Improved synthesis of pentabenzylcyclopentadiene and study of the reaction between pentabenzylcyclopentadiene and iron pentacarbonyl

Article abstract of DOI:10.1021/om9506532

An improved synthetic route to pentabenzylcyclopentadiene, C₅Bz₅H (1), has been developed, utilizing a larger amount of dicyclopentadiene, sodium, and excess benzyl alcohol as both reactant and solvent. Subsequent extraction and crystallization using hexane produced 1 in 62% yield. A reaction between 1 and iron pentacarbonyl in refluxing toluene led to the formation of [(η⁵-C⁵Bz⁵)Fe(CO)²]₂ (2) and (η⁴-C₅Bz₅H)Fe(CO)₃ (3). Unlike the parent compound (η⁴-C₅H₆)Fe(CO)₃, 3 exhibited exceptional air and thermal stability. A single-crystal X-ray diffraction study of 3 has been undertaken and confirms the proposed structure.

Full text of DOI:10.1021/om9506532

Organometallics 1996, 15, 2591-2594
2591
Articles
Im p r oved Syn th esis of P en ta ben zylcyclop en ta d ien e a n d
Stu d y of th e Rea ction betw een
P en ta ben zylcyclop en ta d ien e a n d Ir on P en ta ca r bon yl
Woei-Min Tsai and Marvin D. Rausch*
Department of Chemistry, University of Massachusetts, Amherst, Massachusetts 01003
Robin D. Rogers*
Department of Chemistry, Northern Illinois University, DeKalb, Illinois 60115
Received August 21, 1995X
An improved synthetic route to pentabenzylcyclopentadiene, C5Bz5H (1), has been
developed, utilizing a larger amount of dicyclopentadiene, sodium, and excess benzyl alcohol
as both reactant and solvent. Subsequent extraction and crystallization using hexane
produced 1 in 62% yield. A reaction between 1 and iron pentacarbonyl in refluxing toluene
led to the formation of [(η5-C5Bz5)Fe(CO)2]2 (2) and (η4-C5Bz5H)Fe(CO)3 (3). Unlike the parent
compound (η4-C5H6)Fe(CO)3, 3 exhibited exceptional air and thermal stability. A single-
crystal X-ray diffraction study of 3 has been undertaken and confirms the proposed structure.
In tr od u ction
C5Bz5)2M (M ) Ge, Sn, Pb)8 were also described at that
time. Since then, studies on a variety of other η5-
pentabenzylcyclopentadienyl derivatives of transition,
lanthanide, and main group metals have been
undertaken.9-21 Compared to η5-C5H5 or even η5-C5Me5,
the η5-C5Bz5 ligand is very bulky and extremely steri-
cally demanding, resulting in enhanced kinetic stabili-
zation of corresponding (η5-pentabenzylcyclopentadienyl)-
metal compounds.22
In this paper, we describe an improved synthetic route
to pentabenzylcyclopentadiene (1) and its reaction with
iron pentacarbonyl, leading to several new (η5-penta-
benzylcyclopentadienyl)- and (η4-pentabenzylcyclopen-
tadiene)iron compounds. In order to investigate steric
The η5-cyclopentadienyl group (η5-C5H5 or Cp), de-
rived from cyclopentadiene, has become one of the most
important and common ligands in organometallic chem-
istry. Compounds containing this ligand are known for
virtually all the transition, main group, and f-block
metals. The extensive series of known cyclopenta-
dienylmetal derivatives has also created interest in the
corresponding chemistry of other metal complexes in
which the η5-cyclopentadienyl ring is completely sub-
stituted.1
Since the first definitive study on η5-pentamethyl-
cyclopentadienyl derivatives of the metals in 1967,2 the
η5-C5Me5 (or Cp*) ligand has likewise played a major
role in the development of organometallic chemistry.
Replacement of all the hydrogen atoms by methyl
substituents alters both the steric and electronic influ-
ence of the η5-cyclopentadienyl ring, resulting in differ-
ing reactivities and stabilities of (η5-C5Me5)-metal
(8) Schumann, H.; J aniak, C.; Hahn, E.; Kolax, C.; Loebel, J .;
Rausch, M. D.; Zuckerman, J . J . Chem. Ber. 1986, 119, 2656.
(9) Schumann, H.; J aniak, C.; Khani, H. J . Organomet. Chem. 1987,
330, 347.
(10) Schumann, H.; J aniak, C.; Pickardt, J .; Borner, U. Angew.
Chem., Int. Ed. Engl. 1987, 26, 789.
(11) Schumann, H.; J aniak, C.; Khan, M. A.; Zuckerman, J . J . J .
Organomet. Chem. 1988, 354, 7.
(12) Rausch, M. D.; Tsai, W.-M.; Chambers, J . W.; Rogers, R. D.;
Alt, H. G. Organometallics 1989, 8, 816.
(13) Schumann, H.; J aniak, C.; Kohn, R. D.; Loebel, J .; Dietrich, A.
J . Organomet. Chem. 1989, 365, 137.
(14) Lorberth, J .; Shin, S.-H.; Wocadlo, S.; Massa, W. Angew. Chem.,
Int. Ed. Engl. 1989, 28, 735.
(15) Schumann, H.; J aniak, C.; Gorlitz, F.; Loebel, J .; Dietrich, A.
J . Organomet. Chem. 1989, 363, 243.
(16) Schumann, H.; Gorlitz, F. H.; Dietrich, A. Chem. Ber. 1989,
122, 1423.
compounds relative to their
(η5-C5H5)-metal
counterparts.3-6
In 1986, we reported the first η5-pentabenzylcyclo-
pentadienyl derivatives of the transition metals,7 and
a series of perbenzylated metallocenes of the type (η5-
X Abstract published in Advance ACS Abstracts, May 1, 1996.
(1) J aniak, C.; Schumann, H. Adv. Organomet. Chem. 1991, 33, 291.
(2) King, R. B.; Bisnette, M. B. J . Organomet. Chem. 1967, 8, 287.
(3) King, R. B. Coord. Chem. Rev. 1976, 20, 155.
(17) Schmidt, G.; Thewalt, U.; Troyanov, S. I.; Mach, K. J . Organo-
met. Chem. 1993, 453, 185.
(18) Loos, D.; Schnockel, H. J . Organomet. Chem. 1993, 463, 37.
(19) Schumann, H.; Gorlitz, F. H.; Schafers, M. Acta Crystallogr.,
Sect. C: Cryst. Struct. Commun. 1993, C49, 688.
(20) Zanello, P.; Cinquantini, A.; Mangani, S.; Opromolla, G.; Pardi,
L.; J aniak, C.; Rausch, M. D. J . Organomet. Chem. 1994, 471, 171.
(21) Schumann, H.; Suhring, K.; Weimann, R. J . Organomet. Chem.
1995, 496, C5.
(4) Maitlis, P. M. Acc. Chem. Res. 1978, 11, 301.
(5) Calabro, D. C.; Hubbard, J . L.; Blevins, C. H.; Campbell, A. C.;
Lichtenberger, D. L. J . Am. Chem. Soc. 1981, 103, 6389.
(6) Miller, E. J .; Landon, S. J .; Brill, T. B. Organometallics 1985, 4,
533.
(7) Chambers, J . W.; Baskar, A. J .; Bott, S. G.; Atwood, J . L.; Rausch,
M. D. Organometallics 1986, 5, 1635.
(22) For the excellent review Bulky or Supracyclopentadienyl De-
rivatives in Organometallic Chemistry, see ref 1.
S0276-7333(95)00653-4 CCC: $12.00 © 1996 American Chemical Society

2592 Organometallics, Vol. 15, No. 11, 1996
Tsai et al.
Rea ction betw een C5Bz5H (1) a n d F e(CO)5. A
reaction between 1 and Fe(CO)5 in refluxing toluene
produced a purple solid which was chromatographed on
a long alumina column using CH2Cl2-hexane (30/70)
as the eluent. A yellow band and a red band developed
and were collected separately.
The second band after removal of the solvent and
recrystallization produced a red crystalline solid, mp
166.5-167.0 °C. On the basis of the IR and NMR
spectral data as well as microanalysis, the red product
can be assigned as [(η5-C5Bz5)Fe(CO)2]2 (2), having a
effects in these bulky organic and organometallic com-
pounds, a single-crystal X-ray diffraction study of one
of the reaction products has been undertaken.
Resu lts a n d Discu ssion
Syn t h et ic St u d ies on 1. Pentabenzylcyclopenta-
diene (1) was first reported by Hirsch and Bailey23 in
1978, as part of a program to study multiple alkylations
of compounds containing cyclopentadiene rings by the
action of alcohols in the presence of their corresponding
alkoxides. Compound 1 was obtained in ca. 19% yield
from a reaction between dicyclopentadiene and an
excess of benzyl alcohol and sodium metal, using diiso-
propylbenzene as the solvent. The product was purified
by vacuum distillation at ca. 250-275 °C/0.8 mmHg.
Chambers et al. subsequently simplified the procedure
by omitting the distillation step and utilizing trituration
and crystallization from methanol as a means of puri-
fication. Unfortunately, this modified route to 1 still
involved a high-boiling solvent that was tedious to
remove, and the yields of 1 were often low and variable.
In order to develop a successful research program in
(pentabenzycyclopentadienyl)metal chemistry, it was
important to have available a sufficient supply of 1. A
study to improve the yield of 1 was therefore conducted.
On the basis of a procedure suggested by J aniak,24 an
improved route to 1 has been developed, utilizing a
larger amount of dicyclopentadiene and an excess of
benzyl alcohol at reflux, without any diisopropylbenzene
as in the earlier methods.
trans-centrosymmetric structure with two bridging and
two terminal carbonyl groups. The structure of 2 is thus
analogous to that found for [(η5-C5Me5)Fe(CO)2]2.27 The
initial yellow band after solvent removal and recrystal-
lization afforded a yellow crystalline solid, mp 204-205
°C. The IR spectrum of the product exhibited three
strong terminal carbonyl bands at 1947, 1972, and 2034
cm-1. On the basis of the similarity of these data to IR
spectral data for (η4-C5H6)Fe(CO)3 [IR (hexane): νCO
1974, 1981, 2048 cm-1 28
and on microanalytical data,
]
the second reaction product was tentatively assigned the
1
structure (η4-C5Bz5H)Fe(CO)3 (3). Both the H and 13C
NMR spectra of the yellow product were likewise
consistent with its formulation as 3. The mass spec-
trum of the product exhibited a molecular ion peak for
3 as well as fragmentation peaks resulting from losses
of each of the three CO ligands.
Compound 3, (η4-C5Bz5H)Fe(CO)3, exhibited unex-
pected stability. The cyclopentadiene analog, (η4-C5H6)-
Fe(CO)3, is very reactive and converts thermally to the
corresponding dimer, [(η5-C5H5)Fe(CO)2]2, even under
argon.28 In addition to its thermal instability, (η4-C5H6)-
Fe(CO)3 has been reported to decompose to its dimer
upon exposure to air in solution at room temperature.
Compound 3, however, proved to be air-stable in the
crystalline state, and upon heating of a solution of 3 in
xylene to 135 °C, no significant decomposition was
observed.
All previous methods used to prepare 1 have em-
ployed methanol as the crystallization solvent. How-
ever, subsequent reactions of 1 with n-butyllithium
would be adversely affected by even trace amounts of
this solvent. Therefore, as another modification, we
found that 1 could be conveniently crystallized instead
from hot hexane. Using these modifications, 1 (mp
72.5-73.5 °C) could be obtained in 62% yield.
Str u ctu r a l Stu d ies on 1. Pentabenzylcyclopenta-
diene (1) has been the subject of two independent X-ray
crystallographic investigations.25,26 Both studies con-
firm the original structural assignment proposed by
Hirsch and Bailey.23 The studies indicate that the
cyclopentadiene ring is planar within standard devia-
tions, and that CdC double bonds are located between
C(1) and C(2) and between C(3) and C(4). Moreover,
the orientation of the five benzyl groups indicates that
Since (η4-C5H6)Fe(CO)3 has been suggested to be an
intermediate to [(η5-C5H5)Fe(CO)2]2,29 an attempt was
made to convert 3 to 2. However, when a xylene
solution containing both 2 and 3 was heated to reflux
in air over a 40 min period, the intensities of the
carbonyl frequencies for 2 and not for 3 gradually
decreased while the solution was being heated. At 135
°C, absorption bands for 2 had completely disappeared,
while those for 3 had not changed. These results
suggest that the pentabenzylcyclopentadiene complex
3 is more oxidatively stable in solution than is the dimer
2.
1
1 is a very sterically constrained molecule. Both H and
13C NMR spectra for 1 have been obtained in the present
study. Detailed spectral information including peak
assignments is presented in the Experimental Section.
(23) Hirsch, S. S.; Bailey, W. J . J . Org. Chem. 1978, 43, 4090.
(24) J aniak, C. Personal communication, J uly 1987.
(25) Tsai, W.-M. Doctoral Dissertation, University of Massachusetts,
Amherst, 1991. See: Diss. Abstr. Int. B 1992, 52 (9), 4724 (Chem. Abst.
1993, 118, 147594k).
(26) Schumann, H.; Gorlitz, F. H.; Esser, L. Acta Crystallogr., Sect.
C: Cryst. Struct. Commun. 1993, C49, 598.
X-r a y Cr ysta llogr a p h ic Stu d ies. In order to fur-
ther examine steric effects resulting from the coordina-
(27) Raymond, G. T.; Williams, J . M. Inorg. Chem. 1980, 19, 2770.
(28) Kochhar, R. K.; Pettit, R. J . Organomet. Chem. 1966, 6, 272.
(29) Pauson, P. L. Proc. Chem. Soc. 1960, 297.

Pentabenzylcyclopentadiene
Organometallics, Vol. 15, No. 11, 1996 2593
Ta ble 1. Cr ysta l Da ta a n d Su m m a r y of In ten sity
Da ta Collection a n d Str u ctu r e Refin em en t for
(η4-C5Bz5H)F e(CO)3
compd
color/shape
fw
space group
temp, °C
cell constsa
a, Å
(η4-C5Bz5H)Fe(CO)3
yellow/cube
656.60
P1h
21
10.513(3)
b, Å
10.725(3)
c, Å
16.349(9)
R, deg
79.26(3)
73.45(3)
78.89(2)
1716.9
2
1.27
4.93
â, deg
γ, deg
cell vol, Å3
formula units/unit cell
D
µ
calc, g cm-3
calc, cm-1
diffractometer/scan
Enraf-Nonius CAD-4/ω-2θ
radiation, graphite monochromator Mo KR (λ ) 0.710 73)
max cryst dimens, mm
scan width
std reflns
decay of stds
no. of reflns measd
2θ range, deg
range of h,k,l
no. of reflns obsd [Fo g 5σ(Fo)]
computer program
struct solution
no. of params varied
weights
0.30 × 0.33 × 0.33
0.80 + 0.35 tan θ
400, 020, 006
(2%
F igu r e 1. Molecular structure and atom-labeling scheme
for (η4-C5Bz5H)Fe(CO)3 (3).
5953
tion of 1 to an Fe(CO)3 moiety, an X-ray crystallographic
study of 3 was undertaken. The study demonstrates
that crystals of 3 consist of discrete molecules of (η5-
C5Bz5H)Fe(CO)3 separated by normal van der Waals
distances. Figure 1 shows the molecular structure and
atom-labeling scheme for 3. A complete table of bond
lengths and angles is given in the Supporting Informa-
tion.
2 e 2θ e 50
+12,(12,(19
3518
SHELX
SHELXS
424
[σ(Fo)2]-1
1.43
GOF
R ) ∑||Fo| - |Fc||/∑|Fo|
largest feature final diff map, e/Å-3 0.3
0.055
0.062
Rw
From Figure 1, it is clear that the pentabenzylcyclo-
pentadiene ligand in 3 is bonded to the iron atom in an
η4-manner. In order to minimize steric repulsions, C(8)
is out of the ring plane and bent away from the iron
atom. The benzyl group that is attached to C(8) also
points away from the iron center. Methylene carbons
C(9), C(16), C(23), and C(30) are basically coplanar with
the ring. The benzyl groups attached to the ring
carbons C(5) and C(6) are bent away from the iron atom.
Unlike (η5-pentabenzylcyclopentadienyl)metal com-
pounds, the benzyl groups which are attached to ring
carbons C(4) and C(7) do not bend up or down but are
oriented horizontally away from the other benzyl groups.
The two benzyl groups attached to C(5) and C(6) are
bent away from the iron atom. On the basis of the bond
lengths between the iron atom and the ring carbon
atoms (see Table S1 of the Supporting Information), the
Fe-Cent vector is not perpendicular to the η4-plane. The
bond lengths Fe-C(5) (2.067(5) Å) and Fe-C(6) (2.062(6)
Å) are shorter than Fe-C(4) (2.130(5) Å) or Fe-C(7)
(2.105(5) Å).
a
Least-squares refinement of ((sin θ)/λ)2 values for 25 reflections
θ > 19°.
genated CAMAG neutral grade alumina. Hexane, tetrahydro-
furan (THF), and toluene were distilled under argon from
sodium-potassium alloy before use. Benzyl alcohol was used
as received from Fisher Scientific Co., whereas dicyclopenta-
diene and iron pentacarbonyl were purchased from Aldrich
Chemical Co.
Syn th esis of P en ta ben zylcyclop en ta d ien e (1). A 500-
mL three-necked flask equipped with a mechanical stirrer and
a Dean-Stark receiver attached to a reflux condenser was
charged with 450 g (4.16 mol) of benzyl alcohol. After the flask
was evacuated and back-flushed with argon three times, 11.5
g (0.50 mol) of sodium was added and the mixture was heated
with stirring by means of a heating mantle at 120 °C until all
the sodium was consumed. The temperature was then raised
to 160-170 °C, and 23 g (0.17 mol) of dicyclopentadiene was
added dropwise into the solution over 4 h. The mixture was
stirred for another 15 h at reflux. The mechanical stirrer was
then removed and refluxing was continued for another 24-48
h. A white semisolid was formed during the reaction, and
about 30 mL of H2O was collected in the Dean-Stark re-
ceiver.30 Most of the benzyl alcohol was then removed in vacuo
with heating. The residue was treated in air with 5%
hydrochloric acid until all the solid dissolved. The organic
layer was collected, and the remaining benzyl alcohol was
removed in vacuo at ca. 100 °C. The resulting oily yellow
residue was allowed to cool to room temperature and was
repeatedly extracted (ca. 4 times using ca. 250 mL portions)
with hot hexane. The combined hexane extract was stored at
-20 °C overnight, resulting in the formation of an oily layer.
The hexane solution was decanted into another flask and
stored at -20 °C for another 3 d, producing a white crystalline
Exp er im en ta l Section
All operations were carried out under an argon atmosphere
using Schlenk techniques except where specified. The argon
was deoxygenated with BTS catalyst and dried with molecular
sieves and magnesium perchlorate. IR spectra were recorded
in CH2Cl2 solution on a Perkin-Elmer Model 1310 or a Perkin-
Elmer FTIR Model 1600 infrared spectrometer, whereas NMR
spectra were recorded in CDCl3 solution on either Varian XL-
200 or XL-300 spectrometers. 1H and 13C NMR chemical shifts
are reported relative to Me4Si, all referencing done internally.
Melting points were determined in air and are uncorrected.
Microanalyses were performed by the Microanalytical Labora-
tory, University of Massachusetts. Chromatography columns
were packed under argon, using 5% deactivated and deoxy-
(30) The reaction should be monitored carefully after ca. two-thirds
of the solution turns to solid. If the resulting white semisolid material
coating the bottom of the flask turns light yellow, continued heating
can result in extensive decomposition.

2594 Organometallics, Vol. 15, No. 11, 1996
Tsai et al.
solid. This crystallization procedure was repeated 4-5 times
for the oily layer until no more white solid was formed after
hexane extraction and cooling. All the precipitated white
solids were then combined and dried under vacuum overnight,
yielding 109.5 g (0.21 mol, 62%) of pentabenzylcyclopentadiene
(1). The product was further purified by redissolving it in hot
hexane and storage at room temperature for 2 d, producing 1
as a white crystalline solid, mp 72.5-73.5 °C (lit.23 mp 69.2-
75.5 °C; lit.7 mp 68-70 °C). Anal. Calcd for C40H36: C, 92.98;
H, 7.02. Found: C, 93.10; H, 6.89. 1H NMR (CDCl3): δ 3.10
(d, 2 H, CH2C6H5), 3.21 (t, 1 H, CH), 3.45 (s, 4 H, CH2C6H5),
3.5-3.9 (2 d, 4 H, CH2C6H5), 6.65-7.28 (m, 25 H, C6H5). 13C
NMR (assignments confirmed by APT): δ 31.65, 33.25, 34.13
(CH2C6H5), 52.55 (CH), 125.4-142.8 (C6H5 + CdC). MS: m/ e
516 (M+), 425 (M - Bz)+, 334 (M - 2Bz)+, 243 (M - 3Bz)+.
P r ep a r a tion of Bis[(η5-p en ta ben zylcyclop en ta d ien yl)-
d ica r bon ylir on ] (2) a n d (η4-P en ta ben zylcyclop en ta d i-
en e)tr ica r bon ylir on (3). In a 250-mL three-necked flask
equipped with a gas inlet tube, magnetic stirrer, and reflux
consenser were placed 5.00 g (25.5 mmol) of Fe(CO)5, 10.0 g
(19.3 mmol) of pentabenzylcyclopentadiene, and 150 mL of
toluene. The reaction mixture was stirred at reflux for 24 h,
during which time the reaction progress was monitored by IR
spectroscopy. The resulting solution was then filtered through
a plug of alumina under argon, the solvent was removed from
the filtrate, and 100 mL of methylene chloride was added. After
the solution was again filtered through a plug of alumina, the
filtrate was concentrated to ca. 50 mL, hexane (ca. 75 mL) was
added, and the solvent was removed slowly in vacuo. During
this solvent removal process, the more volatile methylene
chloride is removed in preference to the less volatile hexane,
causing a purple precipitate which is almost insoluble in
hexane to crystallize from solution. The resulting crystals
were filtered out, washed with pentane, and dried under
vacuum. The purple solid obtained in this manner was
chromatographed on an alumina column (2 × 45 cm) packed
using hexane and was eluted with CH2Cl2-hexane (30/70). A
yellow and a red band developed and were collected separately.
After removal of the solvents, both were recrystallized from
CH2Cl2-hexane. Red crystals of [(η5-C5Bz5)Fe(CO)2]2 (2) (4.6
g, 8%), mp 166.5-167.0 °C, and yellow crystals of (η4-C5Bz5H)-
Fe(CO)3 (3) (3.2 g, 25%), mp 204-205 °C, were obtained in
this manner.
[(η5-C5Bz5)F e(CO)2]2 (2). Anal. Calcd for C84H70Fe2O4: C,
80.38; H, 5.62. Found: C, 80.12; H, 5.56. IR (CH2Cl2): ν(CO)
1750, 1935 cm-1 1H NMR (CDCl3): δ 3.61 (s, 10 H, CH2C6H5),
.
6.60-7.25 (m, 25 H, C6H5). 13C NMR (CDCl3): δ 30.38
(CH2C6H5), 102.7 (C5Bz5), 126.1, 128.0, 129.1, 138.5 (C6H5),
200.3 (CO).
(η4-C5Bz5H)F e(CO)3 (3). Anal. Calcd for C43H36FeO2: C,
78.66; H, 5.53. Found: C, 78.58; H, 5.59. IR (CH2Cl2): ν(CO)
1947, 1972, 2034 cm-1
.
1H NMR (CDCl3): δ 2.33 (d, 2 H,
CH2C6H5), 2.72 (t, 1 H, CH), 2.74-3.11 (2 d, 4 H, CH2C6H5),
3.94-4.28 (2 d, 4 H, CH2C6H5), 6.62-7.30 (m, 25 H, C6H5).
13C NMR (CDCl3): δ 73.46, 35.50, 46.18 (CH2C6H5), 60.60 (CH),
79.76, 103.6 (CdC), 126.3-140.0 (C6H5), 211.3 (CO).
X-r a y Da ta Collection , Str u ctu r e Deter m in a tion , a n d
Refin em en t for (η4-C5Bz5H)F e(CO)3 (3). A yellow single
crystal of the title compound was mounted in a thin-walled
glass capillary under argon and transferred to the goniometer.
The space group was determined to be either the centric P1h
or acentric P1. The subsequent solution and successful
refinement of the structure was carried out in the centric space
group P1h. A summary of data collection parameters is given
in Table 1.
Least-squares refinement with isotropic thermal parameters
led to R ) 0.118. The hydrogen atoms were placed in
calculated positions 0.95 Å from the bonded carbon atom and
allowed to ride on that atom with B fixed at 5.5 Å2. Refine-
ment of non-hydrogen atoms with anisotropic temperature
factors led to the final values of R ) 0.055 and Rw ) 0.062.
Su p p or tin g In for m a tion Ava ila ble: Tables of bond
distances and angles, atomic coordinates, fractional coordi-
nates for hydrogen atoms, thermal parameters, and least-
squares results for compound 3 (14 pages). Ordering infor-
mation is given on any current masthead page.
OM9506532