Planar silicon and germanium heterocyclotriynes and their isomorphous nickel(0) complexes

Article abstract of DOI:10.1021/om960868r

The syntheses of three strained silicon or germanium heterocyclotriynes, from the dilithium dianion of 2,2′-diethynyltolane (Li₂(OBET)) and the dialkyldichlorosilanes or dialkyldichloro-germane, are described. Reactions of the heterocyclynes with Ni(COD)₂ give the nickel(0) complexes in very high yield. The heterocyclynes and their nickel complexes have been characterized by a variety of spectral techniques, and the X-ray crystal structures of compounds Si(i-Pr)₂(OBET), Ni[Si(i-Pr)₂(OBET)], SiPh₂(OBET), Ni[SiPh₂(OBET)], GePh₂-(OBET), and Ni[GePh₂(OBET)] are reported. The heterocyclynes and their nickel complexes possess isomorphous structures.

Full text of DOI:10.1021/om960868r

Organometallics 1997, 16, 1685-1692
1685
P la n a r Silicon a n d Ger m a n iu m Heter ocyclotr iyn es a n d
Th eir Isom or p h ou s Nick el(0) Com p lexes
Li Guo, J ohn D. Bradshaw, David B. McConville, Claire A. Tessier,* and
Wiley J . Youngs*
Department of Chemistry, The University of Akron, Akron, Ohio 44325-3601
Received October 14, 1996X
The syntheses of three strained silicon or germanium heterocyclotriynes, from the dilithium
dianion of 2,2′-diethynyltolane (Li2(OBET)) and the dialkyldichlorosilanes or dialkyldichloro-
germane, are described. Reactions of the heterocyclynes with Ni(COD)2 give the nickel(0)
complexes in very high yield. The heterocyclynes and their nickel complexes have been
characterized by a variety of spectral techniques, and the X-ray crystal structures of
compounds Si(i-Pr)2(OBET), Ni[Si(i-Pr)2(OBET)], SiPh2(OBET), Ni[SiPh2(OBET)], GePh2-
(OBET), and Ni[GePh2(OBET)] are reported. The heterocyclynes and their nickel complexes
possess isomorphous structures.
In tr od u ction
Polyalkynylsilanes have attracted considerable at-
tention recently because of the possibility of σ-π
interactions between the silicon atom and the alkyne
triple bond.1 There has also been a surge of activity in
construction of strained cyclic organoethynylsilanes.2
Some rigid cyclic ethynylsilanes can undergo ring-
opening polymerization.2f,3
F igu r e 1. Structures of TBC and Ni(TBC).
The interaction of TBC and related cyclotriynes with
metal moities has resulted in the synthesis of a wide
variety of novel metallic derivatives, including Ag(I)
sandwich compounds,4 copper(I) aggregates,5 cobalt
clusters,6 and, most relevant to the current paper,
planar metallocyclynes of Ni(0)7 and Cu(I),8 Figure 1.
In this paper we report the synthesis and characteriza-
tion of three strained silicon and germanium containing
heterocyclynes in which one of the benzo rings is
replaced with an SiR2 or GeR2 moiety. Nickel(0)
complexes of these heterocyclynes are also described.
Portions of this work have appeared as a preliminary
communication.9
Exp er im en ta l P r oced u r es
Ma ter ia ls: All chemicals were purchased from Aldrich
Chemical, Co., and used as received unless otherwise stated.
Solvents used for reactions were dried and distilled before use.
THF was predried over sodium hydroxide and distilled from
sodium benzophenone ketyl, to which a small amount of
tetraethylene glycol dimethyl ether was added. Diisopropyl-
amine and piperidine were distilled from sodium hydroxide.
Trimethylsilylacetylene (Farchan) was dried over 4 Å molec-
ular sieves and degassed using freeze-pump-thaw cycles.
PdCl2(NCPh)2 was prepared by a literature method.10 The
dichlorosilanes and diphenyldichlorogermane (Gelest) were
distilled from anhydrous potassium carbonate. n-Butyllithium
(1.6 M) in hexane was freshly standardized with diphenylacetic
acid before use.11 o-2,2′-diethynyltolanetolane, (OBET)H2, was
synthesized by modifications of published procedures.12
Ni(COD)2 (COD ) 1,5-cyclooctadiene) was purchased from
Strem and used as received. All reactions were carried out
under nitrogen using standard Schlenk and vacuum-line
X Abstract published in Advance ACS Abstracts, March 15, 1997.
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metallics 1993, 12, 2078. (e) Ishikawa, M.; Hasegawa, Y.; Kunai, A. J .
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1985, 107, 3046. (f) Ishikawa, M.; Hatano, T.; Hasegawa, Y.; Horio,
T.; Kunai, A.; Miyai, A.; Ishida, T.; Tsukihara, T.; Yamanaka, T.; Kolke,
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Y.; Hosomi, A.; Makadaira, Y.; Kabuto, C. Chem. Lett. 1984, 595.
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manaka, T. Organometallics 1989, 8, 2741. (b) Ishikawa, M.; Hatano,
T.; Horio, T.; Kunai, A. J . Organomet. Chem. 1991, 412, C31. (c)
Ishikawa, M.; Horio, T.; Hatano, T.; Kunai, A. Organometallics 1993,
12, 2078. (d) Zhang, X. P.; Bazan, G. C. Macromolecules 1994, 27, 4627.
(e) Toyoda, E.; Kunai, A.; Ishikawa, M. Organometallics 1995, 14, 1089.
(4) Ferrara, J . D.; Djebli, A.; Tessier-Youngs, C.; Youngs, W. J . J .
Am. Chem. Soc. 1988, 110, 647.
(7) (a) Ferrara, J . D.; Tessier-Youngs, C.; Youngs, W. J . J . Am. Chem.
Soc. 1985, 107, 6719. (b) Ferrara, J . D.; Tanaka, A. A.; Fierro, C.;
Tessier-Youngs, C. A.; Youngs, W. J . Organometallics 1989, 8, 2089.
(c) Ferrara, J . D.; Tessier-Youngs, C.; Youngs, W. J . J . Am. Chem. Soc.
1988, 110, 3326. (d) Youngs, W. J .; Kinder, J . D.; Bradshaw, J . D.;
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metallics 1995, 14, 586.
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S0276-7333(96)00868-0 CCC: $14.00 © 1997 American Chemical Society

1686 Organometallics, Vol. 16, No. 8, 1997
Guo et al.
procedures unless otherwise noted.13 Evaporation and con-
centration in vacuo were done at water aspirator pressure.
o-Iodo((tr im eth ylsilyl)eth yn yl)ben zen e (1). o-Bromoiodo-
benzene (50 g, 0.177 mol) and trimethylsilylacetylene (26.98
mL, 0.191 mol) were added to a stirred mixture of PdCl2-
(NCPh)2 (1.695 g, 4.42 mmol), CuI (0.842 g, 4.42 mmol), and
triphenylphosphine (2.32 g, 8.84 mmol) in 1300 mL of diiso-
propylamine at 0 °C. The orange solution became lighter, and
a white precipitate formed at the end of addition of trimeth-
ylsilylacetylene. The solution turned gray to black after a half
hour. The mixture was warmed to room temperature and was
stirred overnight. The white salt was removed by filtration,
and the solvent was removed under reduced pressure. The
residue was purified by flash-chromatography on silica gel.
Elution with hexane gave 41.7 g (93% yield) of 1 as a yellowish
oil. 1H-NMR (300 MHz, CDCl3): δ 7.55 (d, 1H), 7.47 (d, H),
7.22 (t, overlap with solvent peak), 7.13 (t, 1H), 0.26 (s, 9H).
o-Br om oeth yn ylben zen e (2). A solution of 1 (41.71 g,
0.165 mol), KF (9.59 g, 0.165 mol), and water (5.94 mL, 0.33
mol) in methanol (250 mL) was stirred at room temperature
in air for 12 h. Water, hexane, and methylene chloride were
added at 0 °C. The solution was washed with water and dried
over magnesium sulfate. After evaporation of the solvent in
vacuo, the product was purified by chromatography on silica
gel. Elution with hexane gave 27.7 g (93% yield) of 2. 1H-
NMR (300 MHz, CDCl3): δ 7.57 (d, 1H), 7.51 (d, 1H), 7.26 (t,
1H), 7.18 (t, 1H), 3.36 (s, 1H).
Di-o-br om otola n e (3). Diisopropylamine (1150 mL) was
added to a flask charged with PdCl2(NCPh)2 (1.017 g, 2.65
mmol), CuI (0.505 g, 2.65 mmol), and triphenylphosphine
(1.390 g, 5.30 mmol). o-Bromoiodobenzene (42.846 g, 0.151
mol) and compound 2 (27.7 g, 0.153 mol) were introduced by
cannula to the reaction mixture. The reaction was stirred for
12 h, with the formation of a heavy precipitate. The solution
was filtered, and the solvent was removed under reduced
pressure. The residue was chromatographed on silica gel with
hexane, which was gradually changed to hexane and methyl-
ene chloride (6:1) to afford 3 in 92% yield (45.2 g) as a white
solid. 1H-NMR (300 MHz, CDCl3): δ 7.62 (q, 2H), 7.59 (q, 2H),
7.29 (t, 2H), 7.19 (t, 2H). 13C-NMR (75 MHz, CDCl3): δ 133.6,
132.5, 129.7, 127.0, 125.5, 125.1, 92.2.
Gen er a l P r oced u r e for th e Syn th esis of Sila cyclyn es
a n d Dip h en ylger m a n ecyclyn e. (3,4:7,8-Diben zod eca -3,7-
d ien e-1,5,9-tr iyn e-1,10-d iyl)d iisop r op ylsila n e (Si(i-P r )2-
(OBET)). n-Butyllithium (1.25 mL, 2.21 mmol) was added
to (OBET)H2 (250 mg, 1.105 mmol) in 50 mL of THF. The
solution turned deep red immediately. After the solution was
stirred for 7 h at room temperature, the mixture was added
to diisopropyldichlorosilane (204.6 mg, 0.199 mL, 1.105 mmol)
in 350 mL THF. After the reaction mixture was stirred at 55
°C for 24 h, the yellowish mixture was opened to air and
worked up by removal of the volatiles at reduced pressure,
extraction with CH2Cl2/H2O, and drying of the organic phase
over magnesium sulfate. The volatiles were removed under
vacuum. Chromatography on silica gel, eluting with hexane,
gave 177 mg (53% yield) of Si(i-Pr)2(OBET) as a white solid.
Crystals suitable for X-ray diffraction were grown from a
hexane and methylene chloride mixture by slow evaporation
of solvents. 1H-NMR (300 MHz, C6D6): δ 7.44 (d, 4H), 7.34
(d, 2H), 6.77 (m, 4H), 1.26 (d, 12H), 1.15 (m, 2H). 13C-NMR
(75 MHz, C6D6): δ 133.0, 131.2, 129.2, 128.9, 128.5, 126.0,
110.3, 97.1, 93.6, 18.5, 12.7. FDMS: m/z 338 (M+). Anal.
Calcd for SiC24H22: C, 85.15; H, 6.55. Found: C, 85.26; H,
6.60. IR (CtC stretch): 2153 cm-1(s).
(3,4:7,8-Diben zod eca -3,7-d ien e-1,5,9-t r iyn e-1,10-d iyl)-
d ip h en ylsila n e (SiP h 2(OBET)). (OBET)H2 (384.7 mg, 1.7
mmol) was deprotonated with n-butyllithium (1.99 mL, 3.4
mmol) in 50 mL THF for 3.5 h and added to Ph2SiCl2 (430
mg, 1.7 mmol) in 800 mL THF. After the mixture was stirred
for 14 h at 60-65 °C, the mixture was worked up as above.
Elution with hexane, changed gradually to hexane/methylene
chloride (15:1), on silica gel gave a 64% yield of SiPh2(OBET)
(444.1 mg) as a white solid. Crystals suitable for X-ray
diffraction were grown from a hexane and methylene chloride
mixture by slow evaporation of solvents. 1H-NMR (300 MHz,
C6D6): δ 7.98 (m, 4H), 7.48 (d, 2H), 7.33 (d, 2H), 7.13 (m,
overlap with solvent), 6.81 (t, 2H), 6.75 (t, 2H). 13C-NMR (75
MHz, CDCl3): δ 135.1, 132.5, 131.9, 130.7, 130.5, 128.8, 128.2,
128.2, 128.1, 124.6, 110.0, 95.8, 92.5. 13C-NMR (75 MHz, THF-
d8): δ 136.0, 133.5, 133.1, 131.7, 131.4, 130.0, 129.4, 129.3,
129.1, 125.7, 110.9, 96.9, 93.4. 1H{29Si}-HMBC NMR (600
MHz, THF-d8): δ -45.00. EI MS: m/z 406. Anal. Calcd for
C
30H18Si (406.56): C, 88.63; H, 4.46. Found: C, 88.54; H, 4.82.
Bis-o-((t r im et h ylsilyl)et h yn yl)t ola n e (4). Trimethyl-
silylacetylene (27.8 mL, 196.5 mmol) was added by syringe to
a mixture of compound 3 (22 g, 65.5 mmol), PdCl2(NCPh)2
(1.256 g, 3.28 mmol), CuI (0.624 g, 3.28 mmol), and tri-
phenylphosphine (1.718 g, 6.55 mmol) in 500 mL of piperidine.
The reaction was stirred at room temperature for 12 h, 50 °C
for 10 h, and 80 °C for 2 h. The mixture was cooled, and the
solvent was removed under vacuum. The residue was ex-
tracted with CH2Cl2 and water. The black residue was
chromatographed on silica gel, with hexane gradually changed
to a hexane and CH2Cl2 mixture (5:1) to afford 4 as a white
solid in 86% yield (20.93 g). 1H-NMR (300 MHz, C6D6): δ 7.60
(d, 2H), 7.42 (d, 2H), 6.84 (t, 2H), 6.75 (t, 2H).
IR (CtC stretch): 2153 cm-1(s).
(3,4:7,8-Diben zod eca -3,7-d ien e-1,5,9-t r iyn e-1,10-d iyl)-
d ip h en ylger m a n e (GeP h 2(OBET)). (OBET)H2 (0.1743 g,
0.77 mmol) was combined with n-butyllithium (0.885 mL, 1.54
mmol) in 25 mL of THF. After the mixture was stirred for
4.5 h, the dilithium dianion was transferred to a flask charged
with 500 mL THF. Diphenyldichlorogermane (0.229 mg, 0.77
mmol) in 20 mL of THF was added via cannula. The reaction
mixture turned to green/brown. The mixture was stirred for
14 h at room temperature and worked up in air as described
above. Elution with a hexane and methylene chloride mixture
(8:1) on silica gel gave 86.3% of GePh2(OBET) (0.426 g) as a
white solid. 1H-NMR (300 MHz, CDCl3): δ 7.72-7.76 (m, 4H),
7.63 (d, 2H), 7.51 (d, 2H), 7.39-7.43 (m, 6H), 7.32 (m, 4H).
13C-NMR (75 MHz, CDCl3): δ 134.2, 133.1, 132.5, 130.8, 130.1,
128.6, 128.5, 128.1, 128.0, 124.7, 107.8, 95.7, 92.4. 13C{1H}-
NMR (75 MHz, CDCl3): δ 107.8 (d, J ) 5.4 Hz), 95.7 (s), 92.4
(d, J ) 5.0 Hz).
P r ep a r a tion of (Ni[Si(i-P r )2(OBET)]). To a colorless
solution of Si(i-Pr)2(OBET) (75 mg, 0.22 mmol) in 30 mL
benzene was added Ni(COD)2 (68 mg, 0.247 mmol). The
solution immediately turned deep red. The reaction mixture
was stirred at room temperature for 12 h. After removal of
the volatile components in vacuo, the deep red powder Ni[Si(i-
Pr)2(OBET)] was isolated (85% yield by NMR). Crystals
suitable for X-ray structure analysis were obtained from
benzene. 1H-NMR (300 MHz, C6D6): δ 7.86 (d, 2H), 7.72 (d,
2H), 6.91 (m, 4H), 1.40 (m, 2H), 1.17 (d, 12H). 13C-NMR (75
MHz, C6D6): δ 140.7, 137.7, 132.7, 130.8, 130.0, 129.7, 127.6,
108.2, 75.0, 17.6, 13.6.
Di-o-eth yn yltola n e (OBET)H2. In air, compound 4 (6.5
g, 17.5 mmol), KF (2.036 g, 17.5 mmol), and water (1.2 mL,
70.1 mmol) were stirred in a THF/MeOH (50/40) mixture at
room temperature overnight. The reaction mixture was then
extracted with methylene chloride two times. The combined
organic phase was then dried over magnesium sulfate. The
pale yellow residue was chromatographed on silica gel, with
hexane gradually changed to a hexane and methylene chloride
mixture to afford (OBET)H2 as a white solid product in 99%
yield (3.92 g). 1H-NMR (300 MHz, C6D6): δ 7.46 (d, 2H), 7.36
(d, 2H), 6.77 (m, 4H), 2.99 (s, 2H). 1H-NMR (300 MHz,
CDCl3): δ 7.57 (d, 2H), 7.52 (d, 2H), 7.30 (m, 4H). FDMS:
m/z 362 (M+). Anal. Calcd for C18H10
: C, 95.55; H, 4.55.
Found: C, 95.45; H, 4.59. IR (CtC stretch): 2326 cm-1(w),
2106 cm-1(s).
(13) (a) Shriver, D. F.; Drezdzon, M. A. The Manipulation of Air-
Sensitive Compounds, 2nd ed.; J ohn Wiley and Sons: New York, 1986.

Planar Silicon and Germanium Heterocyclotriynes
Organometallics, Vol. 16, No. 8, 1997 1687
Ta ble 1. Cr ysta l a n d Da ta Collection P a r a m eter s
for Com p ou n d s Si(i-P r )2(OBET) a n d
Ni[Si(i-P r )2(OBET)]
P r ep a r a tion of Ni[SiP h 2(OBET)]. To a colorless solution
of SiPh2(OBET) (90 mg, 0.22 mmol) in 10 mL benzene was
added Ni(COD)2 (60.5 mg, 0.22 mmol). The solution im-
mediately turned to a deep red color. The reaction mixture
was stirred at room temperature for 8 h. Removal of the
volatile components in vacuo led to the isolation of the deep
red powder Ni[SiPh2(OBET)] (quantitative yield by NMR).
Crystals suitable for X-ray structure analysis were obtained
from benzene. 1H-NMR (300 MHz, C6D6): δ 8.05 (m, 4H), 7.85
(d, 2H), 7.72 (d, 2H), 7.15 (m, overlap with solvent), 6.93 (m,
4H). 13C-NMR (75 MHz, THF-d8): δ 141.1, 138.0, 135.5, 135.3,
131.3, 131.1, 130.5, 129.2, 2 signals at 129.0, 128.2, 107.1, 73.8.
1H{29Si}-HMBC NMR (600 MHz, THF-d8): δ -52.39. MS: m/z
464 (58Ni). IR (CtC stretch): 1996 cm-1(s), 1929 cm-1(w).
P r ep a r a tion of Ni[GeP h 2(OBET)]. To a colorless solution
of GePh2(OBET) (73.8 mg, 0.16 mmol) in 30 mL benzene was
added Ni(COD)2 (45 mg, 0.16 mmol). The solution im-
mediately turned red and gradually grew darker. The reaction
mixture was stirred at room temperature for 24 h. After
removal of the volatile components in vacuo, the deep red
powder Ni[GePh2(OBET)] was isolated (1:3 ratio of starting
material to the complex by NMR). Crystals suitable for X-ray
structure analysis were obtained from benzene. 1H-NMR (300
MHz, C6D6): δ 7.95 (d, J ) 7.9 Hz, 2H), 7.87-7.91 (m, 4H),
7.76 (d, J ) 7.0 Hz, 2H), 7.10 (td, 6H), 6.95 (m, 4H). 13C-NMR
(75 MHz, C6D6): δ 140.6, 138.4, 135.7, 135.0, 134.4, 130.8,
130.3, 130.2, 127.9, 126.0, 108.5, 68.3.
Si(i-Pr)2(OBET)
Ni[Si(i-Pr)2(OBET)]
formula
mol wt
C24H22Si
338.51
NiC24H22Si
397.2
cryst. color
cryst size (mm)
space group
a (Å)
b (Å)
c (Å)
colorless
0.21 × 0.30 × 0.42
P1h
red
0.30 × 0.40 × 0.40
P1h
8.201(2)
10.966(2)
11.451(2)
94.44(3)
90.79(3)
111.39(3)
955.0(3)
1.177
8.177(2)
10.977(2)
11.386(2)
94.12(3)
90.45(11)
111.31(3)
949.0(3)
1.390
R (deg)
â (deg)
γ (deg)
V (Å3)
Fcalcd (g cm-3
Z
)
2
2
T (K)
123
97
no. reflns (indep)
no. reflns (obs)
no. params refined
R1 (%)
2494
1972 (I > 2.0σ(I))
230
3330
2995 (F > 2σ(F))
239
9.03
3.73
R2 (%, all data)
10.8
4.29
Resu lts a n d Discu ssion
Scheme 1 presents the synthetic route to the target
ligands. Reaction of 2,2′-diethynyltolane, (OBET)H2,15
with n-butyllithium in THF at room temperature re-
sulted in immediate formation of the deep red dilithium
dianion (OBET)Li2. The heterocyclynes were obtained
by adding dialkyldichlorosilanes or dialkyldichloro-
germanes to (OBET)Li2 in highly dilute solutions (0.002
M) to avoid the formation of oligomers and polymers.17
The conditions for the formation of silicon cyclynes
included heating to 60-70 °C. The formation of the
germanium cyclyne (GePh2(OBET)) was carried out at
room temperature. Workup results in formation of the
colorless air-stable heterocyclynes. The germanium
cyclyne was prepared in a higher yield (86% for GePh2-
(OBET)) than were the silicon cyclynes (64% for SiPh2-
(OBET) and 53% for Si(i-Pr)2(OBET)). The higher yield
and milder reaction conditions for synthesizing the
germanium cyclynes than those required for silicon
cyclynes indicates that the dialkyldichlorogermanes are
more reactive toward the intermediate dilithium dianion
than the dialkyldichlorosilanes. Reactions of the three
heterocyclynes with Ni(COD)2 gave red complexes in
very high yields. The complexes are less soluble than
their ligands.
Rea ction s of Ni[SiP h 2(OBET)] w ith Ca r bon Mon oxid e
in THF Solu tion . Ni[SiPh2(OBET)] (10 mg) was added to 8
mL of THF under inert atmosphere. The red solution was
frozen with liquid N2, and the flask was evacuated. The
system was warmed to room temperature, and carbon mon-
oxide was added. The red color of the initial solution was
totally gone after 2.5 minutes. The volatile components were
1
removed under vacuum. The H-NMR spectrum showed that
Ni[SiPh2(OBET)] was completely converted to its free ligand
SiPh2(OBET).
R ea ct ion s of Solid Ni[SiP h 2(OBE T)] w it h Ca r b on
Mon oxid e. A 100 mL flask was charged with the deep red
complex Ni[SiPh2(OBET)] (10 mg). The flask was evacuated,
and carbon monoxide added. No color change was observed,
even after 1 year.
Rea ction s of Ni[SiP h 2(OBET)] w ith O2. In solution,
Ni[SiPh2(OBET)] rapidly reacts with O2, as do the other nickel
complexes reported here. In the solid state, these complexes
are very stable to O2. The crystal used for the Ni[SiPh2-
(OBET)] crystal structure was mounted in air on a glass fiber.
After 1 year of exposure to air, this crystal showed no
decomposition by X-ray diffraction.
Cr ysta l Str u ctu r e Deter m in a tion s. X-ray crystallo-
graphic data were collected using Mo KR radiation (λ ) 0.710
73 Å) on a Syntex P21 diffractometer updated to a Siemens
R3m/v and equipped with a Molecular Structure Corp. low-
temperature device. X-ray data were collected using ω scans.
Laue group symmetry was determined by photographs. Cell
dimensions were refined using selected reflections from 20° e
2θ e 30°. Three check reflections were monitored every 97
reflections during the data collection. Systematic absences
agree with the space groups. Structures were solved by direct
methods,14 and models were completed by assigning reasonable
Fourier difference electron densities.15 Hydrogen positions
were calculated using a riding model and returned before each
cycle of least-squares refinement.16 Final results are listed
in Table 1 for Si(i-Pr)2(OBET) and Ni[Si(i-Pr)2(OBET)] and
Table 2 for SiPh2(OBET), GePh2(OBET), Ni[SiPh2(OBET)], and
Ni[GePh2(OBET)].
1
The H-NMR spectra of compounds Si(i-Pr)2(OBET),
SiPh2(OBET), GePh2(OBET), and their corresponding
nickel complexes exhibit very similar patterns for the
1
protons on the tolane moieties. Signals in the H-NMR
spectra of Ni[Si(i-Pr)2(OBET)], Ni[SiPh2(OBET)], and
Ni[GePh2(OBET)] are shifted downfield from the reso-
nances in the spectra of the free ligands. Similar results
were observed for Ni(TBC) relative to TBC.7 The 13C-
NMR spectra of the representative ligand SiPh2(OBET)
and its nickel complex show that all of the signals of
SiPh2(OBET) are shifted downfield except the signal for
the alkyne carbons R to the silicon atom, C1 and C10
(see the labeling diagram in Figure 2), which was
assigned by using a 1H-coupled 13C-NMR experiment.
This resonance shifts upfield from 96.9 ppm in the free
ligand SiPh2(OBET) to 73.8 ppm in Ni[SiPh2(OBET)],
(14) SHELXS-86: Sheldrick, G. M. Acta Crystallogr., Sect. A 1990,
46, 467.
(15) SHELXTL-Plus Vers. 4.03 and 5.03: Siemens Analytical X-ray
Instruments, Inc.: Madison, WI, 1990 and 1994, respectively.
(16) SHELXL-93: Sheldrick, G. M. Universita¨t Go¨ttingen: Go¨ttin-
gen, Germany, 1993.
(17) Knops, P.; Sendhoff, N.; Mekelburger, H-B.; Vo¨gtle, F. Top.
Curr. Chem. 1991, 161, 1.

1688 Organometallics, Vol. 16, No. 8, 1997
Guo et al.
Ta ble 2. Cr ysta l a n d Da ta Collection P a r a m eter s for SiP h 2(OBET), GeP h 2(OBET), Ni[SiP h 2(OBET)], a n d
Ni[GeP h 2(OBET)]
SiPh2(OBET)
GePh2(OBET)
Ni[SiPh2(OBET)]
Ni[GePh2(OBET)]
formula
mol wt
C30H18Si
406.53
C30H18Ge
451.03
C30H18SiNi
465.24
C30H18GeNi
509.74
cryst color
cryst size (mm)
space group
a (Å)
b (Å)
c (Å)
colorless
0.20 × 0.40 × 0.60
P21/n
12.321(2)
10.034(2)
18.736(4)
108.08(3)
2201.9(7)
1.226
colorless
0.30 × 0.50 × 0.60
P21/n
12.376(2)
10.012(2)
18.858(4)
107.97(3)
2222.9(7)
1.348
red
red(darker)
0.25 × 0.30 × 0.50
P21/n
12.292(2)
10.033(2)
18.865(4)
107.45(3)
2219.5(7)
1.526
0.15 × 0.20 × 0.40
P21/n
12.231(2)
10.028(2)
18.718(4)
107.62(3)
2188.1(7)
1.412
â (deg)
V (Å3)
Fcalcd (g cm-3
Z
)
4
4
4
4
T (K)
130
95
130
109
no. reflns (indep)
no. reflns (obs)
no. params refined
R1 (%)
2875
2133 (I > 2σ(I))
283
3883
3277 (I > 2σ(I))
283
2860
2148 (I > 2σ(I))
291
3909
3020 (I > 2σ(I))
291
4.18
3.51
4.59
4.13
R2 (%, all data)
7.01
4.71
7.53
6.46
Sch em e 1
techniques (DEPT and INEPT).
A
1H{29Si}-HMBC
NMR experiment18 showed that complexing SiPh2-
(OBET) with nickel(0) also shifts the Si signal upfield
from -45.00 ppm for SiPh2(OBET) to -52.39 ppm for
Ni[SiPh2(OBET)]. HMBC is particularly useful for
observing long-range (two- or three-bond) connectivities
and can be applied to the detection of nuclei bound to
phenyl rings. The IR spectra of the ligands exhibit one
strong band at 2153 cm-1 for the νCtC stretch. The
complexation of the nickel atom to the alkynes distorts
the symmetry of the alkynes so that the complexes show
two strong νCtC stretching bands at 1996 and 1922 cm-1
.
The electronic absorption spectrum shows that the
maximum absorption occurs at 332, 334, 332, 332, and
290 nm for (OBET)H2, Si(i-Pr)2(OBET), SiPh2(OBET),
GePh2(OBET), and TBC, respectively. Among these
compounds, TBC has the lowest absorption maximum.
The rest of the compounds have similar values. Their
molar absorption coefficients are 1.90 × 104, 1.97 × 104,
2.37 × 104, 2.35 × 104, and 2.24 × 105 for OBET, Si(i-
Pr)2(OBET), SiPh2(OBET), GePh2(OBET), and TBC,
respectively.
We have examined the reactivities of Ni[SiPh2-
(OBET)] with air and CO in solution and in the solid
state. The complex Ni[SiPh2(OBET)] dissolved in THF
reacts with air to form the free ligand within 5 min. It
also decomposes to its free ligand within 2 min when
CO is bubbled into an air-free THF solution of Ni[SiPh2-
(OBET)]. These reactions are more rapid than those of
Ni(TBC). Ni[SiPh2(OBET)] as a solid does not react
with CO or air, even after being exposed to either for 1
year.
We have obtained the X-ray structures of Si(i-Pr)2-
(OBET), Ni[Si(i-Pr)2(OBET)], SiPh2(OBET), Ni[SiPh2-
(OBET)], GePh2(OBET), and Ni[GePh2(OBET)]. One of
the interesting features of these crystal structures is
that the ligands and their nickel complexes possess
isomorphous structures. Isomorphous crystals are those
in which the atomic positions are the same but differ
in the identity of the atoms; inclusion of additional
atoms also conforms with the definition.19 Both the
ligand of Si(i-Pr)2(OBET) and its nickel(0) complex
Ni[Si(i-Pr)2(OBET)] crystallize in the space group P1h
indicating the coordination of Ni(0) strongly shields the
alkyne carbons adjacent to the silicon. In TBC, the
alkyne carbon resonance shifts downfield upon coordi-
nation with nickel(0). Measurement of the 29Si NMR
of Ni[SiPh2(OBET)] was not possible using Cr(acac)3 as
a relaxation agent or by use of polarization transfer
(18) Bax, A.; Summers, M. F. J . Am. Chem. Soc. 1986, 108, 2093.
(19) Dunitz, J . K. X-Ray Analysis and the Structure of Organic
Molecules, 2nd Reprint; VCH: New York, 1995; p 123.

Planar Silicon and Germanium Heterocyclotriynes
Organometallics, Vol. 16, No. 8, 1997 1689
F igu r e 2. Thermal ellipsoid plots of Si(i-Pr)2(OBET), Ni[Si(i-Pr)2(OBET)], SiPh2(OBET), Ni[SiPh2(OBET)], GePh2(OBET),
and Ni[GePh2(OBET)], with thermal ellipsoids drawn at the 50% probability level.
with nearly equivalent unit cell dimensions and atom
positions (Table 1). Compounds SiPh2(OBET), Ni[SiPh2-
(OBET)], GePh2(OBET), and Ni[GePh2(OBET)] crystal-
lize in the space group P21/n with again nearly equiva-
lent unit cell dimensions and atom positions among the
four compounds (Table 2). This is not the case with TBC
and NiTBC nor TPC and NiTPC, which posses a similar
coordination pattern to that of the heterocyclynes
discussed here.7 The molecular structures of Si(i-Pr)2-
(OBET), Ni[Si(i-Pr)2(OBET)], SiPh2(OBET), Ni[SiPh2-
(OBET)], GePh2(OBET), and Ni[GePh2(OBET)] are
shown in Figure 2. Selected bond lengths and angles
are listed in Table 3.
The central pockets consisting of the group 14 atom
and C1-C10 in the free ligand are nearly planar. In
the complexes, this pocket and the nickel atom are
likewise nearly planar. In the four phenyl-substituted
silicon and germanium cyclynes and their complexes,
the maximum deviations from planarity for the atoms
forming the central pocket always occur at the hetero-
atoms (0.112(1) Å for Ge and 0.098(1) Å for Si) and
minima at C1 (0.001(2)-0.007(2) Å) or Ni (0.001(1)-
0.002(1) Å), indicating similar packing forces in each of
the crystals as would be expected for ismorphous
structures. Si(i-Pr)2(OBET) and Ni[Si(i-Pr)2(OBET)]
show slightly greater deviations from planarity with
maxima at C8 (0.088(2) and 0.086(2) Å) and minima at
C1 (0.007(2) and 0.005(2) Å).
For the free ligands, the pocket size is estimated by
calculating the distance from each alkyne carbon to the
centroid of the six alkyne carbons (C1, C2, C5, C6, C9,
and C10), whereas for their complexes, pocket size is
determined by calculating the distance from each alkyne
carbon to the nickel atom (Table 3). The Ni to alkyne
carbon distances are largest for the alkyne carbons R
to the silicon or germanium with Ni-C1 and Ni-C10
distances ranging from 2.047(5) to 2.094(4) Å. The
corresponding centroid to alkyne carbon distances in the
free ligands are not significantly different and range
from 2.027 to 2.087 Å. The bond lengths for the nickel
to alkyne carbons â to the Si or Ge (Ni-C2, Ni-C9) are
significantly shorter and range from 1.999(3) to 2.014(4)
Å. For the free ligands, the distances from the centroid
to alkyne carbons â to the Si or Ge, C2 and C9, range

1690 Organometallics, Vol. 16, No. 8, 1997
Ta ble 3. Selected In ter a tom ic Dista n ces (Å) a n d An gles (d eg)a
Guo et al.
Si(i-Pr)2(OBET)
Ni[Si(i-Pr)2(OBET)]
SiPh2(OBET)
Ni[SiPh2(OBET)]
GePh2(OBET)
Ni[GePh2(OBET)]
Si(Ge)-C1
Si(Ge)-C10
C1-C2
1.818(5)
1.827(5)
1.215(7)
1.206(7)
1.197(7)
1.435(7)
1.421(7)
1.428(7)
1.434(7)
2.655*
2.047*
2.029*
2.116*
2.115*
2.042*
2.055*
1.852(3)
1.842(3)
1.248(4)
1.260(5)
1.243(4)
1.443(4)
1.435(4)
1.446(4)
1.435(5)
2.548(1)
2.049(3)
2.049(3)
1.999(3)
2.001(3)
2.002(3)
1.999(3)
1.818(3)
1.826(3)
1.208(4)
1.205(3)
1.194(4)
1.430(4)
1.435(4)
1.429(4)
1.434(4)
2.615
2.041
2.027
2.140
2.143
2.029
2.028
1.840(5)
1.840(5)
1.250(6)
1.253(6)
1.237(6)
1.437(7)
1.447(7)
1.439(7)
1.450(7)
2.509(2)
2.052(4)
2.047(5)
1.999(5)
2.005(5)
1.990(5)
1.989(4)
1.895(3)
1.903(3)
1.204(4)
1.205(4)
1.205(4)
1.431(4)
1.428(4)
1.431(4)
1.440(4)
2.684
2.087
2.067
2.160
2.166
2.031
2.031
1.931(5)
1.931(4)
1.237(6)
1.250(6)
1.239(6)
1.443(6)
1.439(6)
1.437(6)
1.444(6)
2.592(1)
2.092(4)
2.094(4)
2.002(4)
2.014(4)
1.991(4)
1.997(4)
C9-C10
C5-C6
C2-C3
C4-C5
C6-C7
C8-C9
Ni-Si(Ge)
Ni-C1
Ni-C10
Ni-C2
Ni-C9
Ni-C5
Ni-C6
C1-Si(Ge)-C10
Si(Ge)-C1-C2
Si(Ge)-C10-C9
C1-C2-C3
100.1(2)
162.7(4)
163.6(4)
175.6(5)
175.1(5)
177.1(5)
177.2(5)
105.4(1)
151.2(3)
151.3(2)
169.4(3)
169.6(3)
172.1(3)
171.5(3)
101.6(1)
162.5(2)
163.5(3)
174.7(3)
174.4(3)
177.5(3)
178.3(3)
107.0(2)
149.8(4)
150.0(4)
168.5(5)
169.7(5)
171.6(5)
171.3(5)
100.6(1)
161.5(2)
162.6(3)
176.0(3)
175.2(3)
177.2(3)
178.1(3)
105.1(2)
148.6(4)
148.5(4)
167.0(4)
167.7(5)
170.7(4)
171.7(5)
C10-C9-C8
C4-C5-C6
C7-C6-C5
a
Distances indicated by * are from the calculated centroid of the alkyne carbons to each alkyne carbon for the free ligands.
from 2.115 to 2.166 Å. The nickel to alkyne carbon
distances for the alkyne carbons bridging two phenyl
groups range from 1.989(4) to 2.002(3) and are signifi-
cantly shorter than the centroid to alkyne carbon
distances in the free ligands (2.028-2.055 Å) but are
not significantly different from those for the nickel to
alkyne carbons â to the Si(Ge). The nickel to alkyne
carbon distance in Ni(TBC) is 1.958(5) Å. The Si(i-Pr)2-
(OBET), SiPh2(OBET), and GePh2(OBET) free ligands
appear to have pockets slightly smaller than TBC,
whereas their corresponding nickel complexes, Ni[Si(i-
Pr)2(OBET)], Ni[SiPh2(OBET)], and Ni[GePh2(OBET)],
have significantly larger pockets than Ni(TBC).
An unusual mode of an alkyne bonding to a metal is
observed in the three nickel complexes. The alkyne
moieties next to the heteroatoms of the nickel complexes
adopt a trans geometry rather than a cis geometry, as
expected from the Dewar-Chatt-Duncanson bonding
model.20 The trans geometry is all the more surprising
if one considers that planarity of the central pocket is
preserved in the nickel complexes. The silicon or
germanium atoms do not deviate any more from the
plane of the ligand in the nickel complexes toward what
would be a cis configuration than they do in the
corresponding free ligands (see Table 3). In all three
nickel complexes, C1 and C10 are displaced away from
the nickel(0) slightly. In comparison with their corre-
sponding ligands, the E-C1-C2 and E-C10-C9 angles
(E ) Si or Ge) are shifted by averages of 11.95°, 13.10°,
and 13.45° for Ni[Si(i-Pr)2(OBET)], Ni[SiPh2(OBET)],
and Ni[GePh2(OBET)], respectively. Carbons 2 and 9
are displaced toward the nickel atom causing the C1-
C2-C3 and C8-C9-C10 angles to shift upon complex-
ation by averages of 15.15°, 16.35°, and 17.05° for
Ni[Si(i-Pr)2(OBET)], Ni[SiPh2(OBET)], and Ni[GePh2-
(OBET)], respectively. The E-CtC angles range from
148.5(4)° to 151.3(2)°, and the CtC-Ph angles adjacent
to the heteroatoms range from 167.0(4)° to 169.7(5)° in
the three nickel(0) complexes.
The alkynes next to the heteroatom, C1tC2 and
C9tC10, have average bond distances of 1.254(5),
1.252(6), and 1.244(6) Å for Ni[Si(i-Pr)2(OBET)],
Ni[SiPh2(OBET)], and Ni[GePh2(OBET)], respectively,
which is an increase of approximately 0.05 Å from the
free ligands. These are longer, but not significantly so,
than the alkynes, C5tC6, bridging the two phenyl rings,
which have bond distances of 1.243(4), 1.237(6), and
1.239(6) Å for Ni[Si(i-Pr)2(OBET)], Ni[SiPh2(OBET)],
and Ni[GePh2(OBET)], respectively. This indicates that
complexation of C1tC2 and C9tC10 to nickel may be
slightly stronger than that of C5tC6. The average
alkyne bond lengths in Ni(TBC) and Ni(TPC) are
1.240(10) and 1.244(5) Å, respectively. The reported
CtC length in L2Ni(XCtCY) type complexes is ca. 1.27
-1.28 Å.21
The coordination of the nickel into the trialkyne
pockets enlarges the C1-E-C10 (E ) Si or Ge) angles
from 100.1(2)°, 101.6(1)°, and 100.6(1)° for Si(i-Pr)2-
(OBET), SiPh2(OBET), and GePh2(OBET), respectively,
to 105.4(1)°, 107.0(2)°, and 105.1(2)° for the correspond-
ing complexes (Table 3). Incremental release of the
strain on the heteroatoms toward the normal tetrahe-
dral angle is observed in the series. The silicon and
germanium alkyne carbon bond lengths are increased
significantly upon complexation. However, in both the
complexes and in the free ligands, E-C distances show
the shortening expected for E-C(sp) as compared to
E-C(sp3).22
In Ni[Si(i-Pr)2(OBET)], Ni[SiPh2(OBET)], and Ni-
[GePh2(OBET)], relatively short Ni-E separations are
observed of 2.548(1), 2.509(2), and 2.592(4) Å, respec-
tively. The question arises whether these short Ni-E
contacts represent a bonding interaction. The sum of
(21) Bonrath, W.; Po¨rschke, R. K.; Wilke, G.; Angermund, K.;
Kru¨ger, C. Angew. Chem., Int. Ed. Engl. 1988, 27, 833.
(22) (a) Sheldrick, W. S. In The Chemistry of Organsilicon Com-
pounds; Patai, S., Rappoport, Z., Eds.; J ohn Wiley & Sons: New York;
Chapter 3. (b) Lukevics, E.; Pudova, O.; Strukovich, R. Molecular
Structure of Organosilicon Compounds; Ellis Horwood: Chichester,
England, 1989; Chapter 1. (c) Baines, K. M.; Stibbs, W. G. Coord. Chem
Rev. 1995, 145, 157. (d) Molloy, K. C.; Zuckerman, J . J . Adv. Inorg.
Chem. Radiochem. 1983, 27, 113.
(20) (a) Dewar, M. J . S. Bull. Soc. Chim. Fr. 1951, 18, C71. (b) Chatt,
J .; Duncanson, L. A. J . Chem. Soc. 1953, 2939.

Planar Silicon and Germanium Heterocyclotriynes
Organometallics, Vol. 16, No. 8, 1997 1691
the covalent radii of nickel and silicon or germanium
are in the range 2.32-2.41 Å and 2.37-2.43 Å.23-25
Using Pauling’s equation to estimate bond order,26 the
observed Ni-E separations correspond to bond orders
of 0.48-0.89 for the silicon complexes and 0.49-0.59
for the germanium complex, when compared to the sum
of covalent radii. Ni-Si single-bond lengths are found
to be at or below the sum of the covalent radii for the
halide-substituted compounds Ni(SiCl3)2(CO)3 (2.383(3)
and 2.289(3) Å)27 and Ni(SiF3)2(PMe3)3 (2.182(4) Å)28 and
for the theoretical compounds Ni(SiH2)5 (2.20 Å) and
Ni(SiH2)6 (2.41 Å).29 Actual Ni-Ge single-bond dis-
tances range from smaller to larger than the sum of
covalent radii in [Ni(GePh3)(Cp)(CdGePh3)]2Cd (2.308
Å),30 [N(PPh3)2]2[Ni10(µ10-Ge)(CO)20] (2.470(1) Å), and
[N(PPh3)2]2[Ni12(µ12-Ge)(CO)22] (2.493(1) and 2.691(1)
Å).31 The distance of the E atom from the calculated
centroid (determined from C1, C2, C5, C6, C9, and C10)
is 2.655, 2.615, and 2.648 Å for the free ligands Si(i-
Pr)2(OBET), SiPh2(OBET), and GePh2(OBET), respec-
tively, a distance which is considerably larger than the
Ni-E distance observed in the complexes. This sug-
gests a Ni-E bonding interaction because it appears the
E atom has been pulled in by complex formation. The
significantly longer Ni-Si distance (by 0.039 Å) in
Ni[Si(i-Pr)2(OBET)] than that in Ni[SiPh2(OBET)] is
consistent with a Ni f Si dative interaction because a
SiPh2 moiety would be a better acceptor of electron
density than a Si(i-Pr)2 moiety. A Ni f E dative
interaction rather than a normal Ni-E covalent bond
is consistent with the observed long distances and
calculated weak bond orders. As discussed below, a Ni
f E is not the only possible explanation for the Ni-E
distances.
F igu r e 3. Packing diagram of Ni[Si(i-Pr)2(OBET)].
Polycarbosilanes containing main-chain acetylenic
units have electron delocalization through the silicon
atoms via σ*-π hyperconjugation.32 By way of σ*-π
hyperconjugation, it is generally accepted that silicon
can stabilize partial â-positive and R-negative charges.33
Asymmetrically substituted acetylenes, especially those
substituted by SiR3 (R ) Me or Ph), show a significant
increase in polarization on coordination to Ni(0) in the
complexes (Ph3P)2Ni(µ2-PhCtCSiR3).34 Polarization of
an alkyne C≡C bond should give rise to different
F igu r e 4. Packing diagram of SiPh2(OBET).
bonding distances for each of the acetylenic carbons to
the complexed metal as in (Ph3P)2Ni(µ2-PhCtCSiMe3)
where the Ni-C(Ph) distance is 1.884(6) Å and the Ni-
C(SiMe3) distance is 1.926(6) Å. Consistent with this,
in the three nickel complexes reported here, the Ni-
C1 and Ni-C10 distances are significantly longer (ca.
0.06 Å) than the Ni-C2 and Ni-C9 distances. This
may partially account for the expansion of the C1-E-
C10 angle, the novel trans geometry of the complexed
acetylenes directly adjacent to the silicon, and the short
Ni-E contact. However, the nickel complexes reported
herein show some differences from (Ph3P)2Ni(µ2-
PhCtCSiR3). In the 13C NMR spectra of (Ph3P)2Ni(µ2-
PhCtCSiR3), both alkyne carbon resonances shift down-
field from those of the free ligand. As discussed earlier,
this is different from what is observed for Ni[Si(i-Pr)2-
(OBET)], Ni[SiPh2(OBET)], and Ni[GePh2(OBET)].
These differences may be due to the strain imposed by
the cyclic system or may indicate some other difference
in the bonding, such as a Ni-E interaction. It is unclear
whether the upfield shift in the 29Si NMR observed
between SiPh2(OBET) and Ni[SiPh2(OBET)] is indica-
tive of a Ni-Si bonding interaction. Unfortunately 29Si
NMR of (Ph3P)2Ni(µ2-PhCtCSiR3), which could serve
as reference molecules for an unstrained system, were
not reported. More definitive answers with respect to
any metal to group 14 bonding may be obtained if we
(23) The available values of covalent radii are for Ni(II) complexes.
It would be expected that Ni(0) would be slightly larger than Ni(II).
(24) Huheey, J . E.; Keiter, E. A.; Keiter, R. L. Inorganic Chemistry,
4th ed.; Harper Collins: New York, 1993; p 292.
(25) Emsley, J . The Elements, 2nd ed.; Clarendon Press: Oxford,
1991; pp 78, 126, 174.
(26) Pauling, L. The Nature of the Chemical Bond, 3rd ed.; Cornell
University: Ithaca, NY, 1960; p 239.
(27) J anikowski, S. K.; Radonovich, L. J .; Groshens, T. J .; Klabunde,
K. J . Organometallics 1985, 4, 396.
(28) Bierschenk, T. R.; Guerra, M. A.; J uhlke, T. J .; Larson, S. B.;
Lagow, R. J . J . Am. Chem. Soc. 1987, 109, 4855.
(29) Tang, H.; Hoffman, D. M.; Albright, T. A.; Deng, H.; Hoffmann,
R. Angew. Chem., Int. Ed. Engl. 1993, 32, 1616-1618.
(30) Titova, S. N.; Bychkov, V. T.; Domrachev, G. A.; Ruzavaev, G.
A.; Struchkov, Yu. T.; Zakharov, L. N. J . Organomet. Chem. 1980, 187,
167.
(31) Ceriotti, A.; Demartin, F.; Heaton, B. T.; Ingallina, P.; Longoni,
G.; Manassero, M.; Marchonna, M.; Masciocchi, N. J . Chem. Soc.,
Chem. Commun. 1989, 786.
(32) Corriu, R. J . P.; Douglas, W. E.; Yang, Z; Karakus, Y.; Cross,
G. H.; Bloor, D. J . Organomet. Chem. 1993, 455, 69-76.
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1692 Organometallics, Vol. 16, No. 8, 1997
Guo et al.
prepare the platinum complexes Pt[SiR2(OBET)]. The
magnitude of the couplings between 195Pt and 29Si and
13C may help us determine the types of bonding involved
in such complexes.
isomorphs do not stack, but the interplanar distances
between the two molecules related by an inversion
center is 3.590, 3.567, 3.573, and 3.561 Å for SiPh2-
(OBET), Ni[SiPh2(OBET)], GePh2(OBET), and Ni[GePh2-
(OBET)], respectively. The interplanar distance in
Ni(TBC) is 3.35(1) Å. The close interplanar stacking
in Si(i-Pr)2(OBET) and Ni[Si(i-Pr)2(OBET)], if present
in doped systems, would be expected to provide in-
creased conductivity.
For the purpose of predicting one-dimensional con-
ductivity, it is important to compare Ni-Ni intermo-
lecular distances and packing patterns among the nickel
cyclyne complexes. There are two packing patterns
among the six compounds due to their isomorphous
crystal structures, depending on whether the group 14
atom has isopropyl or phenyl substituents. One pattern
is of Si(i-Pr)2(OBET) and its nickel complex (Figure 3).
The other is that of the phenyl-substituted heterocy-
clynes of SiPh2(OBET), Ni[SiPh2(OBET)], and the ger-
manium analogs (Figure 4). The central pockets of Si(i-
Pr)2(OBET) and Ni[Si(i-Pr)2(OBET)] molecules are
stacked parallel to each other. The interplanar distance
of 3.463 Å in the free ligand decreases to 3.258 Å in the
nickel complex. In contrast, Ni[SiPh2(OBET)] and its
Ack n ow led gm en t. We thank the National Science
Foundation for financial support and Dr. Robert Lat-
timer of BFGoodrich for providing the FD-MS data.
Su p p or tin g In for m a tion Ava ila ble: Tables of anisotro-
pic thermal parameters, bond lengths and angles, hydrogen
parameters, and least squares planes (42 pages). Ordering
information is given on any current masthead page.
OM960868R