed an absorption

maximum in the visible region at approximately 420 nm

(Figure 1). Theoretical studies suggested that these

absorptions in compounds 1, 2, and 10 are essentially due to

π_{(C F )} π*_(ATI), π_{(C F )} π*_(ATI), and n_(F)+ π_{(C F )} π*_(ATI)

5

6

transitions, respectively (Table S1; see the SI for details).

Furthermore, there are two high-energy transitions in each of

these compounds with _maxvalues of approximately 350 and

285 nm (Figure 1), which are due to multiple transitions (Table

S1; see the SI for details). The optical properties of compounds

with formal M=OLA moieties (M = Ge, Si) have rarely been

studied. For germanone VII with a Ge=OGeCl₂moiety,

optical properties have been reported. In comparison to

compounds 1, 2, and 10, the absorption maximum of VII in the

visible region (437 nm) is slightly redshifted, and this

Figure 1. UV−vis spectra of compounds 1, 2, and 10 (30 μM solution) in toluene.

absorption is due to a HOMO [s^nb

+ p^nb

+ π_(C=C)] 

(N,O,Cl)

(Ge2)

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The structures of compounds D1, D3-D5, 1-7, and 9-10 in the distorted tetrahedral geometry with two ATI ligand nitrogens,

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solid state were determined by single-crystal X-ray diffraction one germaacyl oxygen, and one Cl (1), O^D(^O2^I)^:,¹N^0.1(⁰3³)⁹,^/C^C8(^S4^C),⁰O⁵³⁸(5^0D),

analysis (Figures 2-4 and S53-S62, Tables S2−S5, and C (6), C (7), or S (10) atom. The average length of the Ge–N_ligand

Experimental Section; see the SI).²²Compounds 1-4 and 6 bonds in compounds 1 (1.838 Å), 2 (1.848 Å), and 3 (1.843 Å) is

crystallised in the triclinic space group Pī (Tables S3 and S4; see shorter than that in their precursors D1 (1.913 Å), D2 (1.946

the SI). Compounds 5, 7, and 10 crystallised in the Å), and D5 (1.942 Å), respectively. Similarly, the Ge‒Y bond in

orthorhombic, monoclinic, and monoclinic space groups P2₁/n, compounds 1 (2.117(1) Å; Y = Cl), 2 (1.719(2) Å; Y = OSiPh₃),

P2₁2₁2₁, and P2₁/c, respectively (Table S4; see the SI).

and 3 (1.820(4) Å; Y = NC₄H₄) is also shorter than that in

compounds D1 (2.20(8) Å), D2 (1.767(3) Å), and D5 (1.892(3)

Å), respectively. These differences are due to the

electrophilicity of the oxygen atom in the Ge=OB(C₆F₅)₃

moiety of compounds 1, 2, and 3 being higher than that of the

oxygen atoms in the Ge(-O)₂Ge moiety of D1, D2, and D5,

which makes the germanium atom in the former set of

compounds more electrophilic than that in the latter set.

Though these effects are observed in germanone IV, in

comparison to the electron-donating i-Pr group bound to the

germanium atom of germanone IV, the Cl, OSiPh₃, NC₄H₄,

CCPh, and SPh atom/group bound to the germanium atom in

germaacid chloride 1, germaester 2, N-germaacyl pyrrole 3,

germaynone 4, and germaacyl thioester 10, respectively, exert

electron-withdrawing (+I) effects and compete for the

germanium atom’s electron density, thus increasing the

interaction between the germanium and oxygen atoms of the

Ge=O bond. Therefore, the length of the formal Ge=O bond in

compounds 1 (1.698(2) Å), 2 (1.696(2) Å), 3 (1.695(3) Å), 4

(1.708(2) Å), and 10 (1.698(3) Å) is shorter than that in

germanones IV (1.718(2) Å), V (1.724(2) and 1.728(2) Å), VI

(1.728(5) Å), and VII (1.718(2) Å).¹⁰

Figure 2. Molecular structure of germaacid chloride 1 with thermal ellipsoids at the

50% probability level. All hydrogen atoms and a solvent molecule 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.

These data also reveal that relative to the polarisation of the

Ge=O bond in germanone IV,¹⁰the same bonds in germaacid

chloride 1, germaester 2, N-germaacyl pyrrole 3, germaynone

4, and germaacyl thioester 10 are less polarised due to the

electron-withdrawing effect of the Cl, OSiPh₃, NC₄H₄, CCPh,

and SPh atoms/groups bound to the germanium atom,

respectively. A consequence of the increased interaction

between the germanium and oxygen atoms of the germaacyl

bond in these compounds is the reduced Lewis basicity of the

oxygen atom. This result is reflected in the interaction of this

oxygen atom with the Lewis acid B(C₆F₅)₃, where the OB

bond in compounds 1 (1.493(5) Å), 2 (1.497(3) Å), 3 (1.494(6)

Å), 4 (1.489(4) Å), and 10 (1.501(5) Å) is longer than the

corresponding bond in germanone IV (1.473(4) Å).¹⁰The OB

bond lengths observed in these compounds are similar to

those observed in analogous silicon derivatives (VIII 1.503(3),

IX 1.492(3), and X 1.490(3); M = Si) and boraacid chloride (XII

1.518(3); M = B) with an M=OB(C₆F₅)₃bond (Table 1).^{12g, 12c,}

Figure 3. Molecular structure of germaynone 4 with thermal ellipsoids at the 50%

probability level. All hydrogen atoms and a solvent molecule 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.

12d, 21

However, in the monoalumoxane²⁰XI with an

Al=OB(C₆F₅)₃bond, the OB bond is shorter (1.444(3) Å)

than those in compounds 1-4, 10, VIII, IX, X, and XII. All the

bonding aspects discussed here are supported by theoretical

studies (vide infra). Furthermore, the Ge=O bond (vide supra)

in compounds 1-4 and 10 is slightly longer than the Ge=O bond

The molecular structures of compounds 1-7 and 10 [Figures 2

(1), 3 (4), 4 (13), S57 (2), S58 (3), S59 (5), S60 (6), and S61 (7)]

confirmed the presence of a (Y)Ge=OB(C₆F₅)₃moiety [Y = Cl

(1), OSiPh₃(2), NC₄H₄(3), CCPh (4), O^tBu (5), Ph (6), Me (7), and

SPh (10)]. In these compounds, the germanium atom has a

in the base-stabilised germanones [LL’Ge=O] (L

[CH{(C=CH₂)(CMe)(NAr)₂}], Ar 2,6-i-Pr₂C₆H₃; L’

=

[{(Me)CN(Me)}₂C] (XIV), [{(Me)CN(i-Pr)}₂C] (XV), 4-(Me₂N)-

C₅H₄N(DMAP) (XVI)) without an acceptor at an oxygen atom

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(1.646(2)‒1.672(3) Å)⁸and shorter than the Ge-O single bonds N_ATIbonds (Figure 6b; 100.3 kcal/mol and Fig_Vu_ier_we_Ar6_tic_cl;_{e O}5_n2_lin.8_e

in germanium--oxo dimers D1, D2, and D5 (1.848(2)‒1.787(3) kcal/mol). However, in addition to the^Dse^OI:in¹⁰t^.e¹r⁰a³c⁹t^/Cio⁸n^Ss^C,⁰⁵t³h⁸e⁰r^De

Å).

are two strong stabilising interactions between the sp^3.82

(Figure 6d; 44.8 kcal/mol) and sp^0.29(Figure 6e; 43.6 kcal/mol)

orbitals of oxygen and the π^*orbital of the Ge-N₄bond.

Compounds 2, 3, and 10, instead of showing the

aforementioned n (lone pair of electrons on oxygen) to σ^*/π^*

orbital interactions, showed strong NBO donor-acceptor

interactions from the sp^xorbitals of oxygen atoms to vacant s,

p or sp^xorbitals of the germanium atoms [Figures 6f-6h (2), 6i-

6l (3), and 6m-6p (10)]. However, in compound 10, a

moderately strong NBO donor-acceptor interaction was found

between the p orbital of oxygen and the σ^*orbital of the Ge-S

bond (27.9 kcal/mol) (Figure 6q). In comparison, germanone IV

showed three σ interactions: two OGe interactions and one

Oσ^*(Ge−C_i-Pr) interaction; these interactions result in a total

stabilisation energy of 236.3 kcal/mol.¹⁰Thus, the total

stabilisation energy due to the donor-acceptor interactions in

compounds 1 (320.8 kcal/mol), 2 (284.7 kcal/mol), 3 (303.7

kcal/mol), and 10 (329.2 kcal/mol) is higher than that in

germanone IV, which is due to the difference in the nature of

the atoms/moieties bound to germanium atom in these

compounds (-Cl, -OSiPh₃, -NC₄H₄, and –SPh, respectively)

instead of an i-Pr group. The Wiberg bond index (WBI)

calculations for compounds 1, 3, and 10 also showed a slightly

increased bond order for the Ge=O bond (0.74-0.76) relative to

that in germanone IV (0.70)¹⁰(Table S6; see the SI). A similar

bond order (0.79) was calculated for silaaldehyde II (with BEt₃

as an acceptor bound to the oxygen atom); for silaacid chloride

I and silaester III (without any acceptor bound to the oxygen

atom), the calculated WBI values are 1.09 and 1.04,

respectively.^12aIn compounds 1, 2, and 10, the HOMO is

localised on the phenyl ring of the B(C₆F₅)₃moiety (Figure S64;

see the SI), and in compound 3, it is localised on the pyrrole

ring, which also reveals the stabilisation of the formal Ge=O

bonds in these compounds (Figure S64; see the SI).

Furthermore, NBO donor-acceptor interactions between

oxygen and boron atoms can be observed in all these

compounds (Figure S65; see the SI); the stabilisation energies

due to these interactions are 280.3 kcal/mol, 315.6 kcal/mol,

296.3 kcal/mol, and 294.6 kcal/mol in compounds 1 (Figure

S65a), 2 (Figure S65b), 3 (Figure S65c), and 10 (Figure S65d),

respectively. All these stabilisation energies are lower than

that observed in germanone IV (334.9 kcal/mol),¹⁰indicating

the reduced electron donation from oxygen atoms to boron

atoms in compounds 1-3, and 10.

Figure 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.

The nature of the Ge=O bond in compounds 1-3 and 10 was

analysed through natural bond orbital (NBO)^23,24studies, and

the details are provided in Table S6 (see the SI). The Ge-O σ-

bond in compounds 1 and 10 is formed by the overlap of the

sp^2.59and sp²hybrid orbitals of germanium with the sp^1.62and

sp^2.66hybrid orbitals of oxygen, respectively (Figure 5 and

Table S6; see the SI). In compounds 2 and 3, the sp^2.53and

sp^2.43hybrid orbitals of germanium overlap with the sp^2.89and

sp^2.57hybrid orbitals of oxygen to form the Ge-O bond,

respectively (Figure

5 and Table S6; see the SI). MO

calculations also reveal the presence of Ge-O bonds in

compounds 1-3 and 10, and these bonds are deeply buried

(Figure S63, see the SI).

As none of the monoanionic ligands, such as -diketiminate

and amidinate ligands, are known to stabilise compounds with

formal Ge=O bonds, it is of interest to examine how the bulky

monoanionic aminotroponiminate (ATI) ligand used in the

present study helps to stabilise various compounds with

formal Ge=O bonds. NBO second-order perturbation theory

analysis reveals the existence of donor-acceptor interactions

between (a) sp^xorbitals of nitrogen atoms of the ATI ligand to

vacant s, p or sp^xorbitals of germanium in compounds 1-3 and

10 (Figures S66a-b, S67a-d, S68a-d, and S69a-d; see the SI); (b)

Figure 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.

NBO second-order perturbation theory analysis reveals that in

germaacid chloride 1, the sigma bond between germanium

and oxygen is formed by the donation of the lone pair of

electrons on the oxygen atom to the σ^*orbital of the Ge-Cl

bond (Figure 6a; 79.3 kcal/mol). The lone pair of electrons on

the oxygen atom also interacts with the π^*orbitals of the Ge-

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N_ATIorbitals to the σ^*orbital of the Ge-Cl bond in compound 1

(Figures S66c-d; see the SI) and N_ATIorbitals to the σ^*orbital of

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DOI: 10.1039/C8SC05380D

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(a) p(O)-σ^*(Ge-Cl): 79.3

(b) p(O)-π^*(Ge-N₄): 100.3

(c) p(O)-π^*(Ge-N₅): 52.8

(d) sp^3.82(O)-π^*(Ge-N₄): 44.8

(e) sp^0.29(O)-π^*(Ge-N₄): 43.6

(f) p(O)-s(Ge): 174.5

(j) p(O)-p(Ge): 71.7

(n) p(O)-p(Ge): 101.8

(g) p(O)-p(Ge): 69.3

(k) sp^0.32(O)-p(Ge): 38.3

(o) s(O)-p(Ge): 53.1

(h) s(O)-p(Ge): 40.9

(l) sp^4.59(O)-p(Ge): 34.4

(p) p(O)-p(Ge): 32.5

(i) p(O)-s(Ge): 159.3

(m) p(O)-s1^.45(Ge): 113.9

(q) p(O)-σ^*(Ge-S): 27.9

Figure 6. Pictorial view of NBO donor-acceptor interactions between p or sp^x(x = 3.82, 0.29) orbitals of oxygen and the σ^*orbital of the

Ge-Cl bond/π^*orbitals of the Ge-N_ATIbonds 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 sp^x(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

s1^.45orbitals 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. Hydrogen atoms are omitted for clarity. The cut-off interaction energies for LPLP^*and LPBD^*are ≥30 kcal/mol

and 20 kcal/mol, respectively.

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the Ge-S bond in compound 10 (Figures S69e-f; see the SI); and (SR/FST/CS-1-195/2008) facilities in the Department of

(c) s or p orbitals of the chlorine atom to π^*orbitals of Ge-N_ATIChemistry, IIT Delhi.

bonds in compound 1 (Figures S66e-f; see the SI). Owing to the

interactions of types (b) and (c), the energies of the σ^*orbital

of the Ge-Cl bond in compound 1, π^*orbitals of the Ge-N_ATI

bonds in compound 1, and the σ^*orbital of the Ge-S bond in

compound 10 are lower, and these orbitals are available for

accepting electrons donated by the O atom of the Ge=O bond.

Further, energy decomposition analysis (EDA)²⁵was performed

using {Y-Ge=OB(C₆F₅)₃} (Y = Cl (1), OSiPh₃(2), NC₄H₄(3), SPh

(10)) as one fragment and the {ATI} ligand as another fragment

with frozen geometries obtained from DFT calculations; the

results are summarised in Table S7 (see the SI). The large

interaction energy (E_int) observed for these compounds arises

essentially due to the favourable ∆E_orbterm that describes the

stabilising interaction between the ATI ligand and the Y-

Ge=OB(C₆F₅)₃moiety (Y = Cl (1), OSiPh₃(2), NC₄H₄(3), SPh

(10)).

Author contributions

M. K. S. carried out all the experimental studies and drafted

the manuscript. S. S. and P. M. helped M. K. S. with the UV-vis

studies. The theoretical studies were carried out by G. M., who

also wrote the theoretical section of the manuscript. B. P.

assisted G. M. with some of the theoretical calculations/write-

up. S. N. and G. R. corrected the experimental and theoretical

write-ups of the manuscript, respectively.

Notes and references

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Conclusions

Donor-acceptor-stabilised

Bu)₂ATIGe(O)(Cl)B(C₆F₅)₃

germaacyl

(1),

chloride

germaester

(i-

Bu)₂ATIGe(O)(OSiPh₃)B(C₆F₅)₃(2), and N-germaacyl pyrrole

(i-Bu)₂ATIGe(O)(NC₄H₄)B(C₆F₅)₃(3) compounds were

successfully isolated as stable species for the first time.

Compounds 1, 2, and 3 can undergo nucleophilic substitution

reactions without any disturbance to the Ge=OB(C₆F₅)₃

moiety to afford germaynone (i-Bu)₂ATIGe(O)(CCPh)B(C₆F₅)₃

2

(4),

germaester

(i-Bu)₂ATIGe(O)(O^tBu)B(C₆F₅)₃

(5),

3

4

germanone (i-Bu)₂ATIGe(O)(R)B(C₆F₅)₃(R = Ph 6, Me 7), and

germaacyl thioester (i-Bu)₂ATIGe(O)(Cl)B(C₆F₅)₃(10)

compounds in good yields. Interestingly, through the reactivity

of 1 and 2, the feasibility to interconvert germaesters and

germaacid chlorides is exposed. Attempts were also made to

synthesise germaamides and germacarboxylic acids, and it is

anticipated that the wisdom obtained during these

endeavours will offer new directions to the isolation of these

compounds as stable species in the near future.

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M. K. S., P. M. and S. S. B. thank the Indian Institute of

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Grants Commission (UGC), New Delhi, India, for research

fellowships. S. N. thanks the SERB, Department of Science and

Technology (DST), New Delhi, India, for funding

(EMR/2017/005519) and DST-FIST for establishing single-

crystal X-ray diffraction (SR/FST/CSII-027/2014) and HRMS

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Graphic For Table of Content Entry

View Article Online

DOI: 10.1039/C8SC05380D

Hitherto unknown germaacid chloride (1), germaester (2), and N-germaacyl pyrrole (3) compounds are

stabilised as Lewis acid complexes. Reactivity studies on compounds 1, 2, and 3 yielded compounds such

as germaynone (4) and germaacyl thioester (10). Quantum chemical calculations were carried out to

understand the bonding in these compounds.

i-Bu

N

O B(C₆F₅)₃

Ge

Y

N

i-Bu

Germaacid Chloride (Y = Cl) 1

Germaester (Y = OSiPh₃) 2

N-Germaacyl Pyrrole (Y = NC₄H₄) 3

Germaynone (Y = CCPh) 4

Germaacyl Thioester (Y = SPh) 10

Article Doi

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

DOI: 10.1039/c8sc05380d

Source and publish data:

Authors:

Article abstract of DOI:10.1039/c8sc05380d

Full text of DOI:10.1039/c8sc05380d

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