Synthesis and characterization of Ge(II), Sn(II), and Pb(II) monoamides with -NH2 ligands

Article abstract of DOI:10.1021/ic048362l

The synthesis and characterization of the first divalent germanium, tin, and lead monoamide derivatives of the parent amide group -NH₂ are presented. They have the general formula (ArMNH₂)₂ (M = Ge, Ar = Ar′ (C₆H₃-2,6-Prⁱ₂) or Ar* (C₆H₃-2,6(O₆H₂-2,4,6- Prⁱ₃)); M = Sn, Ar = Ar*; M = Pb, Ar = Ar*). For germanium and tin, they were obtained by reacting the corresponding terphenyl halides of the group 14 elements with liquid ammonia in diethyl ether. The lead amide derivative (Ar*PbNH₂)₂ was synthesized by reaction of LiNH₂ with Ar*PbBr in diethyl ether. The compounds were characterized by IR and multinuclear NMR spectroscopies and by X-ray crystallography in the case of the (Ar′GeNH₂) ₂ or (Ar*SnNH₂)₂ derivatives. They possess dimeric structures with two -NH₂ groups bridging the germanium and tin centers. For lead, the reaction with ammonia led to isolation of a stable ammine complex of formula Ar*PbBr(NH₃) which was characterized by IR and NMR spectroscopies and by X-ray crystallography. It is the first structural characterization of a divalent lead ammine complex.

Full text of DOI:10.1021/ic048362l

Inorg. Chem. 2005, 44, 2774−2780
Synthesis and Characterization of Ge(II), Sn(II), and Pb(II) Monoamides
with NH2 Ligands
−
Corneliu Stanciu, Shirley S. Hino, Matthias Stender, Anne F. Richards, Marilyn M. Olmstead, and
Philip P. Power*
Department of Chemistry, UniVersity of California, DaVis, One Shields AVenue,
DaVis, California 95616
Received November 18, 2004
The synthesis and characterization of the first divalent germanium, tin, and lead monoamide derivatives of the
parent amide group NH2 are presented. They have the general formula (ArMNH2)2 (M Ge, Ar Ar
(C6H3-2,6-Pri2) or Ar* (C6H3-2,6(C6H2-2,4,6-Pri3)); M
Sn, Ar Ar*; M Pb, Ar Ar*). For germanium and tin,
−
)
)
′
)
)
)
)
they were obtained by reacting the corresponding terphenyl halides of the group 14 elements with liquid ammonia
in diethyl ether. The lead amide derivative (Ar*PbNH2)2 was synthesized by reaction of LiNH2 with Ar*PbBr in
diethyl ether. The compounds were characterized by IR and multinuclear NMR spectroscopies and by X-ray
crystallography in the case of the (Ar
′GeNH2)2 or (Ar*SnNH2)2 derivatives. They possess dimeric structures with
two NH2 groups bridging the germanium and tin centers. For lead, the reaction with ammonia led to isolation of
−
a stable ammine complex of formula Ar*PbBr(NH3) which was characterized by IR and NMR spectroscopies and
by X-ray crystallography. It is the first structural characterization of a divalent lead ammine complex.
Introduction
also a few stable -NH2 derivatives of germanium(IV).5,9,10
These M(IV) compounds were obtained with the use of bulky
coligands which prevent self-association by elimination of
NH3. These results have not been expanded to divalent
derivatives however. There has been considerable recent
interest in the synthesis of stable -NH2 derivatives of the
neighboring group 13 elements,11 as well as stable divalent
group 14 element derivatives of the isoelectronic -OH group,
which were stabilized by bulky bidentate â-diketiminate
ligands.12 Like tetravalent species, the scarcity of divalent
-NH2 derivatives is mainly due to their tendency to condense
with elimination of ammonia. This process is especially
feasible in divalent compounds where the group 14 element
can carry only one other substituent which renders steric
protection more difficult. We now report that the use of very
crowding terphenyl ligands13 enables the synthesis and
stabilization of stable Ge(II), Sn(II), and Pb(II) amides of
Stable low-valent amide derivatives of the heavier group
14 elements have been known for almost 3 decades.1 They
have the general formula M(NR2)2, (M ) Ge, Sn, and Pb)
where the nitrogen substituents can be a variety of bulky
silyl, aryl, or alkyl groups.1-3 To date, however, no examples
of stable divalent group 14 element amides featuring the
parent -NH2 group have been reported. A number of stable
-NH2 derivatives of silicon(IV) are known,4-8 and there are
* To whom correspondence should be addressed. Fax, (international)
+1-530/752-8995; e-mail, pppower@ucdavis.edu.
(1) Harris, D. H.; Lappert, M. F. Chem. Commun. 1974, 895. Schaeffer,
C. D.; Zuckerman, J. J. J. Am. Chem. Soc. 1974, 96, 7160-7162.
Gynane, M. J. S.; Harris, D. H.; Lappert, M. F.; Power, P. P.; Riviere,
P.; Riviere-Baudet, M. J. Chem. Soc., Dalton Trans. 1977, 2004-
2009.
(2) Chorley, R. W.; Hitchcock, P. B.; Lappert, M. F.; Leung, W.-P, Power,
P. P.; Olmstead, M. M. Inorg. Chim. Acta 1992, 198-200, 203-209.
(3) Lappert, M. F.; Power, P. P. J. Chem. Soc., Dalton Trans. 1985, 51-
57.
(4) Siefken, R.; Teichert, M.; Chakravorty, D.; Roesky, H. W. Organo-
metallics 1999, 18, 2321.
(5) Wraage, K.; Schmidt, H.-G.; Noltemeyer, M.; Roesky, H. W. Eur. J.
Inorg. Chem. 1999, 863.
(6) Ruhlandt-Senge, K.; Bartlett, R. A.; Olmstead, M. M.; Power, P. P.
Angew. Chem., Int. Ed. Engl. 1993, 32, 425.
(7) Ackerhans, C.; Bottcher, P.; Muller, P.; Roesky, H. W.; Uson, I.;
Schmidt, H.-G.; Noltemeyer, M. Inorg. Chem. 2001, 40, 3766.
(8) Wraage, K.; Kunzel, A.; Noltemeyer, M.; Schmidt, H.-G.; Roesky,
H. W. Angew. Chem., Int. Ed. Engl. 1995, 34, 2645.
(9) Wraage, K.; Lameyer, L.; Stalke, D.; Roesky, H. W. Angew. Chem.,
Int. Ed. 1999, 38 (4), 522-523.
(10) Riviere-Baudet, M.; Morere, A.; Britten, J. F.; Onyszchuk, M. J.
Organomet. Chem. 1992, 423, C5.
(11) Jancik, V.; Pineda, L.; Pinkas, J.; Roesky, H. W.; Neculai, D.; Neculai,
A. M.; Herbst-Irmer, R. Angew. Chem., Int. Ed. 2004, 43, 2142.
(12) Pineda, L. W.; Jancik, V.; Roesky, H. W.; Neculai, D.; Neculai, A.
M. Angew. Chem., Int. Ed. 2004, 43, 1419.
(13) Twamley, B.; Haubrich, S. T.; Power, P. P. AdV. Organomet. Chem.
1999, 44, 1. Clyburne, J. A. C.; McMullen, N. Coord. Chem. ReV.
2000, 210, 73.
2774 Inorganic Chemistry, Vol. 44, No. 8, 2005
10.1021/ic048362l CCC: $30.25
© 2005 American Chemical Society
Published on Web 03/22/2005

Ge(II), Sn(II), and Pb(II) Monoamides
solvent) ppm. 13C{1H} NMR (75.44 MHz, C6D6, 25 °C): δ ) 23.67
(o-CH(CH3)2), 24.64 (o-CH(CH3)2), 26.45 (p-CH(CH3)2), 31.35
(o-CH(CH3)2), 34.37 (p-CH(CH3)2), 121.64 (m-C6H3), 124.62
(o-C6H3), 130.85 (p-C6H3), 138.36 (i-C6H2-2,4,6-Pri3), 144.69
(p-C6H2-2,4,6-Pri3), 146.52 (m-C6H2-2,4,6-Pri3), 147.99 (o-C6H2-
2,4,6-Pri3), 154.22 (i-C6H2-2,4,6-Pri3) ppm. IR (Nujol): ν ) 3370
and 3300 cm-1 (νNH2, weak).
formula (Ar*MNH2)2 (M ) Ge, Sn, or Pb) or (Ar′GeNH2)2,
where Ar* ) C6H3-2,6(C6H2-2,4,6-Pri3)2 and Ar′ )
C6H3-2,6(C6H3-2,6-Pri2)2. In addition, the isolation and
structural characterization of the lead(II) ammine complex
Ar*PbBr(NH3) are described. This is the first structural
determination of an ammine complex of divalent lead and
only the second example of a structurally characterized
ammine complex of a divalent group 14 element.14
(Ar*SnNH2)2 (3). By following the same general reaction
protocol as that of 1 and 2, we obtained 0.51 g (0.82 mmol, 83%)
of large colorless crystals of 3 from cooling a hexane solution. The
crystals were of X-ray quality and were analyzed by this technique.
Mp ) 88 °C (dec to yellow, became black above 190 °C). Anal.
Calcd for C30H39NSn: C, 67.69, H, 7.88, N, 2.63. Found: C, 67.98;
H, 7.45; N, 2.60. 1H NMR (300 MHz, C6D6, 25 °C): δ ) 0.38 (s,
Experimental Section
General Procedures. All manipulations were carried out with
use of modified Schlenk techniques under an argon atmosphere
or in a Vacuum Atmospheres HE-43 drybox. All solvents
were distilled from Na/K alloy and degassed twice before use.
{Pb(µ-Br)Ar*}2 was prepared according to literature procedures.15
1H and 13C NMR data were recorded on a Varian 300 MHz or
Varian 400 MHz instrument and referenced to the deuterated sol-
vent. The 119Sn NMR spectrum was referenced to a Sn(CH3)4 stand-
ard. The 207Pb NMR spectrum was referenced to Pb(NO3)2 corrected
to PbMe4. Melting points were recorded in glass capillaries under
N2 and are uncorrected. Infrared spectra were recorded as Nujol
mulls between CsI plates on a Perkin-Elmer-1430 spectrometer.
(Ar′GeNH2)2 (1). Ar′GeCl (0.506 g, 1 mmol) was dissolved in
ca. 20 mL of diethyl ether, and the solution was cooled in a dry
ice/acetone bath. An excess of dry ammonia was added via can-
nula at low temperature with rapid stirring. The reaction was
allowed to warm to room temperature overnight, whereupon the
ether was removed under reduced pressure. The residue was
extracted with hexane, filtered through Celite, concentrated to about
half the initial volume of solvent, and placed in a ca. -20 °C freezer
for 3 days. The product 1 was obtained as small, colorless crystals,
and crystals suitable for X-ray crystallography could be grown by
gradual cooling of a toluene solution. Yield: 0.38 g (0.8 mmol,
81%). Mp ) 87-88 °C (dec to yellow solid). Anal. Calcd for
C30H39GeN: C, 74.10; H, 8.09; N, 2.88. Found: C, 74.83; H, 8.18;
N, 2.76. 1H NMR (400 MHz, C6D6, 25 °C): δ ) 0.87 (s, 2H, NH2),
0.98 (d, 3JH-H ) 6.8 Hz, 12H, o-CH(CH3)2), 1.10 (d, 3JH-H ) 7.2
Hz, 12H, o-CH(CH3)2), 2.94 (sept, 3JH-H ) 6.8 Hz, 4H, CH(CH3)2),
6.94 (d, 3JH-H ) 7.6 Hz, 4H, m-C6H3-2,Pri2), 7.00 (d, 3JH-H ) 7.2
Hz, 2H, m-C6H3), 7.09-7.13 (m, 3H, p-C6H3-2,Pri2 and p-C6H3)
ppm. 13C{1H} NMR (100.59 MHz, C6D6, 25 °C): δ ) 23.37
(o-CH(CH3)2), 26.63 (o-CH(CH3)2), 31.05 (o-CH(CH3)2), 123.76
(m-Dipp), 126.19 (p-C6H3), 128.90 (m-C6H3), 129.78 (p-C6H3-2,6-
Pri2), 139.87 (i-C6H3-2,6-Pri2), 144.50 (o-C6H3-2,6-Pri2), 146.36
(o-C6H3), 156.53 (i-C6H3) ppm. IR (Nujol): ν ) 3380 and 3308
cm-1 (νNH2, weak).
3
2H, NH2), 1.11 (d, JH-H ) 6.9 Hz, 12H, o-CH(CH3)2), 1.29 (d,
3JH-H ) 6.6 Hz, 12H, o-CH(CH3)2), 1.36 (d, 3JH-H ) 6.9 Hz, 12H,
3
p-CH(CH3)2), 2.92 (sept, JH-H ) 6.9 Hz, 2H, p-CH(CH3)2), 3.15
3
(sept, JH-H ) 6.9 Hz, 4H, o-CH(CH3)2), 7.16 (s, 4H, m-C6H2-
2,4,6-Pri3), 7.18-7.22 (m, 3H, (m and p) C6H3) ppm. 13C NMR
(75.44 MHz, C6D6, 25 °C): δ ) 23.65 (o-CH(CH3)2), 24.71
(o-CH(CH3)2), 26.57 (p-CH(CH3)2), 31.13 (o-CH(CH3)2), 34.90
(p-CH(CH3)2), 121.30 (m-C6H3), 126.20 (o-C6H3), 130.13 (p-C6H3),
139.20 (i-C6H2-2,4,6-Pri3), 146.64 (m-C6H2-2,4,6-Pri3), 146.96
(o-C6H2-2,4,6-Pri3), 148.22 (p-C6H2-2,4,6-Pri3), 167.65 (i-C6H3)
ppm. 119Sn{1H} NMR (111.8 MHz, C6D6, 25 °C): δ ) 286.04
ppm. IR (Nujol): ν ) 3370 and 3290 cm-1 (νNH2, weak).
15
[Ar*PbBr(NH3)] (4). Orange crystals of {Pb(µ-Br)Ar*}2
(0.684 g, 0.448 mmol) were dissolved in toluene (25 mL) and
cooled to ca. -78 °C with rapid stirring. An excess of ammonia
was condensed into this solution, whereupon the solution became
pale yellow. Stirring was continued for 1 h, and the reaction mixture
was allowed to warm to room temperature overnight. The toluene
was removed under reduced pressure, and the residue was extracted
with hexanes (60 mL) and filtered through Celite. The filtrate was
placed in a ca. -20 °C freezer, whereupon yellow crystals of 4
were obtained upon storage for 2 d. Yield: 0.388 g, 56%. Mp )
94-96 °C (became colorless; at 118-121 °C, the solid melts with
decomposition to a dark orange solid). 1H NMR (400 MHz, C6D6,
3
25 °C): δ ) 1.10 (d, JHH ) 6.8 Hz, 6H, p-CH(CH3)2), 1.18 (d,
3JHH ) 6.8 Hz, 6H, o-CH(CH3)2), 1.26 (s, 3H, NH3), 1.30 (d, 3JHH
3
) 6.8 Hz, 6H, o-CH(CH3)2), 1.39 (d, JHH ) 6.8 Hz, 6H, p-CH-
3
(CH3)2), 2.88 (sept, JHH ) 6.8 Hz, 1H, p-CH(CH3)2), 2.98 (sept,
3
3JHH ) 6.8 Hz, 4H, o-CH(CH3)2), 3.17 (sept, JHH ) 6.8 Hz, 1H,
3
p-CH(CH3)2), 7.13 (s, 4H, m-C6H2-2,4,6-Pri3), 7.31 (t, JHH
)
3
7.6 Hz, 1H, p-C6H3), 7.94 (d, JHH ) 7.6 Hz, 2H, m-C6H3) ppm.
13C{1H} NMR (100.59 MHz, C6D6, 25 °C): δ ) 23.59 (o-CH-
(CH3)2), 24.29 (o-CH(CH3)2), 26.29 (p-CH(CH3)2), 30.64 (o-CH-
(CH3)2), 34.73 (p-CH(CH3)3, 120.60 (m-C6H2-2,4,6-Pri3), 121.16
(o-C6H2-2,4,6-Pri3), 127.63 (p-C6H3), 131.82 (i-C6H2-2,4,6-Pri3),
137.44 (m-C6H3), 141.11 (o-C6H3), 148.26 (p-C6H2-2,4,6-Pri3).
(Ar*GeNH2)2 (2). The same procedure and the same scale as
that employed for 1 afforded 0.43 g (0.75 mmol, 75%) of 2 as
small, colorless crystals which could not be grown large enough
for X-ray diffraction studies. Mp ) 101-102 °C (dec to yellow
solid which turns black above 210 °C). Anal. Calcd for
C36H51GeN: C, 75.80; H, 9.01; N, 2.46. Found: C, 76.1; H, 9.02;
UV-vis (hexane): λmax ) 416.0 nm, ꢀ ) 460 M-1 cm-1
.
(Ar*PbNH2)2 (5). {Pb(µ-Br)Ar*}2 (0.723 g, 0.5 mmol) in diethyl
ether (30 mL) was added dropwise to a suspension of LiNH2 (1
mmol, generated from ammonia and 0.625 mL of a 1.6 M hexane
solution of n-BuLi) in hexane (20 mL) with rapid stirring and
cooling in an ice bath. The resulting off-white mixture was stirred
overnight at room temperature. The solvent was removed under
reduced pressure, and the residue was extracted with hexane (35
mL) and filtered through Celite. Reduction of the solution volume
to incipient cloudiness and storage in a freezer for 2 d afforded the
product 5 as colorless crystals. Despite efforts to grow crystal-
lographic quality crystals, the compound was always obtained as a
microcrystalline powder. In a typical experiment, 0.58 g (0.41
N, 2.36. 1H NMR (300 MHz, C6D6, 25 °C): δ ) 1.06 (d, 3JH-H
)
3
6.3 Hz, 12H, o-CH(CH3)2), 1.13 (d, JH-H ) 6.6 Hz, 12H, o-CH-
(CH3)2), 1.38 (d, 3JH-H ) 6.9 Hz, 12H, p-CH(CH3)2), 1.62 (s, 2H,
3
NH2), 2.96 (sept, JH-H ) 6.9 Hz, 2H, p-CH(CH3)2), 3.12 (sept,
3
3JH-H ) 6.3 Hz, 4H, o-CH(CH3)2), 6.94 (d, JH-H ) 6.9 Hz, 2H,
m-C6H3), 7.01 (s, 4H, m-C6H2-2,4,6-Pri3), 7.15 (m, 1H, p-C6H3 and
(14) Weinert, C. S.; Fanwick, P. E.; Rothwell, I. P. J. Chem. Soc., Dalton
Trans. 2002, 2948.
(15) Pu, L.; Olmstead, M. M.; Power, P. P.; Schiemenz, B. Organometallics
1998, 17, 5602.
Inorganic Chemistry, Vol. 44, No. 8, 2005 2775

Stanciu et al.
Table 1. Selected Crystallographic Data for Compounds 1, 3, and 4
the isopropyl groups that was refined in two sets of atoms with
occupancy 0.75:0.25.
Some details of the data collection and refinement are given in
Tables 1 and 2. Further details are in the Supporting Information.
compound
1‚1.5 toluene
70.5H90Ge2N2 C78H116N2Sn2 C36H51.25Br0.75N0.75Pb0.75
formula weight 1110.63 1319.11 709.85
colorless, plate colorless, rod yellow, block
3‚hexane
4
formula
C
Results and Discussion
color, habit
cryst syst
space group
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
monoclinic
C2/c
43.490(5)
16.840(2)
18.469(2)
90
114.265(2)
90
12331(2)
8
triclinic
P1h
monoclinic
P21/c
12.9533(10)
17.0324(14)
16.5380(13)
90
107.029(3)
90
3488.7(5)
4
Synthesis and Spectroscopy. Two different reaction
routes were employed to obtain the amide products. In the
case of the germanium and tin derivatives, it was sufficient
to treat the terphenylmetal(II) halide with excess ammonia
below room temperature to obtain the amides 1-3, as shown
in eq 1:
9.7531(4)
13.2513(5)
13.7548(5)
92.978(1)
93.222(1)
94.684(1)
1766.1(1)
1
Z
2ArM(II)Cl + excess NH3(l)
T, K
90(3)
90(2)
90(2)
Et2O
cryst dimens, 0.21 × 0.18
0.48 ×
0.23 ×
0.15 × 0.12
1.351
4.516
11081
-78 °C8 (ArM(II)NH2)2 + 2NH4Cl (1)
mm3
× 0.14
0.23 × 0.18
1, M ) Ge, Ar ) Ar′
2, M ) Ge, Ar ) Ar*
3, M ) Sn, Ar ) Ar*
d calcd, g cm-3 1.196
1.240
0.749
6269
5841
µ, mm-1
no. of reflns
no. of obsd
reflns
1.016
11141
7896
9105
For the lead derivative, however, the reaction with ammonia
afforded only the ammine adduct Ar*PbBr(NH3) (4), as
shown in eq 2:
R, obsd reflns 0.0434
wR2, all reflns 0.1270
0.0226
0.0587
0.0397
0.1096
mmol, 82%) of white powder was obtained which was further
characterized by IR and NMR spectroscopies. Mp ) 135-136 °C
(dec to brown). Anal. Calcd for C36H51NPb: C, 61.33; H, 7.30; N,
1.99. Found: C, 62.05; H, 7.99; N, 1.70. 1H NMR (400 MHz, C6D6,
Et2O
Ar*PbBr(NH )
Ar*PbBr + excess NH3(l) -78 °C8
(2)
3
4
3
Lewis base adducts of monomeric divalent group 14 species
are usually confined to derivatives of chelating ligands,
although in recent years isonitrile, ylide, and Arduengo
carbene adducts have been isolated.18 Compound 4 is the
first well-characterized ammine adduct of a Pb(II) species.
The lead amide (Ar*PbNH2)2 analogue of 1-3 was only
obtained upon reaction of Ar*PbBr with LiNH2, as shown
in eq 3:
25 °C): δ ) -0.50 (s, 2H, NH2), 1.10 (d, JH-H ) 6.8 Hz, 12H,
3
o-CH(CH3)2), 1.24 (d, JH-H ) 6.8 Hz, 12H, o-CH(CH3)2), 1.31
3
3
(d, JH-H ) 6.8 Hz, 12H, p-CH(CH3)2), 2.87 (sept, JH-H ) 6.8
Hz, 2H, p-CH(CH3)2), 3.13 (sept, 3JH-H ) 6.8 Hz, 4H, o-CH(CH3)2),
7.13 (s, 4H, m-C6H2-2,4,6-Pri3), 7.26 (t, JH-H ) 7.2 Hz, 1H,
3
p-C6H3), 7.44 (d, 3JH-H ) 7.6 Hz, 2H, m-C6H3) ppm. 13C{1H} NMR
(100.59 MHz, C6D6, 25 °C): δ ) 23.40 (o-CH(CH3)2), 24.60
(o-CH(CH3)2), 26.36 (p-CH(CH3)2), 30.81 (o-CH(CH3)2), 34.83
(p-CH(CH3)2), 120.90 (m-C6H3), 125.29 (o-C6H3), 132.59 (p-C6H3),
139.82 (i-C6H2-2,4,6-Pri3), 146.71 (m-C6H2-2,4,6-Pri3), 148.05
(o-C6H2-2,4,6-Pri3), 148.22 (p-C6H2-2,4,6-Pri3), 224.96 (i-C6H3)
ppm. 207Pb NMR (62.77 MHz, C6D6, 25 °C): δ ) 3209.6 ppm. IR
(Nujol): ν ) 3364 and 3280 cm-1, (νNH2, weak).
Et2O
(Ar*PbNH )
2 2 + 2LiBr (3)
2Ar*PbBr + 2LiNH2 0 °C8
5
The reaction of ammonia with the organometal halide to
afford 1-3 was quite rapid. The initial orange-colored
solutions of the precursors became a pale-yellow color at
low temperature. Upon the addition of an excess of dry
ammonia, the aryl germanium and tin halide solutions
immediately became colorless, and a white precipitate of
ammonium chloride was formed. For the lead compound
4, there was little change in color, and the solution re-
mained clear and yellow even at room temperature. After
workup, X-ray quality crystals of 1, 3, and 4 were obtained
from hexane or toluene. Changes in the reaction condi-
tions or changes of solvent always led to the formation of
the same ammine adduct for lead, and there was no evidence
in the IR (lack of the characteristic split band in the range
X-ray Crystallographic Studies. Crystals of 1, 3, or 4 were
covered with a hydrocarbon oil under a rapid flow of argon,
mounted on a glass fiber attached to a copper pin, and placed in
the N2 cold stream on the diffractometer. X-ray data were collected
on a Bruker SMART 1000 diffractometer at 90(2) K with use of
Mo KR (λ ) 0.710 73 Å) radiation. Absorption corrections were
applied using SADABS.16 The structures were solved with use of
direct methods or the Patterson option in SHELXS and refined by
the full-matrix least-squares procedure in SHELXL.17 All non-
hydrogen atoms were refined anisotropically, while hydrogens were
placed at calculated positions and included in the refinement by
using a riding model. In all cases, ammine and amide H atoms
were located in a difference Fourier map. In the case of 1, H atoms
were fully refined. In 3 and 4, they were kept as riding. The structure
of Ar*PbBr(NH3), 4, suffers from occupational disorder in the atoms
Pb, Br, and NH3. These three moieties were refined with variable
occupacy to 0.768(2) and subsequently fixed at 0.75 occupancy.
The final difference map shows residual density in this region that
could not be modeled. The structure also shows disorder in one of
1
3200-3400 cm-1) or in the H NMR spectrum for the for-
mation of a lead amide by this route. However, the reaction
of Ar*PbBr with LiNH2, according to eq 3, afforded the
amide (Ar*PbNH2)2 (5) in good yield, which was character-
(16) SADABS: Area Detection Absorption Corrections; Bruker AXS Inc.:
Madison, WI, 1996.
(17) SHELXS PC, version 5.03; Bruker AXS Inc.: Madison, WI, 1994.
(18) Kinkhammer, K. W. The Chemistry of Organic Germanium, Tin and
Lead Compounds; Rappoport, Z., Ed.; Wiley: New York, 2002; Vol.
2, Part 1, Chapter 4.
2776 Inorganic Chemistry, Vol. 44, No. 8, 2005

Ge(II), Sn(II), and Pb(II) Monoamides
Table 2. Selected Bond Distances (Å) and Angles (deg) for 1, 3, and 4
a
b
1 (Ar′GeNH2)2
3 (Ar*SnNH2)2
4 Ar*PbBr(NH3)
Ge(1)-N(2)
Ge(1)-N(1)
Ge(1)-C(1)
2.005(3)
2.009(3)
2.033(3)
2.021(3)
2.031(3)
2.047(3)
2.009(3)
2.005(3)
1.411(4)
1.415(4)
79.92(13)
97.86(9)
98.02(9)
99.95(17)
80.01(12)
101.99(12)
99.75(12)
99.99(12)
Sn(1)-N(1)
2.2142(16)
2.2228(17)
2.2375(17)
2.2228(17)
1.411(2)
1.418(3)
1.400(3)
1.399(3)
77.98(7)
2.214(2)
2.223(2)
2.238(2)
2.223(2)
Pb(1)-C(1)
2.368(3)
2.490(4)
2.8037(5)
0.91
1.402(4)
1.406(4)
99.81(13)
97.70(8)
82.21(12)
Sn(1)-N(1)#1
Sn(1)-C(1)
Pb(1)-N(1)
Pb(1)-Br(1)
Ge(2)-N(3)#1
N(1)-Sn(1)#1
C(1)-C(2)qq
N(1)-H(1C)
Ge(2)-N(3)
C(1)-C(6)
Ge(2)-C(31)
C(1)-C(6)
C(1)-C(2)
N(1)-Ge(1)#2
C(2)-C(3)
C(1)-Pb(1)-N(1)
C(1)-Pb(1)-Br(1)
N(1)-Pb(1)-Br(1)
N(2)-Ge(1)#2
C(5)-C(6)
C(1)-C(2)
N(1)-Sn(1)-N(1)#1
N(1)-Sn(1)-C(1)
N(1)#1-Sn(1)-C(1)
Sn(1)-N(1)-Sn(1)#1
C(1)-C(6)
90.67(6)
97.04(6)
102.02(7)
N(2)-Ge(1)-N(1)
N(2)-Ge(1)-C(1)
N(1)-Ge(1)-C(1)
Ge(1)#1-N(1)-Ge(1)
N(3)-Ge(2)-N(3)#2
N(3)-Ge(2)-C(31)
N(3)#2-Ge(2)-C(3)
Ge(2)-N(3)-Ge(2)#2
a Symmetry code: #1 ) -x, y, 0.5 - z; #2 ) 0.5 - x, 1.5 - y, 1 - z. b Symmetry code: #1 ) 1 - x, 2 - y, 1 - z.
ized by IR and 1H, 13C, and 207Pb NMR spectroscopies. The
isolation of the ammine adduct Ar*PbBr(NH3) (4) strongly
suggests that the initial step in the preparation of the
germanium and tin amides 1-3 also involves the formation
of an ammonia complex in which NH3 behaves as a lone
pair donor to the empty p orbital of the metal in accordance
with eq 4.
in the more covalent germanium or tin analogues. In 4, the
1H NMR signal due to complexed ammonia is observed at
1.26 ppm which is almost 2 ppm further downfield than the
-0.50 ppm observed for the amide 5. This downfield shift
is consistent with the incipient ionic character of 4. In the
1H NMR spectra of (Ar*GeNH2)2, (Ar*SnNH2)2, and
(Ar*PbNH2)2, the -NH2 signals are observed at 1.62, 0.38,
and -0.50 ppm, respectively. These shifts are in agreement
with the increase in electropositive character upon descending
the group from Ge to Pb. The 119Sn NMR spectrum of 3
afforded a signal at 286.0 ppm. This signal lies ca. 800 ppm
upfield of the 1196.8 ppm signal observed for the two-
coordinate aryl amide species SnAr*{N(SiMe3)2}.15 The very
large difference between the chemical shifts, which implies
an increase in shielding for 3, can be attributed to the increase
in the coordination number of tin from 2 to 3. While 1H and
13C NMR spectra for molecule 4 were easily obtained, no
207Pb NMR signal could be observed. The difficulty in
detecting this signal could be associated with the large
anisotropies expected for the components of the chemical
shift tensor, or the presence of the quadrupolar nuclei 79Br
and 81Br linked to the lead atom could be a factor in broad-
ening the 207Pb NMR signal. The difficulty associated with
obtaining a 207Pb NMR signal for this complex is con-
sistent with the reports of Eaborn, Smith, and co-workers20
on the organolead chlorides and [Pb(µ-Cl){C(SiMe3)3}]3,
For germanium and tin, the eliminated HCl is immediately
complexed by ammonia to give NH4Cl. Where such an
elimination pathway is unavailable, an ammine complex can
be isolated. This was recently shown by the isolation of
(R)-[Ge{O2C20H10(SiMe2Ph)2-3,3′}(NH3)] which was formed
by the desilylation of the -N(SiMe3) ligand when
Ge{N(SiMe3)2}2 was treated with a bidentate phenol. This
is the only other well-characterized divalent group 14 element
ammine complex.14 The lead(II) ammine complex 4 is quite
stable (mp ) 94-96 °C). It seems probable that HCl
elimination takes place less readily than that for the
germanium and tin analogues due to the greater size of lead
which decreases the steric pressure for elimination and allows
the complex to be isolated. Another factor involves the more
ionic nature of the lead halogen bond, as depicted by eq 5:
{Pb(µ-Cl)C(SiMe3)2(SiMe2OMe)}]2, [Pb(µ-Cl)C(SiMe3Ph)3}2],
as well as our previous work15,21 on the related organolead
bromides of {Pb(µ-Br){C6H3-2,6(C6H2-2,6-Pri2-4-But)}}2,
{Pb(µ-Br)Ar′}2, {Pb(µ-Br)Ar*}2, and Ar*Pb(py)Br species.
In contrast to the difficulties in obtaining 207Pb NMR
spectrum of 4, a C6D6 solution of 5 afforded a broad signal
at 3209.6 ppm (υ1/2 ) 260 Hz). Most organolead(II) 207Pb
NMR data that are currently known concern two-coordinate
diorgano lead or closely related species whose signals are
+
-
Ar*PbBr(NH )
h [Ar*Pb(NH3)] + [Br]
(5)
3
4
The possibility of ionization is supported by a recent re-
port19 that described the formation and structure of the
[Ar*Pb(py)2]+ cation. The incipient [Ar*Pb(NH3)]+[Br]-
character of 4 makes HBr elimination much less likely than
(19) Hino, S.; Brynda, M.; Phillips, A. D.; Power, P. P. Angew. Chem.,
Int. Ed. 2004, 43, 2655-2658.
(20) Eaborn, C.; Hitchcock, P. B.; Smith, J. D.; Soezerli, S. E. Organo-
metallics 1997, 16, 5653.
(21) Pu, L.; Twamley, B.; Power, P. P. Organometallics 2000, 19, 2874.
Inorganic Chemistry, Vol. 44, No. 8, 2005 2777

Stanciu et al.
usually observed in the range 8000-10 000 ppm.22 Thus, a
chemical shift at a considerably higher field for 5 is consistent
with a higher coordination number for lead in the dimer
despite the more electronegative, electron withdrawing -NH2
substituent.
A further aspect of the spectroscopic studies of these
compounds concerns their IR spectra. It is notable that the
four isolated amides display clear, characteristic bands
between 3260 and 3400 cm-1. There are two bands in each
case which is consistent with the presence of an -NH2 group.
On the other hand, the ammonia complex of lead does not
show a band in this range, but it displays a weak band at a
higher frequency of 3492 cm-1, along with others at 1605
and 715 cm-1, which have been tentatively assigned to
stretching, deformation vibrational modes, asymmetric and
symmetric, respectively, of the coordinated NH3 molecule.
Structures. The asymmetric unit of the structure of
(Ar′GeNH2)2, 1, a toluene solvate, is unusual in that two half-
molecules of the dimeric species have different crystal-
lographic symmetry elements: a 2-fold axis passes through
the two N atoms in the case of Ge(1), and a center of
inversion is located in the center of the Ge2N2 rhombus in
the case of Ge(2). Nevertheless, the two distinct dimers are
practically identical, and in both, the Ar′ groups are disposed
trans to the Ge2N2 rhombus. There are no close contacts to
the open coordination site of Ge nor H-bonding contacts to
the amide H atoms. Figure 1a shows the structure of the
dimer with 2-fold crystallographic symmetry, and Figure 1b
shows a different view of the dimer with inversion symmetry.
Structure 3, (Ar*SnNH2)2, a hexane solvate, has crystal-
lographic inversion symmetry as well as no close contacts
to either Sn or the -NH2 groups. A drawing of the dimer is
given in Figure 2. Structure 4, Ar*PbBr(NH3), has no
crystallographically imposed symmetry. Figure 3 shows the
molecule with 50% thermal ellipsoids. In contrast to the Ge
and Sn amides, one of the ammine H atoms shows a weak
intermolecular contact to an inversion-related Br at a distance
of 2.87 Å.
The main feature of the structures 1 and 3 is that they are
both dimers in which the -NH2 groups bridge the germa-
nium and tin atoms symmetrically. The Ge2N2 or Sn2N2 cores
are planar with rhombohedral shapes and with acute angles
near 80° at Ge or Sn and a wider angle of 100° at N. The
hydrogen atoms lie in a plane perpendicular to that formed
by the Ge2N2 or Sn2N2 units. The Ge and Sn centers have
trigonal pyramidal coordination as shown by the sums of
the angles at germanium of 275.8[281.7°] and at tin of
265.7°. The Ge-N and Sn-N bond lengths are near 2.02
and 2.21 Å. These are ca. 0.13 Å longer than terminal Ge-N
and Sn-N bonds in a variety of monomeric divalent species,
for example, the Ge-N bond length of 1.89(1) Å in
Ge{N(SiMe3)2}2 or of 2.09(1) Å in Sn{N(SiMe3)2}2.23 The
observed Ge-N bridging distances in 1 are in good agree-
ment with the reported range 2.022(7)-2.068(4) Å in the
chelated derivatives MeSi(NBut)3Ge2X (X ) Cl, N(SiMe3)2,
Figure 1. Thermal ellipsoid (30%) drawing of two independent molecules
(a and b) of 1. Hydrogens atoms, except those at nitrogen, are not shown
for clarity.
and PPh2)24 in which one of the nitrogen atoms bridges two
germaniums. The bridging Sn-N distances in 3 are signifi-
cantly shorter than the 2.265(4) Å observed for the structure
of Me2NSn(µ-NMe2)2SnNMe2.25 In addition, it is much
shorter than the ca. 2.39 Å observed in the structure of the
weakly dimerized {Sn(NBut)2SiMe2}2.26 The steric effects
of the larger substituents on the bridging nitrogens may
lengthen the bridging bonds in these cases.
The lead-ammonia adduct isolated from the reaction of
Ar*PbBr and NH3(l) is a unique example of a Pb(II) complex
of ammonia. Ammine complexes are well-known for most
transition metals. For main group elements, however, stable
complexes are most numerous for group 13 and earlier
groups, although a number of ammine complexes of silicon,27
germanium,28 and tin29 have been structurally characterized.
Nonetheless, these structures concern tetravalent species, and
(24) Veith, M.; Zimmer, M. Z. Anorg. Allg. Chem. 1996, 622, 1471.
(25) Olmstead, M. M.; Power, P. P. Inorg. Chem. 1984, 23, 413.
(26) Veith, M. Z. Naturforsch. 1978, B33, 7.
(27) For example, [NH4][Si(NH3)F5] and Si(NH3)2F4 in the following
references: Plitzko, C.; Meyer, G. Z. Anorg. Allg. Chem. 1996, 622,
1646. Popov, A. I.; Valkovskii, M. D.; Sukhoverkhov, V.; Chumaevski,
N. A.; Sakhorav, A. V.; Gelmboldt, V. O.; Ennam, A. A. Zh. Neorg.
Khim. 1991, 36, 375.
(22) Wrackmeyer, B. Annu. Rep. NMR Spectrosc. 2002, 47, 1.
(23) Fjelberg, T.; Hope, H.; Lappert, M. F.; Power, P. P.; Thorne, A. J.
Chem. Commun. 1983, 639.
2778 Inorganic Chemistry, Vol. 44, No. 8, 2005

Ge(II), Sn(II), and Pb(II) Monoamides
although no structural details could be given. In addition,
the formation of lead(II) thionitrosyl complex of ammonia
has been described.31 It was examined by X-ray diffraction,
but the position of the ammonia nitrogen could not be
determined with certainty. An X-ray crystallographic analysis
of the structure of 4 clearly shows that the complex is
monomeric with a Pb-N bond distance of 2.490(4) Å, which
is about 0.23 Å longer than that expected for a Pb-N single
bond in a Pb(II) amide such as that in Pb{N(SiMe3)2}2
(Pb-N ) 2.26(2) Å).23 The lead is pyramidally coordinated
(Σ° ) 279.82°) by the C(1) of the aryl, the ammonia nitrogen,
and a bromine. The ammonia nitrogen lone pair is coordi-
nated through the “empty” 6p orbital on lead. This results
in a wider C(2)-C(1)-Pb(1) angle on the side at which NH3
is coordinated. The Pb(1)-C(1) (2.368(3) Å) bond dis-
tance is slightly longer than those seen for {Pb(µ-Br)Ar*}2
(2.329(11) Å)21 and Ar*Pb(py)Br (2.322(4) Å),21 while the
Pb(1)-Br(1) (2.8037(5) Å) distance is ca. 0.1 Å longer than
the 2.7063(6) Å in Ar*Pb(py)Br. The longer bond lengths
and greater pyramidalization of the geometry of the lead
center in 4 (cf. Σ° ) Pb 286.65° in Ar*Pb(py)Br) can be
attributed to the greater Lewis basicity of ammonia. The
Pb(1)-N(1) distance of 2.490(4) Å is marginally (only
3σ) shorter than the Pb-N distance (2.502(4) Å) found in
Ar*Pb(py)Br consistent with its greater Lewis base character.
But this has to be viewed in light of the higher coordination
number at nitrogen in 4 which predicts a longer Pb-N bond
and not the shortening experimentally observed.
Figure 2. Thermal ellipsoid (30%) drawing of 3. Hydrogen atoms, except
those at nitrogen, are not shown for clarity.
A final comment concerns the isoelectronic relationship
between 1-3 and 5 and the corresponding methyl derivatives
which display three different structures for their Ge,32a Sn,32b
and Pb21 derivatives, respectively. The preservation of the
bridged structure in the amides is due undoubtedly to the
superior bridging properties of -NH2 in comparison to
-CH3.
Conclusions
The reactions of bulky low-valent organo group 14 halides
of germanium and tin with liquid ammonia have proven to
be an effective pathway for the synthesis of the first low-
valent group 14 element derivatives of the parent amide
group -NH2. These allowed the first crystal structures of
-NH2 derivatives of germanium(II) and tin(II) to be
determined. An unique ammonia adduct of lead(II) was also
characterized. A simple mechanism has been proposed for
the ammonolysis reaction which accounts for the isolation
of the ammine adduct rather than the amide in the case of
lead. The lead -NH2 derivative could only be obtained by
use of the more reactive lithium amide.
Figure 3. Thermal ellipsoid (30%) drawing of 4. Hydrogen atoms, except
those at nitrogen, are not shown for clarity.
only one divalent ammine derivative of these elements, the
species (R)-[Ge{O2C20H10(SiMe2Ph)2-3,3′}(NH3)], has been
characterized.14 Lead ammine complexes of any kind are
much rarer. An early report30 described the addition of
ammonia to lead(II) nitrate and sulfate and the formation
of monoammonate, triammonate, and hexammonates of
Pb(NO3)2 as well as di- and tetrammonates of Pb(SO4)2
Acknowledgment. We are grateful to the National
Science Foundation for financial support.
(28) For example, [NH4](Ge(NH3)F5] in the following reference: Weber,
W.; Schweda, E. Z. Anorg. Allg. Chem. 1997, 623, 1529.
(29) For example, Sn(ND3)2F4 in the following reference: Woodward, P.;
Vogt, T.; Weber, W.; Schweda, E. J. Solid State Chem. 1998, 138,
350.
(31) Weiss, J.; Neubauer, D. Z. Naturforsch. 1958, B13, 459.
(32) (a) Eichler, B. E.; Power, P. P. Inorg. Chem. 2000, 39, 5444-5449.
(b) Stender, M.; Pu, L.; Power, P. P. Organometallics 2001, 20, 1820-
1824.
(30) Krings, W. Z. Anorg. Allg. Chem. 1929, 181, 306.
Inorganic Chemistry, Vol. 44, No. 8, 2005 2779

Stanciu et al.
Supporting Information Available: CIF files for 1, 3, and 4.
This material is available free of charge via the Internet at
http://pubs.acs.org.
Note Added after ASAP: As a result of a production
error, this manuscript was released ASAP on March 22, 2005,
with a minor text error in the last paragraph of Results and
Discussion. The correct version was published on March 24,
2005.
IC048362L
2780 Inorganic Chemistry, Vol. 44, No. 8, 2005