Synthesis and structures of monomeric divalent germanium and tin compounds containing a bulky diketiminato ligand

Article abstract of DOI:10.1021/om000871h

Reaction of the β-diketiminato lithium salt Li(OEt₂)[HC(CMeNAr)₂] (Ar = 2,6-i-Pr₂C₆H₃) with GeCl₂·(dioxane) and SnCl₂ in diethyl ether provided the monomeric complexes [HC-(CMeNAr)₂]MCl (M = Ge (2), Sn (3), respectively) with a three-coordinated metal center. The reductive dehalogenation reactions of 3 with C₈K and LiAlH₄ afforded [HC(CMeNAr)₂]₂Sn (7) and [HC(CMeNAr)₂]AlH₂, respectively. The metathesis reactions of 3 with t-BuLi, AgSO₃-CF₃, and NaN₃ resulted in the formation of [HC(CMeNAr)₂]Sn(t-Bu) (4), [HC(CMeNAr)₂]-Sn(OSO₂CF₃) (5), and [HC(CMeNAr)₂]SnN₃ (6), respectively. Compounds 2, 3, 5, and 7 were characterized by single-crystal X-ray structural analysis. The structures indicate that the β-diketiminato backbone is essentially planar and the metal centers reside in distorted-tetrahedral environments with one vertex occupied by a lone pair of electrons. The bond angles at the metal center are in the range 85.2(8)-106.8(2)°, and the most acute angle is associated with the bite of the chelating ligand.

Full text of DOI:10.1021/om000871h

1190
Organometallics 2001, 20, 1190-1194
Syn th esis a n d Str u ctu r es of Mon om er ic Diva len t
Ger m a n iu m a n d Tin Com p ou n d s Con ta in in g a Bu lk y
Dik etim in a to Liga n d †
Yuqiang Ding, Herbert W. Roesky,* Mathias Noltemeyer, and
Hans-Georg Schmidt
Institut fu¨r Anorganische Chemie der Universita¨t Go¨ttingen,
Tammannstrasse 4, D-37077 Go¨ttingen, Germany
Philip P. Power
Department of Chemistry, University of California, Davis, California 95616
Received October 11, 2000
Reaction of the â-diketiminato lithium salt Li(OEt2)[HC(CMeNAr)2] (Ar ) 2,6-i-Pr2C6H3)
with GeCl2‚(dioxane) and SnCl2 in diethyl ether provided the monomeric complexes [HC-
(CMeNAr)2]MCl (M ) Ge (2), Sn (3), respectively) with a three-coordinated metal center.
The reductive dehalogenation reactions of 3 with C8K and LiAlH4 afforded [HC(CMeNAr)2]2Sn
(7) and [HC(CMeNAr)2]AlH2, respectively. The metathesis reactions of 3 with t-BuLi, AgSO3-
CF3, and NaN3 resulted in the formation of [HC(CMeNAr)2]Sn(t-Bu) (4), [HC(CMeNAr)2]-
Sn(OSO2CF3) (5), and [HC(CMeNAr)2]SnN3 (6), respectively. Compounds 2, 3, 5, and 7 were
characterized by single-crystal X-ray structural analysis. The structures indicate that the
â-diketiminato backbone is essentially planar and the metal centers reside in distorted-
tetrahedral environments with one vertex occupied by a lone pair of electrons. The bond
angles at the metal center are in the range 85.2(8)-106.8(2)°, and the most acute angle is
associated with the bite of the chelating ligand.
In tr od u ction
steric flexibility is afforded by variation of the substit-
uents on the ligand backbone, can be used as a spectator
ligand. Such ligands already have been employed in
transition-metal chemistry.4 Recently the coordination
chemistry of such ligands with main-group elements has
drawn attention.5 We have prepared the first monomeric
aluminum(I) compound, [{HC(CMeNAr)2}Al] (Ar ) 2,6-
i-Pr2C6H3), by taking advantage of such a ligand.6
Herein we report on the preparation of compounds of
divalent heavier group 14 elements using such a ligand,
LGeCl (2) and LSnCl (3) (L ) HC(CMeNAr)2), and the
resulting derivatives LSn(t-Bu) (4), LSn(OSO2CF3) (5),
LSnN3 (6), and L2Sn (7). Compounds 2, 3, 5, and 7 have
been characterized by single-crystal X-ray structural
analysis.
There is widespread interest in the chemistry of
divalent derivatives of the heavier group 14 elements,
due to their carbene-like properties. Stable tin(II)
compounds of formula (SnR2)1,2 and (RSnX1)1,2 (R )
bulky ligand, X1 ) halide) are well-characterized.1 In
contrast, derivatives of tin(II) of the type Sn(X2)R, where
X2 is a small ligand other than halide, have received
much less attention. To the best of our knowledge, only
few such compounds are known, including Sn(C7H7)-
[C6H3-2,6-(CH2NMe2)2],1e [(n-Pr)2ATI]SnN3 (where
[(n-Pr)2ATI]- ) N-(n-propyl)-2-(n-propylamino)tropon-
iminate),1l Sn[B(C6F5)4]Cp,2 and [Sn(SO3CF3){N(Si-
Me3)2}]2.3 The anionic chelating â-diketiminato ligand
[HC(CRNR′)2]- (R ) Me, Ph; R′ ) SiMe3, aryl), where
† Dedicated to Professor Rolf Appel on the occasion of his 80th
birthday.
Exp er im en ta l Section
Gen er a l Con sid er a tion s. All manipulations were carried
out using standard Schlenk techniques or in a glovebox under
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Chem. Soc., Dalton Trans. 1997, 1945. (c) Rahim, M.; Taylor, N. J .;
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Piers, W. E.; Elsegood, M. R. J .; Clegg, W.; Parvez, M. Organometallics
1999, 18, 2947.
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17, 3070. (b) Qian, B.; Baek, S. W.; Smith, M. R., III. Polyhedron 1999,
18, 2405. (c) Bailey, P. J .; Dick, C. M. E.; Fabre, S.; Parsons, S. J . Chem.
Soc., Dalton Trans. 2000, 1655. (d) Gibson, V. C.; Segal, J . A.; White,
A. J . P.; Williams, D. J . J . Am. Chem. Soc. 2000, 122, 7120. (e)
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Chem., 1977, 16, 1414.
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Pierssens, L. J . J . Organomet. Chem. 2000, 601, 142.
(6) Cui, C.; Roesky, H. W.; Schmidt, H.-G.; Noltemeyer, M.; Hao,
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Ed. 2000, 39, 4274.
10.1021/om000871h CCC: $20.00 © 2001 American Chemical Society
Publication on Web 02/16/2001

Ga and Sb Diketiminato Compounds
Organometallics, Vol. 20, No. 6, 2001 1191
a nitrogen atmosphere. Diethyl ether was freshly distilled from
Na and n-pentane from LiAlH4 prior to use. Elemental
analyses were performed by the Analytisches Labor des
Instituts fu¨r Anorganische Chemie der Universita¨t Go¨ttingen.
A Bruker AM 200 instrument was used to record 1H NMR
(200.1 MHz), 119Sn NMR (186.5 MHz), and 19F NMR (188.3
MHz) spectra, with reference to TMS, SnMe4, and BF3(OEt2),
respectively. Mass spectra were obtained on a Finnigan Mat
8230 instrument. The compounds [HC(CMeNAr)2]H7 and
GeCl2‚(dioxane)8 were prepared by literature procedures. Other
chemicals were purchased from Aldrich and used as received.
3.72-3.82 (sept, 2 H, CHMe2), 4.82 (s, 1 H, γ-CH), 6.95-7.11
(m, 6 H, 2,6-i-Pr2C6H3). 119Sn NMR (C6D6): δ 259.
LSn (OSO2CF 3) (5). A solution of 3 (0.572 g, 1.0 mmol) in
toluene (20 mL) was added to a stirred suspension of AgSO3-
CF3 (0.239 g, 1.0 mmol) in toluene (10 mL) at -78 °C. The
reaction mixture was warmed to room temperature and was
stirred for 1 h. The precipitate was filtered, and the solvent
was partially removed (ca. 15 mL) under reduced pressure
from the pale yellow filtrate. Storage of the remaining solution
in a -10 °C freezer for 2 days afforded colorless crystals of 5
suitable for X-ray diffraction analyses (0.55 g, 80%). Mp: 150
1
°C dec. EI-MS (70 eV): m/e 686 [M+]. H NMR (C6D6): δ 1.16
LLi(OEt2) (1). A solution of MeLi (13.0 mL, 1.6 M in diethyl
ether, 20.0 mmol) was added dropwise to a stirred solution of
[HC(CMeNAr)2]H (8.36 g, 20.0 mmol) in n-hexane (40 mL) at
-78 °C. The reaction mixture was warmed to room tempera-
ture and was stirred for 3 h. After filtration, storage of the
filtrate in a -32 °C freezer for 2 days afforded colorless crystals
of 1 (8.91 g, 90%). 1H NMR (C6D6): δ 0.49 (t, 6 H, O(CH2Me)2),
1.16 (d, 12 H, CHMe2), 1.22 (d, 12 H, CHMe2), 1.88 (s, 6 H,
Me), 2.70-2.82 (q, 4 H, O(CH2Me)2), 3.22-3.45 (sept, 4 H,
CHMe2), 4.98 (s, 1 H, γ-CH), 7.00-7.10 (m, 6 H, 2,6-i-Pr2C6H3).
(d, 12 H, CHMe2), 1.20 (d, 12 H, CHMe2), 1.62 (s, 6 H, Me),
3.21-3.38 (sept, 4 H, CHMe2), 5.31 (s, 1 H, γ-CH), 6.95-7.09
(m, 6 H, 2,6-i-Pr2C6H3). 119Sn NMR (C6D6): δ -239. 19F NMR
(C6D6): δ 85.28.
LSn N3 (6). A solution of 3 (1.14 g, 2.0 mmol) in THF (20
mL) was added to a stirred suspension of NaN3 (0.13 g, 2,0
mmol) in THF (10 mL) at room temperature. The reaction
mixture was stirred for 3 days. After the solvent was removed,
the residue was extracted with toluene (20 mL). Storage of
the extract in a -32 °C freezer for 2 days afforded slightly
yellow crystals of 6 (1.05 g, 90%). Mp: 205-212 °C. Anal. Calcd
for C29H41N5Sn (578.38): C, 60.22; H, 7.15; N, 12.11. Found:
C, 60.11; H, 7.04; N, 12.25. EI-MS (70 eV): m/e (%) 537 (100)
LGeCl (2). A solution of 1 (0.498 g, 1.0 mmol) in diethyl
ether (20 mL) was added dropwise to a stirred suspension of
GeCl2‚(dioxane) (0.27 g, 1.0 mmol) in diethyl ether (10 mL) at
-78 °C. The reaction mixture was warmed to room tempera-
ture and was stirred for another 6 h. After removal of all the
volatiles, the residue was extracted with n-hexane (20 mL).
Storage of the extract in a -32 °C freezer for 3 days afforded
colorless crystals of 2 (0.33 g, 63%). Mp: 197-199 °C. Anal.
Calcd for C29H41ClGeN2 (525.68): C, 66.21; H, 7.79; Cl, 6.75;
N, 5.32. Found: C, 66.01; H, 7.97; Cl, 6.99; N, 5.22. EI-MS
1
[M - N3]+. H NMR (C6D6): δ 1.02 (d, 6 H, CHMe2), 1.15 (d, 6
H, CHMe2), 1.21 (d, 6 H, CHMe2), 1.49 (d, 6 H, CHMe2), 1.66
(s, 6 H, Me), 2.90-3.15 (sept, 2 H, CHMe2), 3.70-3.82 (sept, 2
H, CHMe2), 4.93 (s, 1 H, γ-CH), 6.99-7.14 (m, 6 H, 2,6-i-
Pr2C6H3). 119Sn NMR (C6D6): δ -237.
L2Sn (7). A solution of 3 (1.14 g, 2.0 mmol) in n-hexane (30
mL) was added to C8K (excess) at room temperature. The
reaction mixture was stirred for 3 days. After filtration (of the
tin, graphite, and potassium chloride) and partial removal of
the solvent from the filtrate (ca. 15 mL), storage of the filtrate
in a -32 °C freezer for 7 days afforded colorless crystals of 7
(0.19 g, 10%). Mp: 232-237 °C. Anal. Calcd for C58H82N4Sn
(954.97): C, 73.02; H, 8.66; N, 5.87. Found: C, 72.96; H, 8.58;
1
(70 eV): m/e (%) 526 (M+, 65), 491 ([M - Cl] +, 100). H NMR
(C6D6): δ 1.01 (d, 6 H, CHMe2), 1.19 (d, 6 H, CHMe2), 1.20 (d,
6 H, CHMe2), 1.46 (d, 6 H, CHMe2), 1.60 (s, 6 H, Me), 3.05-
3.20 (sept, 2 H, CHMe2), 3.80-4.00 (sept, 2 H, CHMe2), 5.14
(s, 1 H, γ-CH), 7.00-7.10 (m, 6 H, 2,6-i-Pr2C6H3).
LSn Cl (3). A solution of 1 (0.498 g, 1.0 mmol) in diethyl
ether (15 mL) was added dropwise to a stirred suspension of
SnCl2 (0.19 g, 1.0 mmol) in diethyl ether (10 mL) at -50 °C.
The reaction mixture was warmed to room temperature and
was stirred for 12 h. The precipitate was filtered, and the
solvent was partially reduced (ca. 10 mL). Storage of the
remaining solution in a -32 °C freezer for 2 days afforded
yellow crystals of 3 (0.42 g, 73%). Mp: 207-211 °C. Recrys-
tallization from n-hexane (15 mL) in a -10 °C freezer for 2
days afforded crystals suitable for X-ray diffraction analysis.
Anal. Calcd for C29H41ClN2Sn (571.78): C, 60.91; H, 7.23; Cl,
6.20; N, 4.90. Found: C, 60.33; H, 7.12; Cl, 6.32; N, 4.98. EI-
MS (70 eV): m/e 572 (M+). 1H NMR (C6D6): δ 1.03 (d, 6 H,
CHMe2), 1.16 (d, 6 H, CHMe2), 1.19 (d, 6 H, CHMe2), 1.42 (d,
6 H, CHMe2), 1.61 (s, 6 H, Me), 3.00-3.20 (sept, 2 H, CHMe2),
3.85-3.98 (sept, 2 H, CHMe2), 5.05 (s, 1 H, γ-CH), 7.06 (m, 6
H, 2,6-i-Pr2C6H3). 119Sn NMR (C6D6): δ -224.
1
N, 5.95. EI-MS (70 eV): m/e 537 [M - L]+. H NMR (C6D6): δ
0.88-1.58 (m, 60 H, Me and CHMe2), 2.80-3.40 (m, 8 H,
CHMe2), 4.25 (s, 1 H, γ-CH), 4.77 (s, 1 H, γ-CH), 6.99-7.03
(m, 12 H, 2,6-i-Pr2C6H3). 119Sn NMR (C6D6): δ -246.
X-r a y Cr ysta llogr a p h y. Single crystals of 2, 3, 5, and 7
were taken from the flask under nitrogen gas and mounted
on a glass fiber in rapidly cooled perfluoropolyether.9 Diffrac-
tion data were collected on a Stoe-Siemens-Huber four-circle
diffractometer coupled to a Siemens CCD area detector at
200(2) K with graphite-monochromated Mo KR radiation (λ )
0.710 73 Å). The structures were solved by direct methods
(SHELXS-9610) and refined against F2 using SHELXL-97.11 All
non-hydrogen atoms were refined anisotropically with similar-
ity and rigid bond restraints. All hydrogen atoms were
included in the refinement in geometrically ideal positions.
LSn (t-Bu ) (4). A solution of t-BuLi in n-hexane (0.4 mL,
1.6 M) was added dropwise to a stirred solution of 3 (0.35 g,
0.62 mmol) in n-hexane (20 mL) at -78 °C. The reaction
mixture was warmed to room temperature and was stirred for
an additional 3 h. The precipitate was filtered, and the solvent
was partially removed (ca. 10 mL) from the red filtrate. Storage
of the remaining solution in a -10 °C freezer for 5 days
afforded red crystals of 4 (0.32 g, 85%). Mp: 188-190 °C. Anal.
Calcd for C33H50N2Sn (593.47): C, 66.79; H, 8.49; N, 4.72.
Found: C, 66.58; H, 8.55; N, 4.55. EI-MS (70 eV): m/e 537 [M
Crystallographic data for 2, 3, 5, and 7 are given in Table
1.
Resu lts a n d Discu ssion
Syn th esis of Com p ou n d s 1-7. The â-diketiminato
lithium salt [HC(CMeNAr)2]Li (Ar ) 2,6-i-Pr2C6H3) had
been reported previously and used in situ without
isolation and characterization.5a,c Therefore, the crystal-
line [HC(CMeNAr)2]Li(Et2O) (1) was isolated and char-
acterized spectroscopically. Reagent 1 is soluble in
hydrocarbon solvents and stable under an inert atmo-
1
- t-Bu]+. H NMR (C6D6): δ 0.88 (s, 9 H, t-Bu), 1.12 (d, 6 H,
CHMe2), 1.14 (d, 6 H, CHMe2), 1.32 (d, 6 H, CHMe2), 1.40 (d,
6 H, CHMe2), 1.61 (s, 6 H, Me), 3.30-3.42 (sept, 2 H, CHMe2),
(7) Feldman, J .; McLain, S. J .; Parthasarathy, A.; Marshall, W. J .;
Calabrese, J . C.; Arthur, S. D. Organometallics 1997, 16, 1514.
(8) Fjelberg, T.; Haaland, A.; Schilling, B. E. R.; Lappert, M. F.;
Thorne, A. J . J . Chem. Soc., Dalton Trans. 1986, 1551.
(9) Kottke, T.; Stalke, D. J . Appl. Crystallogr. 1993, 26, 615.
(10) Sheldrick, G. M. Acta Crystallogr., Sect. A 1990, 46, 467.
(11) Sheldrick, G. M. SHELX 97; Universita¨t Go¨ttingen, Go¨ttingen,
Germany, 1997.

1192 Organometallics, Vol. 20, No. 6, 2001
Ta ble 1. Cr ysta llogr a p h ic Da ta for Com p ou n d s 2, 3, 5, a n d 7
Ding et al.
2
3
5
7
formula
fw
C
29H41ClGeN2
C29H41ClN2Sn
571.78
C30H41F3N2O3SSn‚C7H8
777.53
C58H82N4Sn
953.97
525.28
color
colorless
triclinic
P1h
8.656(2)
11.571(3)
14.946(4)
98.154(15)
99.438(14)
104.47(2)
1403.2(6)
2
pale yellow
triclinic
P1h
colorless
monoclinic
P21/n
12.1397(12)
13.063(19)
23.955(6)
90.00
92.597(12)
90
3795.0(11)
4
1.361
colorless
orthorhombic
P212121
15.845(12)
17.024 (3)
22.820(3)
90
cryst syst
space group
a (Å)
b (Å)
c (Å)
10.437(2)
12.138(3)
12.419(4)
89.80(3)
72.327(12)
71.147(14)
1410.8(6)
2
R (deg)
â deg)
γ (deg)
V (Å3)
Z
90
90
6155.5(15)
4
1.029
0.449
2032
dcalcd (g cm-3
)
1.244
1.205
556
1.346
1.019
592
µ (mm-1
F(000)
)
0.779
1608
cryst size (mm)
2θ range (deg)
index range
0.80 × 0.20 × 0.20
3.66-22.52
-9 e h e 9,
-12 e k e 12,
-10 e l e 16
3821
3677 (R(int) ) 0.0399)
0.0380, 0.1051
0.0408, 0.1086
1.065
1.00 × 0.40 × 0.40
3.57-25.04
-11 e h e 12,
-14 e k e 14,
-13 e l e 14
6610
4981 (R(int) ) 0.0572)
0.0354, 0.0978
0.0360, 0.0989
1.061
1.00 × 0.50 × 0.20
3.54-25.03
-14 e h e 14,
-15 e k e 15,
-27 e l e 28
8959
6687 (R(int) ) 0.0253)
0.0410, 0.1081
0.0454, 0.1132
1.050
0.60 × 0.50 × 0.40
3.51-25.03
-3 e h e 18,
-20 e k e 20,
-27 e l e 27
7396
6878 (R(int) ) 0.0294)
0.0545, 0.1682
0.0622, 0.1834
1.143
no.of rflns collected
no. of indep rflns
R1, wR2 (I > 2(σ)I)
R1, wR2 (all data)
goodness of fit, F2
no. of data/restaints/params
3675/0/308
0.537 to -0.540
4980/0/308
1.697 to -0.921
6687/396/417
1.373 to -1.070
6872/0/588
1.378 to -0.647
largest diff peak, e Å-3
Sch em e 1
Sch em e 3
Sch em e 2
ature did not give LSnH but, rather, the known alumi-
13
num hydride LAlH2 (Scheme 2). Further attempts to
prepare LSnH by reduction of 3 with various other
reducing agents, including NaBH4, KBH4, KH, and
NaH, were not successful.
Furthermore, we examined the substitution reactions
of 3 with selected nucleophiles in order to prepare other
tin(II) derivatives. Treatment of 3 with t-BuLi, AgSO3-
CF3, and NaN3 resulted in the formation of 4-6,
respectively (Scheme 3). The addition of t-BuLi to 3 in
n-hexane at low temperature proceeded smoothly to
provide 4 in high yield. The triflate anion (SO3CF3) has
long served as an excellent leaving group in nucleophilic
displacement reactions.14 Organotin triflates may act
as a precursor for further reactions. LSn(OSO2CF3) (5)
was prepared in toluene in high yield as colorless
sphere without loss of coordinated solvents for a long
period of time.
The â-diketiminato Sn(II) chloride (3) was easily
obtained in high yield by the reaction of 1 with 1 equiv
of SnCl2 in diethyl ether (Scheme 1). However, attempts
to prepare di-â-diketiminato complexes by using 2 equiv
of 1 were unsuccessful, even under more drastic condi-
tions.
The reduction of complex 3 with C8K unexpectedly
resulted in the formation of L2Sn (7) in low yield and a
significant amount of tin metal (Scheme 2). No other
reduced species could be isolated. Organotin(IV) hy-
drides generally can be prepared by the reduction of the
corresponding chlorides with LiAlH4.12 However, treat-
ment of 3 with LiAlH4 in diethyl ether at room temper-
(12) Fischer, E. O.; Moser, E. Inorg. Synth. 1970, 12.
(13) Cui, C.; Roesky, H. W.; Hao, H.; Schmidt, H.-G.; Noltemeyer,
M. Angew. Chem. 2000, 112, 1888; Angew. Chem., Int. Ed. 2000, 39,
1815.
(14) Howells, R. D.; McCown, J . D. Chem. Rev. 1977, 77, 69.

Ga and Sb Diketiminato Compounds
Organometallics, Vol. 20, No. 6, 2001 1193
crystals which are soluble in common organic solvents,
such as n-hexane and toluene. Metal and nonmetal
species containing the azide functionality are of interest
as starting materials, and the tin(IV) azides are well-
known.15 However, to our knowledge, the sole example
of a tin(II) azide, [(n-Pr)2ATI]SnN3, was reported only
recently.1l The azide compound 6 was readily prepared
as slightly yellow crystals by the reaction of 3 with NaN3
in THF at room temperature in high yield.
Compound 2, the germanium analogue of 3, was
prepared from 1 and GeCl2‚(dioxane) for comparison
(Scheme 1). The solid-state structural data of 2 and 3
were obtained by single-crystal X-ray analysis.
Compounds 1-7 were fully characterized by elemen-
1
tal analyses, EI-MS, and multinuclear NMR. In the H
F igu r e 1. Thermal ellipsoid plot (50%) of 2. H atoms are
NMR spectra, the resonances of methyl groups of the
aryl substituents, which appear as doublets in the range
δ 1.01-1.58, could be distinguished due to their differ-
ent environments. However, 1H NMR signals of 7
overlapped in the range δ 0.88-3.44 because of the
multiple chemical environments of their protons as
shown in the solid-state structure. The 119Sn NMR
spectra of 3-7 are comparable with those of tin(II) poly-
(1-pyrazolyl)borates, in which the metal centers reside
in a similar environment. 119Sn NMR spectroscopy
seems to be a useful probe for the determination of the
coordination of tin(II) in the poly(1-pyrazolyl)borates,
whose 119Sn chemical shifts vary with coordination
number: -730 to -950 ppm for six-coordinate tin, -650
to -730 ppm for four-coordinate tin, and -270 to -350
ppm for three-coordinate tin.16 For compounds 3, 5, and
7, in which the tin is three-coordinate in the solid state,
the 119Sn NMR chemical shifts are in the range -224
to -246 ppm. Although the coordination number of the
metal center in the solution may be different from that
in the solid state, when these chemical shifts are
compared with those of the tin(II) poly(1-pyrazolyl)-
borates, the tin atoms in compounds 3, 5, and 7, as well
as that in 6 (119Sn NMR: -237 ppm), probably are three-
coordinate in solution as well. The 119Sn NMR resonance
of the tert-butyl derivative 4 is found at low field (259
ppm), suggesting that the tin atom in 4 may be two-
coordinate in solution. All the EI-MS spectra of 2, 3,
and 5 give the corresponding molecular ion peak M+.
X-r a y Diffr a ction An a lyses for 2, 3, 5, a n d 7. The
solid-state structures of compounds 2, 3, 5, and 7 as
determined by single-crystal X-ray diffraction are shown
in Figures 1-4. Selected bond lengths and angles are
listed in Table 2; additional bond distances and angles
are included in the Supporting Information. The X-ray
single-crystal structures of 2, 3, 5, and 7 show that all
compounds are monomeric. The metal centers adopt
similar three-coordinated sites and reside in distorted-
tetrahedral environments with one vertex occupied by
a lone pair of electrons.
not shown. Important structural data are given in Table
1.
F igu r e 2. Thermal ellipsoid plot (50%) of 3. H atoms are
not shown. Important structural data are given in Table
1.
F igu r e 3. Thermal ellipsoid plot (50%) of 5. H atoms are
not shown. Important structural data are given in Table
1.
backbone of the chelating ligand is essentially planar
and the metal atom is always out of the plane (0.56 Å
in 2, 0.66 Å in 3, 0.65 Å in 5, and 0.24 Å in 7). In
compound 8 the central C (0.086 Å) and the Sn atom
(0.76 Å) are out of the NC-CN plane. In compound 9,
the skeletal atoms, including Sn, are almost coplanar.
Furthermore, the difference of the two bond lengths of
the metal center to the chelating nitrogen atoms in the
2, 3, 5, and 7 ranges from 0.003 to 0.019 Å. However,
the comparable differences in 8 and in 9 (0.201 Å in 8
and 0.109 Å in 9) are significantly longer. Obviously,
The structural features of these divalent compounds
2, 3, 5, and 7 are different from those of the comparable
tetravalent SnCl(Me)2[CH(CPhNSiMe3)2] (8) and SnCl-
(Me)2[CH(CPhNH)2] (9), in which similar ligands are
coordinated to tin.17 In compounds 2, 3, 5, and 7, the
(15) Thayer, J . S. Organomet. Chem. Rev. 1966, 1, 157.
(16) Hansen, M. N.; Niedenzu, K.; Serwatowska, J .; Serwatowski,
J .; Woodrum, K. R. Inorg. Chem. 1991, 30, 866.
(17) Hitchcock, P. B.; Lappert, M. F.; Liu, D. J . Chem. Soc., Chem.
Commun. 1994, 1699.

1194 Organometallics, Vol. 20, No. 6, 2001
Ding et al.
as expected. This indicates that the ionic interactions
of the central metal atom with the ligand decrease from
Ge to Sn due to the difference of the atomic radii
(Ge(II) 0.93 Å, Sn(II) 1.12 Å).
The observed M-N bond lengths in 2, 3, 5, and 7 are
in the normal range (1.910-2.042 Å for Ge-N single
bonds18 and 2.121-2.397 Å for Sn-N13), but the bond
length of Ge(1)-Cl(1) (2.295(12) Å) in 2 is 0.092 Å longer
than that found in Ge(Cl)(C6H3-2,6-Trip2) (2.203(10) Å)1k
and the Sn(1)-Cl(1) bond length (2.473(9) Å) is
0.257 Å longer than that in Sn(Cl)[C6H3(NMe2)2-2,6]
(2.216(5) Å).1i
A noteworthy feature of metal triflates is the diversity
of bonding systems, ranging from ionic to mono-, bi-, or
tridentate terminal or bridging modes.3 For tin(II)
triflate, the weakly coordinating ionic compound Sn(CF3-
SO3)[HB{3,5-(CF3)2Pz}3] (10) was reported by Dias19
and the bidentate compound [Sn(η2-CF3SO3){N(SiMe3)2}]2
(11) by Lappert.3 In compound 5, (Figure 3), the triflate
group is monodentate. The Sn(1)-O(1) distance
(2.254(2) Å) in 5 is shorter than those in 10 (2.507(3)
Å)19 and 11 (2.291(4) and 2.489(4) Å).3 This closer
contact of the triflate moiety with the metal center in 5
than is the case in 10 and 11 probably is caused by the
differences of the coordinating environment of the metal
center.
The structure of 7 shows that one ligand is chelated
to tin, while the other is monodentate. This is a result
of the steric demand of the two ligands. In compound
7, the Sn-N bond distances of the chelating nitrogen
atoms (2.233(6) and 2.251(6) Å) are longer than that of
the monodentate ligand (2.166(6) Å), as well as those
in 3 and 5 (2.139(3)-2.185(2) Å). This finding suggests
that the chelating ligand in 7 is not as close to the Sn
atom as are those in 3 and 5.
F igu r e 4. Thermal ellipsoid plot (50%) of 7. H atoms are
not shown. Important structural data are given in Table
1.
Ta ble 2. Selected Bon d Dista n ces (Å) a n d Bon d
An gles (d eg) for Com p ou n d s 2, 3, 5, a n d 7
bond distance
bond angle
Complex 2
Ge(1)-N(1)
Ge(1)-N(2)
Ge(1)-Cl(1)
1.988(2)
1.997(3)
2.295(12)
N(1)-Ge(1)-N(2)
N(1)-Ge(1)-Cl(1)
N(2)-Ge(1)-Cl(1)
90.89(10)
95.00(8)
95.60(8)
Compound 3
Sn(1)-N(1)
Sn(1)-N(2)
Sn(1)-Cl(1)
2.185(2)
2.180(2)
2.473(9)
N(1)-Sn(1)-N(2)
N(1)-Sn(1)-Cl(1)
N(2)-Sn(1)-Cl(1)
85.21(8)
90.97(6)
93.47(6)
Compound 5
Sn(1)-N(1)
Sn(1)-N(2)
Sn(1)-O(1)
2.142(3)
2.139(3)
2.254(2)
N(1)-Sn(1)-N(2)
N(1)-Sn(1)-O(1)
N(2)-Sn(1)-O(1)
87.78(10)
87.39(10)
90.62(10)
Compound 7
Sn(1)-N(1)
Sn(1)-N(2)
Sn(1)-N(3)
2.235(6)
2.251(6)
2.166(6)
N(1)-Sn(1)-N(2)
N(1)-Sn(1)-N(3)
N(2)-Sn(1)-N(3)
85.2(2)
102.7(2)
106.8(2)
the larger ionic radius of M(II) (Sn(II) 1.12 Å) compared
to that of M(IV) (Sn(IV) 0.71 Å) results in longer MII-N
bond lengths, which are less influenced by the substit-
uents at the metal center. We have recently shown by
ab initio calculation on a comparable Al analogue that
delocalization of electrons does not play an important
role in this system.6
Figures 1 and 2 provide the molecular geometries for
2 and 3, respectively, and show that the two complexes
have similar structural features. However, the bond
angle of N(1)-Ge(1)-N(2) (90.89(10)°) in 2 is larger
than the corresponding angle in 3 (N(1)-Sn(1)-N(2) )
85.21(8)°), and the bond length of N-Ge (1.998(2) and
1.997(3) Å) in 2 is slightly shorter than the correspond-
ing N-Sn bond length in 3 (2.185(2) and 2.180(2) Å),
Ack n ow led gm en t. This work was supported by the
Deutsche Forschungsgemeinschaft and the Fonds der
Chemischen Industrie.
Su p p or t in g In for m a t ion Ava ila b le: Figures giving
ORTEP diagrams and tables giving full details of the crystal-
lographic data and data collection parameters, atom coordi-
nates, bond distances, bond angles, anisotropic thermal pa-
rameters, and hydrogen coordinates for 2, 3, 5, and 7. This
material is available free of charge via the Internet at
http://pubs.acs.org.
OM000871H
(18) Foley, S. R.; Zhou, Y.; Yap, G. P. A.; Richeson, D. S. Inorg. Chem.
2000, 39, 924.
(19) Dias, H. V. R.; J in, W. Inorg. Chem. 2000, 39, 815.