Cobalt Complexes of Silicon and Germanium Heterocyclotriynes with One or Two Cyclyne Rings

Article abstract of DOI:10.1021/om9901675

The synthesis and structural characterization of Ge(OBET)₂, SiPh₂(OBET)(Co₂(CO)₆)₂, and Ge(OBET)₂(Co₂(CO)₆)₂ are reported. Reaction of Li₂(OBET), generated in situ from the reaction of nBuLi and o-(bisethynyl)tolane (OBET)H₂, with GeCl₄ in a 2:1 molar ratio gave Ge(OBET)₂ in 64% yield. Ge(OBET)₂ was characterized by ¹H NMR, ¹³C NMR, elemental analysis, FDMS, and X-ray crystallography. Co₂(CO)₈ selectively complexes to the bent alkynes adjacent to Ge or Si of Ge(OBET)₂ and SiPh₂(OBET) and severely distorts the ligands. Comparisons are made to related complexes.

Full text of DOI:10.1021/om9901675

Organometallics 1999, 18, 1767-1773
1767
Coba lt Com p lexes of Silicon a n d Ger m a n iu m
Heter ocyclotr iyn es w ith On e or Tw o Cyclyn e Rin gs
Li Guo, J oseph M. Hrabusa III, Mark D. Senskey, David B. McConville,
Claire A. Tessier,* and Wiley J . Youngs*
Department of Chemistry, The University of Akron, Akron, Ohio 44325-3601
Received March 9, 1999
The synthesis and structural characterization of Ge(OBET)2, SiPh2(OBET)(Co2(CO)6)2, and
Ge(OBET)2(Co2(CO)6)2 are reported. Reaction of Li2(OBET), generated in situ from the
reaction of nBuLi and o-(bisethynyl)tolane (OBET)H2, with GeCl4 in a 2:1 molar ratio gave
1
Ge(OBET)2 in 64% yield. Ge(OBET)2 was characterized by H NMR, 13C NMR, elemental
analysis, FDMS, and X-ray crystallography. Co2(CO)8 selectively complexes to the bent
alkynes adjacent to Ge or Si of Ge(OBET)2 and SiPh2(OBET) and severely distorts the ligands.
Comparisons are made to related complexes.
In tr od u ction
with alkynes,9 whereas the third alkyne remains un-
complexed even if excess dicobalt octacarbonyl is used.
Another way to alter the size of the central pocket is
to substitute a heteroatom such as silicon or germanium
for one of the benzene rings in TBC. We have previously
described one such compound, SiPh2(OBET).10 Here we
report the synthesis and crystallographic characteriza-
tion of the dipocket heterocyclyne Ge(OBET)2 and the
selective complexation of Co2(CO)8 with SiPh2(OBET)
and Ge(OBET)2.
Tribenzocyclotriyne (TBC) and its analogues have
demonstrated intriguing and diverse reactivities toward
transition metals.1 The important feature of this ligand
system is that three soft, polarizable alkynes are fixed
in a trigonal plane. It has been shown that the size of
the transition metal is extremely important in deter-
mining its coordination pattern toward TBC and the
structure of mono metal complexes. The smaller transi-
tion metals, cobalt,2 nickel,3 and copper,4 reside in the
pocket of TBC; whereas larger transition metals such
as silver5 form sandwich complexes.6 The size of the
central pocket of TBC can be altered by using thieno
groups instead of benzene rings in the system (TTC).7
This change results in dramatically different coordina-
tion chemistry, demonstrated by the differences between
the two cobalt complexes of TBC2 and TTC8 (see below
for structures). In the TBC tetracobalt complex, one
cobalt atom resides in the cavity of TBC. The other three
cobalt atoms, one above each of the three alkynes, form
a total of three Co-Co bonds with the cobalt atom at
the center. In the TTC cobalt complex two dicobalt-
hexacarbonyl moieties are bound to two alkynes, in the
typical way that dicobalthexacarbonyl forms complexes
(1) (a) Ferrara, J . D.; Tanaka, A. A.; Fierro, C.; Tessier-Youngs, C.
A.; Youngs W. J . Organometallics 1989, 8, 2089. (b) Ferrara, J . D.;
Tessier-Youngs, C.; Youngs, W. J . J . Inorg. Chem. 1988, 27, 2201. (c)
Kinder, J . D.; Tessier, C. A.; Youngs, W. J . Synlett 1993, 149. (d)
Youngs, W. J .; Kinder, J . D.; Bradshaw, J . D. Organometallics 1993,
12, 2406.
Exp er im en ta l P r oced u r es
(2) Djebli, A.; Ferrara, J . D.; Tessier-Youngs, C.; Youngs, W. J . J .
Chem. Soc., Chem. Commun. 1988, 548.
Ma ter ia ls. All chemicals were purchased from Aldrich and
used as received unless otherwise stated. Solvents for reactions
were dried and distilled before use. Tetrahydrofuran (THF)
(Fisher), diethyl ether, and hexane were predried over sodium
hydroxide and distilled from sodium benzophenone ketyl to
which a small amount of tetraethylene glycol dimethyl ether
was added. Germanium tetrachloride was purchased from
Gelest and was distilled from anhydrous potassium carbonate
(3) Ferrara, J . D.; Tessier-Youngs, C.; Youngs, W. J . J . Am. Chem.
Soc. 1985, 107, 6719.
(4) Ferrara, J . D.; Tessier-Youngs, C.; Youngs, W. J . Organometallics
1987, 6, 676.
(5) Ferrara, J . D.; Djebli, A.; Tessier-Youngs, C.; Youngs, W. J . J .
Am. Chem. Soc. 1988, 110, 647.
(6) (a) Dunbar, R. C.; Solooki, D.; Tessier, C. A.; Youngs, W. J .;
Asamoto, B. Organometallics 1991, 10, 52. (b) Dunbar, R. C.; Uechi,
G. T.; Solooki, D.; Tessier, C. A.; Youngs, W. J . J . Am. Chem. Soc. 1993,
115, 12477.
(7) Solooki, D.; Kennedy, V. O.; Tessier, C. A.; Youngs, W. J . Synlett
1990, 7, 427.
(8) Solooki, D.; Bradshaw, J . D.; Tessier, C. A.; Youngs, W. J .
Organometallics 1994, 13, 451.
(9) Sly, W. G. J . Am. Chem. Soc. 1959, 81, 18
(10) Guo, L.; Bradshaw, J . D.; Tessier, C. A.; Youngs, W. J .
Organometallics 1995, 14, 586.
10.1021/om9901675 CCC: $18.00 © 1999 American Chemical Society
Publication on Web 04/08/1999

1768 Organometallics, Vol. 18, No. 9, 1999
Guo et al.
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 SiP h 2(OBET)(Co2(CO)6)2, Ge(OBET)2, a n d
Ge(OBET)2(Co2(CO)6)2
SiPh2(OBET)(Co2(CO)6)2
Ge(OBET)2
Ge(OBET)2(Co2(CO)6)2
formula
mw
cryst color
cryst size [mm]
space group
a [Å]
Co4SiO12C42H18
978.37
deep red
0.40 × 0.50 × 0.60
P21/n
12.099(7))
15.627(8)
21.699(10)
90
90.32(4)
90
4102(4)
1.584
GeC36H16 C4H8O
593.18
colorless
0.16 × 0.26 × 0.38
P1h
10.443(2)
11.400(2)
13.459(3)
104.61(3)
111.46(3)
94.28(3)
1418.0(5)
1.389
Co4GeO12C48H16
1092.92
deep red
0.25 × 0.50 × 0.55
P21/n
11.540(7)
20.99(2)
18.60(2)
90
90.48(6)
90
4503(7)
1.621
b [Å]
c [Å]
R [deg]
â [deg]
γ [deg]
V [Å3]
F
calcd [g cm-3
Z
]
4
2
4
T [K]
137
131
103
no. of reflec [indep]
7209
4725
7278
no. of reflec [obs, I > 2.0σ(I)]
no. of params refined
R1 [%] (obs data on F)
R2 [%] (all data on F2)
5219
532
6.33
9.54
3443
379
5.95
9.61
2732
571
9.64
24.92
to remove dissolved HCl. n-Butyllithium (1.6 M) in hexane was
purchased from Aldrich and was standardized with diphenyl-
acetic acid.11 Dicobalt octacarbonyl was purchased from Strem
and used as received. o-(Bisethynyl)tolane ((OBET)H2)12 and
3,4:7,8-dibenzocyclo-3,7-diene-1,5,9-triyne-diphenylsilane (SiPh2-
(OBET))10,12b were prepared as described previously. All reac-
tions were carried out under nitrogen using standard Schlenk,
vacuum line, and glassware techniques unless otherwise
noted.13
of hexane in an inert atmosphere box. The brown mixture was
stirred at room temperature for 22 h. The solvent and any
unreacted dicobalt octacarbonyl were pumped off under vacuum
for 1.5 h. The residue was dissolved in diethyl ether and
hexane, filtered, and crystallized. The NMR results indicated
the reaction was quantitative. With a large excess of Co2(CO)8
the same product is obtained in quantitative yield based on
1
SiPh2(OBET). H NMR (300 MHz, C6D6): δ 8.07 (d, 4H), 7.64
(d, 2H), 7.44 (d, 2H), 7.19 (m, overlap with solvent peak), 6.95
(sextet, 4H). 13C NMR (75 MHz, C6D6): δ 200.4, 141.1, 137.2,
136.7, 133.8, 131.0, 130.2, 128.6, 128.5, 128.2. IR: 2082, 2061,
2052, 2021, 1865, 1606 cm-1. Several attempts to get elemental
analysis of the cobalt complex, Co4SiO12C42H18, which was
shown to be clean by NMR, were unsatisfactory. Spectra of
the complex have been included in the Supporting Infor-
mation.
Bis(3,4:7,8-d ib e n zocyclo-3,7-d ie n e -1,5,9-t r iyn e )ge r -
m an e (Ge(OBET)2). To a 100 mL flask charged with (OBET)H2
(226.3 mg, 1.0 mmol) in 40 mL of THF was added n-
butylithium (1.32 mL, 1.51 M, 2.0 mmol) in a drybox. The
solution turned deep red immediately. After 5 h of stirring at
room temperature, the mixture was added via cannula to
germanium tetrachloride (107 mg, 0.057 mL, 0.5 mmol) in 460
mL of THF at room temperature. The reaction mixture was
brownish after adding half of the dilithium acetylide. The
reaction mixture was stirred at room temperature for 12 h. It
was opened to air, the THF was removed under vacuum, the
solid residue was dissolved in CH2Cl2 and washed with H2O,
and the organic phase was dried over magnesium sulfate. The
volatiles were evaporated under vacuum. The crude products
were purified by chromatography on silica gel. Eluting with
hexanes that were gradually changed to hexane/CH2Cl2 (3:1)
gave 46% (121 mg) of the white solid product Ge(OBET)2.
Ge(OBET)2 has relatively poor solubility in hydrocarbon
solvents, but is soluble in THF at 40-50 °C. 1H NMR (300
MHz, CDCl3): δ 7.65 (dd, 4H), 7.51 (dd, 4H), 7.40 (td, 4H),
7.32 (td, 4H). 13C NMR (75 MHz, CDCl3): δ 132.8, 131.4, 129.4,
Coba lt Com p lex of Bis(3,4:7,8-d iben zocyclo-3,7-d ien e-
1,5,9-tr iyn e)ger m a n e (Ge(OBET)2(Co2(CO)6)2). A Schlenk
flask was charged with Ge(OBET)2 (52.1 mg, 0.1 mmol) and
50 mL of hexane. Dicobalt octacarbonyl (144 mg, 0.4 mmol)
with 5% of hexane was added to the suspension of Ge(OBET)2
in hexane in a drybox. The mixture was stirred at room
temperature. After 18 h the white solid Ge(OBET)2 was gone.
After an additional 24 h the solvent and any unreacted dicobalt
octacarbonyl were pumped off under vacuum for 5 h. The
residue was dissolved in hexane and filtered. X-ray quality
deep red crystals were successfully grown from a mixture of
hexane and diethyl ether. The NMR results indicated an 80%
1
yield. H NMR (300 MHz, C6D6): δ 7.76 (d, 2H), 7.44 (q, 4H),
7.25 (d, 2H), 6.88 (m, 2H) 6.74 (m, 2H). 13C NMR (75 MHz,
C6D6): δ 199.4, 138.9, 134.4, 133.1, 132.6, 131.0, 129.7, 128.7,
128.5, 128.2, 125.1, 122.8, 108.3, 99.3, 98.2, 97.9, 92.7, 79.0.
IR 2086, 2061, 2054, 2029, 1865 cm-1. Several attempts to get
elemental analysis of the cobalt complex, which was shown to
be clean by NMR, were unsatisfactory. Spectra of the complex
have been included in the Supporting Information.
128.5, 128.4, 124.0, 107.4, 92.5, 91.9. IR (CtC): 2161 cm-1
.
FDMS: m/z 522 (M+), 261 (M2+), molecular ion peaks are
observed at 518, 519, 520, 521, 522, 523, and 524 due to the
isotopes of germanium and carbon. Anal. Calcd for GeC36H16
C 82.98, H 3.18. Found: C 82.13; H 3.24.
:
Cobalt Com plex of 3,4:7,8-Diben zocyclo-3,7-dien e-1,5,9-
tr iyn e-d ip h en ylsila n e (SiP h 2(OBET)(Co2(CO)6)2). To a
solution of SiPh2(OBET) (102 mg, 0.25 mmol) in 20 mL of
diethyl ether was added Co2(CO)8 (185 mg, 0.5 mmol) with 8%
Cr yst a l St r u ct u r e Det er m in a t ion s. X-ray crystallo-
graphic data were collected using graphite-monochromated 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. Crystals of complexes suitable for
X-ray diffraction were grown from a mixture of hexane and
diethyl ether by slow evaporation of solvents. Crystals of
Ge(OBET)2 were obtained from THF. Cell dimensions were
refined using 20-30 reflections with 20° e 2θ e 30°. Three
check reflections were monitored every 97 reflections during
(11) Kofron W. G.; Baclawski L. M. J . Org. Chem. 1976, 41, 1879.
(12) (a) Diercks, R.; Vollhardt, K. P. C. Angew. Chem., Int. Ed. Engl.
1986, 3, 266-267. (b) Guo, L.; Bradshaw, J . D.; McConville, D. B.;
Tessier, C. A.; Youngs, W. J . Organometallics 1997, 16, 1685.
(13) (a) Shriver, D. F.; Drezdzon, M. A. The Manipulation of Air-
Sensitive Compounds, 2nd ed.; J ohn Wiley and Sons: New York, 1986.
(b) Wayda, A. L.; Bianconi, P. A. In Experimental Organometallic
Chemistry; Wayda, A. L., Darensbourg, M. Y., Eds.; ACS Symposium
Series 357; American Chemical Society: Washington, DC, 1987; pp
76-78.

Co Complexes of Si and Ge Heterocyclotriynes
Organometallics, Vol. 18, No. 9, 1999 1769
Sch em e 1
F igu r e 1. Molecular structure of Ge(OBET)2 with thermal
ellipsoids drawn at 50% probability. Hydrogen atoms are
omitted for clarity.
data collection. The structures were solved by direct methods.14
Hydrogens were calculated, and further refinements15 were
done using a riding model for the hydrogen atoms. Further
details, refinement parameters, and results are listed in Table
1.
Resu lts a n d Discu ssion :
Scheme 1 outlines the synthetic route for Ge(OBET)2.
The precursor o-(bisethynyl)tolane (OBET)H2 was pre-
pared by literature methods.12 Deprotonation of (OBET)-
H2 with 2 equiv of n-butyllithium produced Li2(OBET).
Addition of 0.5 mol of germanium tetrachloride per mole
of Li2(OBET) at room temperature resulted in the
formation of Ge(OBET)2 with a 46% yield. Ge(OBET)2
was characterized by 1H NMR, 13C NMR, elemental
analysis, FDMS, and X-ray crystallography. Ge(OBET)2
is an air stable white solid with relatively poor solubility
compared to SiPh2(OBET)2. The UV spectra for Ge-
(OBET)2 and SiPh2(OBET) are similar with absorption
maxima at 334 nm (ꢀ ) 8.1 × 104) and 332 nm (ꢀ ) 2.4
× 104), respectively.
F igu r e 2. Packing diagram of Ge(OBET)2.
and C(15)-C(16), are 1.208(7) and 1.197(7) Å, respec-
tively, while the bond lengths of the four alkynes next
to germanium range from 1.191(7) to 1.207(7) Å. The
four Ge-alkyne bond lengths range from 1.884(5) to
1.889(6) Å. The inner germanium alkyne angles of C1-
Ge-C10 and C11-Ge-C20 are 100.9(2)° and 100.6(2)°,
respectively. These angles are approximately 8° smaller
than a normal tetrahedral angle. The comparable angle
in SiPh2(OBET) is 101.6(1)°. A THF solvent molecule
cocrystallized with Ge(OBET)2. The packing diagram of
Ge(OBET)2 is shown in Figure 2. The principal feature
is that one of the cyclyne rings in the first molecule is
parallel to another in the second molecule.
A crystal of Ge(OBET)2 suitable for crystallographic
characterization was obtained by slow evaporation of
THF from a Ge(OBET)2/THF solution. Ge(OBET)2 crys-
tallized in the triclinic space group P1h with one molecule
per asymmetric unit. The thermal ellipsoid labeling
diagram of Ge(OBET)2 is shown in Figure 1, and the
packing diagram is shown in Figure 2. Selected bond
lengths and angles are listed in Table 2. Each hetero-
cyclyne ring in the molecule of Ge(OBET)2 is planar.
The principal plane composed of atoms Ge and C1-C10
deviates from planarity by a mean deviation of 0.0510
Å, with individual deviations ranging from -0.1159 Å
at C1 to -0.0046 Å at C9. The other principal plane
composed of Ge and C11-C20 deviates from planarity
by a mean deviation of 0.0552 Å, with deviations
ranging from -0.1343 Å at Ge to -0.0002 Å at C14. Due
to the tetrahedral geometry of the germanium atom, the
two pockets are nearly perpendicular to each other with
a dihedral angle of 96.8°. The bond lengths of the two
alkynes located between two phenyl rings, C(5)-C(6)
Syn th esis of Coba lt Com p lexes of SiP h 2(OBET)
a n d Ge(OBET)2 a n d Th eir Cr ysta l Str u ctu r es. In
the hope that an analogue of the TBC cobalt complex,
TBC(Co4(CO)9), might be obtained, we combined 2 molar
equiv of Co2(CO)8 with SiPh2(OBET) in diethyl ether
at room temperature. The synthetic route is outlined
in Scheme 2. Both the starting material and the product
1
were soluble. H and 13C NMR results indicated that
SiPh2(OBET) reacted completely with the formation of
only one product. Crystals suitable for X-ray crystal-
lographic analysis were obtained from a solvent mixture
of diethyl ether and hexane. We have found that this is
a very effective solvent mixture for crystallization for
these and related molecules. The more volatile and polar
solvent, diethyl ether, evaporates first. Thus the polarity
of the mixture decreases gradually, solubility of the
solute decreases, and crystals form. The complex SiPh2-
(OBET)(Co2(CO)6)2 has a deep red color.
(14) SHELXS-86: Sheldrick, G. M. Acta Crystallogr., Sect. A 1990,
46, 467.
(15) SHELXL-93: Sheldrick, G. M. Universita¨t Go¨ttingen, Go¨ttin-
gen, Germany, 1993.
SiPh2(OBET)(Co2(CO)6)2 crystallizes in the monoclinic
space group P21/n with one molecule per asymmetric
unit. The thermal ellipsoid labeling diagram for SiPh2-

1770 Organometallics, Vol. 18, No. 9, 1999
Guo et al.
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for Ge(OBET)2 a n d Ge(OBET)2(Co2(CO)6)2
Ge(OBET)2-
Ge(OBET)2
(Co2(CO)6)2
Ge-C(1)
1.884(5)
1.889(6)
1.889(5)
1.884(5)
1.196(7)
1.440(7)
1.410(7)
1.429(7)
1.208(7)
1.442(7)
1.410(7)
1.425(7)
1.202(7)
1.191(7)
1.436(7)
1.415(7)
1.441(7)
1.197(7)
1.426(7)
1.409(7)
1.430(7)
1.207(7)
100.9(2)
111.4(2)
117.2(2)
113.8(2)
113.7(2)
100.6(2)
159.7(5)
177.4(5)
119.4(4)
121.0(5)
178.8(6)
179.6(6)
120.2(5)
120.1(5)
177.9(6)
159.7(5)
161.1(5)
177.3(5)
119.1(4)
120.7(4)
178.9(5)
178.8(5)
121.0(4)
119.3(4)
176.8(6)
159.3(5)
1.96(2)
1.92(2)
1.95(2)
1.86(2)
1.34(2)
1.42(2)
1.40(2)
1.48(2)
1.18(2)
1.42(2)
1.45(2)
1.42(2)
1.39(2)
1.17(2)
1.49(2)
1.37(2)
1.38(2)
1.22(2)
1.47(2)
1.44(2)
1.43(2)
1.28(2)
116.4(6)
114.8(7)
106.9(6)
107.7(7)
108.2(6)
101.7(7)
152.2(12)
144(2)
Ge-C(10)
Ge-C(11)
Ge-C(20)
C(1)-C(2)
C(2)-C(3)
C(3)-C(4)
C(4)-C(5)
C(5)-C(6)
C(6)-C(7)
C(7)-C(8)
C(8)-C(9)
C(9)-C(10)
C(11)-C(12)
C(12)-C(13)
C(13)-C(14)
C(14)-C(15)
F igu r e 3. Molecular structure of SiPh2(OBET)(Co2(CO)6)2
with thermal ellipsoids drawn at 50% probability. Hydro-
gen atoms are omitted for clarity.
C(15)-C(16)
C(16)-C(17)
C(17)-C(18)
C(18)-C(19)
C(19)-C(20)
C(1)-Ge-C(10)
C(1)-Ge-C(11)
C(1)-Ge-C(20)
C(10)-Ge-C(11)
C(10)-Ge-C(20)
C(11)-Ge-C(20)
C(2)-C(1)-Ge
C(1)-C(2)-C(3)
C(2)-C(3)-C(4)
C(3)-C(4)-C(5)
C(4)-C(5)-C(6)
C(5)-C(6)-C(7)
C(6)-C(7)-C(8)
C(7)-C(8)-C(9)
C(8)-C(9)-C(10)
C(9)-C(10)-Ge
C(12)-C(11)-Ge
C(11)-C(12)-C(13)
C(12)-C(13)-C(14)
C(13)-C(14)-C(15)
C(14)-C(15)-C(16)
C(15)-C(16)-C(17)
C(16)-C(17)-C(18)
C(17)-C(18)-C(19)
C(18)-C(19)-C(20)
C(19)-C(20)-Ge
Co(1)-C(1)
124(2)
123.4(13)
170(2)
171(2)
123.6(13)
120.3(13)
142.6(14)
138.1(11)
159(2)
177(2)
118(2)
124(2)
177(2)
178(2)
121(2)
119(2)
176(2)
158.9(13)
1.95(2)
1.969(14)
2.491(4)
1.96(2)
1.97(2)
2.001(14)
1.936(14)
2.486(4)
1.967(14)
1.993(14)
70.6(10)
70.4(10)
132.5(8)
123.2(9)
69.4(9)
134.2(12)
69.7(10)
133.1(12)
70.5(8)
134.9(11)
66.8(8)
135.2(11)
71.9(9)
144.8(8)
68.4(8)
124.7(7)
F igu r e 4. Packing diagram of SiPh2(OBET)(Co2(CO)6)2.
Sch em e 2
Co(1)-C(2)
Co(1)-Co(2)
Co(2)-C(1)
Co(2)-C(2)
Co(3)-C(9)
Co(3)-C(10)
Co(3)-Co(4)
Co(4)-C(9)
Co(4)-C(10)
C(2)-C(1)-Co(1)
C(2)-C(1)-Co(2)
Co(1)-C(1)-Ge
Co(2)-C(1)-Ge
C(1)-C(2)-Co(1)
C(3)-C(2)-Co(1)
C(1)-C(2)-Co(2)
C(3)-C(2)-Co(2)
C(10)-C(9)-Co(4)
C(8)-C(9)-Co(4)
C(10)-C(9)-Co(3)
C(8)-C(9)-Co(3)
C(9)-C(10)-Co(3)
Ge-C(10)-Co(3)
C(9)-C(10)-Co(4)
Ge-C(10)-Co(4)
(OBET)(Co2(CO)6)2 is shown in Figure 3, and the pack-
ing diagram is shown in Figure 4. Selected bond lengths
and angles are listed in Table 3. For reference and
comparison with SiPh2(OBET)(Co2(CO)6)2, the corre-
sponding bond lengths and angles of its free ligand
SiPh2(OBET) are also included in Table 3. The cobalt
carbonyls selectively coordinate to the strained alkynes
adjacent to the silicon heteroatom, even though there
are two bulky phenyl groups on this atom. The third
alkyne remains uncomplexed, as is the case with the
cobalt complex of TTC. The fact that the alkynes are
bent appears to be responsible for the selectivity of the

Co Complexes of Si and Ge Heterocyclotriynes
Organometallics, Vol. 18, No. 9, 1999 1771
Ta ble 3. Selected Bon d Len gth s [Å] a n d An gles [d eg] for SiP h 2(OBET)(Co2(CO)6)2 a n d SiP h 2(OBET)
SiPh2(OBET)-
(Co2(CO)6)2
SiPh2(OBET)-
(Co2(CO)6)2
SiPh2(OBET)
SiPh2(OBET)
Co(1)-C(1)
Co(1)-C(2)
Co(1)-Co(2)
Co(2)-C(1)
Co(2)-C(2)
Co(3)-C(9)
Co(3)-C(10)
Co(3)-Co(4)
Co(4)-C(9)
Co(4)-C(10)
Si-C(1)
2.007(7)
1.993(7)
2.458(2)
2.007(7)
1.972(7)
1.989(7)
1.997(7)
2.473(2)
1.977(8)
2.005(7)
1.860(8)
1.870(7)
1.880(7)
1.882(7)
1.345(10)
1.465(10)
1.423(10)
1.436(11)
1.208(11)
1.448(10)
1.417(11)
1.418(11)
1.405(10)
1.458(10)
1.334(10)
114.9(3)
106.3(3)
107.9(3)
105.4(3)
105.7(3)
C(19)-Si-C(25)
Si-C(1)-C(2)
117.0(3)
148.4(6)
69.8(4)
139.0(4)
68.9(4)
122.8(4)
146.5(7)
71.6(4)
133.8(5)
70.9(4)
129.1(5)
120.0(6)
121.3(7)
176.7(8)
177.2(8)
119.8(7)
121.8(7)
121.7(7)
147.5(7)
71.6(4)
112.1(1)
162.5(2)
Co(1)-C(1)-C(2)
Co(1)-C(1)-Si
Co(2)-C(1)-C(2)
Co(2)-C(1)-Si
C(1)-C(2)-C(3)
C(1)-C(2)-Co(2)
C(3)-C(2)-Co(2)
C(1)-C(2)-Co(1)
C(3)-C(2)-Co(1)
C(4)-C(3)-C(2)
C(3)-C(4)-C(5)
C(6)-C(5)-C(4)
C(5)-C(6)-C(7)
C(8)-C(7)-C(15)
C(8)-C(7)-C(6)
C(7)-C(8)-C(9)
C(10)-C(9)-C(8)
C(10)-C(9)-Co(4)
C(8)-C(9)-Co(4)
C(10)-C(9)-Co(3)
C(8)-C(9)-Co(3)
Co(4)-C(9)-Co(3)
C(9)-C(10)-Si
174.7(3)
1.818(3)
1.826(3)
1.854(3)
1.863(3)
1.208(4)
1.430(4)
1.412(3)
1.435(4)
1.194(4)
1.429(4)
1.411(4)
1.396(4)
1.389(4)
1.434(4)
1.205(3)
101.6(1)
113.8(1)
110.7(1)
109.1(1)
108.9(1)
Si-C(10)
119.0(2)
120.7(2)
177.5(3)
178.3(3)
118.9(2)
121.1(2)
118.4(2)
174.4(3)
Si-C(19)
Si-C(25)
C(1)-C(2)
C(2)-C(3)
C(3)-C(4)
C(4)-C(5)
C(5)-C(6)
C(6)-C(7)
C(7)-C(8)
133.4(5)
70.8(4)
128.2(5)
77.2(3)
156.3(6)
70.1(4)
130.2(4)
69.3(4)
C(7)-C(15)
C(8)-C(18)
C(8)-C(9)
C(9)-C(10)
C(1)-Si-C(10)
C(1)-Si-C(19)
C(10)-Si-C(19)
C(1)-Si-C(25)
C(10)-Si-C(25)
163.5(3)
C(9)-C(10)-Co(3)
Si-C(10)-Co(3)
C(9)-C(10)-Co(4)
Si-C(10)-Co(4)
122.9(4)
F igu r e 5. Molecular structure of Ge(OBET)2(Co2(CO)6)2
with thermal ellipsoids drawn at 50% probability. Hydro-
gen atoms are omitted for clarity.
F igu r e 6. Packing diagram of Ge(OBET)2(Co2(CO)6)2.
in its cobalt complex. The alkyne bonds of the free ligand
TTC are also bent, though only slightly so, with CtC-C
bond angles ranging from 175.5(4)° to 176.4(3)°. The
Co-Co bond lengths of 2.458(2) and 2.473(2) Å in SiPh2-
(OBET)(Co2(CO)6)2 are comparable to those of 2.446(1)
and 2.450(1) Å in TTC(Co2(CO)6)2. As will be described
later, the planarity of the free ligand SiPh2(OBET) is
complexation with dicobalt octacarbonyl. The inner
silicon alkyne C1-Si-C10 bond angles are expanded
from 101.6(1)° in the free ligand to 114.9(3)° in the cobalt
complex. The CtC alkyne bonds adjacent to silicon are
lengthened from 1.208(4) and 1.205(3) Å in the free
ligand to 1.345(10) and 1.334(10) Å in its cobalt complex,
which is comparable to the complexed CtC alkyne
bonds of 1.340(8) and 1.326(8) Å in TTC(Co2(CO)6)2.9 The
Si-C1-C2 and Si-C10-C9 angles in SiPh2(OBET) of
162.5(2) and 163.5(3) are decreased to 148.4(6)° at Si-
C1-C2 and 156.3(6)° at Si-C10-C9 in the complex.
The angles at C1-C2-C3 and C10-C9-C8 of 174.5(2)°
and 174.4(3)° in the free ligand are decreased to
146.5(7)° for C1-C2-C3 and 147.5(7)° for C10-C9-C8
1
dramatically twisted in its complex. The H NMR and
13C NMR spectral results are consistent with the crystal
structure.
The high selectivity of the complexation of cobalt
toward the bent alkynes observed in SiPh2(OBET)-
(Co2(CO)6)2 led us to examine the cobalt chemistry of
the dipocket ligand Ge(OBET)2 (see Scheme 1). With
expectations of similar reactivity to that of SiPh2-

1772 Organometallics, Vol. 18, No. 9, 1999
Guo et al.
F igu r e 7. Geometries of the ligands in their cobalt complexes.
(OBET), i.e., dicobalthexacarbonyl moieties would com-
plex with the four bent alkynes adjacent to the germa-
nium atom in Ge(OBET)2, 4 molar equiv of dicobalt
octacarbonyl were used. The starting free ligand Ge-
(OBET)2 was not immediately soluble in hexane. How-
ever, it was no longer present as a solid after stirring
for 1 day. It has been observed that the solubility of
cobalt alkyne complexes is considerably greater than the
uncomplexed ligands.9 The reaction was completed in
Å in the free ligand to 1.365(3) Å on average for the
alkynes coordinated to the cobalt atoms. The Ge-CtC
angles, such as Ge-C1-C2 and Ge-C10-C9, range
from 159.7(5)° to 161.1(5)° in the Ge(OBET)2 and are
decreased to 138.1(11)° at Ge-C10-C9 and 152.2(12)°
at Ge-C1-C2 for the complexed alkynes in Ge(OBET)2-
(Co2(CO)6)2. The C-CtC angles adjacent to Ge range
from 176.8(6) to 177.9(6) in the free ligand and are
decreased to 144(2)° for C1-C2-C3 and 142.6(14)° for
C10-C9-C8 in the complex. The Co-Co bond lengths
are 2.486(4) and 2.491(4) Å.
1
80% yield based on the H NMR spectra in C6D6, which
showed only one final product and starting materials.
The 13C NMR spectrum shows one sharp carbonyl signal
at 199.4 ppm, which indicates the carbonyl carbons are
equivalent on the NMR time scale, and 17 sharp signals
from 79.0 to 138.9 ppm with one peak apparently buried
in the solvent peaks. However, six alkyne signals are
observed instead of three. The solution of the product
in hexane is deep red in color as is SiPh2(OBET)-
(Co2(CO)6)2. A crystal suitable for X-ray determination
was obtained from a mixture of diethyl ether and hexane
solvents. Ge(OBET)2(Co2(CO)6)2 crystallizes in the mono-
clinc space group P21/n with one molecule per asym-
metric unit. A thermal ellipsoid labeling diagram of this
complex is displayed in Figure 5, and a packing diagram
is shown in Figure 6. Selected bond lengths and angles
are listed in Table 2 for ease of comparison with relevant
distances and angles in Ge(OBET)2. Surprisingly only
two alkynes of one of the pockets are complexed. The
three alkynes of the other pocket were left intact even
though a large excess of dicobalt octacarbonyl was
present. The two alkynes next to germanium in the
other pocket (C11tC12 and C19tC20) apparently do
not react with dicobaltoctacarbonyl because of the steric
hindrance from the two dicobalthexacarbonyl moieties
complexed to C1tC2 and C9tC10. The unreacted
pocket is similar to the pockets in free Ge(OBET)2 with
a mean deviation from planarity of 0.0716 Å, ranging
from -0.0045 Å at C18 to 0.1427 Å at C17 of the least-
squares plane defined by Ge and C11-C20. The inner
angle at germanium with the neighboring alkynes is
widened 1° in the uncomplexed ring, whereas the
complexed ring shows a 15.7° widening angle at ger-
manium. The complexed pocket shows changes similar
to those observed in SiPh2(OBET)(Co2(CO)6)2. The alkyne
bonds adjacent to germanium lengthened from 1.199(6)
A comparison of the two complexes SiPh2(OBET)-
(Co2(CO)6)2 and Ge(OBET)2(Co2(CO)6)2 is of interest.
The ligands in both complexes are considerably distorted
from planarity. Figure 7 shows the ligands SiPh2(OBET)
and Ge(OBET)2 in their complexes with the dicobalt-
hexacarbonyl moieties omitted. In SiPh2(OBET)(Co2-
(CO)6)2, the ligand is twisted in an “S” fashion with one
alkyne going above the plane and the other going below
the plane of the tolane moiety, whereas in Ge(OBET)2-
(Co2(CO)6)2, both alkynes bend in the same direction so
that the whole plane is “hanging” down (see Figure 7).
The uncoordinated alkyne in SiPh2(OBET)(Co2(CO)6)2
is relatively linear (176.7(8)° at C4-C5-C6 and 177.2(8)°
at C5-C6-C7), but the uncoordinated alkyne in the
coordinated cyclyne ring in Ge(OBET)2(Co2(CO)6)2 is
bent (170(2)° at C4-C5-C6 and 171(2)° at C5-C6-C7).
In their free ligands, C4-C5-C6 and C5-C6-C7 angles
are 177.5(3)° and 178.3(3)°, respectively in SiPh2-
(OBET), and range from 178.8(6)° to 179.6(6)° in Ge-
(OBET)2. A distortion similar to that found in the
SiPh2(OBET) ligand in SiPh2(OBET)(Co2(CO)6)2 has
been found in the cobalt complex of cyclooct-3-ene-7,8-
diphenyl-1,5-diyne (Figure 8).16 In this molecule two
cobalt atoms bind to one alkyne below the cyclic plane
and the other two cobalt atoms bind to another alkyne
above the cyclic plane. The distortion of the Ge(OBET)2
ligand in Ge(OBET)2(Co2(CO)6)2 is similar to that of the
TTC ligand in TTC(Co2(CO)6)2. As mentioned above, in
each complex the angles at C1 and C10, both of which
are adjacent to the heteroatoms Si or Ge, are signifi-
cantly different, which is not the case in their free
ligands. The difference between angles of Ge-C1-C2
(16) Melikyan, G. G.; Khan, M. A.; Nicholas, K. M. Organometallics
1995, 14, 2170.

Co Complexes of Si and Ge Heterocyclotriynes
Organometallics, Vol. 18, No. 9, 1999 1773
This work has led us to the hypothesis that Co2(CO)8
will selectively complex to bent alkynes in the presence
of linear alkynes in the same molecule. The selectivity
is presumably due to the fact that Co2(CO)8 usually
forms complexes with an alkyne in such a way that the
alkyl or aryl groups on the alkyne are bent away from
the metal. An uncomplexed bent alkyne would be of
higher energy due to strain than a linear alkyne and
would therefore be more reactive. Complexation would
give a decrease in strain in the bent alkyne because
alkynes bound to Co2(CO)8 are typically bent. It is
probable that other metals and reagents will exhibit
similar selectivity with bent versus linear alkynes. We
are currently examining this possibility.
F igu r e 8. Cobalt complex of cyclooct-3-ene-7,8-diphenyl-
1,5-diyne.
and Ge-C10-C9 in Ge(OBET)2(Co2(CO)6)2 is 14°, and
the difference between Si-C1-C2 and Si-C10-C9 in
SiPh2(OBET)(Co2(CO)6)2 is 8°.
To compare the size of the cavity in the SiPh2(OBET)
ring with the cavity size in TBC and TTC, the distance
from each alkyne carbon to the centroid of the six alkyne
carbons has been calculated. In the SiPh2(OBET) ligand
the average distance from the calculated centroid to
each alkyne carbon is 2.069 Å, ranging from 2.142 Å
for the alkyne carbons â to the silicon, 2.037 Å for the
alkyne carbons R to the silicon, and 2.029 Å for the
alkyne carbons between the two phenyl groups. Similar
distances are observed in the Ge(OBET)2 ligand. The
comparable values are 2.140 Å for TTC and 2.08 Å for
TBC.
Ack n ow led gm en t. We thank the National Science
Foundation for financial support under Grant CHE97-
08181 and Dr. Robert Lattimer of BFGoodrich for
providing the FDMS 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, and hydro-
gen parameters. This material is available free of charge via
the Internet at http://pubs.acs.org.
OM9901675