Reactivity of 2,6-diethyl-4,8-dimethyl-1,5-dioxo-s-hydrindacene towards radical, anionic and cationic germylation

Article abstract of DOI:10.1016/j.ica.2003.10.017

The synthesis and diastereoisomeric resolution of 2,6-diethyl-4,8-dimethyl- 1,5-dioxo-s-hydrindacene allowed the determination of the structure of the meso compound by X-ray diffractometry. The diastereoisomers were inactive towards radical germylation but reacted with acidic hydrogermanes or germylithium yielding α-germylated alcohols. By contrast, they were poorly reactive towards germylamines or SET reactions. This diketone acts as an efficient spin trap in radical hydrogermylation of alkenes.

Full text of DOI:10.1016/j.ica.2003.10.017

Inorganica Chimica Acta 357 (2004) 1256–1264
www.elsevier.com/locate/ica
Reactivity of 2,6-diethyl-4,8-dimethyl-1,5-dioxo-s-hydrindacene
towards radical, anionic and cationic germylation q
a
A. El Kadib , A. Castel , F. Delpech , P. Riviere , M. Riviere-Baudet ,
a
a
a,
a
*
ꢀ
ꢀ
H. Gornitzka , P. Aguirre , J.M. Manriquez , I. Chavez , D. Abril
a
b
b
b
b
a
Laboratoire dÕHꢁetꢁerochimie Fondamentale et Appliquꢁee, UMR 5069 du CNRS, Universitꢁe Paul Sabatier, Chimie, 118 Route de narbonne,
31062 Toulouse Cedex 4, France
b
Departamento de Quimica Inorganica, Facultad de Quimica, Pontificia Universidad Catolica de Chile, Santiago, Casilla 306, Chile
Received 20 October 2003; accepted 25 October 2003
Abstract
The synthesis and diastereoisomeric resolution of 2,6-diethyl-4,8-dimethyl-1,5-dioxo-s-hydrindacene allowed the determination
of the structure of the meso compound by X-ray diffractometry. The diastereoisomers were inactive towards radical germylation but
reacted with acidic hydrogermanes or germylithium yielding a-germylated alcohols. By contrast, they were poorly reactive towards
germylamines or SET reactions. This diketone acts as an efficient spin trap in radical hydrogermylation of alkenes.
ꢀ 2003 Elsevier B.V. All rights reserved.
Keywords: 2,6-Diethyl-4,8-dimethyl-1,5-dioxo-s-hydrindacene; Germylation; Radical inhibitor; Hydrogermylation
1. Introduction
solvents. NMR spectra were recorded on Bruker AC 80
(1H, 80 MHz) and AC 200 (1H and 13C in the sequence J
mod, 50.3 MHz) spectrometers. Mass and gas chroma-
tography (GC) and mass spectra were recorded with a
Hewlett Packard HP5989 in the electron impact mode
(Ei, 70 eV) or with a Rybermag R10-10 spectrometer
operating in the Ei mode. Field desorption was obtained
on a Varian MAT 311A spectrometer.
Recently, we synthesized 2,6-diethyl-4,8-dimethyl-
1,5-dioxo-s-hydrindacene as a transient material for the
preparation of 1,5-dihydro polyalkylated s-indacenes as
new ligands in organometallic (transition metal and
group 14 metal) chemistry [1]. It was obtained and used
as a mixture of the two diastereoisomeric forms, without
any separation or structural identification. We report
here the isomeric resolution of the diketone, and we
studied its reactivity towards progermanium-centered
radicals, anions and cations.
Infrared spectra were recorded with a Perkin–Elmer
1600FT spectrometer. Elemental analyses were done by
the Centre de Microanalyse de lÕEcole Nationale
ꢁ
Superieure de Chimie de Toulouse. Molecular calcula-
tions were performed with Hyperchem PM3 level. ESR
spectra were recorded on a Bruker ER200 instrument
with frequency meter EIP.
2. Experimental
All reactions were performed under nitrogen using
standard Schlenk tube techniques, Carius tubes and dry
2.1. Preparation of 2,6-diethyl-4,8-dimethyl-1,5-dioxo-s-
hydrindacene (1)
q Supplementary data associated with this article can be found, in the
online version, at doi: 10.1016/j.ica.2003.10.017.
* Corresponding author. Tel.: +33-5-61-55-83-48; fax: +33-5-61-55-
82-04.
The diketone 1 was prepared according to Dahrouch
et al. [1] in 90% yield, with its two diastereoisomeric
forms in the ratio of 60/40. They were separated by pre-
parative HPLC on a column of silicagel microsphere 12
ꢀ
E-mail address: riviere@chimie.ups-tlse.fr (P. Riviere).
0020-1693/$ - see front matter ꢀ 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2003.10.017

A. El Kadib et al. / Inorganica Chimica Acta 357 (2004) 1256–1264
1257
lm (20 g, Merck), pressure 10 bars, eluent: 90% petro-
leum ether and 10% of (CH2Cl2: 75%, ethylacetate: 25%).
Each diastereoisomer was crystallized and identified.
The predominant isomer was identified as the meso
compound whose structure was established by X-ray
diffractometry.
Bruker-AXS CCD 1000 diffractometer with Mo Ka
ꢂ
radiation (k ¼ 0:71073 A). The structure was solved by
direct methods (SHELXS-97) [2] and all non-hydrogen
atoms were refined anisotropically using the least-
squares method on F 2 [3]. Largest electron density res-
ꢂꢀ3
idue: 0.407 e A , R1 (for I > 2rðIÞÞ ¼ 0:0533 and
P
P
wR2 ¼ 0:1542 (all data) with R1 ¼
jjFoj ꢀ jFcjj= jFoj
P
P
2
2 0:5
2.1.1. The isolated threo isomer
and wR2 ¼ ð wðFo2 ꢀ Fc2Þ = wðFo2Þ Þ
.
2.3. Action of Ph3GeH on 1
A mixture of diketone 1 (0.20 g, 0.74 mmol), Ph3GeH
(0.27 g, 0.88 mmol) and 1 mL of C6D6 was heated in a
Carius tube: (i) with AIBN (80 ꢁC, 12 h); (ii) with
C6H5COO-OtBu (120 ꢁC, 12 h) and (iii) with tBu2O2
(180 ꢁC, 12 h). In each case, analysis of the reaction
mixture by GC and proton NMR showed that no re-
action had occurred. The same experiment in THF gave
the same results.
1
3
m.p. 155 ꢁC. H NMR (CDCl3) d: 1.04 (t, J ¼ 7:4
2
3
Hz, 6Hd); 1.56 (d.d.q, J ¼ 14:9 Hz, JHaHc ¼ 8:8 Hz,
3JHa–CH3 ¼ 7:4 Hz, 2Ha); 1.99 (d.d.q, 2J ¼ 14:9 Hz,
3JHbHc ¼ 4:4 Hz, 3JHb–CH3 ¼ 7:4 Hz, 2Hb); 2.62 (s, 6He);
2.65 (d.d.d, 3JHb Hc ¼ JHaHc ¼ 8:8 Hz, 3JHbHc ¼ 4:4 Hz,
3
0
2Hc); 2.68 (d, 2J ¼ 17 Hz, 2Ha0); 3.22 (d.d, 2JHa Hb ¼ 17
0
0
2.4. Action of PhCl2GeH on 1
Hz, JHb Hc ¼ 8:8 Hz, 2Hb0). 13C NMR (CDCl3) d: 11.8
3
0
(Cd), 13.1 (Ce), 24.8 (CH2Et), 30.2 (C3, C7), 49.9 (C2,
C6), 132.9 (C4, C8), 137.5 (Cy), 152.8 (Cx), 210.8 (C1).
IR(KBr): m(C@O): 1698 cmꢀ1. MS/EI: m/z 270 (Mþ,
47%), 242 ([Mþ–C2H4], 52%), 214 ([Mþ–2C2H4], 100%).
A mixture of diketone 1 (0.20 g, 0.74 mmol) and
PhCl2GeH (0.18 g, 0.82 mmol) and 1 mL of THF was
kept at 20 ꢁC for 2 h without any reaction, and then
heated in a Carius tube at 80 ꢁC for 8 h. THF was re-
placed by C6D6 and the reaction mixture analyzed by
1
GC, GC/mass and H{13C} NMR: 1 (38%), PhCl2GeH
2.1.2. The isolated meso isomer
(40%), adduct 3 (60%). There were no traces of diger-
mane PhCl2GeGeCl2Ph, nor of ketol derived from 1 and
expected from a SET reaction [4,5]. The remaining
PhCl2GeH was then extracted with pentane (1 mL) and
the remaining a-chlorogermylalcohol, which has low
thermal stability [6], was extracted with C6D6 (1mL) as a
mixture of diastereoisomers 3 and readily analyzed.
1
3
m.p. 166 ꢁC. H NMR (CDCl3) d: 1.02 (t, J ¼ 7:2
2
3
Hz, 6Hd); 1.54 (d.d.q, J ¼ 13:2 Hz, JHaHc ¼ 8:8 Hz,
3JHa–CH3 ¼ 7:2 Hz, 2Ha); 1.97 (d.d.q, 2J ¼ 14:9 Hz,
3JHbHc ¼ 4:4 Hz, 3JHb–CH3 ¼ 7:2 Hz, 2Hb); 2.62 (s, 6He);
2.65 (d.d.d, 3JHb Hc ¼ JHaHc ¼ 8:8 Hz, 3JHbHc ¼ 4:4 Hz,
3
0
2Hc); 2.68 (d, J ¼ 17:5 Hz, 2Ha0); 3.20 (d.d, J ¼ 17:5
2
2
Hz, JHb Hc ¼ 8:8 Hz, 2Hb0). 13C NMR (CDCl3) d: 11.8
3
0
(Cd), 13.1 (Ce), 24.8 (CH2Et), 30.2 (C3, C7), 49.9 (C2,
C6), 132.9 (C4, C8), 138.0 (Cy), 152.8 (Cx), 210.9 (C1).
IR(KBr): m(C@O): 1697 cmꢀ1. MS/EI: m/z 270 (Mþ,
88%), 242 ([Mþ–C2H4], 98%), 214 ([Mþ–2C2H4], 100%).
1H NMR (C6D6) d: 0.86 (t, 3J ¼ 7 Hz, 6H, CH3CH2);
1.43 (m, 2H, 50% of 4H, CH2CH3); 1.80 (m, 2H, 50% of
4H, CH2CH3); 2.13 (m, 1H, H6); 2.28 (m, 1H, H2); 2.30
(m, 50% of 4H, CH2); 2.67 (m, 50% of 4H, CH2); 2.53 (s,
6H, CH3–C4 and CH3–C8); 6.95 (m, 3H, Ph); 7.25(m,
2H, Ph); 7.75 (s, 1H, OH).13C NMR (C6D6) d: 11.78,
12.01 (C H3CH2); 13.05 (CH3–C4 and CH3–C8); 25.43,
24.84 (CH2CH3); 30.01 (C3); 35.26 (C7); 48.25 (C6);
49.81 (C2); 65.98 (C5); 129.60, 131.44, 133.11 (C20, C30,
C40); 132.73, 133.72, 134.92, 135.82, 137.59, 152.69 (C10,
C4, C8, Cquat. Arom); 209.73 (C1). IR(KBr): m(OH):
3340 cmꢀ1; m(C@O): 1707 cmꢀ1. Mass (DCi/CH4): m/z
2.2. Crystal data for the meso isomer 1
C18H22O2, M ¼ 270:36, monoclinic, P21=c, a ¼
ꢂ
ꢂ
ꢂ
4:796ð4Þ A, b ¼ 14:636ð11Þ A, c ¼ 10:317ð10Þ A, b ¼
3
ꢂ
90:40ð3Þꢁ, V ¼ 724:1ð10Þ A , Z ¼ 2, T ¼ 193ð2Þ K. Four
thousand five hundred and sixty reflections (1232 inde-
pendent, Rint ¼ 0:0495Þ were collected at low tempera-
tures using an oil-coated shock-cooled crystal on a

1258
A. El Kadib et al. / Inorganica Chimica Acta 357 (2004) 1256–1264
533 ([M + 41], 8%), 491 ([M + 29-C2H6], 10%), 271
([M ) PhCl2Ge], 100%), 221 ([PhCl2Ge], 80%).
From the former solution, C6D6 was replaced by an
excess (1 mL) of dimethylbutadiene and the solution
heated at 100 ꢁC for 6 h to complete the decomposition
of the chlorogermylalcohol. Then, GC and GC/Mass
analysis showed the expected phenylchlorogermacycl-
opentene [6] (27%).
The same experiment from 1 (0.20 g, 0.74 mmol) and
PhCl2GeH (0.40 g, 1.81 mmol) gave a small increase in
the yield of adduct (67%), but no traces of the diadduct
(13C NMR analysis). Decomposition occurred at a
higher temperature.
The same experiment starting from 1 (0.27 g, 1 mmol)
and Ph3GeLi (2 mmol) led, after hydrolysis, to a mixture
of 4 (40%) and Ph3GeH (60%) (1H NMR analysis).
The same experiment performed at solvent reflux for
6 h, after hydrolysis, extraction (ether), drying (SO4Na2)
and concentration of the solvents under vacuum gave a
residue analyzed as a mixture of 5 (37%), (Ph3Ge)2O
(60%), and a non-identified compound (3%) which
showed an ethylenic proton at dCH. 5.9 ppm (C6D6).
The reaction mixture was extracted with 5 mL of ether,
leaving a sticky polymer on the walls of the Schlenk tube.
Slow evaporation of ether under nitrogen gave crystals
identified as (Ph3Ge)2O (0.28 g, 49%, M.P: 184 ꢁC). The
digermyldiol 5 was then extracted from the remaining
residue by 0.6 mL of C6H6 leading, after evaporation of
the solvent under vacuum, a mixture of the diastereo-
isomeric forms of 5 (93%) and (Ph3Ge)2O (7%).
2.5. Action of Ph3GeLi on 1
To a solution of diketone 1 (0.27 g, 1 mmol) in 2.5
mL of THF was added Ph3GeLi (1 mmol) (from
Ph3GeH (0.30 g, 1 mmol) and n-BuLi 1.6 M, 0.6 mL, (1
mmol) in THF 2.5 mL, ether 2.5 mL). The reaction
mixture was kept at 20 ꢁC for 2 h and then hydrolyzed.
After extraction with ether, drying on SO4Na2, the
solvents were removed under vacuo and the residue
dissolved in 3 mL of ether. Slow evaporation of ether
under nitrogen led to 0.07 g of a bright yellow solid
identified as a mixture of diastereoisomeric forms of a-
triphenylgermylketol 4.
1H NMR (C6D6) d: 0.85 (t, 3J ¼ 7 Hz, 6H, CH3CH2,);
1.10 (m, 2H, 50% of 4H, CH2CH3); 1.50 (m, 2H, 50% of
4H, CH2CH3); 1.93 (m, 2H, H2 and H6); 2.28 (m, 50% of
4H, CH2); 2.56 (m, 50% of 4H, CH2); 2.57 (s, 6H, CH3–C4
and CH3–C8); 7.10 (m, 18H, Ph); 7.62 (m, 12H, Ph). 13
C
NMR (C6D6) d: 11.43 (CH3CH2); 14.09 (CH3–C4 and
CH3–C8); 24.71 (CH2CH3); 29.90 (C3, C7); 49.87 (C2,
C6); 67.25 (C1, C5); 128.80, 130.00, 134.60 (C20, C30, C40);
132.73, 137.04, 152.69 (C10, C4, C8, Cquat. Arom); 209.44
(C1). IR(KBr): m(OH): 3338 cmꢀ1. Mass (Dci/NH3): m/z
881 (MHþ, 4%), 867 ([MH ) CH2], 60%), 789 ([MH )
CH2–C6H6], 30%), 711 ([MH ) CH2–2C6H6], 80%).
This last reaction was repeated with 1 (1 mmol) and
Ph3GeLi (2 mmol) until reflux, but instead of hydrolysis,
Et3GeCl (0.29 g, 1.5 mmol) was added and the reaction
mixture refluxed for 2 h more. The formation of
Et3GeOGePh3 (see hereafter) was detected by GC and
GC/mass (27%).
1
3
m.p. 126–130 ꢁC. H NMR (C6D6) d: 0.85 (t, J ¼ 7
Hz, 6H, CH3CH2); 1.40 (m, 2H, 50% of 4H, CH2CH3);
1.85 (m, 2H, 50% of 4H, CH2CH3); 2.24 (m, 2H, H2 and
H6); 2.40 (m, 50% of 4H, CH2); 2.57 (s, 6H, CH3–C4 and
CH3–C8); 2.75 (m, 50% of 4H, CH2); 7.18 (m, 9H, Ph);
7.43 (m, 6H, Ph); 7.80 (s, 1H, OH). 13C NMR (C6D6) d:
11.80, 12.16 (CH3CH2); 13.08 (CH3–C4 and CH3–C8);
24.66, 25.91 (CH2CH3); 30.01 (C3); 35.62 (C7); 48.49
(C6); 49.80 (C2); 67.95 (C5); 129.50, 130.71, 135.57 (C20,
C30, C40); 132.72, 133.03, 133.60, 134.49, 137.65, 152.66
(C10, C4, C8, Cquat. Arom); 209.44 (C1). IR(KBr):
m(OH): 3340 cmꢀ1; m(C@O): 1704 cmꢀ1. Mass (Ei): m/z
576 (Mþ, 50%), 548 ([M ) C2H4], 5%), 533 ([M ) C2H4–
CH3], 48%), 511 ([M ) C2H4–CH3–H2O], 100%). Anal.
Calc. for C36H38GeO2: C, 75.16; H, 6.66. Found. C,
74.97; H, 6.47%.
2.6. Synthesis of (triethylgermyl)(triphenylgermyl)ox-
ide, Et3GeOGePh3
To Ph3GeOH [7] (0.85 g, 2.6 mmol) in C6H6 (2 mL)
and THF (2 mL) was added dropwise n-BuLi (2.6 mmol
in hexane) at 20 ꢁC. The mixture was kept 1 h at 20 ꢁC
and then Et3GeCl (0.30 g, 2.6 mmol) was added drop-
wise. The reaction mixture was kept at 60 ꢁC for 1 h.
The solvents were removed under vacuum and the res-
idue dissolved in benzene (2 mL) and then hydrolyzed
(H2O, 1 mL). After extraction by benzene, drying on
The remaining concentrate was analyzed (GC, NMR)
and identified as a mixture of 4 (84%), Ph3GeGePh3
(5%), Ph3GeH (11%), with no traces (GC/Mass) of ke-
toalcohol or diol expected from an SET reaction.

A. El Kadib et al. / Inorganica Chimica Acta 357 (2004) 1256–1264
1259
SO4Na2 and concentration (100 ꢁC/3 ꢁ 10ꢀ2 mm Hg),
Et3GeOGePh3 was isolated as a pure oil (GC analysis).
1H NMR (C6D6) d: 0.97 (m, 15H, C2H5); 7.00–7.80
(m, 15H, C6H5). IR(film): m(GeOGe): 847 cmꢀ1. Mass
(field desorption): m/z 480 (MþÅ). (Ei) m/z 451 ([M ) Et],
100%), 422 ([M ) 2Et], 16%), 393 ([M ) 3Et], 10%), 305
([M ) Et3GeO], 55%). Anal. Calc. for C24H30Ge2O: C,
60.12; H, 6.26. Found: C, 60.34, H, 6.49%.
1H NMR (CDCl3) d: (mixture of four diastereoiso-
meric forms) 1.03 (m, 6H, CH2CH3); 1.45 (m, 25% CH2–
CH3); 1.60 (m, 50%, 4H, CH2–CH3); 1.92 (m, 25%, 4H,
CH2–CH3); 2.15 (m, 1H, C6–H); 2.28 (s, 21%, 6H, CH3–
C4, CH3–C8); 2.36 (s, 21%, 6H, CH3–C4, CH3–C8); 2.51
(s, 27%, 6H, CH3–4, CH3–8); 2.60 (s, 31%, 6H, CH3–4,
CH3–8); 2.60 (m, 50% 4H, C3–H, C7–H); 2.90 (m, 1H,
C2–H); 3.13 (m, 50% 4H, C3–H, C7–H); 4.92(d,
3JHCCH ¼ 3:1 Hz, 27%, 1H, C5–H); 4.97 (d, 3JHCCH ¼ 4:3
Hz, 31%, 1H, C5–H); 5.11 (d, 3JHCCH ¼ 5:3 Hz, 21%, 1H,
2.7. Action of Me3GeNMe2 on 1
3
C5–H); 5.14 (d, JHCCH ¼ 3:1 Hz, 21%, 1H, C5–H). 13C
A mixture of Me3GeNMe2 (0.18 g, 1.11 mmol) and 1
(0.27 g, 1 mmol) was kept for 6 h at 20 ꢁC without any
reaction and then heated in a Carius tube at 100 ꢁC for 6
h. The reaction mixture was analyzed by GC, GC/mass
and mass (by direct introduction). Besides the starting
materials (87%), we detected (Me3Ge)2O (23%) and the
ketoenamine 8 (Mþ ¼ 297). From the mass analysis
(direct introduction, Dci/CH4), we detected traces of the
transient adduct 6 (M + 1) ¼ 434; (M + 41) ¼ 474.
NMR (CDCl3) d: (mixture of diastereoisomers) 11.74,
12.50, 13.00, 13.85 (CH3CH2); 14.10, 14.40, 14.90, 15.08
(C6); 22.20, 22.40, 24.70 (CH2CH3); 26.84, 27.05, 29.80,
30.10 (C7); 30.40, 33.70, 34.40, 34.90 (C3); 46.91, 49.55,
49.78, 50.86 (C2); 74.7, 74.9, 80.9, 81.20 (C5), 129.80,
131.91, 132.80, 134.33, 137.38, 140.80, 141.15, 141.83,
144.11, 148.19, 149.24, 152.60, 153.06, 153.31 (C4,C8,
Cquat. Arom); 210.5 and 210.7 (C1). IR(KBr): m(OH):
3377 cmꢀ1; m(C@O): 1682 cmꢀ1. Mass (Ei): m/z 272 (Mþ,
61%); 244 ([M ) C2H4], 100%). Anal. Calc. for C18H24O2:
C, 79.37; H, 8.88. Found: C, 79.43; H, 8.67%.
2.8. Action of Ph3GeH on 1 under UV irradiation
A solution of Ph3GeH (0.14 g, 0.45 mmol) and 1 (0.10
g, 0.37 mmol) in 1.5 mL of THF D8 was irradiated (254
nm) for 12 h at room temperature. Analysis ofthe reaction
mixture by mass spectrometry (Ei) showed the monoad-
ducts (Mþ ¼ 576). GC, 1H NMR and 13C NMR analysis
confirmed two different monoadducts: the germylcarbi-
nol 4 (ꢂ60%) characterized by1H NMR (THF D8) d: 2.60
(s, CH3–C4 and CH3–C8) and 13C NMR (THF D8) d:
68.0 (C7), and the alkoxygermane 9 (15%) characterized
3. Results and discussion
3.1. Synthesis and diastereoisomeric resolution of 2,6-
diethyl-4,8-dimethyl-1,5-dioxo-s-hydrindacene 1
The 2,6-diethyl-4,8-dimethyl-1,5-dioxo-s-hydrinda-
cene was prepared following the procedure described in
[1], through a regioselective cyclization of the corre-
sponding diacid by means of aqueous polyphosphoric
acid (Eq. (1)).
1
from H NMR (THF D8) d: 4.85 (m; OCH) and 13C
NMR (THF D8) d: 74.7 (OCH), besides the remaining
Ph3GeH (25%) and Ph3GeGePh3 (<1%). The reaction
mixture was then hydrolyzed by HCl 2 N, extracted with
ether (1 mL) and analyzed by GC and GC/mass (Ei):
Ph3GeCl (Mþ ¼ 340), ketoalcohol 10 (Mþ ¼ 272).
2.9. Synthesis of ketoalcohol 10
ð1Þ
To the diketone 1 (0.27 g, 1 mmol) in THF (3 mL)
was added dropwise a suspension of LiAlH4 (0.02 g, 0.5
mmol) in THF (3 mL). The reaction was followed by
GC and stopped with the first appearance of the corre-
sponding diol [1]. After hydrolysis with a solution of
sodium bicarbonate, ether extraction and drying on
SO4Na2, the solution obtained was filtered and then
concentrated under vacuum to give 10, 0.21 g as a white
powder. Yield: 78%. m.p. 115 ꢁC.
An HPLC analysis of 1 showed that this regioselec-
tive reaction [1] is also stereoselective, the two expected
diastereoisomers being obtained in the ratio 60/40. We
separated the two diastereoisomers by preparative
HPLC. The major and first migrating one was isolated
as a pure crystalline product and its structure was ana-
lyzed by X-ray diffractometry. It was identified as the
meso compound. The second one was also isolated as a
solid and identified as the second diastereoisomer.

1260
A. El Kadib et al. / Inorganica Chimica Acta 357 (2004) 1256–1264
Scheme 1.
Fig. 1. X-ray structure of meso 2,6-diethyl-4,8-dimethyl-1,5-dioxo-s-
hydrindacene.
radical initiators (Eq. (2)). This shows that conjugation
of the carbonyl group in the diketone in its singlet
fundamental state makes radical hydrogermylation dif-
ficult [4], and also that this conjugated carbonyl com-
pound 1 is not able to initiate a spontaneous single
electron transfer from the hydrogermane.
The X-ray analysis of the meso compound revealed
an almost planar tricyclic system (Fig. 1, Table 1). The
C(6), C(5) and C(8) atoms are, respectively, )0.22, 0.06
and 0.58A out of the best plane formed by C(1), C(2),
C(3) and C(4). The bond distances: C(4)–C(5): 1.520(3)
ꢂ
ꢂ
ꢂ
A and C(4)–O(1): 1.220(2) A correspond, respectively,
to r carbon–carbon bond and carbon–oxygen double
bond confirming the diketonic form. The most impor-
tant feature is the trans position of the two ethyl groups
relative to the coplanar cycles indicating the exclusive
presence of the meso compound.
ð2Þ
Functional organogermanes (hydrogermanes, ger-
myllithium and germylamine) which can act, respec-
tively, as progermylradicals, progermylanions and
progermylcations allow a large variety of reaction to-
ward carbonyl compounds [4]. In order to test the
chemical behavior of this new ketone, we have per-
formed a series of reactions with these reactives.
The absence of activity can be explained by the rad-
ical mechanism in Scheme 1. Radical (A) generated by
the trapping of metal-centered radicals (Scheme 1, step
b) coming from the initiation step (Scheme 1, a) are too
delocalized [6] to be able to abstract hydrogen (Scheme
1, step c) and thus to initiate the chain reaction. Instead
of being reactive towards Ph3GeH, diketone 1 acts as a
radical inhibitor.
To test this hypothesis experimentally, we studied the
inhibition of the well known radical hydrogermylation
of hex-1-ene by Ph3GeH [9] in the presence of diketone 1
and compared it with inhibition by galvinoxyl. The re-
sults given in Table 2 show that diketone 1 is just as
powerful an inhibitor as galvinoxyl.
On the other hand, it was shown that in the particular
case of acidic hydrogermanes, polar additions occur,
leading to a-germylated alcohols [4]. The thermally in-
duced decomposition of the a-halogermylalcohols into
germylene had been previously established [4]. In the case
of highly conjugated carbonyl compounds, SET reactions
were also observed, yielding digermanes and the corre-
sponding alcohols, both characteristic of the SET reac-
tion [4]. In the case of 2,6-diethyl-4,8-dimethyl-1,5-dioxo-
s-hydrindacene, phenyldichlorogermane gave only a
polar nucleophilic addition resulting in the mono a-ger-
mylated alcohol 3 which was characterized but underwent
the expected thermal decomposition [10] (Eq. (3)).
3.2. Reactivity towards hydrogermanes
Organohydrogermanes having a low polarity of the
germanium–hydrogen bond, as in Ph3GeH, for example,
usually react with carbonyl compounds (aldehydes and
ketones) according to a radical mechanism, yielding
alkoxygermanes [4] (Scheme 1).
In the case of highly conjugated carbonyl compounds
having a low laying LUMO (3,5-di-t-butyl-o-quinone 2,
for example), competitive SET reactions take place and
in some case become preponderant [8]. In the case of
2,6-diethyl-4,8-dimethyl-1,5-dioxo-s-hydrindacene, the
triphenylgermane did not give any reaction, even under
drastic conditions (180 ꢁC) and even in the presence of
Table 1
Selected bond lengths and angles for meso 2,6-diethyl-4,8-dimethyl-
1,5-dioxo-s- hydrindacene
Bond
lengths (Aꢁ)
Angles (ꢁ)
C(2)–C(3)
C(4)–O(1)
C(4)–C(5)
C(5)–C(6)
1.402(3)
1.220(2)
1.520(3)
1.539(3)
C(2)–C(1)–C(3)#1
C(2)–C(1)–C(7)
C(1)–C(2)–C(6)
O(1)–C(4)–C(5)
C(3)–C(4)–C(5)
115.20(19)
121.37(18)
126.63(18)
124.8(2)
108.11(17)

A. El Kadib et al. / Inorganica Chimica Acta 357 (2004) 1256–1264
1261
Table 2
Reaction of Ph3GeH with hex-1-ene
T (ꢁC)
Inhibitor 5% molar
Reaction time (h)
% Addition
Ph3GeH + hex-1-ene
100
100
100
6
6
6
97
0
galvinoxyl
diketone 1
0
effects which are able to prevent the nucleophilic attack
by the germanium-centered anion. This SET reaction,
through a transient alkoxygermane, produces a diger-
mane and the corresponding alcohol [11].
In the case of 2,6-diethyl-4,8-dimethyl-1,5-dioxo-s-
hydrindacene, we observed the polar nucleophilic mo-
nogermylation leading to the expected germylketoalco-
hol (Eq. (4)).
ð3Þ
ð4Þ
The participation of a competitive SET reaction can
be excluded from the absence (GC/mass analysis) of
diphenyltetrachlorodigermane and the corresponding
keto-alcohol, which would be expected from such a re-
action [5]. Because digermylation would require higher
temperatures, it was never observed.
Surprisingly, the SET reaction usually observed as
the main one in the case of highly conjugated carbonyl
compounds (fluorenone [11] and quinone [5,11]) did not
occur. Traces of digermanes were observed, but could
not come from the expected SET reaction since, neither
the corresponding ketoalcohol (or diol) nor any radical
or radical ion were detected in an ESR study of the
reaction.
3.3. Reactivity towards organogermyllithium
Organogermyllithiums are source of germylanions
which lead to nucleophilic additions to aldehydes and
ketones [4,11]. A change in the addition mechanism
from nucleophilic to single electron transfer is often
initiated by high conjugation of the substrate and steric
Scheme 2.

1262
A. El Kadib et al. / Inorganica Chimica Acta 357 (2004) 1256–1264
Scheme 3.
As observed in the case of PhCl2GeH, the nucleo-
In the case of highly conjugated carbonyl compounds
like quinones, SET reactions take place, as evident by
the characterization of the transient germylated alk-
oxyradical (A0) and anilinoradical (B) (Fig. 2) [5].
Up to 80 ꢁC we did not observe any reaction between
N-trimethylgermyldimethylamine and 2,6-diethyl-4,8-
dimethyl-1,5-dioxo-s-hydrindacene. Above this temper-
ature, we detected by GC/mass only (Me3Ge)2O and
small amounts of the corresponding ketoenamine 8
(Scheme 4).
philic digermylation requires more drastic conditions.
When the reaction mixture was heated to 80 ꢁC, a more
complicated reaction occurred resulting in the expected
digermylated diol 5 (Scheme 2, step a), but also to the
unexpected bis(triphenylgermyl)oxide, (Ph3Ge)2O. Since
the hydrolysis of Ph3GeLi would lead to Ph3GeH, the
oxidation of the germanium center certainly comes from
the intermediate adduct (Scheme 2, step b). A thermally
initiated decomposition process affecting the intermedi-
ate lithiated adduct by a-elimination of triphenyllithi-
umgermanolate could lead to bis(triphenylgermyl)oxide
with formation of polymers. The formation of triphe-
nylgermanolate as an intermediate was evident in its
reaction (in situ) with Et3GeCl and this last reaction
(Scheme 2, step c) was reproduced independently.
In the case of N-triethylgermyldiphenylamine
Et3GeNPh2, which easily gives SET reactions [5], ESR
spectrometry revealed the transient formation of the
3.4. Reactivity with organogermylamines
Organogermylamines give nucleophilic additions with
carbonyl compounds, leading to unstable adducts, the
decomposition of which has been clearly established
[4,12] (Scheme 3) and are one of the few known routes to
aminals [12–14].
Fig. 2. Transient radicals observed in the addition of N- tri-
ethylgermyldiphenylamine on di-t-butyl-o-quinone [5].
Scheme 4.

A. El Kadib et al. / Inorganica Chimica Acta 357 (2004) 1256–1264
1263
Table 3
Relative scale HOMO-LUMO in the case of diketone 1, 1* (excited state of the diketone), quinone 2 and Ph3GeH (PM3 calculation)
Ph3GeH
1*
LUMO (eV)
HOMO (eV)
)0.37
)9.54
)1.35
)9.84
)1.24
)9.49
)3.19
)7.00
expected Ph2NÅ radical [5] generated in a monoelec-
tronic process. However, after 24 h at 80 ꢁC, the reac-
tion product could not be detected in appreciable
amounts. This result shows that germylamines have,
when compared to quinone [5], an unexpected low
reactivity towards 2,6-diethyl-4,8-dimethyl-1,5-dioxo-s-
hydrindacene in the two alternative nucleophilic addi-
tion or SET reactions.
very unusual reactivity towards organogermanium
compounds. Only nucleophilic additions were observed.
The quasi absence of thermally induced SET reactions is
unexpected. This can be explained by theoretical calcu-
lations and comparisons of the HOMO/LUMO gap
between C@O and germylderivatives in the case of
diketone 1 and quinone 2 (Table 3 ).
These results lead to the following comments:
Therefore, the preceding reactions (with hydrogerm-
anes, germyllithiums and germylamines) show that 2,6-
• Among the reactives (Table 3), diketone 1 presents a
higher LUMO to the electron coming from Ph3GeH,
therefore a less favorable transition.
diethyl-4,8-dimethyl-1,5-dioxo-s-hydrindacene has
a
Scheme 5.

1264
A. El Kadib et al. / Inorganica Chimica Acta 357 (2004) 1256–1264
• If one considers the excited state 1* of the diketone
(s* excited singlet state), the LUMO is lower than
the starting diketone in the fundamental state. Thus,
the SET reaction should be favored under UV irradi-
ation for the transitions np* and pp* of diketone 1.
These theoretical observations are supported by the
fact that it was also demonstrated that an ethylenic
ketone such as carvone in its excited state (hmÞ reacted
with silylated amines by an SET reaction which had not
occurred in the absence of UV irradiation [15].
These comments prompted us to react triphenylger-
mane with diketone 1 in its excited state by irradiation
either at 254 nm (pp*) or 312 nm (np*). In both cases we
observed (Scheme 5) the products expected from the
SET reaction (Scheme 5, step a) and byproducts result-
ing from side-reaction of triphenylgermylradical and
diketone (Scheme 5, step b). The two final products
observed in the reaction mixture were identified by
chemical and physicochemical means. The germyl-
carbinol 4 was also synthesized by reacting trip-
henylgermyllithium with 1 (see Eq. (4)). The alkoxy-
germane 9 was identified by acid hydrolysis, which led to
Ph3GeCl and the corresponding ketoalcohol 10 (cf.
Scheme 5).
mentary publications CCDC No. 221894 for 1. Copies
of the data can be obtained free of charge on application
to The Director, CCDC, 12 Union Road, Cambridge
CB2 1EZ, UK (Fax: +44 1223 336033; e-mail: deposit@
ccdc.cam.ac.uk or (www: http://www.ccdc.cam.ac.uk).
Acknowledgements
The authors thank the ECOS-CONICYT program
C01 E06 and Proyecto Fondecyt 1020314, Proyecto
Fondecyt 1020525 and Fundacion ANDES (P.A.
scholarship) for partial financial support.
References
[1] M.R. Dahrouch, P. Jara, L. Mendez, Y. Portilla, D. Abril, G.
ꢀ
Alfonso, I. Chavez, J.M. Manriquez, M. Riviere-Baudet, P.
Riviere, A. Castel, J. Rouzaud, H. Gornitzka, Organometallics 20
ꢀ
(2001) 5591.
[2] G.M. Sheldrick, Acta Crystallogr. A46 (1990) 467.
[3] G.M. Sheldrick, sc shelxl-97, Program for Crystal Structure
€
Refinement, University of Gottingen, 1997.
ꢀ
ꢀ
ꢁ
[4] (a) P. Riviere, M. Riviere-Baudet, J. Satge, Germanium, in: G.
Wilkinson, F. Gordon, A. Stone, E.W. Abel (Eds.), Comprehen-
sive Organometallic Chemistry, COMC I, vol. 2, Pergamon Press,
New York, 1982 (Chapter 10);
4. Conclusion
(b) Comprehensive Organometallic Chemistry, COMC II, vol. 2,
1995 (Chapter 5).
ꢀ
ꢀ
Our results demonstrate that, depending on their
polar characters, organogermanium derivatives can re-
act with conjugated carbonyl compounds such as 2,6-
diethyl-4,8-dimethyl-1,5-dioxo-s-hydrindacene through
monoelectronic or polar mechanisms. In the case of
monoelectronic processes (radical or SET), the radical
mechanism strongly depends on the electronic character
of the metallated intermediate carbon-centered radical,
and the SET reaction depends mainly on the HOMO/
LUMO gap for the electron involved.
[5] P. Riviere, M. Riviere-Baudet, A. Castel, Main Group Met.
Chem. 17 (1994) 679.
[6] T.I. Drozdova, E.T. Denisov, Kinet. Catal. 43 (2002) 14.
[7] A.G. Brook, H. Gilman, J. Am. Chem. Soc. 76 (1954) 77.
ꢀ
ꢁ
[8] P. Riviere, A. Castel, J. Satge, D. Guyot, Y.H. Ko, J. Organomet.
Chem. 339 (1988) 51.
ꢀ
ꢁ
[9] P. Riviere, J. Satge, Bull. Soc. Chim. Fr. (1967) 4039.
ꢀ
ꢁ
[10] P. Riviere, J. Satge, J. Organomet. Chem. 49 (1973) 157.
ꢀ
ꢀ
[11] P. Riviere, A. Castel, M. Riviere-Baudet, R3M anions: M ¼ Ge,
Sn, Pb, in: S. Patai, Z. Rappoport, Y. Apeloig (Eds.), The
Chemistry of Organic Germanium, Tin and Lead Compounds,
vol. 2, John Wiley, Chichester, England, 2002, pp. 653–747
(Chapter 11).
ꢀ
[12] M. Riviere-Baudet, Main Group Met. Chem. 18 (1995) 353.
[13] A. Kiennemann, R. Kieffer, J. Organomet. Chem. 60 (1973)
255.
5. Supplementary material
[14] J.E. Manoussakis, J. Inorg. Nucl. Chem. 30 (1968) 3100.
[15] E. Hasegawa, W. Xu, P.S. Mariano, U.C. Yoon, J.U. Kim, J. Am.
Chem. Soc. 110 (1988) 8099.
Crystallography data have been deposited with the
Cambridge Crystallography Data Centre as supple-