Reaction of H2 or NH3 with Ge and Sn Molecules
A R T I C L E S
°C. 1H NMR (C7D8): δ 1.83 (s, 12H, o-CH3), 2.26 (s, 6H, p-CH3),
4.61 (s, 1H, Ge-H), 6.68 (d, 2H, m-C6H3), 6.82 (s, 4H, m-Mes),
6.97 (t, 1H, p-C6H3). 13C{1H} NMR (C7D8): δ 21.4 (p-CH3), 21.8
(o-CH3), 128.6, 129.1, 129.5, 136.1, 136.3, 136.4, 141.5, 148.9
(ArC). IR (Nujol): ν (Ge-H): 2113, 1731.
described. Bertrand and his group showed that stable carbenes
could react, not only with H2 but also with NH3, to afford N-H
bond inserted products as shown by eq 1. Experimental and
theoretical work showed that the carbon substituents exerted a
large effect via control of the carbene singlet-triplet energy
gap, and when this gap exceeded ca. 50 kcal mol-1 the reaction
was prevented.3
Ar# GeH(NH2) (2). To a deep purple solution of GeAr# 15 (0.20
2
2
g, 0.29 mmol) in toluene (50 mL), cooled to ca. -78 °C, were
added several drops of liquid ammonia. The solution immediately
became pale yellow and was stirred for a further 30 min. Warming
slowly to room temperature afforded a colorless solution which
was concentrated to 30 mL to give colorless crystals of 2. Yield:
1
75%. Mp: 208 °C. H NMR (C7D8): δ -0.37 (s, 2H, NH2), 1.79
(s, 12H, o-CH3), 1.93 (s, 12H, o-CH3), 2.25 (s, 12H, p-CH3), 5.47
(s, 1H, Ge-H), 6.68 (d, 4H, m-C6H3), 6.72 (s, 4H, m-Mes), 6.76
(s, 4H, m-Mes), 7.00 (t, 2H, p-C6H3).13C{1H} δ 21.8 (p-CH3), 22.8
(o-CH3), 22.9 (o-CH3), 149.3, 141.9, 140.1, 137.7, 137.5, 137.1,
131.2 (ArC), signal of i-C6H3 was not observed. IR (Nujol): V
We showed recently that tin(II) carbene analogue, the diaryl-
stannylene SnAr′2, reacted with H2, D2, or NH3 to give {Ar′Sn(µ-
H)}2 (6), {Ar′Sn(µ-D)}2 (7), or {Ar′Sn(µ-NH2)}2 (8) with arene
elimination to give exclusively Sn(II) products (eq 2).5
(Ge-H): 2110 cm-1; V (NH2, weak): 3397, 3323 cm-1
.
Ar′2GeH(NH2) (3). A deep blue solution of GeAr′216 (0.4 g, 0.46
mmol) in toluene (60 mL) was cooled to ca. -78 °C, and several
drops of liquid ammonia were added. The solution immediately
became pale yellow. Warming slowly to room temperature afforded
a colorless solution which was concentrated to ca. 30 mL to give
This reaction differed from that of the carbene in eq 1 where no
elimination was observed. It was proposed that it proceeded via
the tetravalent intermediate Ar′2Sn(H)X (X ) H or NH2) which
eliminated Ar′H presumably because of the steric pressure of the
two large Ar′ substituents. We have now investigated this hypoth-
esis by changing the substituent size to relieve steric pressure. In
addition we extended these studies to the lighter element germa-
nium derivatives. We show that, in contrast to those of tin, the
reactions of H2 or NH3 with GeAr#2 (Ar# ) C6H3-2,6-(C6H2-2,4,6-
Me3)2) and GeAr′2 (Ar′) C6H3-2,6-(C6H3-2,6-iPr2)2) afford tet-
ravalent products. For GeAr#2, the Ge(IV) species Ar#2GeH2 (1)
or Ar#2Ge(H)NH2 (2) were obtained in high yield with no arene
elimination. With the more crowded GeAr′2, reaction with NH3
gave the analogous Ge(IV) amido hydride Ar′2Ge(H)NH2 (3),
whereas the Ge(IV) species Ar′GeH3 (4) was obtained upon
reaction with H2. The reactions of the less crowded SnAr#2 with
NH3 also afforded the Sn(II) arene eliminated product {Ar#Sn(µ-
NH2)}2 (5) whereas no reaction was observed between SnAr#2 and
H2. The very different results obtained for the germanium and tin
reactions show that steric effects are of secondary importance in
comparison to the electronic and bond strength differences between
these two elements.
1
colorless crystals of 3. Yield: 70%. Mp: 285 °C. H NMR (C6D6)
3
δ -0.37 (s, 2H, NH2), 0.78 (d, 6H, JHH ) 6.6 Hz, CH(CH3)2),
3
3
0.90 (d, 6H, JHH ) 6.6 Hz, CH(CH3)2), 0.93 (d, 6H, JHH ) 6.6
3
Hz, CH(CH3)2), 1.17 (d, 6H, JHH ) 6.6 Hz, CH(CH3)2), 1.20 (d,
3
3
6H, JHH ) 6.6 Hz, CH(CH3)2), 1.22 (d, 6H, JHH ) 6.6 Hz,
3
CH(CH3)2), 1.27 (d, 6H, JHH ) 6.6 Hz, CH(CH3)2), 1.36 (d, 6H,
3JHH ) 6.6 Hz, CH(CH3)2), 2.58 (septets, 2H, CH(CH3)2), 2.83
(septets, 2H, CH(CH3)2), 3.26 (septets, 2H, CH(CH3)2), 3.39
(septets, 2H, CH(CH3)2), 5.84 (s, 1H, Ge-H), 6.35(d, m-C6H3),
6.59 (d, m-C6H3), 6.71 (t, p-C6H3), 6.82 (t, p-C6H3), 6.87-7.37
(Dipp-H). 13C{1H} δ 23.9 (CH(CH3)2), 26.3 (CH(CH3)2), 30.7
(CH(CH3)2), 147.6, 146.5, 141.5, 139.3, 127.4, 127.0, 124.7, 124.4,
123.8 (ArC). IR (Nujol): V (Ge-H): 2080 cm-1; V (NH2, weak):
3383, 3313 cm-1
.
16
Ar′GeH3 (4). A deep blue solution of GeAr′2 (0.30 g, 0.35
mmol) in toluene (50 mL) was stirred at 65 °C for 2 h under a H2
atmosphere to give a pale yellow solution. The solvent was removed
under reduced pressure to afford a white powder which was
characterized by 1H NMR spectroscopy. 1H NMR (C6D6): Ar′GeH3:
3
3
δ 1.08 (d, 12H, JHH ) 6.6 Hz, CH(CH3)2), 1.25 (d, 12H, JHH
)
6.6 Hz, CH(CH3)2), 2.82 (septets, 4H, CH(CH3)2), 3.58 (s, 3H,
Ge-H), 6.89-7.31 (Ar-H). Ar′H: δ 1.11 (d, 12H, 3JHH ) 6.6 Hz,
CH(CH3)2), 1.14 (d, 12H, 3JHH ) 6.6 Hz, CH(CH3)2), 2.90 (septets,
4H, CH(CH3)2), 6.89 (s, 1-C6H4), 7.09 (d, 2H, 3-C6H4), 7.10 (d,
3
3
4H, JHH ) 6.6 Hz, m-C6H3-Pri2)), 7.22 (t, 1H, JHH ) 7.5 Hz,
Experiment Section
4-C6H4), 7.31 (t, 2H,3JHH ) 6.6 Hz, p-C6H3-Pri2).
General Procedures. All reactions were performed with the use
of modified Schlenk techniques under anaerobic and anhydrous
conditions. H2 gas was purchased from commercial sources and
was dried over a P2O5 column. Liquid NH3 was dried over sodium.
1H and 13C{1H} NMR spectra were obtained on a Varian Mercury
300 MHz spectrometer (75.5 MHz, respectively) and referenced
internally to residual protio benzene or toluene in C6D6 or C7D8
solvent. Solution 119Sn NMR spectra were recorded on a Varian
Inova 600 MHz spectrometer (224.2 MHz) and referenced exter-
[Ar#Sn(µ-NH2)2]2 (5). To a deep purple solution of SnAr# 15 (0.2
2
g, 0.27 mmol) in toluene (40 mL), cooled to ca. -78 °C, were
added several drops of liquid ammonia. The solution immediately
became pale yellow and was stirred for a further 30 min. Warming
slowly to room temperature afforded a pale yellow solution which
was concentrated to 30 mL to give colorless crystals of 5. Yield:
1
60%. Mp: 176 °C. H NMR (C7D8): δ 0.93 (s, 2H, NH2), 1.91 (s,
6H, p-CH3), 1.97 (s, 12H, o-CH3), 6.62 (s, 4H, m-Mes), 6.75 (d,
2H, m-C6H3), 7.08 (t, 1H, p-C6H3). 13C{1H} NMR(C7D8): δ 22.1
(p-CH3), 21.8 (o-CH3), 148.5, 142.7, 141.6, 140.2, 136.9, 136.8,
136.4(ArC), signal of i-C6H3 was not observed. 119Sn{1H}: 313.
nally to neat SnBun . Infrared spectra were recorded as Nujol mulls
4
between CsI plates using a Perkin-Elmer 1430 instrument. Melting
points were measured in sealed glass capillaries under nitrogen by
using a Mel-Temp II apparatus and are uncorrected.
IR (Nujol): V (NH2, weak): 3358, 3270 cm-1
.
16
[Ar′Sn(µ-H)]2 (6). A solution of SnAr′2 (1.15 g, 1.26 mmol)
in toluene (50 mL) was stirred at 65° for 2 h under a H2 atmosphere
to give a green solution. The mixture was concentrated to ca. 10
mL under vacuum which afforded orange crystals of 6 upon cooling
to ca. -16°. Yield: 39%. 1H NMR (C6D6): 0.93 (d, 6H, 3JHH ) 6.6
Ar# GeH2 (1). A deep purple solution of GeAr# 15 (0.30 g, 0.43
2
2
mmol) in toluene (50 mL) was stirred at 65 °C for 2 h under a H2
atmosphere to give a light purple solution. The mixture was
concentrated to ca. 10 mL under reduced pressure to afford colorless
crystals of 1 upon cooling to ca. -16 °C. Yield: 66%. Mp: 265
3
Hz, CH(CH3)2, 1.02 (d, 6H, JHH ) 6.6 Hz, CH(CH3)2), 1.04 (d,
(15) Simons, R. S.; Pu, L.; Olmstead, M. M.; Power, P. P. Organometallics
1997, 16, 1920.
(16) Spikes, G. H.; Peng, Y.; Fettinger, J. C.; Power, P. P. Z. Anorg. Allg.
Chem. 2006, 632, 1005.
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J. AM. CHEM. SOC. VOL. 131, NO. 44, 2009 16273