Synthesis and solid state structures of tri-t-butyl-cyclopropenyl derivatives of main group elements: Cyp*MPh3 (M = Si, Ge, Sn)

Article abstract of DOI:10.1016/j.jorganchem.2005.12.029

The reaction of Ph₃MLi (M = Si, Ge, and Sn) with tri-t-butylcyclopropenium tetrafluoroborate (Cyp*BF4-) gives the cyclopropenyl compounds Cyp*MPh₃ as air and moisture stable solids in 11%, 74%, and 77% yields, respectively. Attempts

Full text of DOI:10.1016/j.jorganchem.2005.12.029

Journal of Organometallic Chemistry 691 (2006) 1419–1424
www.elsevier.com/locate/jorganchem
Synthesis and solid state structures of tri-t-butyl-cyclopropenyl
derivatives of main group elements: Cyp*MPh3 (M = Si, Ge, Sn)
*
Zi-Ye Hua, Joel T. Mague, Mark J. Fink
Department of Chemistry, Tulane University, New Orleans, LA 70118, United States
Received 12 November 2005; received in revised form 10 December 2005; accepted 11 December 2005
Available online 19 January 2006
Abstract
The reaction of Ph3MLi (M = Si, Ge, and Sn) with tri-t-butylcyclopropenium tetrafluoroborate ðCypꢀBFꢁÞ gives the cyclopropenyl
4
compounds Cyp*MPh3 as air and moisture stable solids in 11%, 74%, and 77% yields, respectively. Attempts to prepare Cyp*PbPh3 by
this method were unsuccessful. The X-ray crystal structures of all three of these compounds were obtained. The M–C(Cyp*) bond dis-
˚
˚
˚
tances increase with the order: Sn–C (2.19 A) > Ge–C (2.00 A) > Si–C (1.91 A). A high degree of steric strain is evidenced for the silicon
derivative which forms an exocyclic bond angle (Si–C(Cyp*)–C(tBu)) of 121.6ꢀ. The high degree of steric strain for the silicon analog is
believed to be responsible for the low yields for its synthesis.
ꢁ 2005 Elsevier B.V. All rights reserved.
Keywords: Cyclopropene; Silane; Germane; Stannane; Synthesis; Crystal structure
1. Introduction
addition of polysilyllithium reagents to stable cycloprope-
nium cations. Several polysilyl-3-cyclopropenes have been
previously prepared in our laboratories by the reaction of
tri-t-butylcyclopropenium cation (Cyp*) with polysilyl lith-
ium reagents [7].
The extension of this synthetic method to other group 14
elements is of interest. In this study, the reactions of tri-t-
butyl cyclopropenium cation with the organometallic
anions, Ph3MLi (M = Si, Ge, Sn, and Pb) was examined
[8]. Except for the case of Pb, good yields of the cyclop-
ropenyl compounds Cyp*MPh3 were obtained. The new
compounds were spectroscopically and crystallographically
characterized. The X-ray structures are the first reported
for cyclopropenyl germanes and stannanes.
3-Cyclopropenyl derivatives of silicon are fruitful
sources for a variety of organic and organosilicon reactive
intermediates. Fluorodesilylation of cyclopropenylsilanes
have proven to be efficient sources of elusive antiaromatic
cyclopropenyl anions in both gas phase [1] and solution
[2]. Some 3-cyclopropenyl polysilanes are photochemical
precursors to novel organosilicon reactive intermediates
including both cyclopropenylsilylenes [3] and their isomeric
silacyclobutadienes [4]. Recently, the tri-t-butyl cyclo-
propenyl group has been utilized for the synthesis of lat-
tice-framework disilenes [5].
Cyclopropenyl derivatives of main group metals and
metalloids, however, are relatively rare. Of the Group 14
elements, only a handful of 3-cyclopropenylsilanes and
germanes have been prepared and characterized. One syn-
thetic route involves the addition of a-silyl and a-germyl
carbenes to alkynes [6]. An alternative approach is the
2. Results and discussion
2.1. Preparation of Cyp*MPh3 (M = Si, Ge, and Sn)
The compounds, Cyp*MPh3 (M = Si (1a), Ge (1b),
Sn(1c)), were synthesized by the reaction of tri-t-butylcyc-
lopropenyl tetrafluoroborate with the corresponding
*
Corresponding author. Tel.: +1 504 862 3568.
E-mail address: fink@tulane.edu (M.J. Fink).
0022-328X/$ - see front matter ꢁ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.12.029

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Z.-Y. Hua et al. / Journal of Organometallic Chemistry 691 (2006) 1419–1424
lithium reagents LiMPh3 (M = Si, Ge, and Sn), Eq. (1).
The lithium reagents were prepared by the reaction of lith-
ium wire in THF with chlorotriphenylsilane, bromotriphe-
nylgermane, and chlorotriphenylstannane, respectively.
corresponds to the aromatic tri-t-butyl cyclopropenium
cation. Other prominent mass peaks correspond to
Ph3M+ and t-Bu (57 amu). The IR spectrum shows a char-
acteristic weak C@C stretching vibration for the cyclopro-
pene ring between 1816 and 1824 cmꢁ1 [13].
CypꢀBF4 þ LiMPh3 ! CypꢀMPh3
1a : M ¼ Si ð11%Þ
2.4. X-ray crystal structures
ð1Þ
1b : M ¼ Ge ð74%Þ
Compounds 1a–c crystallize as two independent mole-
cules occupying general positions in the monoclinic space
groups P21/n (Si and Ge) and P21/c (Sn). Figs. 1–3 show
the ORTEP diagrams of one independent molecule for
each compound. Relevant structural parameters are given
in Table 1.
In comparing all three structures, the most dramatic
differences in metrical parameters occur about the central
metal(loid). The cyclopropenyl-metal(loid) distances increase
1c : M ¼ Sn ð76%Þ
The highly colored lithium reagents were added to hex-
ane suspensions of the cyclopropenium salt at 0 ꢀC, and
then allowed to stir at room temperature for 8 h. The
intense colors of the reaction mixtures faded over the
course of the reaction and lithium tetrafluoroborate pre-
cipitated from solution. Removal of the solvent, followed
by extraction with dry hexane, gave a crude product
which was purified by column chromatography. Com-
pounds 1a–c are white crystalline solids stable to air
and moisture and were easily recrystallized in hexane
solutions. The very low yield of the silicon derivative
(1a) compared to the germanium and tin analogs is attrib-
uted to steric congestion about the relatively short Si–C
bond of this compound.
˚
˚
˚
from 1.91 A (Si), 2.00 A (Ge) to 2.19 A (Sn). Similarly,
phenyl-metal(loid) distances increase progressively from
˚
˚
˚
1.90 A (Si), 1.98 A (Ge) to 2.15 A (Sn). The observed
trends reflect the increasing covalent radius in going from
silicon to tin.
The bond distances and angles of the cyclopropene
rings are very similar for all compounds. The silicon
derivative 1a shows a very slightly elongated cycloprope-
nyl C–C bond and a slightly contracted cyclopropenyl
C@C bond relative to the germanium and tin analogs.
This effect may be due to an increased steric compression
of the SiPh3 group with the Cyp* ring. A more pro-
nounced measure of this steric congestion is the exocyclic
bond angle, M–C(1)–C(4), which reflects the geminal
interaction of the MPh3 group and the allylic t-butyl sub-
stituent. This angle is greatest for M = Si (121.6(2), avg.),
followed progressively by M = Ge (119.1(3), avg.) and
M = Sn (115.9(2), avg.). The steric strain along the Si–C
bond in 1a as manifested by these solid state structural
2.2. Attempted preparation of Cyp*PbPh3
Triphenylplumbyllithium was prepared by three differ-
ent routes: from the reaction of hexaphenyldiplumbane
with lithium metal [9], from the reaction of phenyl lithium
with lead (II) chloride [10], and from the reaction of hexa-
phenyldiplumbane with phenyl lithium [11]. In each case,
the darkly colored plumbyl lithium was not discharged
upon addition to tri-t-butylcyclopropenium ion. No evi-
dence for the expected plumbylcyclopropene was found.
2.3. Spectroscopic properties of Cyp*MPh3
1
The H and 13C NMR spectra of 1a–c are similar and
C19
C18
totally consistent with a classical r bonded cyclopropene
ring system with two distinct t-butyl groups in 2:1 ratio.
The olefinic cyclopropene ring resonances in the 13C spec-
trum appear at approximately 128 ppm for all three com-
pounds. The chemical shift of the allylic ring carbon is
somewhat sensitive to the attached metal atom, moving
downfield as one proceeds from silicon to tin: Si
(37.8 ppm), Ge (42.3 ppm), and Sn (47.8 ppm). The chem-
ical shift of the ipso carbon of the phenyl group also moves
noticeably downfield, from Si (138.0 ppm) to Ge
(140.7 ppm) to Sn (143.2 ppm). A similar trend has been
found for the 13C NMR chemical shifts of MPh4
(M = Si, Ge, Sn) derivatives [12].
C20
C6
C5
C17
C21
C7
C16
C22
C1
Si1
C23
C15
C3
C14
C24
C28
C29
C30
C10
C2
C13
C27
C25
C33
C11
No discernable parent ions were observed for 1a–c in the
EI (70 eV) mass spectra of these compounds. The highest
observed masses were either M+–CH3 or M+-t-Bu and
even these masses had relatively weak intensities. The
strong base peak in all these spectra was at 207 amu which
C31
C26
C32
C9
Fig. 1. ORTEP drawing of one independent molecule of 1a. Thermal
ellipsoids are at the 50% probability level.

Z.-Y. Hua et al. / Journal of Organometallic Chemistry 691 (2006) 1419–1424
1421
group cyclopropenyl derivatives is currently being
investigated.
C19
C20
C6
C18
C5
4. Experimental details
C7
C21
C17
C23
C4
C1
All operations involving synthesis were performed under
a blanket of argon and Schlenk techniques were used as
required. All glassware was oven dried at 150 ꢀC before
use. Reagents were purchased from either Aldrich or Ven-
tron and used without further purification. Tetrahydrofu-
ran was distilled over sodium-benzophenone prior to use.
Hexane and benzene were distilled over CaH2 prior to
use. The synthesis of tri-t-butylcyclopropenium tetrafluo-
borate has been previously described [14].
All NMR spectra were recorded on a GE Omega
400 MHz spectrometer. Chemical shifts are given in ppm
on the scale relative to tetramethylsilane as a reference.
Carbon multiplicities and assignments in the 13C NMR
spectra were determined using standard DEPT and HET-
COR techniques. Mass spectra were obtained on a HP
5890 series GC–MS instrument in EI mode (70 eV). Infra-
red spectra were recorded on a Perkin–Elmer FT-IR spec-
trometer. Elemental analysis was performed by Galbraith
Lab. Inc., Knoxville, TN. Melting points are uncorrected.
C16
C15
Ge1
C14
C12
C22
C29
C3
C28
C2
C13
C10
C33
C32
C24
C25
C30
C27
C8
C11
C31
C26
C9
Fig. 2. ORTEP drawing of one independent molecule of 1b. Thermal
ellipsoids are at the 50% probability level.
C20
C19
C6
C4
C24
C21
C23
C7
C25
C18
C16
Sn1
4.1. Synthesis of 3-triphenylsilyl-1,2,3-tri-t-
butylcyclopropene (1a)
C5
C1
C17
C10
C2
C11
C22
C8
C26
Chlorotriphenylsilane (2.3 g, 7.5 mmol) and finely cut
lithium wire (0.21 g, 30. mmol) were placed into an
argon-filled 50 mL two-neck round bottom flask. Dry
THF (20 mL) was then transferred to the flask and the con-
tents stirred with a magnetic stirrer at room temperature.
After 10–30 min, a white precipitate formed and, after
40 min, the solution color changed to dark brown. The
reaction was continued for another 4 h at room tempera-
ture and the resultant solution cannulated to an argon-
filled 100 mL flask containing tri-t-butylcyclopropenium
tetrafluoborate (1.47 g, 5.00 mmol) in 50 mL of dry hexane
at 0 ꢀC. After 30 min, the color changed from black to pale
brown. The reaction was continued overnight at room tem-
perature, during which the solution color changed to pale
yellow. The solvent was then removed by rotary evapora-
tion and the residue extracted with dry hexane. After
removal of the hexane by rotary evaporation, the resulting
white solid was purified on a silica gel column using pure
hexane as an eluent. The product was obtained as a white
crystalline solid (0.25 g, 11% yield) and recrystallized in
C27
C3
C9
C28
C33
C29
C12
C15
C14
C30
C13
C32
C31
Fig. 3. ORTEP drawing of one independent molecule of 1c. Thermal
ellipsoids are at the 50% probability level.
parameters is most likely responsible for the low yields for
the synthesis of 1a as compared to the less strained ger-
manium and tin analogs.
3. Conclusion
Highly hindered tri-t-butylcyclopropenyl derivatives of
silicon, germanium, and tin have been prepared by the
reaction of the tri-t-butylcyclopropenium ion directly with
the corresponding triphenylmetal lithium derivatives. The
lower yield of the silicon derivative is attributed to a high
degree of strain along the Si–Cyp* bond relative to the
germanium and tin derivatives. The strain is evident in
structural distortions of the cyclopropenyl ring system.
The failure of the reaction to yield the corresponding lead
derivative may result from the weakness of the lead car-
bon bond. The generality of this technique to other main
1
hexane. M.p. 153–155 ꢀC. H NMR (d, CDCl3): 0.98 (s,
9H), 1.13 (s, 18H), 7.69 (m, 6H), 7.34 (m, 9H). 13C NMR
(d, CDCl3) 30.90 (CH3, t-Bu), 31.58 (CH3, t-Bu), 32.02
(q, t-Bu), 34.42 (q, t-Bu), 37.78 (q, allylic, Cyp*), 124.75
(CH, Ph), 127.11 (CH, Ph), 128.75 (q, C@C, Cyp*),
137.86 (CH, Ph), 137.99 (q, Ph). MS (m/e, rel intensity):
409 (M+ t-Bu, 32.5), 259 (Ph3Si+, 67.6), 207 (Cyp*,
100%), 181(34.2%), 154(17.8%), 105(PhSi+, 24.2%), 77
(Ph+, 11.3), 57 (t-Bu, 85%). IR (KBr, cmꢁ1): 3054(m),

1422
Z.-Y. Hua et al. / Journal of Organometallic Chemistry 691 (2006) 1419–1424
Table 1
136.78 (CH, Ph), 140.66 (q, Ph). MS (m/e, rel intensity):
455 (M+-t-Bu, 2.3%) 305 (Ph3Ge+, 20%), 207 (Cyp*,
100%), 154 (11.7%), 150 (17.8%), 148 (13.9%), 146
(10.1%), 77 (Ph+, 13.4%), 57 (t-Bu, 83.2%) Exact mass
for (M+–CH3, C32H39Ge). Calcd. 497.2263554 Found.
497.226471 IR (KBr, cmꢁ1): 3043(s), 2961(vs), 2868(s),
1818(w), 1472(s), 1425(s), 1384(s), 1218(s), 1192(s),
1078(s), 1022(m), 732(vs), 696(vs), 665(vs). Anal. Calc.
for C33H42Ge: C, 77.50; H, 8.30. Found: C, 76.99; H,
8.50%.
Comparison of relevant structural parameters for 1a–c
Si (1a) Ge (1b)
Sn (1c)
2.193 (3)
Bond lengths
M–C(1)
1.909 (3)
1.995 (4)
1.908 (3)
1.901 (3)
1.900 (3)
1.566 (3)
1.571 (4)
1.555 (3)
1.550 (4)
1.554 (4)
1.548 (4)
1.291 (4)
1.291 (4)
2.001 (5)
1.978 (5)
1.977 (5)
1.563 (6)
1.558 (6)
1.529 (6)
1.526 (6)
1.540 (6)
1.536 (6)
1.295 (6)
1.285 (6)
2.196 (3)
2.157 (3)
2.154 (3)
1.562 (5)
1.543 (4)
1.521 (4)
1.526 (4)
1.523 (4)
1.527 (4)
1.295 (5)
1.298 (5)
M–Ph
C(1)–C(4)
C(1)–C(2)
C(1)–C(3)
C(2)–C(3)
4.3. Synthesis of 3-triphenylstannyl-1,2,3-tri-t-
butylcyclopropene (1c)
In a similar procedure to the preparation of 1a, 0.052 g
(75 mmol) of finely cut lithium wire was reacted with 5.78 g
(15.0 mmol) of chlorotriphenylstannane in dry THF at
room temperature. After 3 h, a white precipitate formed
and the solution changed to a deep olive green color. After
6 h, the triphenyltin lithium reagent was added to 2.94 g
(10 mmol) of tri-t-butylcyclopropenium tetrafluoborate in
50 mL dry hexane at 0 ꢀC. After 1 h, the solution changed
from green to light green. The solution was stirred over-
night at room temperature which resulted in a pale yellow
solution. Column chromatography over silica gel, using
hexane as an eluent, yielded 4.27 g (76.6% yield) of the
Bond angles
M–C(1)–C(4)
121.2 (2)
118.6 (3)
115.4 (2)
122.0 (2)
115.0 (2)
113.5 (2)
116.7 (2)
116.3 (2)
49.1 (2)
49.2 (2)
65.4 (2)
65.3 (2)
65.5 (2)
65.4 (2)
119.5 (3)
115.7 (3)
114.3 (3)
117.5 (3)
116.6 (3)
49.9 (3)
49.6 (3)
65.5 (3)
65.6 (3)
64.6 (3)
64.8 (3)
116.4 (2)
115.7 (2)
114.8 (2)
116.5 (2)
116.3 (2)
50.3 (2)
50.3 (2)
64.9 (2)
64.8 (2)
64.7 (2)
64.9 (2)
M–C(1)–C(2)
M–C(1)–C(3)
C(2)–C(1)–C(3)
C(1)–C(2)–C(3)
C(1)–C(3)–C(2)
Bond lengths are in angstroms; bond angles are in degrees. Metrical
parameters are given for both independent molecules in the unit cell.
1
product as a white solid. M.p. 114–115 ꢀC. H NMR (d,
CDCl3): 1.05 (s, 9H), 1.25 (s, 18H), 7.63 (m, 6H), 7.37
(m, 9H). 13C NMR (d, CDCl3) 30.42 (CH3, t-Bu), 31.02
(CH3, t-Bu), 31.48 (q, t-Bu), 39.09 (q, t-Bu), 47.75 (q,
allylic, Cyp*), 127.90 (q, C@C, Cyp*), 130.28 (CH, Ph),
137.62 (CH, Ph), 137.78 (CH, Ph), 143.21 (q, Ph). MS
(m/e, rel inten): 501 (M+-t-Bu), 351(Ph3Sn+, 11.1%), 207
(Cyp*, 100%), 196 (PhSn+, 19.3%), 194(14.2%), 119(Sn+,
11.8), 77 (Ph, 13.9), 57 (t-Bu, 85.7%) CI–MS (CH4): Exact
Mass for (M+ ꢁ1, C33H41120Sn). Calcd. 557.2230256
Found. 557.222900 IR (KBr, cmꢁ1) 3060(m), 2096(s),
1816(m), 1466(s), 1425(w), 1384(m), 1358(m), 1250 (m),
1212(s), 1199(vs), 1006(s), 877(m), 727(vs), 696(vs). Anal.
Calc. for C33H42Sn: C, 71.09; H, 7.61. Found: C, 70.78;
H, 7.68%.
2961(vs), 1824(w), 1472(s), 1425(m), 1384(m), 1358(m),
1094(s), 737(m), 696(vs), 515(vs). Exact mass for (M+–
CH3, C32H39Si). Calcd. 451.2821050 Found. 451.282410
Anal. Calc. for C33H42Si: C, 84.89; H, 9.09. Found: C,
84.31; H, 9.25%.
4.2. Synthesis of 3-triphenylgermyl-1,2,3-tri-t-
butylcyclopropene (1b)
In a similar procedure to the preparation of 1a, 0.245 g
(35.3 mmol) of finely cut lithium wire was reacted with
2.9 g (7.5 mmol) of bromotriphenylgermane in dry THF
at room temperature. After 3 h, a white precipitate formed
and the solution changed to a deep yellow color. After 6 h,
the triphenylgermanium lithium reagent was added to
1.47 g (5.00 mmol) of tri-t-butylcyclopropenium tetrafluob-
orate in 50 mL dry hexane at 0 ꢀC. Over a period of 30 min,
the color changed from yellow to pale yellow. The solution
was then stirred overnight at room temperature, after
which, the solution became a lighter yellow. Column chro-
matography over silica gel, using hexane as an eluent,
yielded 1.9 g (74% yield) of the product as a white solid.
M.p. 102–103 ꢀC. 1H NMR (d, CDCl3): 1.07 (s, 9H),
1.18 ppm (s, 18H), 7.68 (m, 6H), 7.37 (m, 9H). 13C NMR
(d, CDCl3) 30.77 (CH3, t-Bu), 31.50 (CH3, t-Bu), 31.64
(q, t-Bu), 38.69 (q, t-Bu), 42.33 (q, allylic, Cyp*), 127.62
(CH, Ph), 127.33 (CH, Ph), 128.15 (q, C@C, Cyp*),
4.4. Attempted synthesis of 3-triphenylplumbyl-1,2,3-tri-t-
butylcyclopropene
4.4.1. Method A
Lithium wire, 0.112 g (16.1 mmol), was cut into small
pieces, washed in dry hexane, and wiped dry. The dry lith-
ium was quickly placed in 30 mL of dry THF under a con-
stant flow of N2. A solution containing 1.78 g (2.03 mmol)
of hexaphenyldiplumbane in 20 mL dry THF was added
dropwise to the lithium suspension at 0 ꢀC over a 1 h per-
iod. Sonication of the mixture with an ultrasonic bath for
2 h resulted in the formation of a dark green solution of
Ph3PbLi. This solution was cannulated to a nitrogen filled
100 mL round bottom flask containing 1.23 g (4.20 mmol)
of tri-t-butylcyclopropenium tetrafluoborate in 30 mL of

Z.-Y. Hua et al. / Journal of Organometallic Chemistry 691 (2006) 1419–1424
1423
Table 2
dry hexane at 0 ꢀC. After 1 h, the mixture was allowed to
Experimental crystallographic data for Cyp*MPh3
warm to room temperature. Solvent was removed and the
solid was extracted with dry hexane. No significant soluble
materials were obtained.
Si (1a)
Ge (1b)
Sn (1c)
Formula
Molecular
weight
C
33H42Si
C33H42Ge
511.26
C33H42Sn
557.36
466.76
4.4.2. Method B
Crystal
0.59 · 0.40 ·
0.36 · 0.33 · 0.26 0.40 · 0.33 · 26
A fine powder of PbCl2, 1.39 g (5.00 mmol), was
suspended in 10 mL dry of ether in a 100 mL round
bottom flask and chilled to ꢁ10 ꢀC. A solution of PhLi
(8.3 mL, 15.0 mmol) in 15 mL of dry ether was added
via an addition funnel over an 80 min period. This solu-
tion was cannulated to a nitrogen-filled 100 mL round
bottom flask containing 1.47 g (5 mmol) of tri-t-butylcyc-
lopropenium tetrafluoroborate in 30 mL of dry hexane.
The solution was chilled by a salt-ice bath and, after
1 h, the mixture was allowed to warm to room tempera-
ture. Solvent was removed and the solid was extracted
with dry hexane. No significant soluble materials were
obtained.
dimensions 0.40
(mm)
Crystal
system
Space
Monoclinic
Monoclinic
Monoclinic
P21/n
P21/n
P21/c
group
Cell dimensions
˚
a (A)
17.7823(14)
18.663(2)
18.4905(13)
90
109.549(6)
90
17.801(2)
18.7034(11)
18.616(2)
90
109.271(9)
90
32.497(2)
9.6831(8)
19.6470(13)
90
107.234(6)
90
˚
b (A)
˚
c (A)
a (ꢀ)
b (ꢀ)
c (ꢀ)
3
˚
V (A )
5782.7(9)
8
5850.6(8)
8
5904.8(7)
8
Z
q(calcd)
(g cm3)
Radiation
1.072
1.161
1.254
4.4.3. Method C
(k = 0.71073) (k = 0.71073)
(k = 0.71073)
A solution of PhLi (0.45 mL, 0.80 mmol) was added
to a 50 mL round bottom flask containing 0.911 g
(1.04 mmol) of Ph3PbPbPh3 in 30 mL of dry THF. The
solution was stirred at room temperature for 2 h in which
time the color of the solution changed to yellow and a pre-
cipitate, identified as Ph4Pb, had formed. This solution
was cannulated to a nitrogen-filled 100 mL round bottom
flask containing 0.235 g (0.800 mmol) of tri-t-butylcyclo-
propenium tetrafluoborate in 10 mL of dry hexane at
0 ꢀC. After 1 h, the mixture was allowed to warm to room
temperature. Solvent was removed and the solid was
extracted with dry hexane. No significant soluble materials
were obtained.
˚
Mo Ka (A)
h Range (ꢀ)
Scan type
Total data
collected
1.60–25.11
x/2h
10,655
1.59–25.12
x/2h
10,771
1.97–25.09
x/2h
10,835
Unique data
Observed
data with
I0 > 2rI
10,301
5193
10,417
4882
10,488
5976
l (cmꢁ1
)
0.099
1.065
0.5221–0.6364
0.883
0.5500–0.6963
Transmission na
coefficient
F(000)
R
Rw
2032
0.0464
0.1062
2176
0.0465
0.0909
2320
0.0296
0.0778
na – Not applicable, no empirical absorption corrections were made.
4.5. X-ray structure determinations: general data
Diffrangible crystals of 1a–c were obtained by slow
evaporation of hexane solutions at room temperature.
Data collection and refinement parameters are summarized
in Table 2. General procedures for crystal alignment, unit
cell determination and refinement and collection of inten-
sity data have been published [15].
4.8. X-ray crystal structure determination of 1c
A large crystal mass, obtained by slow evaporation of a
hexane solution of the compound at ꢁ30 ꢀC was cleaved to
give a suitably sized fragment which was mounted on a thin
glass fiber with epoxy cement.
4.6. X-ray crystal structure determination of 1a
A large crystal mass, obtained by slow evaporation of a
hexane solution of the compound at ꢁ30 ꢀC was cleaved to
give a suitably sized fragment which was mounted on a thin
glass fiber with epoxy cement.
5. Supplementary materials
Crystallographic data for the structural analysis has
been deposited with the Cambridge Crystallographic Data
Centre, CCDC nos. 289235, 289236, and 289237 for com-
pounds 1b, 1a, and 1c, respectively. Copies of this informa-
tion may be obtained free of charge The Director, CCDC,
12 Union Road, Cambridge CB2 1EZ, UK (fax: +44 1223
336033; email: deposit@ccdc.cam.ac.uk of www: http://
www.ccdc.cam.ac.uk).
4.7. X-ray crystal structure determination of 1b
A large, well-formed crystal, obtained by the slow evap-
oration of a hexane solution of the compound at ꢁ30 ꢀC,
was cut to size and mounted on a thin glass fiber with
epoxy cement.

1424
Z.-Y. Hua et al. / Journal of Organometallic Chemistry 691 (2006) 1419–1424
[7] D.B. Puranik, M.P. Johnson, M.J. Fink, Organometallics 8 (1989)
Acknowledgements
770.
[8] Z.-Y. Hua, MS thesis, Tulane University, 2000.
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We thank NASA (NCC3-946) through the Tulane Insti-
tute for Macromolecular Engineering and Science and NSF
(CHE-0445637) for financial support of this work.
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