Synthesis and characterization of the monomeric diaryls M{C6H3-2,6-Mes2}2 (M = Ge, Sn, or Pb; Mes = 2,4,6-Me3C6H2-) and dimeric aryl-metal chlorides [M(Cl){C6H3-2,6-Mes2}]2 (M = Ge or Sn)

Article abstract of DOI:10.1021/om960929l

The reaction of 2 equiv of LiC₆H₃-2,6-Mes₂ (Mes = 2,4,6-Me₃C₆H₂-) with GeCl₂·dioxane, SnCl₂, or PbCl₂ in ether solution has resulted in the isolation of rare examples of monomeric, σ-bonded, diaryl derivatives M{C₆H₃-2,6-Mes₂}₂ (M = Ge (1), Sn (2), or Pb (3)). The compounds 1-3 are thermally stable, purple, crystalline solids with V-shaped geometries and remarkably wide (ca. 114.5°) interligand bond angles. The monoaryl metal chloride derivatives [M(Cl){C₆H₃-2,6-Mes₂}]₂ (M = Ge (4) or Sn (5)) were isolated by treatment of the appropriate dichlorides with either 1 equiv of LiC₆H₃-2,6-Mes₂ or 1 equiv of the diaryls 1 or 2. The orange germanium compound 4 has a dimeric structure in which the monomers are linked by a relatively weak, 2.443(2) A?, Ge-Ge interaction. In sharp contrast, its yellow tin analogue 5 has a dimeric structure in which three-coordinate tin centers are associated by asymmetrically bridging chlorides. The compounds 1-3 constitute a unique, structurally characterized diaryl series for Ge, Sn, and Pb and display evidence of steric crowding that is significantly greater than that observed in previously known σ-bonded diorgano group 14 derivatives. The compounds 4 and 5 are the first fully structurally characterized organometal halide derivatives of Ge or Sn in which the organic ligand is monodentate, purely σ-bonded, and nonchelating.

Full text of DOI:10.1021/om960929l

1920
Organometallics 1997, 16, 1920-1925
Syn th esis a n d Ch a r a cter iza tion of th e Mon om er ic
Dia r yls M{C6H3-2,6-Mes2}2 (M ) Ge, Sn , or P b; Mes )
2,4,6-Me3C6H2-) a n d Dim er ic Ar yl-Meta l Ch lor id es
[M(Cl){C6H3-2,6-Mes2}]2 (M ) Ge or Sn )
Richard S. Simons, Lihung Pu, Marilyn M. Olmstead, and Philip P. Power*
Department of Chemistry, University of California, Davis, California 95616
Received November 1, 1996X
The reaction of 2 equiv of LiC6H3-2,6-Mes2 (Mes ) 2,4,6-Me3C6H2-) with GeCl2‚dioxane,
SnCl2, or PbCl2 in ether solution has resulted in the isolation of rare examples of monomeric,
σ-bonded, diaryl derivatives M{C6H3-2,6-Mes2}2 (M ) Ge (1), Sn (2), or Pb (3)). The
compounds 1-3 are thermally stable, purple, crystalline solids with V-shaped geometries
and remarkably wide (ca. 114.5°) interligand bond angles. The monoaryl metal chloride
derivatives [M(Cl){C6H3-2,6-Mes2}]2 (M ) Ge (4) or Sn (5)) were isolated by treatment of
the appropriate dichlorides with either 1 equiv of LiC6H3-2,6-Mes2 or 1 equiv of the diaryls
1 or 2. The orange germanium compound 4 has a dimeric structure in which the monomers
are linked by a relatively weak, 2.443(2) Å, Ge-Ge interaction. In sharp contrast, its yellow
tin analogue 5 has a dimeric structure in which three-coordinate tin centers are associated
by asymmetrically bridging chlorides. The compounds 1-3 constitute a unique, structurally
characterized diaryl series for Ge, Sn, and Pb and display evidence of steric crowding that
is significantly greater than that observed in previously known σ-bonded diorgano group 14
derivatives. The compounds 4 and 5 are the first fully structurally characterized organometal
halide derivatives of Ge or Sn in which the organic ligand is monodentate, purely σ-bonded,
and nonchelating.
In tr od u ction
the solid state, with Sn-Sn ) 2.8247(6) Å), Pb{Si-
(SiMe3)3}26 (monomer, Si-Pb-Si ) 113.56(10)°), and the
The chemistry of stable, σ-bonded,1 divalent organic
derivatives of the heavier main group 14 elements (i.e.,
MR2, M ) Ge, Sn, or Pb; R ) monodentate alkyl or aryl
group) has been a major research theme in main group
organometallic chemistry for over 20 years. The first
examples of such compounds were the dialkyls M{CH-
(SiMe3)2}2 (M ) Ge, Sn, or Pb) which were reported by
Lappert and co-workers.2 The germanium and tin
derivatives had M-M bonded dimeric structures in the
solid state, but they were shown to be monomeric in
solution. Moreover, their chemistry proved to be con-
sistent with their formulation as bent, singlet :MR2
species that were essentially heavier analogues of
carbenes.3 Subsequent work has extended the range of
monomeric alkyls to include the structurally character-
7
dimeric germanium compounds Ge2[Si{SiMe(i-Pr)2}3]4
and Ge2[Si{Si(i-Pr)3}3]4 (Ge-Ge distances ) 2.267(1) Å
average).7 Parallel work on diaryls has afforded the
well-characterized species {Ge(C6H3-2,6-Et2)2}2,8 {GeMes-
(C6H3-2,6-(i-Pr)2)2}2,9 MMes*2 (M ) Ge10 or Sn;11 Mes*
) 2,4,6-t-Bu3C6H2-), M{C6H2-2,4,6-(CF3)3}2 (M ) Sn12
or Pb13), the solid Sn{C6H3-2,6-(CF3)2}214 (characterized
by Mo¨ssbauer spectroscopy), and the solution species
M(C6H2-2,4,6-(i-Pr)3) [C6H2-2,4,6-{CH(SiMe3)2}3] (M )
Ge,15 Sn,16a or Pb16b). The GeMes*2 species, however,
undergoes a C-H insertion reaction by the germanium
center below room temperature,10 and its tin analogue11
(5) Kira, M.; Yauchibara, R.; Hirano, R.; Kabuto, C.; Sakurai, H. J .
Am. Chem. Soc. 1991, 113, 7783.
(6) Klinkhammer, K. W.; Schwartz, W. Angew. Chem., Int. Ed. Engl.
1995, 34, 1334.
(7) Kira, M.; Iwamoto, T.; Maruyama, T.; Kabuto, C.; Sakurai, H.
Organometallics 1996, 15, 3767.
(8) Snow, J . T.; Murakami, S.; Masamune, S.; Williams, D. J .
Tetrahedron Lett. 1984, 25, 4191.
(9) Batcheller, S. A.; Tsumuraya, T.; Tempkin, O.; Davis, W. M.;
Masamune, S. J . Am. Chem. Soc. 1990, 112, 9394.
(10) (a) Lange, L.; Meyer, B.; du Mont, W.-W. J . Organomet. Chem.
1987, 329, C17. (b) J utzi, P.; Schmidt, H.; Neumann, B.; Stammler,
H.-G. Organometallics 1996, 15, 741.
(11) Weidenbruch, M.; Schlaefke, J .; Scha¨fer, A.; Peters, K.; von
Schnering, H. G.; Marsmann, H. Angew. Chem., Int. Ed. Engl. 1994,
33, 1846.
(12) (a) Gru¨tzmacher, H.; Pritzkow, H.; Edelmann, F. T. Organo-
metallics 1991, 10, 23. (b) Lay, H.; Prtizkow, H.; Gru¨tzmacher, H. J .
Chem. Soc., Chem. Commun. 1992, 260.
(13) Brooker, S.; Buijink, J .-K.; Edelmann, F. T. Organometallics
1991, 10, 25.
4
ized compounds Ge{CH(SiMe3)2}C(SiMe3)3 and SnC-
(SiMe3)2(CH2)2C(SiMe3)2.5 In addition, there are closely
related silyl derivatives [Sn{Si(SiMe3)3}2]2 (dimeric in
6
X Abstract published in Advance ACS Abstracts, April 1, 1997.
(1) Divalent, π-bonded, group 14 organometallic derivatives have
been known for many years and their chemistry has been well explored.
See for example: Rivie`re, P.; Rivie`re-Baudet, M.; Satge´, J . (Chapter
10); Davies, A. G. (Chapter 11); Harrison, P. G. (Chapter 12) In
Comprehensive Organometallic Chemistry; Pergamon: Oxford, 1982;
Vol. 2. J utzi, P. J . Organomet. Chem. 1990, 400, 1.
(2) (a) Lappert, M. F. Inorganic Compounds with Unusual Proper-
ties; Advances in Chemistry Series 150; King, R. B., Ed.; American
Chemical Society: Washington, DC, 1976; p 256. (b) Davidson, P. J .;
Harris, D. H.; Lappert, M. F. J . Chem. Soc., Dalton Trans. 1976, 2268.
(c) Hitchcock, P. B.; Lappert, M. F.; Miles, S. J .; Thorne, A. J . J . Chem.
Soc., Chem. Commun. 1984, 480. (d) Fjeldberg, T.; Haaland, A.;
Schilling, B. E. R.; Lappert, M. F.; Thorne, A. J . J . Chem. Soc., Dalton
Trans. 1986, 1551.
(14) Bigwood, M. P.; Corvan, P. J .; Zuckerman, J . J . J . Am. Chem.
Soc. 1981, 103, 7643.
(15) Tokitoh, N.; Manmaru, K.; Okazaki, R. Organometallics 1994,
13, 167.
(3) Petz, W. Chem. Rev. 1986, 86, 1019.
(4) J utzi, P.; Becker, A.; Stammler, H. G.; Neumann, B. Organo-
metallics 1991, 10, 1647.
(16) (a) Saito, M.; Tokitoh, N.; Okazaki, R. J . Am. Chem. Soc. 1993,
115, 2065. (b) Tokitoh, N.; Kano, N.; Shibata, K.; Okazaki, R.
Organometallics 1995, 14, 3121.
S0276-7333(96)00929-6 CCC: $14.00 © 1997 American Chemical Society

Monomeric Diaryls M{C6H3-2,6-Mes2}2
Organometallics, Vol. 16, No. 9, 1997 1921
was reduced to incipient crystallization and stored in a ca. -20
°C freezer for 30 h to give 1 as purple crystals. Yield: 0.45 g,
43%; dec 185 °C. Anal. Calcd for C48H50Ge: C, 82.42; H, 7.20.
Found: 82.12; H, 7.31. 1H NMR (C6D6): δ 1.88 (s, 12H, o-CH3),
2.20 (s, 6H, p-CH3), 6.71 (d, 2H, J HH ) 7.5 Hz, m-C6H3), 6.76
(s, 4H, m-Mes), 7.05 (tr, 1H, J HH ) 7.89 Hz, p-C6H3). 13C {1H}
NMR (C6D6): δ 21.20 (p-CH3), 22.01 (o-CH3), 129.01 (m-Mes),
129.59 (p-C6H3), 129.83 (m-C6H3), 136.64 (p-Mes), 136.64 (o-
Mes), 139.41 (i-Mes), 145.08 (o-C6H3), 169.58 (i-C6H3). UV-
vis (ethyl ether): λmax 578 nm. IR (Nujol, cm-1): 3070 (sh),
3020 (sh), 2910 (vs), 1720 (w), 1601 (s), 1560 (m), 1550 (m),
1260 (m), 1210 (w), 1170 (w), 1110 (m), 1080 (m), 1030 (m),
850 (s), 800 (s), 770 (w), 740 (m), 660 (w), 610 (vw), 580 (vw),
480 (vw), 370 (vw), 255 (vw), 245 (vw).
is accessible only through use of the amide precursor
Sn{N(SiMe3)2}2.17 The trifluoromethyl aryl derivatives
may owe their stability to intramolecular-F‚‚‚M (M )
Sn or Pb) interactions.12,13
The use of the above range of monodentate alkyl or
aryl ligands has resulted in the isolation of only two
monosubstituted compounds of formula M(X)R (M ) Ge,
Sn, or Pb; X ) halide; R ) monodentate, σ-bound, alkyl
or aryl ligand) to date, i.e., the species Ge(Cl)Mes* which
was described as a monomer in both the solution and
solid phases, although no other structural details were
given.18 The related lithium halide adduct (Me3-
Si)3CGeCl‚LiCl‚3THF19 has also been reported, and
some of its chemistry has been explored although no
structural details have been published.
We are anxious to develop the chemistry of M(X)R
species (where R is a unidentate20 ligand without lone
pairs on the ligating atom) in order to explore the use
of stable M(X)R compounds as precursors to species in
which the MR fragment could behave in a multiply-
bonded fashion. In this paper, we report the facile
synthesis and characterization of the thermally stable
diaryl compounds M{C6H3-2,6-Mes2}2 (M ) Ge (1), Sn
(2), or Pb (3), Mes ) 2,4,6-Me3C6H2-) and the dimeric
monoaryl metal halides [M(Cl){C6H3-2,6-Mes2}]2 (M )
Ge (4) or Sn (5)).
Sn {C6H3-2,6-Mes2}2 (2). Compound 2 was synthesized in
a manner similar to 1 by adding LiC6H3-2,6-Mes2 (1.22 g, 3.8
mmol) in Et2O (20 mL) to SnCl2 (0.36 g, 1.9 mmol) in Et2O (20
mL) at ca. 0 °C with rapid stirring. A similar work-up
procedure afforded 2 as purple crystals. Yield: 0.66 g, 46.5%;
dec 175 °C. Anal. Calcd for C48H50Sn: C, 77.33; H, 6.76.
Found: C, 77.82; H, 6.98. 1H NMR (C6D6): δ 1.90 (s, 12H,
o-CH3), 2.21 (s, 6H, p-CH3), 6.77 (s, 4H, m-Mes), 6.80 (d, 2H,
J HH ) 7.5 Hz, m-C6H3), 7.12 (tr, 1H, J HH ) 7.8 Hz, p-C6H3).
13C {1H} NMR (C6D6): δ 21.21 (p-CH3), 21.61 (o-CH3), 128.68
(p-C6H3), 129.12 (m-Mes), 130.44 (m-C6H3), 136.75 (p-Mes),
136.87 (o-Mes), 139.54 (i-Mes), 147.38 (o-C6H3). 117Sn {1H}
NMR (C6D6): δ 645. 119Sn {1H} NMR: δ 635. UV-vis (ethyl
ether): λmax 553 nm. IR (Nujol, cm-1): 3080 (sh), 3030 (sh),
2920 (vs), 1601 (m), 1260 (m), 1210 (vw), 1175 (vw), 1100 (m),
1020 (m), 850 (m), 800 (m), 730 (m), 570 (vw), 475 (vw), 360,
250 (m).
Exp er im en ta l Section
Gen er a l P r oced u r es. All manipulations were carried out
using modified Schlenk techniques under an atmosphere of
N2 or in a Vacuum Atmospheres HE-43 drybox. All solvents
were distilled from Na/K alloy and degassed twice immediately
P b{C6H3-2,6-Mes2}2 (3). This compound was synthesized
from LiC6H3-2,6-Mes2 (1.24 g, 3.86 mmol) in Et2O/hexane (3:
1, 20 mL) and PbCl2 (0.54 g, 1.94 mmol) in Et2O/hexane (3:1,
20 mL) and purified in a manner identical to 1 to afford the
product 3 as purple crystals. Yield: 0.98 g, 60.7%; dec 197-
199 °C. Anal. Calcd for C48H50Pb: C, 69.12; H, 6.05. Found:
C, 68.96; H, 6.00. 1H NMR (C6D6): δ 1.92 (s, 12H, o-CH3),
21
before use. The compounds LiC6H3-2,6-Mes2 and GeCl2‚-
dioxane2d were prepared according to literature procedures.
Anhydrous SnCl2 and PbCl2 were purchased commercially and
used as received. 1H, 13C, 117Sn, 119Sn, and 207Pb NMR data
were recorded on a Bruker 300 MHz instrument and refer-
2.21 (s, 6H, p-CH3), 6.80 (s, 4H, m-Mes), 7.26 (tr, 1H, J HH
)
7.8 Hz, p-C6H3), 7.47 (d, 2H, J HH ) 7.5 Hz, m-C6H3). 13C NMR
(C6D6): δ 21.20 (p-CH3), 21.32 (o-CH3), 126.66 (p-C6H3), 129.01
(m-Mes), 136.45 (p-Mes), 136.48 (o-Mes), 137.46 (m-C6H3),
139.91 (i-Mes), 149.34 (o-C6H3). 207Pb {1H} NMR (C6D6): δ
3870. UV-vis (ethyl ether): λmax 526 nm. IR (Nujol, cm-1):
3070 (sh), 3020 (sh), 2900 (vs), 2720 (w), 1605 (m), 1555 (w),
1530 (w), 1255 (w), 1210 (w), 1080 (m), 1005 (m), 1030 (m),
1005 (m), 880 (w), 845 (s), 795 (s), 735 (m), 725 (s), 710 (w),
565 (w), 455 (w), 405 (w), 370 (m), 305 (m), 280 (w), 243 (m).
1
enced to the deuterated solvent in the case of the H and 13C
NMR spectra. The Sn and Pb NMR spectra were referenced
to SnMe3 or Pb(OAc)4. Infrared data were recorded on a
Perkin PE-1430 instrument. UV-vis data were recorded on
a Hitachi-1200 instrument.
Ge{C6H 3-2,6-Mes2}2 (1). LiC6H3-2,6-Mes2 (0.96 g, 3.0
mmol) in Et2O (20 mL) was added to GeCl2‚dioxane (0.35 g,
1.5 mmol) in Et2O (20 mL) at ca. 0 °C with rapid stirring. The
solution, which became an intense purple color, was stirred
at ca. 0 °C for 30 min and then stirred for a further 4 h at
room temperature. The volatile materials were removed under
reduced pressure, and the residue was extracted with warm
toluene (40 mL). After filtration through Celite, the solution
[Ge(Cl){C6H3-2,6-Mes2}]2 (4). Meth od A. With rapid
stirring and cooling to ca. -78 °C, 2,6-Mes2C6H3Li (0.8 g, 2.5
mmol) in THF (20 mL) was added dropwise to GeCl2‚dioxane
(0.6 g, 2.5 mmol in THF (20 mL). After the solution was stirred
for 2 h, the solution was warmed to room temperature and all
of the volatile materials were removed under reduced pressure.
The dark red residual material was extracted with hexane (40
mL), and the solution was filtered and concentrated to incipi-
ent crystallization. Storage at ca. -20 °C for 1 day gave the
product 4 as orange crystals. Yield: 0.41 g, 0.98 mmol, 39.0%.
(17) (a) Harris, D. H.; Lappert, M. F. J . Chem. Soc., Chem. Commun.
1974, 895. (b) Schaeffer, C. D.; Zuckermann, J . J . J . Am. Chem. Soc.
1974, 96, 7160. (c) Lappert, M. F.; Power, P. P. Organotin Com-
pounds: New Chemistry and Applications; Advances in Chemistry
Series 157; Zuckerman, J . J ., Ed.; American Chemical Society: Wash-
ington, DC, 1976; p 70. In addition, numerous examples of divalent
group 14 species with heteroatom ligands involving one or more lone
pairs on the ligating atom (e.g., -NR2, OR, or SR ligands) have been
characterized. For example: (d) Veith, M. Angew. Chem., Int. Ed. Engl.
1987, 26, 1. (e) Hitchcock, P. B.; Lappert, M. F.; Samways, B. J .;
Weinberg, E. L. J . Chem. Soc., Chem. Commun. 1983, 1492. (f)
Fjeldberg, T.; Hitchcock, P. B.; Lappert, M. F.; Smith, S. J .; Thorne,
A. J . J . Chem. Soc., Chem. Commun. 1985, 939. (g) Meller, A.; Gra¨be,
C. P. Chem. Ber. 1985, 118, 2020.
Meth od B. LiC6H3-2,6-Mes2 (2.0 g, 6.23 mmol) in THF (20
mL) was added to a solution of GeCl2‚dioxane (0.72 g, 3.12
mmol) in THF (10 mL) at ca. -78 °C with rapid stirring. The
solution immediately turned purple and was stirred for an
additional 1 h before being introduced via cannula to GeCl2‚-
dioxane (0.72 g, 3.12 mmol) in THF (10 mL) at ca -78 °C with
rapid stirring. After 2 h at ca. -78 °C, the solution had turned
a magenta color. It was warmed to -10 °C, and the volatile
materials were removed under reduced pressure. The residual
solid was extracted with hexane (40 mL), filtered through
Celite, and concentrated to incipient crystallization. Storage
in a ca. -20 °C freezer for 2 days gave the product 4 as orange
crystals. Yield: 0.95 g, 2.25 mmol, 36.2%; mp 185-190 °C.
(18) J utzi, P.; Leue, C. Organometallics 1994, 13, 2898.
(19) Ohtaki, T.; Ando, W. Organometallics 1996, 15, 3103.
(20) A number of examples of M(X)R and MR2 species, in which R
is a multidentate aryl ligand, have been published. For example: J olly,
B. S.; Lappert, M. F.; Engelhardt, L. M.; White, A. H.; Raston, C. L. J .
Chem. Soc., Dalton Trans. 1993, 2653 and references therein.
(21) Ruhlandt-Senge, K.; Ellison, J . J .; Wehmschulte, R. J .; Pauer,
F.; Power, P. P. J . Am. Chem. Soc. 1993, 115, 11353.

1922 Organometallics, Vol. 16, No. 9, 1997
Simons et al.
Ta ble 1. Exp er im en ta l Deta ils for Da ta Collection , Red u ction , a n d Refin em en t for Com p ou n d s 1-5
1
2
3
4
5
formula
fw
C48H50Ge
699.47
C48H50Sn
745.57
C48H50Pb
834.07
C24H25ClGe
421.48
C24H25ClSn
467.58
cryst dimens, mm
color
cryst syst
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
0.20 × 0.07 × 0.04
violet-magneta dichroic
orthorhombic
Fdd2
20.676(3)
42.255(5)
0.68 × 0.24 × 0.14
0.5 × 0.1 × 0.1
0.40 × 0.40 × 0.30
0.4 × 0.4 × 0.4
purple
purple
orange
yellow
orthorhombic
Fdd2
20.991(10)
42.44(2)
orthorhombic
Fdd2
21.078(4)
42.546(9)
8.388(2)
monoclinic
C2/m
10.024(2)
22.667(5)
9.012(2)
triclinic
P1h
8.360(2)
11.595(2)
12.061(2)
75.67(3)
71.28(3)
82.86(3)
1071.5(4)
2
8.4089(9)
8.392(3)
99.64(3)
7347(2)
8
7476(6)
8
7522(3)
8
2018.7(8)
4
Z
d
calc (Mg/m3)
1.265
1.365
1.038
0.0298
0.0684
0.191
1.325
0.716
1.118
0.0375
0.1099
1.734
1.473
1.372
1.012
0.0403
0.0887
0.695
1.387
3.290
0.897
0.0659
0.1748
1.361
1.449
1.321
0.591
0.0391
0.1046
0.609
µ (mm-1
)
GOF
R1 (obsd data)
wR2 (all data)
largest diff peak (e Å-3
)
Anal. Calcd for C24H25ClGe: C, 68.39; H, 5.98. Found: C,
68.71; H, 6.04. 1H NMR (C6D6): δ 2.12 (s, 12H, o-CH3), 2.23
(s, 6H, p-CH3), 6.81 (s, 4H, m-Mes), 6.85 (d, 2H, J HH ) 7.20
Hz, m-C6H3), 7.11 (tr, 1H, J HH ) 7.20 Hz, p-C6H3). 13C NMR
(C6D6): δ 21.33 (p-CH3), 21.56 (o-CH3), 128.77 (o-Mes), 129.27
(m-Mes), 130.64 (o-C6H3), 137.07 (m-C6H3), 137.45 (p-C6H3),
137.99 (p-Mes), 146.38 (i-Mes), 153.93 (i-C6H3). IR (Nujol
cm-1): 2910 (s), 1620 (w), 1560 (w), 1300 (w), 1260 (m), 1109
(m), 1092 (m), 1030 (w), 870 (m), 850 (m), 805 (m), 395 (w),
350 (m), 320 (m), 250 (m).
[Sn (Cl){C6H3-2,6-Mes2}]2 (5). Meth od A. LiC6H3-2,6-
Mes2 (1.87 g, 5.8 mmol) in toluene (30 mL) was added to a
solution of SnCl2 (1.10 g, 5.8 mmol) in toluene (30 mL) at room
temperature with rapid stirring, which was continued for a
further 2 h. The solution was diluted with 10 mL of hexane,
filtered, and stored in a ca. -20 °C freezer for 1 day to give
the product 5 as yellow crystals. Yield: 1.82 g, 3.89 mmol,
67%; mp 186 °C.
experimental details for all compounds are given in Table 1.
The structure of all compounds were solved by direct meth-
ods.23 The phenyl and methyl hydrogen atoms were placed
in idealized positions using a riding model and C-H distances
of 0.96 and 0.97 Å, respectively. An absorption correction was
applied using the program XABS224 for 1, 3, 4, and 5 and by
the method of ψ-scans for 2. All compounds were refined to
convergence by using anisotropic thermal parameters for all
non-hydrogen atoms. For 4, a 50/50 conformational disorder
was modeled by computing the occupancy of the Ge atom at
0.5.
Resu lts a n d Discu ssion
Syn th eses a n d Sp ectr oscop y. The compounds
M{C6H3-2,6-Mes2}2 (M ) Ge (1), Sn (2), Pb (3)) were
obtained in moderate, purified yields of 43%, 47%, and
61%, respectively, by the reaction of 2 equiv of LiC6H3-
2,6-Mes2 with MCl2 in ether (Scheme 1). Crystallization
from toluene provided samples of 1-3 as X-ray quality,
purple crystals, which were stable in the absence of air
and moisture. They also possess considerable thermal
stability with melting points in the range 175-199 °C
(dec)).
Meth od B. 3 (0.35 g, 0.5 mmol) in toluene (20 mL) was
added to a suspension of SnCl2 (0.1 g, 0.525 mmol) in toluene
(10 mL) and stirred at room temperature for 4 h. The solution
was diluted with hexane (ca. 7-8 mL) and filtered through
Celite. Storage in a -20 °C freezer for 30 h afforded 5 as
yellow crystals. Yield 0.21 g (45%). Anal. Calcd for C24H25
-
ClSn: C, 61.65; H, 5.39. Found C, 61.15; H, 5.62. 1H NMR
(C6D6): δ 2.14 (s, 12H, o-CH3), 2.22 (s, 6H, p-CH3), 6.81 (s,
4H, m-Mes), 6.98 (d, 2H, J HH ) 7.80 Hz, m-C6H3), 7.20 (tr,
1H, J HH ) 7.80 Hz, p-C6H3). 13C {1H} NMR (C6D6): δ 21.29
(p-CH3), 21.70 (o-CH3), 129.13 (m-Mes), 129.19 (o-C6H3), 129.29
(m-C6H3), 136.79 (p-C6H3), 137.17 (p-Mes), 138.12 (i-Mes),
147.60 (o-Mes), 177.54 (i-C6H3). 117Sn {1H} NMR (C6D6): δ
572. 119Sn {1H} NMR (C6D6): δ 562. IR (Nujol, cm-1): 2920
(s), 1601 (w), 1090 (w), 1030 (w), 1010 (w), 850 (m), 800 (m),
690 (w), 570 (m), 330 (m).
The monoaryl derivatives 4 and 5 were also prepared
in moderate yields (47% and 45%, respectively), either
by the reaction of 1 equiv of LiC6H3-2,6-Mes2 with the
appropriate dichloride or in comparable yields by the
reaction of the dichloride with 1 or 2. Compounds 4 and
5 are stable at room temperature in toluene or hexane
solutions and in the solid state (mp ) 191-195 and 186
°C, respectively). Several attempts to isolate the cor-
responding monoaryl lead compound according to Scheme
1 were unsuccessful. Instead, 1,3-Mes2C6H4 was the
only pure compound to be isolated. The products 1-5
X-r a y Cr ysta llogr a p h y. Sample preparation consisted of
coating the crystal with hydrocarbon oil, mounting it on a glass
fiber, and placing it under
a cold stream of N2 on the
diffractometer.22 X-ray data for 1 and 4 were collected at 130
K on Siemens P4 and Siemens P21 diffractometers using Cu
KR (λ ) 1.541 78 Å) radiation. The diffractometers were each
equipped with a low-temperature device and a nickel or
graphite monochromator. X-ray data for 2, 3, and 5 were
collected at 130 K on a Siemens R3 m/v diffractometer using
graphite-monochromated Mo KR (λ ) 0.710 73 Å) radiation.
Unit cell parameters were obtained from a least-squares fit of
at least 20 well-centered reflections with 25 e 2θ e 30° for 2,
3, and 5 and 50 e 2θ e 60° for 1 and 4. Additional
1
were also characterized by H and 13C NMR spectros-
copy. No dynamic character was observed in the range
from -90 to 80 °C. In addition, compounds 1-3 were
studied by UV-vis spectroscopy. Absorption maxima
were observed at 578, 553, and 526 nm, respectively.
The wavelength of the maximum absorption seen for 1
(i.e., 578 nm) may be contrasted with the value of 430
nm reported for GeMes*2.10b The blue shift seen for the
latter was attributed10b to the absence of coplanarity of
(22) This method is described by Hope, H. A Practicum in Synthesis
and Characterization. In Experimental Organometallic Chemistry;
Wayda, A. L., Darensbourg, M. Y., Eds.; ACS Symposium Series 357;
American Chemical Society: Washington, DC, 1987; Chapter 10.
(23) SHELXTL, A Program for Crystal Structure Determinations,
Version 5.03; Siemens Analytical Instruments: Madison, WI, 1994.
(24) Parkin, S. R.; Moezzi, B.; Hope, H. J . Appl. Crystallogr. 1995,
28, 53.

Monomeric Diaryls M{C6H3-2,6-Mes2}2
Organometallics, Vol. 16, No. 9, 1997 1923
Sch em e 1
F igu r e 1. Thermal ellipsoid plot of 1. H atoms are not
shown for clarity.
the aryl rings (for steric reasons), which also permitted
the C-Ge-C bond angle to decrease to 108.0(2)°. This
raises the energy of the p-orbital and lowers the energy
of the n-orbital, thereby increasing the HOMO-LUMO
gap. The larger λmax observed for 1 is consistent with
the wider interligand angle observed (ca. 114.5° vide
infra). However, it may be noted that the λmax value
for SnMes*2 is 476 nm11 (cf. 553 nm for 2 or 561 nm in
Sn(C6H2-2,4,6-(i-Pr)3)(C6H2-2,4,6-{CH(SiMe3)2}3)) whereas
the C-Sn-C angle is 103.6(1)°11 vs the 114.5° angle
observed in 2. Thus, it appears that the correlation
between the λmax and the interligand angle is not a full
explanation of the blue shift seen in GeMes*2. It is
possible that the large shift has its origin in an interac-
tion between the germanium p-orbital and a π or π*-
orbital from a very geometrically distorted Mes* group.
The high thermal stability of the compounds 1-5 is also
notable. For instance, 1 is considerably more thermally
robust than the diaryl germylene GeMes*2, which is
stable at ca. -30 °C but decomposes at room tempera-
ture via an intramolecular C-H bond activation or an
ortho-tert-butyl group to give a germaindane.10a The tin
F igu r e 2. Thermal ellipsoid plot of 3. H atoms are not
shown for clarity.
) 723)12 but differs significantly from the shift (980
ppm) observed for SnMes2* and differs greatly from the
values reported for Sn{CH(SiMe3)2}2 (2272 ppm at 345
K),26 SnC(SiMe3)2CH2CH2C(SiMe3)2 (2323 ppm), and
Sn(C6H2-2,4,6-(i-Pr)3)(C6H2-2,4,6-{CH(SiMe3)2}3 (2208
ppm).16 Similarly, the 207Pb NMR chemical shift of 3
(3870 ppm) is well upfield of the value (4878 ppm)
observed for Pb{C6H2-2,4,6-(CF3)3}2.13
11
analogue SnMes*2 and the compound Sn{C6H2-2,4,6-
X-r a y Cr ysta l Str u ctu r es. Crystals of 1-3 were
studied by X-ray diffraction, and the thermal ellipsoid
plots of the germanium and lead compounds are shown
in Figures 1 and 2. Selected bond distances and angles
are given in Table 2. In the solid state, compounds 1-3
are isomorphous and essentially isostructural. They
exist as V-shaped, discrete monomers with the closest
M-M (M ) Ge, Sn, or Pb) distances being 8.409(1),
8.392(3), and 8.388(1) Å, respectively. The M-C (M )
Ge, Sn, or Pb) bond lengths are 2.033(4), 2.225(5), and
2.334(12) Å, with any further metal-ligand interaction
being longer than 3.0 Å. The C(1)-M-C(1A) (M ) Ge,
Sn, or Pb) bond angles are essentially invariant, having
(CF3)3}2 are stable12 at room temperature in solution
and in the solid state (mp 125-130 °C and 73 °C,
respectively). The only structurally characterized diaryl
plumbylene is Pb{C6H2-2,4,6-(CF3)3}2.13 It is stable in
the solid state with a melting point of 58 °C, however,
it decomposes in solution. In contrast to GeMes*2, the
monoaryl compound Ge(Cl)Mes* is stable in solution up
to 80 °C and has a melting point of 56 °C.18 Presumably,
it is sufficiently sterically relaxed compared to GeMes*2
such that C-H activation does not occur.
The 119Sn NMR chemical shift of 2 (635 ppm) is
relatively close to that observed for the monomers Sn-
{N(SiMe3)2}2 (δ ) 776)25 and Sn{C6H2-2,4,6-(CF3)3}2 (δ
(26) Zilm, K. W.; Lawless, G. A.; Merrill, R. M.; Millar, M. M.; Webb,
G. G. J . Am. Chem. Soc. 1987, 109, 7236.
(25) Wrackmeyer, B. J . Magn. Reson. 1985, 61, 536.

1924 Organometallics, Vol. 16, No. 9, 1997
Simons et al.
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for Com p ou n d s 1-5
Compound 1
Ge-C(1)
2.033(4)
1.406(6)
1.419(6)
1.387(6)
C(3)-C(4)
C(4)-C(5)
C(5)-C(6)
1.372(6)
1.382(5)
1.393(5)
C(1)-C(6)
C(1)-C(2)
C(2)-C(3)
C(1)-Ge-C(1A)
Ge-C(1)-C(2)
114.4(2)
112.7(3)
Ge-C(1)-C(6)
128.2(3)
Compound 2
Sn-C(1)
2.225(5)
C(3)-C(4)
C(4)-C(5)
C(5)-C(6)
1.383(8)
1.387(6)
1.397(6)
C(1)-C(6)
C(1)-C(2)
C(2)-C(3)
1.408(6)
1.420(6)
1.401(7)
C(1)-Sn-C(1A)
Sn-C(1)-C(2)
114.7(2)
111.6(3)
Sn-C(1)-C(6)
129.6(3)
Compound 3
Pb-C(1)
C(1)-C(6)
C(1)-C(2)
2.334(12)
1.41(2)
1.41(2)
C(2)-C(3)
C(3)-C(4)
C(4)-C(5)
1.39(2)
1.39(2)
1.38(2)
C(1)-Pb-C(1A)
Pb-C(1)-C(2)
114.5(6)
110.6(9)
Pb-C(1)-C(6)
129.7(9)
F igu r e 3. Thermal ellipsoid plot of 4. H atoms are not
shown for clarity.
Compound 4
Ge-C(1)
Ge-Cl
Ge-Ge(A)
C(1)-C(2)
2.000(6)
2.120(2)
2.443(2)
1.403(5)
C(2)-C(3)
C(3)-C(4)
C(4)-C(3A)
1.387(6)
1.387(6)
1.388(6)
radius of the group 14 element increases) in the order
Ge > Sn > Pb. This should have given rise to a similar
decrease in the bond angle.
The aryl metal halide compound 4 crystallizes as a
dimer, and its structure is illustrated in Figure 3.
Selected bond distances and angles are given in Table
2. The dimeric Ge-Ge bonded arrangement in 4 may
be contrasted with the monomeric formula reported for
the closely related species Ge(Cl)Mes*.10b The difference
in structure may be attributed to the difference in the
steric properties of the Mes* and -C6H3-2,6-Mes2
ligands, which has been discussed elsewhere.29 The
Ge-C(1) and Ge-Cl bond distances of 2.000(6) and
2.120(2) Å are in the normal range and approximately
equal to the sum of their respective covalent radii,30 with
correction for ionic effects.31 The C-Ge-Cl bond angle
is 109.1(2)° which is smaller than the C-Ge-C angles
seen in Ge2{CH(SiMe3)2}4 (112.5(5)°)2c and Ge2{C6H3-
2,6-Et2}4 (115.4(2)°).8 Most probably, the decreased
interligand angle is a consequence of the substitution
by one chloride at each germanium and consequent
lowering of steric crowding. The most striking struc-
tural feature of 4, however, is the Ge-Ge bond distance
of 2.443(2) Å, which is long in comparison to other
structurally characterized digermylenes; e.g., 2.213(2)
Å in Ge2{C6H3-2,6-Et2}4,8 2.347(2) Å in Ge2{CH-
(SiMe3)2}4,2c 2.267(1) Å in Ge2[Si{SiMe(i-Pr)2}3]4,7 and
2.298(11) Å in Ge2[Si{Si(i-Pr)3}3]4.7 The Ge-Ge dis-
tance is in fact more consistent with Ge-Ge single
bonding (Ge-Ge ) 2.44 Å). Also, 4 has a fold angle of
39°, which is much larger than the 5.9-32° range
reported for the above digermylenes.2c,7,8
C(1)-Ge-Cl
109.1(2)
107.49(8)
115.9(2)
161.0
C(2A)-C(1)-Ge
C(1)-Ge-Ge(B)
Cl-Ge-Ge(B)
fold angle
133.9(3)
113.7(2)
111.03(7)
39.0
Ge-Ge(A)-Cl
Ge-Ge(A)-C(1)
C(4)-C(1)-Ge
C(2)-C(1)-Ge
105.0(2)
Compound 5
Sn-C(1)
Sn-Cl
Sn-Cl(A)
C(1)-C(6)
C(1)-C(2)
2.222(5)
2.600(2)
2.685(2)
1.407(8)
1.406(8)
C(2)-C(3)
C(3)-C(4)
C(4)-C(5)
C(5)-C(6)
1.390(8)
1.383(9)
1.384(9)
1.392(8)
C(1)-Sn-Cl
102.11(14)
98.28(6)
81.72(6)
C(4)-C(1)-Sn
C(2)-C(1)-Sn
C(6)-C(1)-Sn
166.0(4)
130.64(4)
111.1(4)
Sn-Cl-Sn(A)
Cl-Sn-Cl(A)
C(1)-Sn-Cl(A)
92.35(14)
values of 114.4(2)°, 114.7(2)°, and 114.5(6)°, respectively.
The M-C (M ) Ge, Sn, Pb) bond distances are close to
the values seen in previously reported σ-bonded, diva-
lent organometallics species;3-13 however, the C-M-C
bond angles are the widest27 for any σ-bonded MR2 (M
) Ge, Sn, or Pb) organometallic derivative with mono-
dentate ligands. The angles can be compared to those
in the sterically crowded species GeMes*2 (108.0(2)°)10b
and SnMes*2 (103.6(1)°)11 and the fluorinated mesityl
derivatives Sn{C6H2-2,4,6-(CF3)3}2 (98.3(1)°)12 and Pb-
{C6H2-2,4,6-(CF3)3}2 (94.5(1)°).13 Oddly, the interligand
angles observed in 1-3 are only approached by the Si-
Pb-Si angle (113.56(10)°) observed in Pb{Si(SiMe3)3}2.6
Perhaps in this case, the more electropositive silyl
substituents give rise to a wider angle in accordance
with Walsh/Bent rules.28 The essentially invariant
nature of the C-M-C bond angles in 1-3 is surprising,
owing to the fact that steric crowding decreases (as the
Compound 5 crystallizes as a centrosymmetric dimer,
and its structure is shown in Figure 4. The dimeric
units are associated through bridging chlorides and the
Sn‚‚‚Sn separation is 3.997(1) Å. A notable feature of
the structure is the asymmetry of the bridging Sn-Cl
(27) They are not as wide, however, as the 118.9° angle observed in
Ge{C(SiMe3)3}(η2-C5Me5). In this case, the germanium is three-
coordinate, having strong interactions with two of the carbons in the
C5Me5 ring. See: J utzi, P.; Becker, C.; Leue, C.; Stammler, G.;
Neumann, B.; Hursthouse, M. B.; Karulov, M. B. Organometallics
1991, 10, 3838.
(29) Wehmschulte, R. J .; Grigsby, W. J .; Schiemenz, B.; Bartlett,
R. A.; Power, P. P. Inorg. Chem. 1996, 35, 6694.
(30) Huheey, J . E.; Keiter, E. A.; Keiter, R. L. Inorganic Chemistry,
4th ed.; Harper and Row: New York, 1993; p 187.
(28) Walsh, A. D. Discuss. Faraday Soc. 1947, 2, 18. Bent, H. A.
Chem. Rev. 1961, 61, 275.
(31) Schomaker, V.; Stevenson, D. P. J . Am. Chem. Soc. 1941, 63,
37. Blom, R.; Haaland, A. J . Mol. Struct. 1985, 129, 1.

Monomeric Diaryls M{C6H3-2,6-Mes2}2
Organometallics, Vol. 16, No. 9, 1997 1925
F igu r e 5. Drawing of half of molecule 4, illustrating some
of the geometrical distortions.
through which they are attached to the central phenyl
ring. In the sterically less crowded 4 and 5, the
corresponding deformation is essentially negligible. A
further deformation in 1-3 relates to the angles formed
by the C(4)-C(1) and the M-C(1) vectors which have
values of 165.8 (1), 166.0° (2), and 161.0° (3) instead of
the expected 180°. In 4, there is a deformation of the
Ge-C(1) bond toward the C(5) mesityl ring (Figure 5)
that results in a close approach of the germanium
center, as evidenced by the Ge‚‚‚C(5), C(6), and C(7)
distances of 2.823, 3.330, and 3.418 Å.
F igu r e 4. Thermal ellipsoid plot of 5. H atoms are not
shown for clarity.
distances (2.600(2) and 2.685(2) Å), which suggests that
there may be a tendency to dissociate to monomers. The
organo groups are arranged in the trans configuration,
presumably for steric reasons. Although the structure
of the germanium compound 4 is unprecedented for a
Ge(Cl)R species, the structure of 5 is related to those
Con clu sion
The structures of 1-5 highlight the difference in
steric properties between the Mes* and -C6H3-2,6-Mes2
ligands. Where one of these aryl substituents is present,
the Mes* moiety appears to be the most crowded29 of
the two; cf. the dimeric structure of 4 versus the
monomeric structure of Ge(Cl)Mes*. When two of these
aryl groups are present, however, the -C6H3-2,6-Mes2
appears to produce the most crowded environment, as
reflected in the wider interligand angles in 1 and 2 in
comparison to the corresponding angles in GeMes*2 and
SnMes*2.
32
observed for the amido derivatives {Sn(Cl)N(SiMe3)2}2
32
and {Sn(Cl)TMP}2 (TMP ) 2,2,6,6-tetramethylpiperi-
dino), which adopt trans and cis chloro-bridged struc-
tures, respectively. Although cis,trans isomerization
could be observed for {Sn(Cl)TMP}2, no such process
could be detected for {Sn(Cl)N(SiMe3)2}2 or 5.
A notable feature of the structures of 1-5 is that some
of the structural parameters show deviation from ideal-
ized values. For the most part, these deviations have
their origin in steric effects. Thus, in 1-3, it is notable
that the closest C‚‚‚C approach involving mesityl rings
from the pairs of terphenyl substituents are quite short
with values of 3.226 (1), 3.221 (2), and 3.228 Å (3). To
relieve this intramolecular crowding, the planes of the
neighboring pairs of mesityl rings are tilted by the
angles 14.9°/5.2° (1), 14.2°/5.2° (2), and 13.4°/4.0° (3)
from the C-C vectors (i.e., C(2)-C(7) and C(6)-C(16))
Ack n ow led gm en t. We are grateful to the National
Science Foundation for financial support.
Su p p or tin g In for m a tion Ava ila ble: Tables giving full
details of the crystallographic data and data collection param-
eters, atom coordinates, bond distances, bond angles, aniso-
tropic thermal parameters, and hydrogen coordinates for 1-5
(41 pages). Ordering information is given on any current
masthead page.
(32) Chorley, R. W.; Hitchcock, P. B.; J olly, B. S.; Lappert, M. F.;
Lawless, G. A. J . Chem. Soc., Chem. Commun. 1991, 1302.
OM960929L