Germane vs. digermane formation

Article abstract of DOI:10.1039/c4cc07921c

Oxidative addition reactions of dialkylchalcogenanes R₂E₂ and [Me₂Si(Nt-Bu)₂]Ge 1 yielded bis(alkylchalcogeno)germanes Me₂Si(Nt-Bu)₂Ge(ER)₂ (R = Et, E = S 2, Se 3; R = Me, E = Se

Full text of DOI:10.1039/c4cc07921c

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Germane vs. digermane formation†‡
P. Steiniger, G. Bendt, D. Blaser, C. Wolper and S. Schulz*
¨
¨
Cite this: Chem. Commun., 2014,
50, 15461
Received 7th October 2014,
Accepted 10th October 2014
DOI: 10.1039/c4cc07921c
www.rsc.org/chemcomm
Oxidative addition reactions of dialkylchalcogenanes R2E2 and
[Me2Si(Nt-Bu)2]Ge 1 yielded bis(alkylchalcogeno)germanes Me2Si(Nt-Bu)2-
Ge(ER)2 (R = Et, E = S 2, Se 3; R = Me, E = Se 4) and digermanes [Me2Si(Nt-
Bu)2Ge(EEt)]2 (E = S 5, Se 6). The reaction of 1 with Et2Te2 proceeds with
formation of Me2Si(Nt-Bu)2Ge(TeEt)2 7, which slowly converts into
the Te-bridged complex [Me2Si(Nt-Bu)2GeTe]2 8. 1–6 and 8 were
characterized by single crystal X-ray diffraction.
Germylenes R2Ge, which have singlet ground states with a low-lying
s lone-pair orbital and a higher-lying p orbital,1 have evolved from
exotic reaction intermediates to important reagents in organic
chemistry.2 They were shown to activate a large variety of bonds
including P–Cl,3 O–H,4 Ge–C5 and C–H bonds6 and to react in
[2+1]- and [4+1]-cycloaddition reactions with alkenes and alkynes.2,7
Fig. 1 Solid state structure of 1 as determined at 100(1) K. Non-H-atoms
shown as thermal ellipsoids at 50% probability levels, H atoms omitted for
clarity.
Germylenes tend to dimerize to digermenes Ge2R4 or oligomerize react with monovalent tin (RSnSnR), antimony (RSb), bismuth
into polygermanes, but monomeric R2Ge were kinetically stabilized (RBi) and zinc complexes (R2Zn2) in oxidative addition reac-
by bulky organic ligands.8 Lappert’s [(Me3Si)2CH]2Ge is monomeric tions.22,23 In addition, we report on the solid state structure of
in the gas phase and in solution9,10 and dimeric in the solid state,11 [Me2Si(Nt-Bu)2]Ge 1 (Fig. 1).
while [(Me3Si)3C]2Ge12 and [(Me3Si)2N]2Ge13 are monomeric in
solution and in the solid state. [Me2Si(Nt-Bu)2]Ge 1 is monomeric under an Ar atmosphere at 100 K (1lt) and 230 K (1ht) using an
in solution, while its solid state structure was not reported.14 IR-laser-assisted technique.30 1 crystallizes in the monoclinic
Crystals of 1 were grown in closed quartz glass capillaries
Germylenes react with elemental chalcogenes with the formation space group P21/n with four molecules in the unit cell. The
of complexes containing chalcogen-bridges15 or terminal GeQE shortest Ge–Ge distance is 4.158 Å, so 1 is monomeric in the
bonds16 as well as polychalcogenides.17 In addition, insertion solid state.
reactions in E–C bonds18 and E–E bonds (E = S, Se)19 as well as
Reactions of equimolar amounts of [Me2Si(Nt-Bu)2]Ge 1 and
reactions with R3PQE20 were reported. Our general interest in the Et2E2 (E = S, Se) at 25 1C yielded two products in 2 : 1 (E = S) and
reactivity of complexes with low-valent main group elements21 4 : 1 (E = Se) molar ratios as was shown using 1H and 77Se NMR
prompted us to investigate reactions of [Me2Si(Nt-Bu)2]Ge 1 with spectroscopy (Scheme 1). The relative intensities of the signals due to
dialkyldichalcogenanes R2E2, which were recently shown to the Me2Si(Nt-Bu)2 and the Et groups within each set of resonances in
¨
University of Duisburg-Essen, Universitatsstr. 5-7, S07 S03 C30, 45117 Essen,
Germany. E-mail: stephan.schulz@uni-due.de; Fax: +49 201 1833830;
Tel: +49 201 1834635
† Dedicated to Prof. H. J. Frohn on the occasion of his 70th birthday.
‡ Electronic supplementary information (ESI) available: Experimental details,
NMR spectra of 2–8; bond lengths and angles of 1–6. CCDC 1009920 (1lt),
1009921 (1ht), 1009925 (2), 1009924 (3), 1009923 (4), 1009922 (5), 1019789 (6)
and 1010028 (8). For ESI and crystallographic data in CIF or other electronic
format see DOI: 10.1039/c4cc07921c
Scheme 1 Synthesis of 2–7.
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Table 2 Selected bond lengths [Å] and angles [1] of 5 and 6
5
6
Ge(1)–N(1)
Ge(1)–N(2)
Ge(1)–E(1)
Ge(1)–Ge(2)
N(1)–Ge(1)–N(2)
N(1)–Si(1)–N(2)
1.855(3)
1.845(4)
2.2271(13)
2.4727(6)
82.05(16)
88.69(17)
1.846(3)
1.851(3)
2.3700(5)
2.4921(5)
81.75(13)
88.40(14)
bonds26 but are longer than those of GeQE double bonds (calc:
S 2.05 Å; Se 2.18 Å27).2d,15b The Ge–Se bond lengths in [MeC-
(NCy)2]Ge(SePh)2 (2.3522(5), 2.4009(5) Å) are slightly elongated.19
The Ge–Ge bond lengths (2.4727(6) 5, 2.4921(5) Å 6) are comparable
to those observed in digermanes (Table 2).28
Fig. 2 Solid state structure of 3. Non-H-atoms shown as thermal ellipsoids
at 50% probability levels, H atoms omitted for clarity.
1
the H NMR spectra were 1 : 2 and 1 : 1, respectively. In contrast,
The ratio of the Ge(III) and Ge(IV) species formed in the
reactions with Et2E2 (E = S, Se) depends on the reaction
temperature and the molar ratio of the starting reagents. 2
and 3 were formed in equimolar ratios at 70 1C. 5 was formed in
36% yield together with 2 in the reaction of 1 and Et2S2 in a 2 : 1
molar ratio at À30 1C, while 6 was obtained in less than 25%
yield together with 3. Equimolar amounts of 1 and Et2S2 reacted
at À30 1C to 2 and 5, while the reaction of 1 with 0.5 equivalents
of Et2S2 at 70 1C gave 2 and unreacted 1. The reaction of 5 with
Et2S2 failed to give 2 even after heating to 70 1C for 1 h, hence
proving that 5 is no reaction intermediate in the formation of 2
(Fig. S22, ESI‡) In contrast, 5 was quantitatively converted at
100 1C in solution into 1 and 2 by disproportionation reaction
(Fig. S11, ESI‡).
reactions of 1 with Me2Se2 and Et2Te2 at 25 1C only yielded [Me2Si(Nt-
Bu)2]Ge(SeMe)2 4 and [Me2Si(Nt-Bu)2]Ge(TeEt)2 7. Fractional crystal-
lisation of the reaction mixtures gave [Me2Si(Nt-Bu)2]Ge(EEt)2 (E =
S 2, Se 3), which are the expected products from the insertion
reaction of 1 into the E–E bond, and the digermanes [Me2Si(Nt-
Bu)2]GeEEt2 (E = S 5, Se 6). Attempts to grow single crystals of 7,
which slowly decomposes in solution into [Me2Si(Nt-Bu)2]Ge(m-Te) 8
and TeEt2 (ESI‡), failed.24
Single-crystals of 2–6 were obtained from solutions in hexane
upon storage at À30 1C, whereas 8 was obtained from a solution
of 7 in C6D6 after 72 h (Fig. 2 and 3). The bond lengths and
angles within the SiN2Ge ring in 2–6 are almost identical to those
of 1 (Table 1). The Ge–E bond lengths agree with the calculated
(S 2.24 Å; Se 2.37 Å)25 and experimental values for Ge–E single
The formation of digermanes 5 and 6 is without precedence
1
in germylene chemistry. H NMR spectroscopy studies on the
reactions of 1 with isolated 2 and 3 did not show the formation
of 5 and 6, hence excluding the formation of 5 and 6 by
insertion of the germylene [Me2Si(Nt-Bu)2]Ge 1 into the Ge–E
bond of initially formed 2 and 3. Since digermenes R2GeQGeR2
are known to react with water, alcohols, carboxylic acids, CCl4,
CHCl3 or HN3 in a 1,2 fashion with the formation of the
corresponding digermanes,29 1H NMR spectra were recorded at
À60 1C and +60 1C to investigate whether 1 formed a temperature-
dependent germylene–digermene equilibrium in solution.
However, only a single set of resonances was observed. In
addition, reactions of 1 with 2-methylbutadiene, a trapping
agent for transient and stable germylenes and digermenes,31 at
25 1C and À60 1C only yielded the germylene products (germa-
cyclopentene) as was reported previously,32 whereas no sign of
the digermane reaction products was observed. A possible
explanation for the formation of 5 and 6 is the presence of a
loosely bound dimer in solution, held together by weak dispersion
forces. Computational studies are currently being performed in
order to address this hypothesis.
Fig. 3 Solid state structure of
H-atoms shown as thermal ellipsoids at 50% probability levels, H atoms
omitted for clarity.
6 (2 independent molecules). Non-
Table 1 Selected bond lengths [Å] and angles [1] of 1–4
1ltb
2
3
4a
Ge(1)–N(1)
Ge(1)–N(2)
Ge(1)–E(1)
1.8574(13)
1.8584(13)
—
1.8400(7)
1.8410(7)
2.2072(2)
2.2070(2)
82.93(3)
101.15(1)
88.70(3)
1.8444(19)
1.8411(18)
2.3355(4)
2.3371(4)
82.74(8)
102.05(2)
88.80(9)
1.8451(9)
1.8451(9)
2.3439(2)
2.3439(2)
82.89(6)
102.53(1)
89.00(6)
Oxidative addition reactions of dichalcogenanes to germylene
1 at elevated temperature yielded the expected Ge(IV) species,
whereas the reactions at low temperatures proceeded with
the predominant formation of digermanes 5 and 6, in which
the Ge atoms adopted the formal oxidation state of +III. These
findings indicate that 1 forms a loosely bound dimer in
solution.
Ge(1)–E(2)
—
81.33(6)
—
N(1)–Ge(1)–N(2)
E(1)–Ge(1)–E(2)
N(1)–Si(1)–N(2)
88.82(6)
a
Special position. Equal values are symmetry equivalent and labeling
b
may differ. Structural parameters of the ‘‘ht’’ version of 1 are almost
identical (ESI).
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