Reactions of aromatic heterocycles with uranium alkyl complexes

Article abstract of DOI:10.1021/ic1009835

The reactivity of a uranium dibenzyl complex supported by a ferrocenediamide ligand toward aromatic N-heterocycles was investigated. The uranium dibenzyl complex reacted with 1 equiv of pyridine or picoline to give the respective ortho-metalated product. In turn, the η²-N,C- pyridyl complexes reacted with benzoxazole or benzothiazole, leading to a cascade of transformations that involves C-C coupling of the two heterocyclic rings, ring opening, and alkyl transfer. A similar cascade was previously reported for 1-methylimidazole. The present results provide support for the mechanism proposed earlier and attest to the generality of the reaction cascade described.

Full text of DOI:10.1021/ic1009835

Inorg. Chem. 2010, 49, 7165–7169 7165
DOI: 10.1021/ic1009835
Reactions of Aromatic Heterocycles with Uranium Alkyl Complexes
ꢀ
Selma Duhovic, Marisa J. Monreal, and Paula L. Diaconescu*
Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095
Received May 17, 2010
The reactivity of a uranium dibenzyl complex supported by a ferrocenediamide ligand toward aromatic N-heterocycles
was investigated. The uranium dibenzyl complex reacted with 1 equiv of pyridine or picoline to give the respective
ortho-metalated product. In turn, the η2-N,C-pyridyl complexes reacted with benzoxazole or benzothiazole, leading to
a cascade of transformations that involves C-C coupling of the two heterocyclic rings, ring opening, and alkyl transfer.
A similar cascade was previously reported for 1-methylimidazole. The present results provide support for the
mechanism proposed earlier and attest to the generality of the reaction cascade described.
Introduction
substrates to produce ortho-metalated complexes that show
subsequent transformations.2,13-25
Since the 1950s, the activation of strong, localized bonds,
particularly C-H, C-N, and C-O, by transition metals has
been researched intensively.1,2 In the last 2 decades, the reactiv-
ity of f-block elements has been increasingly under scrutiny
because of the unique chemical behavior of their complexes and
potential to catalyze a wide range of transformations.3-7
Aromatic heterocycles are substrates widely studied because
they are important components of natural products and
pharmaceuticals and are relevant to hydrodenitrogenation
processes.2,8-11 Complexes with d0fn metal-carbon bonds
show diverse reactivity toward aromatic heterocycles, with
both functionalization and ring-opening examples being
reported.2,8,12 Early-transition-metal, lanthanide, and acti-
nide alkyl or hydride complexes often react with these
We have been investigating the reactivity of group 3
metal26-30 and uranium dialkyl31,32 complexes supported
by a 1,10-ferrocenylenediamide ligand33-35 toward aromatic
N-heterocycles.27,36-40 In particular, the reactivity of a ura-
nium dibenzyl complex, (NNfc)U(CH2Ph)2 (1-(CH2Ph)2,
where NNfc=fc(NSitBuMe2)2 and fc =1,10-ferrocenylene),31
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*To whom correspondence should be addressed. E-mail: pld@
chem.ucla.edu.
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2010 American Chemical Society
Published on Web 06/28/2010
pubs.acs.org/IC

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Duhovic et al.
7166 Inorganic Chemistry, Vol. 49, No. 15, 2010
Scheme 1. Reactions of 1-Methylimidazole Mediated by 1-(CH2Ph)2
Scheme 2. Reactions of 1-(CH2Ph)2 with Pyridine and 2-Picoline
has held our attention because it has two alkyl groups that can
both react with substrates. For example, we recently reported a
novel C-H activation by 1-(CH2Ph)2 showing that both
benzyl ligands engaged an sp2 C-H bond of 1-methylimida-
zole (mi) to give 2mi-mi (Scheme 1).36,41 In addition to the
double C-H activation, an interesting cascade of functiona-
lization reactions was induced thermally. Specifically, upon
heating, one of the η2-N,C-imidazolyl and coordinated imi-
dazole ligands in 2mi-mi underwent C-C coupling to give 3mi,
a process followed by the ring opening of the dearomatized
ring and the migratory insertion of the remaining imidazolyl
ligand, ultimately leading to an isomeric mixture of 4A and 4B
(Scheme 1).36 This cascade of reactions represented the first
example of aromatic N-heterocycle cleavage by actinide com-
plexes in which no oxygen atoms42 or redox processes43 were
involved. At the time when we reported our initial findings, the
mechanistic proposal was based on the isolation of the
1-methylbenzimidazole (mbi) analogue of the proposed inter-
mediate 3mi.36 We decided to investigate the generality of this
reactivity behavior in order to find support for the pathway
proposed. Herein we report the reactions of 1-(CH2Ph)2 with
other aromatic heterocycles. Substrates analogous to imida-
zole, such as benzoxazole and benzothiazole, as well as
pyridine substrates were studied. The products of the reactions
discussed attest to the generality of the reaction cascade
proposed in Scheme 1.
(Cp* = C5Me5, An = Th, U; R = Me, Ph, CH2Ph)19,21,22 and
by the Dormond16 and the Scott groups14 using cyclometalated
amide thorium and/or uranium complexes and pyridine sub-
strates. The reaction of pyridine with 1-(CH2Ph)2 (16 h) was
3 times faster than the analogous reaction with Cp*2UMe2
(reported to take place in 48 h).22
Although two isomers are possible for the η2-N,C-pyridyl
complexes 5py and 5pic, only one was observed in each
case. For 5pic, the isomer featuring the methyl group and the
nitrogen donor of the picolyl ligand pointing toward the
benzyl ligand is analogous to the isomer reported by the
Kiplinger group for Cp*2AnMe[η2-N,C-6-CH3NC5H3]
(An = Th, U).21 The other isomer was isolated, however,
for 5py (Figure 1). Switching the identity of the nitrogen,
N(3), and carbon, C(29), atoms for 5py during the refinement
process resulted in unstable situations.
Results and Discussion
Reactions between 1-(CH2Ph)2 and 1 equiv of pyridine or
picoline (Scheme 2) led to the corresponding ortho-metalated
products (NNfc)U(CH2Ph)(η2-N,C-pyridyl) (5py) or (NNfc)U-
(CH2Ph)(6-Me-η2-N,C-pyridyl) (5pic), with one benzyl group
engaging in C-H activation. These reactions are analogous to
the formation of the imidazolyl complexes (NNfc)U(CH2Ph)-
(η2-N,C-1-methylimidazolyl) (5mi) and (NNfc)U(CH2Ph)(η2-
N,C-1-methylbenzimidazolyl) (5mbi) from 1-(CH2Ph)2 and
1 equiv of mi or mbi, respectively.41 Similar observations were
made by the Kiplinger group when starting from Cp*2AnR2
The solid-state structures of the newly synthesized η2-N,C-
pyridyl complexes (Figure 1) are not unusual and compare
well to those of analogous uranium complexes. For example,
the U-Npy distances of 2.3700(40) A in 5py and 2.3932(25) A
in 5pic, although relatively short, are in the range exhibited by
other pyridyl complexes.14,21,22,41 A similar situation is en-
countered for the U-Cpy distances of 2.4059(46) A in 5py and
2.3967(30) A in 5pic. The X-ray crystal structures also reveal
an η2 coordination of the benzyl ligands with U-C distances
of 2.5076(52) A [U-C(33)] and 2.8433(48) A [U-C(22)] in
py and 2.5215(30) A [U-C(17)] and 2.8558(30) A [U-C(18)]
in 5pic and U-C-C angles of 87.60(30)° in 5py and 87.52(18)°
in 5pic
(41) Monreal, M. J.; Diaconescu, P. L. J. Am. Chem. Soc. 2010, 132, 7676.
(42) Pool, J. A.; Scott, B. L.; Kiplinger, J. L. Chem. Commun. 2005, 2591.
(43) Arunachalampillai, A.; Crewdson, P.; Korobkov, I.; Gambarotta, S.
Organometallics 2006, 25, 3856.
5
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Article
Inorganic Chemistry, Vol. 49, No. 15, 2010 7167
and engages the benzyl ligand in a migratory insertion to form
the final product, 8py-boz or 8pic-btz.
The products 8py-boz and 8pic-btz were both characterized
by X-ray crystallography; the structure of 8py-boz, however,
showed a high degree of thermal disorderand is only included
in the Supporting Information to show atom connectivity
(Figure SX4). The complex 8pic-btz (Figure 2) features
metrical parameters consistent with the structure proposed
in Scheme 3. For example, the U-Namide distance of
2.3534(36) A is longer by ca. 0.1 A than the U-Nfc distances
of 2.2406(36) and 2.2421(38) A. The U-S distance of
2.6914(12) A is in the range reported for other U-S distances
in terminal thiolate complexes.44-47 The other distances also
support the above structural assignment. For example, the
C-Namide distances are 1.4665(55) and 1.5074(63) A, and the
N-C-C and C-C-C angles around C6 are 110.85(38),
112.05(36), and 110.54(38)°.
Figure 1. Thermal ellipsoid (50% probability) representation of 5py
(left) and 5pic (right). Hydrogen atoms were removed for clarity. Selected
metrical parameters for 5py (distances in A and angles in deg): U(1)-N(1),
2.2273(38); U(1)-N(2), 2.2388(39); U(1)-N(3), 2.3700(40); U(1)-C(29),
2.4059(46); U(1)-C(22), 2.8433(48); U(1)-C(33), 2.5076(52); N(3)-
C(29), 1.3388(59); C(22)-C(33), 1.4019(69); U(1)-C(33)-C(22),
87.60(30); N(1)-U(1)-N(2), 135.77(14); N(1)-U(1)-N(3), 90.91(14);
N(2)-U(1)-N(3), 89.65(13). Selected metrical parameters for 5pic
(distances in A and angles in deg): U(1)-N(1), 2.2343(24); U(1)-N(2),
2.2342(25); U(1)-N(3), 2.3932(25) A; U(1)-C(15), 2.3967(30); U(1)-
C(17), 2.5215(30); U(1)-C(18), 2.8558(30); N(3)-C(15), 1.3398(37);
C(17)-C(18), 1.4546(42); U(1)-C(17)-C(18), 87.52(18); N(1)-U-
(1)-N(2), 136.08(8); N(1)-U(1)-N(3), 102.81(9); N(2)-U(1)-N(3),
102.49(8).
Scheme 3. Reactions of Uranium η2-N,C-Pyridyl Complexes with
Benzoxazole and Benzothiazole and the Proposed Mechanism
The reaction observed between 5py and benzoxazole or
between 5pic and benzothiazole was extended to 5mbi and
benzoxazole (eq 1). The isolation of 8mbi-boz in 90% yield,
together with the above reactions, attests to the generality of
the sequence proposed to occur for these transformations.
1
The complex 8mbi-boz was characterized by H NMR spec-
troscopy and elemental analysis; a comparison of its 1H NMR
spectrum with those of 8py-boz and 8pic-btz showed analogous
features.
Conclusions
We have shown that uranium alkyl complexes mediate
various reactions with aromatic N-heterocycles. The reac-
tions between the uranium dibenzyl complex 1-(CH2Ph)2 and
one equivalent of pyridine or 2-picoline led to the formation
of alkyl-η2-N,C-pyridyl complexes through C-H activation.
These ortho-metalated complexes engage in complex reactions
with benzoxazole or benzothiazole. The reaction sequence
proposed to explain the formation of the final products is
reminiscent of the previously reported transformation of the
uranium bis(η2-N,C-imidazolyl) complex 2mi into 4A and 4B.
The intimate reaction steps are based on C-C coupling, hetero-
cycle ring-opening, and alkyl transfer. The reactions reported
herein provide support for the mechanism proposed earlier for
1-methylimidazole and attest to the generality of the reaction
cascade described.
We decided to determine whether the C-C coupling and
heterocycle ring-opening reactions observed for mi (Scheme 1)
would be observed for other aromatic heterocycles as well. The
reaction between 5py and benzoxazole (2 equiv) or between 5pic
and benzothiazole (1 or 2 equiv), substrates analogous to imida-
zoles, led to products reminiscent of 4A and 4B (Scheme 3). We
propose that steps similar to those described in Scheme 1 also
take place in the present cases (Scheme 3): the coordination
of benzoxazole or benzothiazole is followed by C-C coupling
to the pyridyl ligand with concomitant dearomatization of
the diheteroatom ring (6py-boz or 6pic-btz). This intermediate
undergoes ring opening of the dearomatized heterocycle to
form 7py-boz or 7pic-btz. The imine functionality is still reactive
ꢀ
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M. J. Am. Chem. Soc. 2006, 128, 8790.
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7168 Inorganic Chemistry, Vol. 49, No. 15, 2010
solution of 1-(CH2Ph)2 (100 mg in 5 mL of hexanes, 0.116 mmol)
in a 12-mL Schlenk tube. The reaction mixture was stirred at
room temperature for 30 h. The solvent was removed under
reduced pressure, and the dried product was extracted in
hexanes, filtered through Celite, concentrated, and placed in a
-35 °C freezer. Yield: 66 mg, 66%. 1H NMR (C6D6, 500 MHz,
25 °C): δ -71.13 (s, 2H, CH2C6H5), 18.80 and 14.96 (s, 12H,
SiCH3), 15.23 [s, 18H, SiC(CH3)3], 1.91, -13.09, -24.35, and
-32.42 (s, 2H each, CH2C6H5 or C5H4), 9.98, 8.70, -2.12, and
-9.53 (s, 1H each, C5H4 or NC5H4), -9.53 (s, 3H, NCCH3).
Anal. Calcd for C35H51FeN3Si2U: C, 48.66; H, 5.95; N, 4.86.
Found: C, 48.46; H, 6.04; N, 4.77.
Synthesis of 8py-boz. A 2-mL benzene solution of benzoxazole
(13 mg, 0.11 mmol) was slowly added to a 2-mL benzene
solution of 5py (43 mg, 0.051 mmol). The reaction mixture was
stirred at room temperature for 12 h. The volatiles were removed
under reduced pressure, and the resulting dark-red powder was
dissolved in diethyl ether. The solution was filtered through
Celite, concentrated, and stored at -35 °C. X-ray-quality crystals
Figure 2. Thermalellipsoid (50%probability) representationof8pic-btz.
Irrelevant hydrogen atoms and tert-butylmethyl groups were removed for
clarity. Selected metrical parameters for 8pic-btz (distances in A and angles
in deg): U(1)-N(1), 2.2406(36); U(1)-N(2), 2.2421(38); U(1)-N(3),
2.5026(37) A; U(1)-N(4), 2.3534(36) A; U(1)-S(1), 2.6914(12); N(4)-
C(6), 1.4665(55); N(1)-U(1)-N(2), 132.80(14); N(1)-U(1)-S(1),
96.55(10); N(2)-U(1)-S(1), 103.37(10); N(3)-U(1)-S(1), 140.60(9);
N(4)-U(1)-S(1), 74.07(9).
1
formed overnight. Yield: 30.1 mg, 61%. H NMR (C6D6, 500
MHz, 25 °C): δ 51.22, 40.27, 39.62, and 31.57 (s, 3H each, SiCH3),
28.01 and 27.15 [s, 9H each, SiC(CH3)3], 1.85 (t, 2H, CH2Ph), 2.89,
-1.25, -2.28, -2.90, -10.38, and -12.38 (t, 1H each, C5H4, aro-
matic CH, or NC5H3), -3.81, -15.08, -17.41, -17.79,
-19.19, -22.19, and -25.13 (d, 1H each, C5H4, aromatic CH,
or NC5H3), -3.88, -11.42, -13.17, -13.39, -13.95, -27.80,
-38.07, -46.63, and -73.03 (s, 1H each, C5H4, aromatic CH, or
NC5H3). Anal. Calcd for C41H55FeN4OSi2U (970): C, 50.77; H,
5.72; N, 5.78. Found: C, 50.53; H, 5.73; N, 5.53.
Synthesis of 8pic-btz. A 2-mL pentane solution of benzothiazole
(72.7 mg, 0.522 mmol) was slowly added to a 2-mL n-pentane
solution of 5pic (347 mg, 0.401 mmol). The reaction mixture was
left at room temperature without stirring. The pink precipitate
that formed after 10 h (yield: 217.5 mg, 54%) was separated, dried,
dissolved in diethyl ether, filtered through Celite, and stored at
-35 °C. X-ray-quality crystals formed overnight. 1H NMR (C6D6,
500 MHz, 25 °C): δ 49.38, 27.51, 25.17, and 18.45 (s, 3H each,
SiCH3), 27.06 and 24.32 [s, 9H each, SiC(CH3)3], -12.14 (s, 2H,
CH2Ph), 10.08, 9.58, 3.47, 2.77, 2.49, -1.08, and -30.98 (t, 1H
each, C5H4, aromatic CH, or NC5H3), -3.44, -16.94, and -26.17
(d, 1H each, C5H4, aromatic CH, or NC5H3), 12.17, -1.76, -3.15,
-4.44, -4.77, -12.70, -17.61, -29.59, and -62.44 (s, 1H each,
C5H4, aromatic CH, or NC5H3), -70.70 (s, 3H, NCCH3). Anal.
Calcd for C42H57FeN4SSi2U[(C7H8)1/3] (1030): C, 51.64; H, 5.83;
N, 5.44. Found: C, 51.66; H, 5.78; N, 5.63.
Experimental Section
All experiments were performed under a dry nitrogen
atmosphere using standard Schlenk techniques or an MBraun
inert-gas glovebox. Solvents were purified using a two-column
solid-state purification system by the method of Grubbs48 and
transferred to the glovebox without exposure to air. NMR
solvents were obtained from Cambridge Isotope Laboratories,
degassed, and stored over activated molecular sieves prior
to use. Uranium turnings were purchased from Argonne
National Laboratories. Compounds 1-(CH2Ph)231 and 5mbi41
were prepared following published procedures. The aromatic
heterocycles were distilled or recrystallized before use; all other
1
materials were used as received. H NMR spectra were re-
corded on a Bruker 300 or Bruker 500 spectrometer (supported
by NSF Grant CHE-9974928) at room temperature in C6D6
unless otherwise specified. Chemical shifts are reported with
respect to the solvent residual peak, 7.16 ppm (C6D6). CHN
analyses were performed by the UC Berkeley Micro-Mass
facility, 8 Lewis Hall, College of Chemistry, University of
California, Berkeley, CA 94720.
Synthesis of 8mbi-boz. Benzoxazole (7.9 mg, 0.066 mmol) was
dissolved in 2 mL of diethyl ether and added to a 2-mL diethyl
ether solution of 5mbi (58.6 mg, 0.065 mmol). The reaction
mixture was stirred at room temperature for 15 h. The volatiles
were removed under reduced pressure, and the dried product
was extracted with hexanes, filtered through Celite, and dried
again. The pale-orange powder (crude yield of 59.9 mg, 90%,
pure by 1H NMR spectroscopy) was dissolved in fresh hexanes,
passed through Celite, and stored at -35 °C. Clumps of dark-
red needles embedded in salmon-pink powder formed after 48 h.
The product is stable in solution at room temperature indefi-
nitely. 1H NMR (C6D6, 500 MHz, 25 °C): δ 47.41, 42.06, 39.67,
and 32.26 (s, 3H each, SiCH3), 28.31 and 26.45 [s, 9H each,
SiC(CH3)3], 2.43, -0.06, -2.27, -2.92, -4.08, -20.44, -23.24,
and -25.15 (t, 1H each, C5H4, aromatic CH, or NC5H3), -6.44
(d, 2H, CH2Ph), -10.22 (s, 3H, NCCH3), -19.09, -20.78, and
-41.10 (d, 1H each, C5H4, aromatic CH, or NC5H3), -12.63,
-13.59, -15.12, -17.82, -18.02, -27.40, -40.29, and -51.89
(s, 1H each, C5H4, aromatic CH, or NC5H3). Anal. Calcd for
C44H57FeN5OSi2U (1021): C, 51.71; H, 5.62; N, 6.85. Found: C,
52.01; H, 5.70; N, 6.57.
Synthesis of 5py. Pyridine (0.0264 g in ∼3 mL of toluene, 2
equiv) was added dropwise to a stirring toluene solution (5 mL)
of 1-(CH2Ph)2 (0.1441 g, 0.167 mmol) in a 20-mL scintillation
vial and allowed to stir vigorously at room temperature for 16 h.
The solvent was removed under reduced pressure, and the dried
product was extracted with hexanes and filtered through Celite.
The filtrate was dried under reduced pressure, and the above
extraction/filtration procedure was repeated. The filtrate was
concentrated and placed in a -35 °C freezer. Crystals formed
overnight (crop 1: 0.0572 g, 40%). The mother liquor was
decanted and placed back in the freezer. Two additional crops
of crystals were obtained in this manner. Total yield of the three
crops: 0.1257 g, 89%. 1H NMR (C6D6, 500 MHz, 25 °C): δ 21.97
and 18.87 (s, 12H, SiCH3), 17.13 [s, 18H, SiC(CH3)3], 3.33, 0.09,
-9.83, -11.94, -13.23, and -32.69 (s, 2H each, CH2C6H5 or
C5H4), 7.40, 3.53, -3.67, -4.82, and -20.06 (s, 1H each, C5H4
or NC5H4), -82.52 (s, 2H, CH2C6H5). Anal. Calcd for C34H49-
FeN3Si2U: C, 48.05; H, 5.81; N, 4.94. Found: C, 47.68; H, 5.81;
N, 4.93.
Synthesis of 5pic. 2-Picoline (2 mL of a 0.116 M solution in
hexanes, 0.232 mmol, 2 equiv) was added dropwise to a stirring
X-ray Crystal Structures. X-ray-quality crystals were ob-
tained from various concentrated solutions placed in a -35 °C
freezer in the glovebox. Inside the glovebox, the crystals were
(48) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J. Organometallics 1996, 15, 1518.

Article
Inorganic Chemistry, Vol. 49, No. 15, 2010 7169
coated with oil (STP Oil Treatment) on a microscope slide,
which was brought outside the glovebox. The X-ray data
collections were carried out on a Bruker AXS single-crystal
X-ray diffractometer using Mo KR radiation and a SMART
APEX CCD detector. The data were reduced by SAINTþ, and
an empirical absorption correction was applied using the pack-
age SADABS. The structures were solved and refined using
SHELXTL (Bruker 1998, SMART, SAINT, XPREP, and
SHELXTL, Bruker AXS Inc., Madison, WI). All atoms were
refined anisotropically, and hydrogen atoms were placed in cal-
culated positions unless specified otherwise. Tables with atomic
coordinates and equivalent isotropic displacement parameters,
with all of the bond lengths and angles, and with anisotropic dis-
placement parameters are listed in the CIF in the Supporting
Information.
collected at T = 100(2) K with 2θmax=57.43°, of which 8169
were unique (Rint = 0.0221). The residual peak and hole electron
densities were þ1.44 and -0.81 e A-3. The least-squares refine-
ment converged normally with residuals of R1 = 0.0253 and
GOF = 1.021. Crystal and refinement data for 5pic: formula
C35H51N3Si2FeU, space group P1, a= 9.805(4) A, b=11.590(5) A,
c = 18.359(8) A, R = 73.400(4)°, β = 87.716(4)°, γ=66.498(4)°,
V=1826.9(13) A3, Z=2, μ = 4.92 mm-1, F(000) = 856, R1 =
0.0299 and wR2 = 0.0555 (based on all 9077 data).
X-ray Crystal Structure of 8pic-btz. X-ray-quality crystals
were obtained from a concentrated n-pentane solution. A total
of 41 865 reflections (-32 e h e 33, -24 e k e 24, and -31 e l e
32) were collected at T = 100(2) K with θmax = 30.77°, of which
12 252 were unique (Rint=0.0361). The residual peak and hole
electron densities were þ3.00 and -2.61 e A-3. The least-
squares refinement converged normally with residuals of
R1 = 0.0408 and GOF=1.034. Crystal and refinement data
for 8pic-btz: formula C42H56N4Si2FeSU, space group C2/c, a =
23.049(2) A, b=17.1069(16) A, c=22.439(2) A, β = 109.840(1)°,
V = 8322.7(14) A3, Z = 8, μ = 4.377 mm-1, F(000) = 3984,
R1=0.0599 and wR2 = 0.1052 (based on all 12 252 data).
X-ray Crystal Structure of 5py. X-ray-quality crystals were
obtained from a concentrated Et2O solution. A total of 8332
reflections (-13 e h e 13, -15 e k e 15, and -23 e l e 23) were
collected at T = 100(2) K with 2θmax = 56.24°, of which 6737
were unique (Rint = 0.0406). The residual peak and hole electron
densities were þ1.47 and -2.35 e A-3. The least-squares refine-
ment converged normally with residuals of R1 = 0.0593 and
GOF = 1.043. Crystal and refinement data for 5py: formula
C34H49N3Si2FeU, space group P1, a = 9.8710(16) A, b =
11.7017(19) A, c=17.624(3) A, R=76.825(2)°, β=74.133(2)°,
Acknowledgment. This work was supported by the Univer-
sity of California, Los Angeles, Sloan Foundation, and DOE
(Grant ER15984).
γ = 65.740(2)°, V = 1769.7(5) A3, Z = 2, μ = 5.07 mm-1
,
F(000)=840, R1=0.0412 and wR2=0.0759 (based on all 8332
data).
Supporting Information Available: Experimental details for
compound characterization and full crystallographic descrip-
tions in CIF format. This material is available free of charge via
the Internet at http://pubs.acs.org.
X-ray Crystal Structure of 5pic. X-ray-quality crystals were
obtained from a concentrated hexanes solution. A total of 9077
reflections (-13 e h e 13, -15 e k e 15, and -24 e l e 24) were