Synthesis and structural characterization of a series of dimeric metal(II) Imido complexes {M(μ-NAr#)}2 [M = Ge, Sn, Pb; Ar # = C6H3-2,6-(C6H 2-2,4,6-Me3)2] and the related monomeric primary amido derivatives M{N(H)Ar#}2 (M = Ge, Sn, Pb)

Article abstract of DOI:10.1021/ic100831c

The solvent-free reaction of M{N(SiMe₃)₂}₂ (M = Ge, Sn, or Pb) with the sterically encumbered primary amine 2,6-dimesitylaniline Ar^#NH₂ [Ar^# = C ₆H₃-2,6(C₆H₂-2,4,6-Me ₃)₂] at ca. 165-175 °C afforded the highly colored imido dimers {M(μ-NAr^#)}₂, where M = Ge (1), Sn (2), or Pb (3), with disilylamine elimination. The compounds were characterized by single-crystal X-ray crystallography and heteronuclear NMR spectroscopy. The structures of 1-3 were very similar and had nonplanar four-membered M ₂N₂ ring cores that are folded along the M -M axis. The nitrogen atoms are planar-coordinated, and the M-N distances are consistent with single bonding. The reaction of M{N(SiMe₃)₂}₂ with Ar^#NH₂ in a 2:1 ratio in solution at lower temperature afforded the relatively stable monomeric primary amido species M{N(H)Ar^#}₂, where M = Ge (4), Sn (5), or Pb (6). Complexes 4-6 displayed V-shaped MN₂ structures, and 5 and 6 revealed close approaches between the metal atom and ipso-carbon atoms of two flanking Mes groups of the terphenyl substituents [Sn^II -C (2.957 A) and Pb^II -C (2.965 A)]. The secondary metal-ligand interactions exerted large effects on their electronic and NMR spectra.

Full text of DOI:10.1021/ic100831c

Inorg. Chem. 2010, 49, 7097–7105 7097
DOI: 10.1021/ic100831c
Synthesis and Structural Characterization of a Series of Dimeric Metal(II) Imido
Complexes {M(μ-NAr#)}2 [M = Ge, Sn, Pb; Ar# = C6H3-2,6-(C6H2-2,4,6-Me3)2] and the
Related Monomeric Primary Amido Derivatives M{N(H)Ar#}2 (M = Ge, Sn, Pb):
Spectroscopic Manifestations of Secondary Metal-Ligand Interactions
William A. Merrill, Robert J. Wright, Corneliu S. Stanciu, Marilyn M. Olmstead, James C. Fettinger, and
Philip P. Power*
Department of Chemistry, One Shields Avenue, University of California, Davis, California 95616
Received May 3, 2010
The solvent-free reaction of M{N(SiMe3)2}2 (M = Ge, Sn, or Pb) with the sterically encumbered primary amine
2,6-dimesitylaniline Ar#NH2 [Ar#=C6H3-2,6(C6H2-2,4,6-Me3)2] at ca. 165-175 °C afforded the highly colored imido
dimers {M(μ-NAr#)}2, where M = Ge (1), Sn (2), or Pb (3), with disilylamine elimination. The compounds were
characterized by single-crystal X-ray crystallography and heteronuclear NMR spectroscopy. The structures of 1-3
were very similar and had nonplanar four-membered M2N2 ring cores that are folded along the M—M axis. The
nitrogen atoms are planar-coordinated, and the M-N distances are consistent with single bonding. The reaction of
M{N(SiMe3)2}2 with Ar#NH2 in a 2:1 ratio in solution at lower temperature afforded the relatively stable monomeric
primary amido species M{N(H)Ar#}2, where M = Ge (4), Sn (5), or Pb (6). Complexes 4-6 displayed V-shaped MN2
structures, and 5 and 6 revealed close approaches between the metal atom and ipso-carbon atoms of two flanking Mes
II
II
˚
˚
groups of the terphenyl substituents [Sn —C (2.957 A) and Pb —C (2.965 A)]. The secondary metal-ligand
interactions exerted large effects on their electronic and NMR spectra.
Scheme 1. Depiction of Two Organoimidogermanium Fragments
Undergoing Association To Form a Dimer
Introduction
The heavier group 14 elements Ge, Sn, and Pb form
numerous oligomeric metal(II) imides of the formula
(MNR)n (M = Ge, Sn, Pb; R = organic or silyl group; n
generally=4) that often display distorted cubane structures.1-4
This behavior is in contrast to the congeneric carbon species
(organic isocyanides), which generally remain in the form
-
þ
of R- N t C : monomers and do not readily associate be-
cause of efficient hybridization, which promotes strong C-N
multiple bonding. Stable heavier group 14 element analogues
of isonitriles are currently unknown because the larger size of
these elements, combined with weaker π bonds, readily
permits association into σ-bonded oligomers, as shown in
Scheme 1, for the dimerization “2RNGe” f {Ge(NR)}2. The
most common heavier group 14 element imido structures are
the tetrameric species {M(μ3-NR)}4 (M=Ge, Sn, or Pb; R=
organic or silyl group), which feature a heterocubane M4N4
arrangement of group 14 element and nitrogen atoms
(Scheme 2).1-9
There also exist heterocubane cores of the formula
LiM3N410, fused double-cubane species of the formula Sn7-
11
(NR)8 as well as the chalcogenide derivative M4N4En
(E=S or Se; n=1, 2, or 3).10,12 Very few lower aggregated
species, which possess the potential for multiple bonding
between the group 14 element p orbital and nitrogen lone
pairs, are known. Rare examples, which are confined to
germanium derivatives,13-15 include the dimeric {Ge(μ-NR)}2
*To whom correspondence should be addressed. E-mail: pppower@
ucdavis.edu.
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r
2010 American Chemical Society
Published on Web 07/02/2010
pubs.acs.org/IC

7098 Inorganic Chemistry, Vol. 49, No. 15, 2010
Merrill et al.
Scheme 2. Aggregation of Heavier Group 14 Element Imides1-15
15
[R=Mes*=C6H2-2,4,6-But313 or R=C6H2-2,4,6-(CF3)3
]
further purification. Ar#NH28 and M{N(SiMe3)2}2 (M=Ge, Sn,
or Pb)19 were prepared according to literature procedures.
All physical measurements were performed under strictly
anaerobic and anhydrous conditions. 1H and 13C NMR spectra
were acquired on a Varian Mercury 300 MHz instrument and
referenced internally to either residual protio benzene or trace
silicone vacuum grease (δ 0.29 ppm in C6D6). 119Sn NMR
spectra were acquired a Bruker 500 MHz (186 MHz) instru-
and the trimeric {Ge(μ-NC6H3-2,6-Pri2)}3.14 Lower aggre-
gates are unknown for either tin or lead. The larger sizes of
these elements16 require exceptionally large substituents to
stabilize low coordination and the lower degree of aggrega-
tion. Herein we report the reaction of the bulky amine Ar#
NH2 [Ar# = C6H3-2,6-(C6H2-2,4,6-Me3)2]17 with M{N-
(SiMe3)2}2 (M = Ge,18,19 Sn,18-20 or Pb18,19) at elevated
temperature. The resulting dimeric imido species are essen-
tially isostructural and possess nonplanar M2N2 core ar-
rangements that are bent along their M---M axes and feature
dihedral angles of ca. 173° for the germanium derivative (1)
and ca. 149° for both the tin (2) and lead (3) derivatives. In
addition, we show that the Ar# group is sufficiently large to
stabilize rare examples of monomeric bis(primary amido)
M{N(H)Ar#}2 species, which are precedented only by the
compounds Ge{N(H)Mes*}213 and Sn{N(H)Mes*}2.21
ment and were referenced externally to SnBun in C6D6 (δ -
4
11.7 ppm).22 207Pb NMR spectra were recorded on a Bruker
500 MHz instrument (ca. 105 MHz) and were externally refer-
enced to Pb(NO3)2 in D2O (δ -2984.4 ppm).23 IR spectra were
recorded as Nujol mulls between CsI plates on a Perkin-Elmer
1430 spectrophotometer. UV-visible spectra were recorded as
dilute hexane solutions in 3.5 mL quartz cuvettes using a HP
8452 diode-array spectrophotometer.12 Melting points were
determined on a Meltemp II apparatus using glass capillaries
sealed with vacuum grease and are uncorrected.
X-ray Crystallography. Crystals of appropriate quality for
X-ray diffraction studies were removed from a Schlenk tube
under a stream of nitrogen and immediately covered with a thin
layer of hydrocarbon oil (Paratone-N). A suitable crystal was
selected, attached to a glass fiber, and quickly placed in a low-
temperature stream of nitrogen [90(2) K].22 Data for all com-
pounds were obtained on a Bruker SMART 1000 or SMART
Experimental Section
General Procedures. All manipulations were performed
with the use of modified Schlenk techniques under N2 or in
a Vacuum Atmospheres drybox under N2. Solvents were dis-
tilled over Na/K and degassed immediately prior to use via
freeze-pump-thaw cycles. Unless otherwise noted, all chemi-
cals were obtained from commercial sources and used without
˚
APEX instrument using Mo KR radiation (λ = 0.710 73 A)
in conjunction with a CCD detector. The collected reflections
were corrected for Lorentz and polarization effects by using
Blessing’s method as incorporated into the program SADABS.24,25
The structures were solved by direct methods and refined with
the SHELXTL, version 6.1, software package.26 Refinement
was by full-matrix least-squares procedures, with all carbon-
bound hydrogen atoms included in calculated positions and
treated as riding atoms. Nitrogen-bound hydrogen atoms were
located in different Fourier maps and refined with N-H dis-
(10) Chivers, T.; Eisler, D. J. Angew. Chem., Int. Ed. 2004, 43, 6686.
(11) Armstrong, D. R.; Benevelli, F.; Bond, A. D.; Feeder, N.; Harron,
E. A.; Hopkins, A. D.; McPartlin, M.; Moncrieff, D.; Saez, D.; Quadrelli,
ꢀ
E. A.; Woods, A. D.; Wright, D. A. Inorg. Chem. 2002, 41, 1492.
(12) Chivers, T.; Clark, T. J.; Krahn, M.; Parvez, M.; Schatte, G. Eur. J.
Inorg. Chem. 2003, 1857.
(13) Hitchcock, P. B.; Lappert, M. F.; Thorne, A. J. J. Chem. Soc., Chem.
Commun. 1990, 1587.
(14) Bartlett, R. A.; Power, P. P. J. Am. Chem. Soc. 1990, 112, 3660.
(15) Ahlemann, J.-T.; Roesky, H. W.; Murugavel, R.; Parisini, E.;
Noltemeyer, M.; Schmidt, H.-G.; Muller, O.; Herbst-Irmer, R.; Markovskii,
L. N.; Shermolovich, Y. G. Chem. Ber. 1997, 130, 1113.
˚
tance restraints of 0.90(2) A in 4-6. A summary of the crystal-
lographic and data collection parameters for 1-6 is given in
Table 1.
(22) Wrackmeyer, B.; Horchler, K. Annu. Rep. NMR Spectrosc. 1989, 22,
249.
(23) Wrackmeyer, B.; Horchler, K.; Zhou, K.; Veith, M. Z. Naturforsch.
1989, 44b, 288.
(24) Hope, H. Prog. Inorg. Chem. 1995, 41, 1.
(25) (a) Blessing, R. H. Acta Crystallogr. 1995, A51, 33–38. (b) Sheldrick,
€
(16) Pyykko, P.; Matsumi, S. Chem.;Eur. J. 2009, 15, 186.
(17) Tilley, T. D.; Gavenonis, J. Organometallics 2000, 21, 5549.
(18) Harris, D. H.; Lappert, M. F. J. Chem. Soc., Chem. Commun. 1974,
895.
(19) 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.
(20) Schaeffer, C. D.; Zuckerman, J. J. J. Am. Chem. Soc. 1974, 98, 7160.
(21) C-etinkaya, B.; Hitchcock, P. B.; Lappert, M. F.; Misra, M. C.;
Thorne, A. J. J. Chem. Soc., Chem. Commun. 1984, 148.
€
G. M. SADABS Siemens Area Detector Absorption Correction; Universitat
€
€
Gottingen: Gottingen, Germany, 2008.
(26) (a) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112.

Article
Inorganic Chemistry, Vol. 49, No. 15, 2010 7099
Table 1. Selected Crystallographic Data for Imido Compounds 1-3
compound
formula
fw
{Ge(μ-NAr#)}2 (1)
Ge2N2C24H25
800.08
{Sn(μ-NAr#)}2 (2)
Sn2N2C24H25
892.28
{Pb(μ-NAr#)}2 (3)
Pb2N2C24H25
1069.28
color, habit
cryst syst
space group
red-orange, block
triclinic
P1
red, rod
monoclinic
P21/n
12.6268(11)
21.1020(19)
16.2797(14)
90
111.470(3)
90
4036.7(6)
4
dark violet, block
monoclinic
P21/n
12.6502(5)
21.1889(8)
16.3957(6)
90
112.2590(10)
90
4067.3(3)
4
˚
a, A
11.1086(12)
11.9616(13)
15.657(2)
93.649(2)
91.118(2)
95.606(2)
2065.6(4)
2
˚
b, A
˚
c, A
R, deg
β, deg
γ, deg
3
˚
V, A
Z
cryst dimens, mm
T, K
0.45 ꢀ 0.38 ꢀ 0.26
0.07 ꢀ 0.04 ꢀ 0.02
0.28 ꢀ 0.32 ꢀ 0.19
90(2)
1.286
1.489
90(2)
1.277
1.273
90(2)
1.746
8.303
dcalc, g/cm3
abs coeff μ, mm-1
θ range, deg
R(int)
obsdreflns [I > 2σ(I)]
data/restraints/param
R1, obsd reflns
wR2, all
1.30-27.48
0.0176
8202
9471/0/481
0.0323
0.0920
1.65-27.48
0.0605
6355
9240/0/481
0.0449
0.1177
1.65-27.54
0.0388
8014
9371/0/481
0.0202
0.0501
compound
formula
fw
Ge{N(H)Ar#}2 (4)
GeN2C48H52
729.51
Sn{N(H)Ar#}2 (5)
SnN2C48H52
775.61
Pb{N(H)Ar#}2 (6)
PbN2C48H52
864.11
color, habit
cryst syst
space group
yellow, parallelepiped
monoclinic
C2/c
19.0482(8)
15.1138(6)
16.7892(7)
90
123.3110(10)
90
4039.3(3)
4
orange, plate
triclinic
P1
yellow, plate
triclinic
P1
˚
a, A
9.7754(9)
11.7530(11)
18.0055(17)
73.768(2)
87.967(2)
88.886(2)
1984.8(3)
2
9.7905(6)
11.8159(8)
17.9985(12)
72.9850(10)
88.1780(10)
89.0400(10)
1973.5(2)
2
˚
b, A
˚
c, A
R, deg
β, deg
γ, deg
3
˚
V, A
Z
cryst dimens, mm
T, K
0.36 ꢀ 0.26 ꢀ 0.16
0.47 ꢀ 0.36 ꢀ 0.17
0.41 ꢀ 0.35 ꢀ 0.17
90(2)
1.200
0.793
90(2)
1.298
0.679
90(2)
1.454
4.310
dcalc, g/cm3
abs coeff μ, mm-1
θ range, deg
R(int)
obsd reflns [I > 2σ(I)]
data/restraints/param
R1, obsd reflns
wR2, all
1.86-30.00
0.0314
4927
5889/2/252
0.0350
0.0975
1.80-30.00
0.0212
9621
11448/2/489
0.0358
0.1017
1.18-27.50
0.0232
8115
9054/2/480
0.0227
0.0568
{Ge(μ-NAr#)}2 (1). Ar#NH2 (0.329 g, 1 mmol) and Ge(N-
(SiMe3)2)2 (0.433 g, 1.1 mmol) were combined in a Schlenk flask
and heated at 165 °C in an oil bath for ca. 10 min with stirring. A
red melt resulted, and the evolution of vapor was observed.
Heating was continued over ca. 5 min, and reduced pressure was
applied to afford an orange-red solid. The volatile HN(SiMe3)2
byproduct and any excess Ge{N(SiMe3)2}2 were removed by
distillation. The residue was extracted with ca. 20 mL hexanes
and filtered over a Celite-padded frit. The filtrate was concen-
trated under reduced pressure to ca. 10 mL, and storage at 7 °C
afforded X-ray-quality crystals of 1 as orange-red blocks. Yield:
0.108 g, 14% based on Ge. Mp: 285 °C. UV-vis [λ, nm (ε, M-1
cm-1)]: 322 (9500), 356 sh (6300), 388 sh (4100), 490 (400). IR
2 as deep-red rod-shaped crystals. Yield: 0.350 g, 38% based on
Sn. Mp: 235-240 °C. UV-vis [λ, nm (ε, M-1 cm-1)]: 348 (8400),
410 (7800), 456 sh (4800). IR (cm-1): ν(N-Sn) 410, 385, 335, 305.
1H NMR (300 MHz, 25 °C, C6D6): δ 2.07 (s, 24H, Mes o-CH3),
2.22 (s, 12H, Mes p-CH3), 6.67 (t, 2H, p-H), 6.84 (s, 8H, Mes-H),
6.96(d, 4H, m-H). 13C{1H} NMR (75MHz, 25 °C, C6D6): δ20.92
(o-CH3), 21.80 (p-CH3), 117.95, 129.39, 129.61, 131.09, 136.97,
137.05 (ArC). 119Sn{1H} NMR (186.49 MHz, C6D6): δ 738.9.
{Pb(μ-NAr#)}2 (3). In a manner similar to that described for
1, Ar#NH2 (0.165 g, 0.50 mmol) and Pb(N(SiMe3)2)2 (0.290 g,
0.55 mmol) were combined in a Schlenk flask and heated to
175 °C in an oil bath with stirring to afford the crude product 3
as a dark-violet solid. Further heating and workup similar to
that described for 1 afforded crystalline 3 as dark-violet blocks
of sufficient quality for X-ray diffraction studies. Yield: 0.100 g
(17% based on Pb). Mp: 261 °C. UV-vis [λ, nm (ε, M-1 cm-1)]:
352 (8400), 490 (14 700). IR (cm-1): ν(N-Pb) 460, 390. 1H
NMR (300 MHz, 25 °C, C6D6): δ 2.12 (s, 24H, Mes o-CH3),
2.18 (s, 12H, Mes p-CH3), 6.38 (t, 2H, p-H), 6.77 (s, 8H,
Mes-H), 6.89 (d, 4H, m-H). 13C{1H} NMR (75 MHz, C6D6):
δ 21.34 (o-CH3), 22.06 (p-CH3), 118.03, 119.46, 129.72, 130.65,
130.86, 137.90, 138.90, 139.82 (ArC). 207Pb{1H} NMR (105.15
MHz, C6D6): δ 5019.
1
(cm-1): ν(N-Ge) 440, 347, 328. H NMR (300 MHz, 25 °C,
C6D6): δ 1.99 (s, 24H, Mes o-CH3), 2.23 (s, 12H, Mes p-CH3),
6.81 (t, 2H, p-H), 6.85 (s, 8H, Mes-H), 6.91 (d, 4H, m-H).
13C{1H} NMR (75 MHz, C6D6): δ 20.19 (o-CH3), 20.50 (p-
CH3), 119.83, 128.45, 130.97, 136.05, 136.17, 137.85, 145.11
(ArC). 73Ge NMR: no signal observed.
{Sn(μ-NAr#)}2 (2). Ar#NH2 (0.329 g, 1.00 mmol) and Sn{N-
(SiMe3)2}2 (0.461 g, 1.05 mmol) were combined in a Schlenk
flask, and reaction and product workup were performed in a
manner similar to that described for 1. This afforded the product

7100 Inorganic Chemistry, Vol. 49, No. 15, 2010
Merrill et al.
Ge{N(H)Ar#}2 (4). To Ar#NH2 (0.861 g, 2 mmol) in toluene
(20 mL) was added dropwise Ge{N(SiMe3)2}2 (0.393 g, 1 mmol)
in toluene (15 mL) at ca. 0 °C. The mixture was stirred and
allowed to warm to roomtemperature over the next 12 h to afford
a pale-yellow solution, which was filtered over a Celite-padded
frit. Concentration of the filtrate under reduced pressure to about
half the original volume and storage at -13 °C afforded yellow
diamond-shaped X-ray-quality crystals of 4. Yield: 0.153 g, 21%
based on Ge. Mp: 198 °C (turns orange). UV-vis [λ, nm (ε, M-1
cm-1)]: 380(13700). IR(cm-1): ν(Ar#N-(H)2) 3480, ν(GeN-H)
3380, 3350, 3320, ν(N-Ge) 450, 395, 280. 1H NMR (300 MHz,
25 °C, C6D6): δ 1.91 (s, 24H, Mes o-CH3), 2.21 (s, 12H, Mes
p-CH3), 2.98 (s, Ar#NH2), 5.46 (s, 2H, Ar#NH-Ge), 6.75 (t, 2H,
p-H), 6.77 (s, 8H, Mes-H), 6.84 (d, 4H, m-H). 13C{1H} NMR
(75 MHz, 25 °C, C6D6): δ 19.91 (o-CH3), 21.19 (p-CH3), 119.22,
128.81, 129.16, 130.97, 136.69, 136.91, 144.17 (ArC).
toluene solution. Attempts to synthesize 4-6 by an ap-
proach similar to that used for 1-3 but with a 2:1 H2NAr#/
M{N(SiMe3)2}2 ratio of reactants resulted in the forma-
tion of the corresponding imido products 1-3. Further-
more, attempts to synthesize 4-6 by the more traditional
salt metathesis route, i.e., 2LiN(H)Ar# with GeCl2(1,4-
dioxane), SnCl2, or PbBr2 in Et2O, resulted in very low
yields of impure products. Thus, the transamination ap-
proach was revisited, and it was found that imide forma-
tion could be suppressed by the slow addition of a solution
of M{N(SiMe3)2}2 to 2 equiv of H2NAr# in a toluene
solution at ca. 0 °C. This afforded crystals of 4-6 from
concentrated toluene solutions at ca. -13 °C. The tem-
perature-related preference for an imido rather than a
bisamido product was further supported by spectroscopic
data. 1H NMR spectroscopy of crude reaction mixtures of
the bisamides 4-6 displayed a signal at δ 2.98, character-
istic of H2NAr#. 1H NMR signals attributable to the imido
products 1-3 were also observed in these reaction mix-
tures. Furthermore, 1H NMR spectroscopy of solutions of
freshly crystallized samples of 4-6 revealed the presence of
small amounts of free H2NAr# (see the Experimental
Section). The appearance of the ν(N-H) stretching ab-
sorption characteristic of the N-H hydrogen atoms of free
H2NAr# at 3480 cm-1 in the IR spectra of Nujol mulls of
crystalline 4-6 also supported the existence of an equilib-
rium between the bisamido compounds 4-6 and the
corresponding imido species 1-3 and H2NAr#, as shown
in eq 2.
Sn{N(H)Ar#}2 (5). To Ar#NH2 (0.861 g, 2 mmol) in toluene
(20 mL) was added dropwise Sn{N(SiMe3)2}2 (0.439 g, 1 mmol)
in 15 mL of toluene at ca. 0 °C. Reaction conditions and pro-
duct workup similar to those described for 4 afforded orange
plates of 5 that were suitable for X-ray diffraction studies. Yield:
0.295 g, 38% based on Sn. Mp: 241 °C (turns red). UV-vis
[λ, nm (ε, M-1 cm-1)]: 420 (5000). IR (cm-1): ν(Ar#N-(H)2)
1
3480, ν(5 N-H) 3380, 3325, ν(N-Sn) 445, 425, 390, 280. H
NMR (300 MHz, 25 °C, C6D6): δ 2.01 (s, 24H, Mes o-CH3), 2.19
(s, 12H, Mes p-CH3), 2.98 (s, Ar#NH2), 4.88 (s, 2H, Ar#NH-
Sn), 6.73 (t, 2H, p-H), 6.82 (s, 8H, Mes-H), 6.88 (d, 4H, m-H).
13C{1H} NMR (75 MHz, 25 °C, C6D6): δ 20.03 (o-CH3), 21.08
(p-CH3), 116.86, 127.16, 128.66, 129.61, 137.19 (ArC). 119Sn-
{1H} NMR (186.49 MHz, 25 °C, C6D6): δ 118.9.
Pb{N(H)Ar#}2 (6). To Ar#NH2 (0.861 g, 2 mmol) in toluene
(20 mL) was added Pb{N(SiMe3)2}2 (0.528 g, 1 mmol) in 40 mL
of toluene at ca. 0 °C. Reaction conditions and product workup
similar to those described for 4 afforded yellow-orange plates of
6 that were suitable for X-ray diffraction studies. Yield: 0.100 g,
11% based on Pb. Mp: 205 °C (dec, turns deep red). UV-vis
[λ, nm (ε, M-1 cm-1)]: 448 (3800). IR (cm-1): ν(Ar#N-(H)2)
3480, ν(N-H) 3430, 3390, 3350, ν(N-Pb) 395. 1H NMR (300
MHz, 25 °C, C6D6): δ 2.05 (s, 24H, Mes o-CH3), 2.16 (s, 12H,
Mes p-CH3), 2.98 (s, Ar#NH2), 5.74 (s, 2H, Ar#NH-Pb), 6.64
(t, 2H, p-H), 6.81 (s, 8H, Mes-H), 6.92 (d, 4H, m-H). 13C{1H}
NMR (75 MHz, 25 °C, C6D6): δ 20.75 (o-CH3), 21.77 (p-CH3),
115.75, 118.50, 129.20, 130.35,137.76, 138.05, 138.90, 152.55
(ArC). 207Pb{1H} NMR (104.92 MHz, 25 °C, C6D6): δ 2871.
2MfNðHÞArg2 f fMðμ-NArÞg2 þ 2H2NAr
ð2Þ
In addition, it was observed that crystalline samples of 4-6
all darken to colors resembling those of the imido species
1-3, respectively, upon heating inside the Meltemp II
apparatus. The facility of this conversion seems to follow
the order Pb (6) > Sn (5) > Ge (4).
1H NMR and IR spectroscopies of crude and “pure”
crystalline samples of the bisamides 4-6 show clearly that
both the imido- and bis(primary amido)metal(II) species
are present in solutions of 4-6. The coexistence of amido
and imido species was also reported for Ge{N(H)Mes*}2
and {Ge(μ-NMes*)}2.13 Equations 3-5 illustrate an alter-
native pathway by which the bisamides 4-6 might trans-
form to free H2NAr# and 1-3 and show how this reaction
might occur through the putative intermediate “{Ar#(H)-
N-M-N(SiMe3)2}2” during the synthetic route to the
imides 1-3. The existence of the heteroleptic
Results and Discussion
Synthesis. At room temperature, it was observed that
both Sn{N(SiMe3)2}2 and Pb{N(SiMe3)2}2 cause rapid
surface darkening of crystalline H2NAr# (the color re-
sembled those later observed for the imidotin and -lead
derivatives 2and 3) when the two solids were placed together
in a Schlenk flask. As a result, it was decided to prepare 1-3
without a solvent by the reaction of M{N(SiMe3)2}2 (M=
Ge, Sn, or Pb) with 2,6-dimesitylaniline H2NAr#, according
to eq 1, while removing the HN(SiMe3)2 byproduct under
reduced pressure. The products could be readily purified by
crystallization from hexane. They were isolated as orange-
red (1), dark-red (2), or dark-purple (3) moderately air- and
moisture-sensitive crystals.
H2NAr þ MfNðSiMe3Þ2g2 /
1
fArðHÞN- M- NðSiMe3Þ2g2 þ HNðSiMe3Þ2 ð3Þ
2
1
fArðHÞN- M- NðSiMe3Þ2g2 / ðMNArÞ2
2
165 - 175 f°C 1
ArNH2 þ MfNðSiMe3Þ2g2
fMðμ-NArÞg2
þ HNðSiMe3Þ2
ð4Þ
ð5Þ
2
þ 2HNðSiMe3Þ2
ð1Þ
fArðHÞN- M- NðSiMe3Þ2g2
þ H2NAr / MfNðHÞArg2 þ HNðSiMe3Þ2
The bis(primary amide) compounds 4-6 were prepared
by the 2:1 reaction of H2NAr# and metal silylamides in a

Article
Inorganic Chemistry, Vol. 49, No. 15, 2010 7101
˚
˚
Figure 1. Thermal ellipsoid (30%) drawings of 1-3. Hydrogen atoms and methyl groups are not shown. Ge(1)---Ge(2) 2.860 A. Ge(1,2)-N(1,2) 1.885 A
˚
˚
˚
˚
(average); metal---centroid interactions range from Ge(1)---X(1) 3.127 A to Ge(2)---X(3) 3.592 A. Sn(1)---Sn(2) 3.193 A. Sn(1,2)-N(1,2) 2.105 A (average);
metal---centroid interactions range from Sn(2)---X(4) 3.159 A to Sn(1)---X(2) 3.286 A. Pb(1)---Pb(2) 3.375 A; N(1,2)-Pb(1,2) 2.211 A (average); metal---
centroid interactions range from Pb(2)---X(4) 3.115 A to Pb(2)---X(3) 3.262 A.
˚
˚
˚
˚
˚
˚
{Ar(H)N-M-N(SiMe3)2}2 in eqs 3-5 is supported by
1H NMR spectroscopy of an orange crystalline product,
which was obtained from a solution reaction mixture of
the known heterocubane {Sn(μ-NC6H3-2,6-Pri2)}4 and
free 2,6-diisopropylaniline under ambient conditions.27,28
In contrast, the bis(primary amide) compounds 4-6 are
much more stable than Sn2{N(H)Dipp}4. It seems prob-
able that the association reactions to afford dimeric struc-
tures occur prior to amine elimination and are inhibited
by the bulkier Ar# substituent at nitrogen. The inhibition
of reactions by the replacement of less bulky organic
substituents with terphenyls was also demonstrated ear-
lier by Protasiewicz and co-workers for chlorine-atom-
transfer equilibria between aryldichlorophosphines and
aryldiphosphenes.19 This influence of steric hindrance on
the reaction rates is also evident from the comparison of
the synthesis of the dimer 1 with that of the trimer{Ge(μ-
NC6H3-2,6-Pri2)}3.7,14 The latter species could be obtai-
ned at a much lower reaction temperature (ca. 60 °C) than
that required for the dimer (ca. 165 °C), most likely
1
Ge{N(SiMe3)2}2 and H2NAr#. A H NMR spectrum of
a C6D6 solution of these crystals revealed a large silyl peak
(δ -0.020), along with 2:1 (Mes-CH3) singlets at δ 2.162
and 2.186, chemical shifts that are different from those of
1 or 4. The integrations of these alkyl and silyl peaks
revealed ca. a 1:1 ratio, consistent with the formulation
Ge{N(H)Ar#}N(SiMe3)2. X-ray diffraction studies re-
vealed them to have a heteroleptic amido-bridged dimeric
structure that was of insufficient quality for publication.
The tendency for an equilibrium to exist between an
-{N(H)R}-bearing heavier group 14 compound and its
related imido derivative was also observed in the recently
reported amido-bridged dimeric species Sn2{N(H)C6H3-
2,6-Pri2}4, which was shown to convert spontaneously to
(27) Merrill, W. A.; Steiner, J.; Betzer, A.; Nowik, I.; Herber, R.; Power,
P. P. Dalton Trans. 2008, 5905.
(28) Smith, R. C.; Shah, S.; Urnezius, E.; Protasiewicz, J. D. J. Am. Chem.
Soc. 2002, 125, 40.

7102 Inorganic Chemistry, Vol. 49, No. 15, 2010
Merrill et al.
˚
Table 2. Selected Interatomic Distances (A) and Angles (deg) for Compounds
1-3a
{Ge(μ-
{Sn(μ-
{Pb(μ-
NAr#)}2 (1)
NAr#)}2 (2)
NAr#)}2 (3)
M(1)-N(1)
M(2)-N(1)
M(1)-N(2)
M(2)-N(2)
N(1)-C(1)
N(1)-C(25)
1.8869(15)
1.8795(15)
1.8906(15)
1.8860(15)
1.396(2)
2.093(4)
2.114(4)
2.113(4)
2.097(4)
1.390(6)
1.388(6)
2.199(3)
2.222(2)
2.219(2)
2.204(3)
1.378(4)
1.377(4)
1.394(2)
N(1)-M(1)-N(2)
N(1)-M(2)-N(2)
M(1)-N(1)-M(2)
M(1)-N(2)-M(2)
81.01(6)
81.32(6)
99.10(7)
98.39(7)
77.66(15)
77.57(14)
98.75(16)
98.66(16)
76.9(4)
76.8(4)
98.50(10)
99.47(10)
M(1)---X(1)
M(1)---X(2)
M(2)---X(3)
M(2)---X(4)
3.127(2)
3.243(2)
3.592(2)
3.310(2)
3.174(5)
3.286(5)
3.254(5)
3.159(5)
3.168(2)
3.250(4)
3.262(4)
3.115(4)
Figure 2. Views of the M2N2 cores in 1-3 (top to bottom) along their
M---Maxes, illustratingthe ca. 7° (1) andca. 31° (2 and 3) foldsawayfrom
coplanar.
X(1)---M(1)---X(2)
X(3)---M(2)---X(4)
dihedral N-M(1)-
N/X---M(1)---X
dihedral N-M(2)-
N/X---M(2)---X
fold angle along the
M---M axis
128.5(2)
131.8(2)
56.6(3)
99.9(5)
104.1(5)
58.5(5)
101.9(4)
105.5(4)
58.9 (4)
49.8(3)
172.4
51.9(5)
148.3
52.9 (4)
148.3
a X represents the centroid of the flanking aryl ring.
because of the lower steric requirements of 2,6-diisopro-
pylaniline in comparison to Ar#NH2 .
Structures. The structures of 1-3 are illustrated in
Figure 1. Selected interatomic distances and angles are
listed in Table 2. The compounds consist of dimeric units
that feature rhomboid M2N2 cores with no imposed sym-
metry. Their M-N distances average 1.886(3) (1), 2.104
˚
(2), and 2.21(1) A (3), which lie within the range of M-N
4
single bonds reported for these elements; cf. 1.849 A in
˚
{Ge(μ-NMes*)}2,13 1.875 A in Ge{N(SiMe3)2}2, 2.03 A
29
˚
˚
29
(avg) in Sn{N(H)Mes*}2,13,21 2.09 A in Sn{N(SiMe3)2}2,
˚
i
27
˚
˚
2.23 A (avg) in Sn{μ-(NC6H3-2,6-Pr 2)}4, and 2.24 A in
Pb{N(SiMe3)2}2.29 The internal ring angles at the metals
average 81.2(2)° (1), 77.62(5)° (2), and 76.9(1)° (3), and
those at the nitrogen are 99.25(14)° (1), 98.71(16)° (2), and
99.00(10)° (3). The distances between the centroids of the
flanking mesityl rings and the group 14 elements (shown
Figure 3. Thermal ellipsoid (30%) drawing of 4. Hydrogen atoms
(except N-H) and disordered component a0toms are not shown. Ge(1)-
0
0
˚
N(1)-N(1) 1.896(2) A; N(1)-Ge(1)-N(1) 88.44°; Ge(1)---X(1)-X(1)
0
˚
3.106(2) A; X(1)---Ge(1)---X(1) 102.1° . Symmetry transformations used
˚
as dashed lines in Figure 2) are all longer than 3.1 A and
1
to generate equivalent atoms (0): -x þ 1, y, -z þ /2.
indicate probable weak dipolar interactions. The nitro-
gen atoms have planar coordination, which is typical for
amido groups bound to heavier group 14 elements4 but
the M2N2 rings are characterized by significant folding
(Figure 2) along the M---M axis. For the germanium
compound 1, however, the folding is relatively small, with
a dihedral angle of 172.4° between the two NM2 planes.
This is in contrast to the essentially planar cores in the less
hindered dimeric {Ge(μ-NMes*)}213 and trimeric {Ge(μ-
NC6H3-2,6-Pri2)}3.7,14 For 2 and 3, the folding is signifi-
cantly greater at 148.3° and is almost equal for both the
tin (2) and lead (3) derivatives (Figure 2). This folding
trend correlates with that seen for the X---M---X (X =
centroid of Mes groups) angles, which are ca. 130° for 1,
ca. 102° for 2, and ca. 103° for 3 (Table 2). This unpre-
cedented folding, with syn disposition of the aryl substit-
uents relative to the imidometal core, seems likely to be
due to the weak flanking aryl---M attraction not possible
in the planar rings stabilized by Mes*13 or C6H3-2,6-Pri2
groups7,13 and is probably increased by the larger size of
tin and lead atoms.
The structures of 4-6 are shown in Figures 3-5, and
selected structural data are given in Table 3. The com-
pounds are monomers with V-shaped MN2 coordination.
The N(H)-M-N(H) angles are each less than 90° and
havethe values88.6(2)° (4), 87.07(8)° (5), and 87.47(9)° (6.)
An acute interligand angle is rare for germanium, tin, or
lead two-coordinate derivatives of monodentate alkyl,
silyl, or amido ligands, with the only example being the
89.6(6)° N-Sn-N angle in Sn{N(H)Mes*}2 (the standard
deviation is large enough to encompass a 90° bending
angle, however).13,21 In contrast, several two-coordinate
(29) Fjeldberg, T.; Hope, H.; Lappert, M. F.; Power, P. P.; Thorne, A. J.
J. Chem. Soc., Chem. Commun. 1983, 639.

Article
Inorganic Chemistry, Vol. 49, No. 15, 2010 7103
a
˚
Table 3. Selected Distances (A) and Angles (deg) for Compounds 4-6
Ge{H(N)Ar#}2 Sn{H(N)Ar#}2 Pb{H(N)Ar#}2
(4)
(5)
(6)
M-N
N-C
1.896(2)
2.103(2)
2.096(2)
1.380(3)
1.381(3)
3.039(2)
2.976(2)
87.07(8)
160.0(2)
82.4(2)
2.205(2)
2.193(2)
1.375(3)
1.367(3)
2.989(2)
2.943(2)
87.47(9)
164.9(2)
83.6(2)
1.384(3)
3.106(2)
M---X
N-M-N
X---M---X
dihedral N-M-
N/X---M---X
88.6(2)
102.1(2)
47.9(3)
a X refers to the centroid of the flanking aryl ring. A prime denotes
atoms generated by the two-fold symmetry (1 - x) operation for the
M = Ge compound 4.
Figure 4. Thermal ellipsoid (30%) drawing of 5, illustrating the coordi-
nation of the tin atom by the nitrogen atoms and centroids X(1) and X(2)
of two flanking mesityl groups. Hydrogen atoms (except N-H) are not
shown, and the positions of the two noninteracting flanking Mes groups
(lower) are indicated only bytheir ipso C(7) andC(31) atoms. Sn(1)-N(1)
2.096 A; Sn(1)-N(2) 2.103 A; Sn(1)---X(1) 3.039 A; Sn(1)---X(2) 2.976 A;
N(1)-Sn(1)-N(2) 87.1°; X(1)---Sn(1)---X(2) 160.0°.
bonds. The structures of 4-6 may be contrasted with the
bridged dimeric structure of the unstable primary amide
Sn2{N(H)C6H3-2,6-Pri2}4;27 4 is characterized by a 2-fold
axis of rotation that bisects the N(1)-Ge(1)-N(1A) bond
angle, whereas the structures of 5 and 6 have no crystal-
lographically required symmetry. The M-N bond lengths
˚
˚
˚
˚
˚
are 1.896(2) (4), 2.103(2) (5), and 2.205(2) A (6), which
are similar to those observed in 1-3. Compounds 4-6
also exhibit M---X interactions to centroids of two of
the flanking mesityl rings, ranging from 2.943(2) (6) to
˚
3.106(2) A (4). These distances are shorter than those in
1-3 and decrease asthe group isdescended, indicating that
the metal-ring dipolar interactions increase in strength
with increasing atomic number, possibly as a result of the
increasing electropositive character of the metals. The
stronger dipolar (δ-)aryl---(δþ)M interactions, combined
16
˚
with the larger sizes of tin and lead (1.41 and 1.45 A),
Figure 5. Thermal ellipsoid (30%) drawing of 6, illustrating the coordi-
nationofthe lead atom bythe nitrogenatoms and centroids X(1) andX(2)
of two flanking arenes. Hydrogen atoms (except N-H) are not shown,
and the positions of the two noninteracting flanking arenes (lower) are
result in a closer approach of the flanking rings to the
metal, and a wider angle between the two M---X vectors
results. The larger sizes of the tin and lead atoms also
permit these interactions to occur on either side of the
MN2 plane such that the resulting X---M---X angles are
164.9(2)° (6) and 160.0(2)° (5), whereas the smaller size of
germanium imposes a much narrower angle of 95.0(2)° in 4
(Figures 3-5). The dihedral angles between the X---M---X
and N-M-N planes, 83.6(2)° (6), 82.4(2)° (5), and
47.9(3)° (3), show a similar trend (Table 3). These angular
differences also suggest a greater tendency for π-electron
density on the flanking arenes to interact with the empty p
orbital on metal(II) for the heavier, more electropositive
members of the group (Sn or Pb). Aryl---M interactions
have been seen in a variety of other terphenyl-supported
low-coordinate metal or metal-metal-bonded complexes
and most frequently in low-coordinate transition-metal
derivatives.35,36
˚
indicated only by their ipso C(7) and C(31) atoms. Pb(1)-N(1) 2.193 A;
˚
˚
˚
Pb(1)-N(2) 2.205 A; Pb(1)---X(1) 2.989 A; Pb(1)---X(2) 2.943 A; N(1)-
Pb(1)-N(2) 87.5°; X(1)---Pb(1)---X(2) 164.9°.
alkoxo and aryloxo group 14 element derivatives with
acute interligand angles at M have been reported.30-34
Seemingly, for these more electronegative ligands, the
electron density in the bond is concentrated close to the
coordinating ligand atom (i.e., oxygen), thereby reducing
the repulsion between the metal-ligand bonding pairs. By
the same token, the lone pair on metal(II) expands, which
causes closure of the interligand angle below 90° as a result
of electrostatic repulsion. For derivatives of primary amido
ligands, angular closure below 90° is possible because of
the small size of the hydrogen substituent. Compound 4
is unique in this series in that N(H)Ar# substituents are
approximatelysyn withrespecttothe GeN2 plane, whereas
5 and 6 demonstrate an anti configuration of the N-H
Electronic Spectra. The large size of the Ar# substituent
stabilizes the two-coordinate, V-shaped geometries at the
metal atom(s) in compounds 1-6. UV-visible spectra
reveal metal lone pair to empty p orbital (n f p) transi-
tions typical for monomeric amidogermylenes, -stanny-
lenes, and -plumbylenes, respectively.4 The energy of this
HOMO f LUMO transition decreases in the sequence
(30) C-etinkaya, B.; Gumrukcu, I.; Lappert, M. F.; Atwood, J. L.; Rogers,
R. D.; Zaworotko, M. J. J. Am. Chem. Soc. 1980, 102, 2088.
(31) Fjeldberg, T.; Hitchcock, P. B.; Lappert, M. F.; Smith, S. J.; Thorne,
A. J. J. Chem. Soc., Chem. Commun. 1985, 923.
(32) Weinert, C. S.; Fanwick, P. E.; Rothwell, I. P. Dalton Trans. 2002,
2948.
(33) Dickie, D. A.; MacIntosh, I. S.; Ino, D. A.; Hi, Q.; Labeodan, O. A.;
Jennings, M. C.; Schatte, G.; Walsby, C. J.; Clyburne, J. A. C. Can. J. Chem.
2008, 20.
(34) Barnhart, D. M.; Clark, D. L.; Watkin, J. G. Acta Crystallogr. 1994,
C50, 702.
(35) Nguyen, T.; Panda, A.; Olmstead, M. M.; Richards, A. F.; Stender,
M.; Brynda, M.; Power, P. P. J. Am. Chem. Soc. 2005, 127, 8545.
(36) Merrill, W. A.; Brynda, M.; Yeagle, G. J.; Stich, T. A.; De Hont, R.;
Fettinger, J. C.; Reiff, W. M.; Schulz, C. E.; Britt, R. D.; Power, P. P. J. Am.
Chem. Soc. 2009, 131, 12693–12702.

7104 Inorganic Chemistry, Vol. 49, No. 15, 2010
Merrill et al.
directly above and below the MN2 coordination plane
(dihedral N-M-N/X---M---X angle 47.9(3)°, canted ca.
45° from perpendicular) unlike in 5 and 6 (canted ca.
15-20° from perpendicular; Table 2) and so do not
strongly interact with the Ge 4p orbital. This is also
refelected in the longer M---X distances in 4 in comparison
to those in 5 and 6. Thus, the n f p transition in 4 may not
be quenched to the same extent as the corresponding
transitions in 5 and 6.
Heteronuclear NMR Spectroscopy. The 119Sn NMR
spectrum of 2 displays a downfield signal at δ 738.9, which
is consistent with its formulation as a two-coordinate
monomer.22,37 The shift is similar to 776 ppm found for
the well-known monomeric tin(II) amide starting material
Sn{N(SiMe3)2}2.38 The chemical shifts are over 400 ppm
downfield of the δ 315 signal reported for the tetrame-
ric {Sn(μ-NC6H3-2,6-Pri2)}4.27 The latter species features
three-coordinate tin atoms, which causes the upfield shift
relative to 2. However, the shifts of the tetramers are quite
sensitive to the nitrogen substituents so that chemical
shifts in the range 742-797 ppm have been observed for
{Sn(NSiButMe2)}439 and {Sn(NEMe3)}4 (E=Si,40 Ge,41 or
Sn41). In contrast to these data, the 118.9 ppm shift found
for the bisamide 4 is ca. 620 ppm downfield of that for 2.
This suggests a more shielded environment for the tin
˚
nucleus and is consistent with the ca. 0.13 A closer aryl---
Sn approaches (Figure 4 and Table 2) such that the tin may
be regarded as quasi-four-coordinate with consequent
greater electronic shielding. The 207Pb NMR signals found
for the lead derivatives 3 and 6 also appear in a region
typical for divalent amides of that metal42 and displayed a
trend similar to that of their tin counterparts, with chemical
shifts of þ5019 (3) andþ2871 (6) ppm, respectively. Like its
tin counterpart 4, the chemical shift of 6 lies well upfield of
that of 3 most likely because of the greater shielding at the
metal by the flanking aryl rings, where the closest aryl---Pb
distance in 6 (2.943 A; Figure 5) is ca. 0.15 A shorter than
˚
that in the amide 3 (3.115 A). The chemical shift observed
for 4 is similar to the þ2956 ppm reported for the dimeric
compound [Pb{N(Pri)(SiMe2)2N(Pri)}]2,43 which probably
dissociates in solution to monomers featuring two-coordinate
lead. No chemical shifts for imidolead dimers have been
reported, but the þ5019 ppm found for 3 is close to those
observed for monomeric amides of lead.42 For example, a
signal at þ4916 ppm was found for the monomeric Pb{N-
(SiMe3)2}2 starting material used in this work, and a signal
Figure 6. Electronic absorption spectra of ca. 0.1 mM hexane solutions
of 1-3.
˚
˚
Ge > Sn > Pb for both the imido series 1-3 (Figure 6)
and the amides 4-6. However, the imido derivatives are
more intensely colored, and their spectra are more com-
plex than those of the amido counterparts. For example,
the molar absorptivity ε calculated for the principal
absorption observed for the deep-red imidotin compound
2 (λ = 410 nm) is around 7800 M-1 cm-1, whereas the
analogous absorption seen in the bisamidotin 5 (λ=420
nm) gives an ε value of 5000 M-1 cm-1. A more dramatic
difference is observed in the electronic spectra of the deep-
purple imide 3 (λ=490 nm, ε=14 700 M-1 cm-1) and the
pale-yellow amide 6 (λ=448 nm, ε=3800 M-1 cm-1). The
less intense absorptions in 5 and 6 in comparison to 2 and
3 may also be due to the partial quenching of the n f p
transition by the stronger metal---arene interactions. As
shown in Figure 6, the centroids of the flanking arenes
interact with M above and below the N-M-N plane and
thus interact directly with the valence 5p or 6p orbitals
involved in the n f p transition.
The pair of germanium compounds 1 and 4 displays a
different intensity pattern from their tin and lead counter-
parts. The intensely red-colored imide 1 features a maxi-
mum at 322 nm (ε = 9500 M-1 cm-1), with less intense
shoulder absorptions at 356 and 388 nm. The yellow amide
4 shows an almost 50% greater ε value of 13 750 M-1 cm-1
for its transition at 380 nm. It is worth noting that the
Ge---flanking ring interactions in 4 are not oriented
at þ4900 ppm was observed for Pb{N(But)(SiMe2)2 N-
(But)}]2.44 It seems clear that both the tin and lead NMR
chemical shifts are very sensitive to relatively weak me-
tal-ligand interactions, and the significant structural dif-
ferences (especially the different secondary metal-ligand
(37) Wrackmeyer, B. Annu. Rep. NMR Spectrosc. 1999, 38, 203.
(38) Wrackmeyer, B. J. Magn. Reson. 1985, 61, 536.
€
(39) Veith, M.; Opsolder, M.; Zimmer, M.; Huch, V. Eur. J. Inorg. Chem.
2000, 1143.
(40) Eichler, J. F.; Just, O.; Rees, W. S. Phophorus, Sulfur, Silicon Relat.
Elem. 2004, 179, 715.
(41) Eichler, J. F.; Just, O.; Rees, W. S. Inorg. Chem. 2006, 45, 6700.
(42) Wrackmeyer, B. Annu. Rep. NMR Spectrosc. 2002, 47, 1.
(43) Wrackmeyer, B.; Stader, C.; Horchler, K.; Zhou, H. Inorg. Chim.
Acta 1990, 176, 205.
(44) Wrackmeyer, B.; Horchler, K.; Stader, C. J. Magn. Reson. 1989, 83,
601.

Article
Inorganic Chemistry, Vol. 49, No. 15, 2010 7105
interactions) between the dimeric imido compounds 1-3
and their monomeric amido counterparts 4-6 are strongly
manifested in their 119Sn and 207Pb NMR experiments, as
well as in their UV-visible spectra.
vary as the group is descended, in large part because of an
increasing attraction (Ge < Sn < Pb) of the flanking aryl π-
electron density on the ligands to the metal. The electron-rich
flanking aryl rings on the ligands are drawn closer to the
coordinatively unsaturated metal atoms in these compounds
in the order Ge < Sn < Pb, and these interactions have a
major effect on their spectral properties.
Conclusions
The imido compounds 1-3 comprise the first homologous
series of dimeric heavier group 14 element imides. They
display a folded M2N2 core not seen in the previously
reported planar {Ge(μ-NAr)}2 structures.13,15 The mono-
meric amides 4-6 also represent an isoleptic series of heavier
group 14 element nitrogen derivatives. Like the series 1-3,
they display notable structural and spectroscopic trends that
Acknowledgment. We thank the National Science
Foundation (Grant CHE-0948417) for financial support.
Supporting Information Available: Crystallographic informa-
tion files (CIFs) for 1-6. This material is available free of charge
via the Internet at http://pubs.acs.org.