Transition metal acetylide rearrangement and coupling induced by coordinative unsaturation

Article abstract of DOI:10.1021/om900542j

The reaction of {Ar′Fe(μ-Br)}₂ (Ar′ = C ₆H₃-2,6-(C₆H₃-2,6-iPr ₂)₂) with LiC=CPh afforded the unusual 1,3-butadiene-1,4-diyl Fe(I)-coupled derivative Fe₂{Ar′C=C(Ph)- C(

Full text of DOI:10.1021/om900542j

5012 Organometallics 2009, 28, 5012–5016
DOI: 10.1021/om900542j
Transition Metal Acetylide Rearrangement and Coupling Induced by
Coordinative Unsaturation
Chengbao Ni,† Gary J. Long,‡ and Philip P. Power*,†
†Department of Chemistry, One Shields Avenue, University of California, Davis, California 95616, and
‡Department of Chemistry, Missouri University of Science and Technology, University of Missouri,
Rolla, Missouri 65409-0010
Received June 22, 2009
The reaction of {Ar0Fe(μ-Br)}2 (Ar0 = C6H3-2,6-(C6H3-2,6-iPr2)2) with LiCtCPh afforded the
unusual 1,3-butadiene-1,4-diyl Fe(I)-coupled derivative Fe2{Ar0CdC(Ph)-C(Ph)dCAr0} (1), whereas
the reaction of {Ar0Fe(μ-Br)}2 with LiCtCtBu yielded the monomeric Fe(II) “ate” complex Ar0Fe-
(CtCtBu)2{Li(THF)2} (2). Complexes 1 and 2 were characterized by X-ray crystallography, NMR,
and UV-vis spectroscopy and magnetic measurements. In 1 the dimeric structure is a result of Ar0
group transfer to the iron-bound carbon of the acetylide ligand and subsequent dimerization via
coupling ofthe phenyl-substitutedcarbons. The irons are antiferromagnetically coupled, and the iron-
ꢀ
˚
iron separation is 2.5559(3) A. In 2 the high-spin iron atom has distorted trigonal-planar coordination
witha THF-complexed lithium ion associatedwiththeAr0Fe(CtCtBu)2 anion via interactions withthe
tBu-substituted alkyne carbons.
Introduction
they display a vast number of insertion and coupling reac-
tions with unsaturated species.12-23 Acetylide derivatives of
iron are well known and are generally stabilized by phos-
phine, Cp or Cp* (Cp = η5-C5H5; Cp* = η5-C5Me5), or
carbonyl co-ligands in high-coordinate complexes (coordi-
nation numbers g5). Low-coordinate (2 or 3) iron acetylide
complexes are rare, but they can be stabilized with use of
bulky β-diketiminate co-ligands, as in HC[C(tBu)N(2,6-iPr2-
C6H3)]2FeCtCR (R = SiMe3 or Ph),24,25 and display single
Fe-C bonds to the acetylide group. We have shown that
several unusual low-coordinate iron complexes can be
synthesized with use of the bulky terphenyl Ar026 and related
ligands27 and wished to extend these results to low-coordinate
The acetylide group (-CtCR) group is an extremely
versatile ligand, which can bond to one, two, or three
transition metal centers in a variety of coordination modes,
while donating up to five electrons in bonding.1-4 Transition
metal acetylides have attracted considerable interest for
numerous reasons that include their reactivity toward a
variety of small molecules to give numerous products,5-8
metal chalcogenides to form C-E (E = S and Se) bonds,9,10
or metal carbonyls to yield a variety of clusters.11 In addition,
*To whom correspondence should be addressed. E-mail: pppower@
ucdavis.edu.
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r
pubs.acs.org/Organometallics
Published on Web 08/12/2009
2009 American Chemical Society

Article
Organometallics, Vol. 28, No. 17, 2009 5013
Scheme 1. Proposed Route for the formation of 1a
Scheme 2. Probable Mechanism for the Formation of 1a
a The intermediate A appears to be plausible for both R = Ph and tBu,
t
but no formation of the Bu-substituted coupled species Ar0-CtC-tBu
complexed or uncomplexed was observed.
Fe(II) acetylides. Herein, we report that the reaction of
{Ar0Fe(μ-Br)}2 with LiCtCPh leads to the unusual coupled
1,3-butadiene-1,4-diyl Fe(I) derivative Fe2{Ar0CdC(Ph)-C-
(Ph)dCAr0} (1). In contrast, reaction with LiCtCtBu af-
forded the “ate” complex Ar0Fe(CtCtBu)2{Li(THF)2} (2)
with a three-coordinate iron(II) atom.
a Isopropyl groups on the flanking rings are not shown for clarity.
Thus, analternativemechanism (Scheme2) seems more likely.
The initial step involves elimination of LiBr to give the
intermediate “Ar0Fe-CtCPh”, which may associate through
the π-donation of the electron-rich acetylide group to the
iron(II) ion. In concert with η6-complexation of the iron by a
flankingarylring, the Ar0 group thenmigratesfrom the iron to
form a C-C bond with concomitant reduction of the metal to
the þ1 oxidation state with generation of radical character at
the R-carbon of the acetylide group. The radical generation is
facilitated and stabilized by the phenyl substituent at the R-
carbon. Radical coupling then leads to dimerization and
formation of a C-C bond to afford complex 1. Nucleophilic
attack at the acetylide carbon is also probably favored for the
phenyl-substituted species because of its greater charge se-
paration across the acetylide moiety, as evidenced by 13C
NMR chemical shift differences.29 In the case of 2, it is
Result and Discussion
Synthesis. Complexes 1 and 2 were prepared by reaction of
the dimer {Ar0Fe(μ-Br)}2 with 2 equiv of the corresponding
lithium acetylide salts in a mixture of hexanes and THF (eqs
1 and 2). 1 was isolated as air-sensitive black crystals from
hexanes in low yield, while 2 was obtained as extremely
air- and moisture-sensitive colorless crystals in good yield.
Several attempts were made to obtain a neutral product
{Ar0FeCtCtBu}n, but only 2 was isolated even when differ-
ent stoichiometric ratios of {Ar0Fe(μ-Br)}2 with respect to
LiCtCtBu were used.
t
probable that the Bu substituent disfavors Ar0 migration
and radical formation because of the charge polarization
between the triply bonded carbon atoms in the
-CtCtBu ligand. The formation of a C-C bond in the final
step in Scheme 2 is also sterically disfavored by the large tBu
substituents. Instead of a rearranged product like 1, the
coordination of another acetylide group to the iron(II) to
yield 2 becomes favored.
The mechanism for the formation of 1 is currently un-
known. It is possible that the initial step involves elimination
of LiBr to afford the Fe(II) intermediate Ar0Fe-CtCPh. The
C-C bond formation between the phenyl acetylide group
and the Ar0 ligand may occur to give the alkyne Ar0-CtC-Ph,
which may be complexed to iron via the acetylene group and
η6-complexation of a flanking aryl ring (Scheme 1). Then,
oxidative regioselective coupling of the alkyne ligands could
occur to form the 1,3-butadiene-1,4-diyl dinuclear iron(I)
complex 1. Such a reaction pathway is similar to the recently
reported reactions by zirconium species.28
However, this leaves the formation of complex 2 unex-
plained since, presumably, C-C bond formation between the
Ar0 ligand and the -CtCtBu group from the initially gener-
ated iron(II) intermediate “Ar0Fe-CtCtBu” might occur in a
similar way to form an Ar0CtCtBu/iron complex. However,
there is no evidence that such C-C bond formation occurs.
Spectroscopy. Complex 1 shows a broad, intense absorp-
tion centered at 420 nm in the visible region, while complex 2
displays a weak absorption in the ultraviolet region (374 nm)
and a featureless spectrum in the visible region. The
1H NMR spectrum of 1 is quite complicated due to the
presence of several types of similar hydrogens. At room
temperature, slightly broadened signals were observed be-
cause of its weak temperature-independent paramagnetism.
Due to the η6-complexation of the C6H3-2,6-iPr2 rings and
hindered rotation of the aryl rings, eight sets of doublets and
i
four sets of septets were observed for the Pr groups. A
feature of the spectrum is that the hydrogen atoms on the
η6-complexed C6H3-2,6-iPr2 and the C6H5 rings are drama-
tically shielded and thus shifted to lower frequencies. This
observation is explained by the proximity of the respective
(28) Tannaci, J. F.; Kratter, I. H.; Rider, E. A.; McBee, J. L.; Miller,
A. D.; Tilley, T. D. Chem. Commun. 2009, 233.
(29) Carty, A. J.; Cherkas, A. A.; Randall, L. H. Polyhedron 1988, 7,
1045.

5014 Organometallics, Vol. 28, No. 17, 2009
Ni et al.
Table 1. Selected Crystallographic Data and Collection Para-
meters for 1 and 2
1 C6H14
2 C4H8O
3
3
formula
fw
C
82H98Fe2
1195.30
black plate
triclinic
P1
C54 H79FeLiO3
838.96
colorless block
monoclinic
P21
12.4091(14)
16.2562(19)
12.4153(14)
90
90.277(2)
90
2504.4(5)
2
1.113
2.81-27.11
0.340
10 782
color habit
cryst syst
space group
˚
a, A
11.6492(6)
12.4385(7)
23.9709(13)
79.751(1)
84.532(1)
70.723(1)
3223.8(3)
2
˚
b, A
˚
c, A
R, deg
β, deg
γ, deg
3
˚
V, A
Z
dcalcd, Mg/m3
θ range, deg
μ, mm-1
1.231
2.90-27.56
0.495
11 792
0.0367
0.0937
obsd data, I > 2σ(I)
R1(obsd data)
wR2(all data)
Figure 1. Thermal ellipsoid (30%) plot of 1. C5 and C11 denote
the two phenyl substituents. H atoms and isopropyl groups
˚
are not shown. Selected bond lengths (A) and angles (deg):
0.0398
0.1038
H atoms to the other aromatic rings. Similarly, some of the
isopropyl hydrogens were also shifted to lower frequencies.
Fe1---Fe2 2.5559(3), Fe1-C1 1.965(2), Fe1-C3 2.128(2),
Fe1-C4 2.058(2), Fe1-Cnt2 1.589(3), C1-C17 1.504(2), C1-
C2 1.422(2), C2-C3 1.533(2), C2-C5 1.493(2), C3-C4
1.420(2), C4-C47 1.502(2), C53-C54 1.445(2), C53-C58
1.436(2), C54-C55 1.406(2), C55-C56 1.403(2), C56-C57
1.414(2), C57-C58 1.409(2), C2-C1-C17 119.5(2), Fe1-
C1-C17 144.5(1), Fe1-C1-C2 95.9(1), C1-C2-C3 107.0(2),
C1-C2-C5 131.1(2), C3-C2-C5 120.2(2), C48-C53-cnt2
163.0.
1
The H NMR spectrum of 2 at room temperature features
very broad signals in the range -35 to þ30 ppm, which is
consistent with the high-spin d6 electron configuration.
Structures. The structures of 1 and 2 were determined by
X-ray crystallography. Important data collection and refine-
ment parameters are provided in Table 1.
The structure of 1 is illustrated in Figure 1. Unlike the
normal planar geometry of the five-membered C4M ring and
unequal metal centers observed in metallacyclopentadiene
complexes,28,30-33 which are usually formed via coupled
alkynes, complex 1 shows a rather distorted geometry of the
C4M ring and similar iron(I) environment. Binuclear transi-
tion metal complexes with 1,3-butadiene-1,4-diyl ligands are
rare, and structurally characterized examples are limited to
{ArNdC(H)C(H)dNAr}2Ni2{(H)CdC(CH2OCH3)}2 (Ar=
C6H3-2,6-iPr2)34 and Rh2{μ2,η5,η2,η2,η5-(3-C6H5-C5H3)-(CH2)3-
CdC(tBu)C(tBu)dC(CH2)3-(3-C6H5-C5H3)},35 which were
(1.929(2) A)37 and is similar to that in [Fe2(CO)6{μ-η2-MeCC-
˚
(NEt2)C(O)Ph}] (1.964(3) A). The Fe-η2 interactions with
38
˚
the double-bonded carbon atoms (C(3) and C(4)) are slightly
˚
different (2.128(2) and 2.058(2) A). The single C(2)-C(3)
bond and the double C(1)-C(2) and C(3)-C(4) bonds within
the 1,3-butadiene-1,4-diyl ligand are elongated by ca. 0.07 A
˚
compared to uncomplexed 1,3-butadiene molecules.39-41 The
˚
Fe-centroid distances are 1.589(3) and 1.595(3) A, which are
considerably shorter than those in the Fe(I) complexes, such
as Ar FeFeAr (1.733(2) and 1.763(2) A),42 (η6-C6H6)FeAr*-
0
0
˚
3,5-iPr2 (Ar*-3,5-iPr2 = C6H-2,6-(C6H2-2,4,6-iPr3)2-3,5-iPr2,
also prepared by alkyne coupling. The Fe Fe separation
3 3 3
˚
43
1.643(2) A), and [{(C6H3-2,6-iPr2)NC(Me)}2CH]Fe(η6-
in 1 is 2.5559(3) A, which is slightly longer than the sum
˚
(2.48 A) of the single-bond covalent radii for iron.36 However,
˚
C6H6) (1.6245(8) A).44 The Fe(1)-C(carbon atoms of C(53)
˚
magnetic studies (see below) indicate that the two irons are
antiferromagnetically coupled rather than single bonded. The
chemical environments of the two iron centers are very
similar, so the rest of the discussion focuses on Fe(1). The
Fe(1) atom is η1-σ-bonded to C(1) and η2-π-bonded to C(3)
and C(4) of the 1,3-butadiene-1,4-diyl moiety. In addition, it is
η6-bonded to one of the flanking C6H3-2,6-iPr2 rings of the Ar0
unit attached to C(4). The Fe-C(1) σ-bonded distance,
˚
aryl ring) distances are in the range 2.050(2) to 2.192(2) A. The
strengthsofthe metal-carbon interactions toC(53)andC(56)
are reflected in the C-C distances involving these atoms (for
example, C(53)-C(54) = 1.445(2) A and C(53)-C(58) =
˚
˚
˚
1.436(2) A), which are on average 0.02-0.03 A longer than
the other C-C distances within the C(53) aryl ring, and
in their deviations from the C54-C55-C57-C58 plane by
˚
ca. 0.146 and 0.076 A, respectively. As a result, the C(57) aryl
˚
1.965(2) A, is slightly longer than that in the butadienyl
complex [Fe2(CO)5{μ-η2,η3-H2CdC(Me)CdCH2}(μ-PPh2)]
(38) Crocq, V.; Daran, J. C.; Jeannin, Y. J. Organomet. Chem. 1989,
373, 85.
(39) Yamaguchi, S.; Endo, T.; Uchida, M.; Izumizawa, T.; Furukawa,
(30) Hock, A. A.; Mills, O. S. Acta Crystallogr. 1961, 14, 139.
(31) Bonrath, W.; Michaelis, S.; Porschke, K. R.; Gabor, B.; Mynott,
R.; Kruger, C. J. Organomet. Chem. 1990, 397, 255.
(32) Todd, L. J.; Hickey, J. P.; Wilkinson, J. R.; Huffman, J. C.;
Folting, K. J. Organomet. Chem. 1976, 112, 167.
K.; Tamao, K. Chem.;Eur. J. 2000, 6, 1683.
(40) Bats, J. W.; Urschel, B. Acta Crystallogr. Sect. E 2006, 62, O748.
(41) Jaroschik, F.; Nief, F.; Le Goff, X. F.; Ricard, L. Organome-
tallics 2007, 26, 1123.
(33) Dettlaf, G.; Weiss, E. J. Organomet. Chem. 1976, 108, 213.
(34) Diercks, R.; Stamp, L.; Kopf, J.; Dieck, H. T. Angew. Chem., Int.
Ed. Engl. 1984, 23, 893.
(42) Nguyen, T.; Merrill, W. A.; Ni, C.; Lei, H.; Fettinger, J. C.; Ellis,
B. D.; Long, G. L.; Brynda, M.; Power, P. P. Angew. Chem., Int. Ed.
2008, 47, 9115.
(35) Schaefer, C.; Gleiter, R.; Rominger, F. J. Organomet. Chem.
(43) Ni, C.; Ellis, B. D.; Fettinger, J. C.; Long, G. J.; Power, P. P.
2007, 692, 4281.
Chem. Commun. 2008, 1014.
(36) Pauling, L. Proc. Natl. Acad. Sci. 1976, 73, 4290.
(37) Breckenridge, S. M.; Maclaughlin, S. A.; Taylor, N. J.; Carty, A.
J. J. Chem. Soc., Chem. Commun. 1991, 1718.
(44) Smith, J. M.; Sadique, A. R.; Cundari, T. R.; Rodgers, K. R.;
Lukat-Rodgers, G.; Lachicotte, R. J.; Flaschenriem, C. J.; Vela, J.;
Holland, P. L. J. Am. Chem. Soc. 2006, 128, 756.

Article
Organometallics, Vol. 28, No. 17, 2009 5015
Figure 2. Thermal ellipsoid (30%) plot of 2. THF molecules
bound to lithium and H atoms are not shown. Selected bond
˚
lengths (A) and angles (deg): Fe1-C1 2.039(2), Fe1-C31
Figure 3. Plot of χM versus T for 1. Inset: χMT versus T of 1. In
both plots the solid line denotes the total fit from 30 to 320 K
with S = 3/2, g = 2, J = -186(14) cm-1, the green component,
and NR = 0.00036(8) emu/mol Fe, the blue component, for a
sample of 1 that is 98.2(1) wt % pure. The red component is
1.8(1) wt % of a paramagnetic high-spin iron(III) impurity with
S = 5/2 and a μeff of 5.92 μB.
2.029(3), Fe1-C37 2.033(2), C31-C32 1.204(4), C1-Fe1-C31
125.6(1), C1-Fe1-C37 130.1(1), C31-Fe1-C37 104.3(1), Fe1-
C31-C32 172.5(3).
ring has a distorted boat geometry. Similar distortions are also
observed in the central aryl ring of the terphenyl ligand.
The structure of 2 (Figure 2) shows that two acetylide
groups become coordinated to the iron atom. There is a
lithium ion that is complexed by two THF molecules and two
R-carbons from the acetylide moieties to afford an oxidation
state of þ2 for iron. The iron is terminally bound to an Ar0
ligand and has a distorted trigonal-planar geometry. The
˚
Fe-C(1) bond length of 2.039(2) A resembles the terminal
Fe-C distance in the three-coordinate Fe(II) complex
45
˚
{Fe(Mes)(μ-Mes)}2 (Mes=C6H2-2,4,6-Me3, 2.023(5) A).
˚
The Fe-C(acetylide) distances (2.029(3) and 2.033(2) A) are
essentially equal, but they are somewhat longer than those in
other three-coordinate Fe(II) acetylide complexes, such as
HC[C(tBu)N(2,6-iPr2-C6H3)]2FeCtCR (R=SiMe3 1.961(6)
24
25
˚
˚
A; R=Ph, 2.000(2) A ). The torsion angle between the
central aryl ring and the C(31)-Fe(1)-C(37) plane is
96.4(2)°. Due to the coordination to the acetylide group
to the Liþ ion, the Fe(1)-C(31)-C(32) angle, 172.5(3)°,
deviates slightly from linearity.
Magnetic Studies. The magnetic properties of 1 (Figure 3)
indicate that it contains two iron(I) ions that display intra-
molecular antiferromagnetic exchange with S=3/2, g=2,
J = -186(14) cm-1 and NR = 0.00036(8) emu/mol Fe. In
both plots shown in Figure 3, the solid line through the data
points corresponds to the total fit between 30 and 320 K with
Figure 4. Plot of μeff versus T for 2. Inset: plot of 1/χM versus
T of 2 and a linear Curie-Weiss law fit between 2 and 320 K.
the H = -2J(S1 S2) Hamiltonian for exchange-coupled
of the iron(II) coordination environment. As would be ex-
pected, the inverse molar magnetic susceptibility (1/χM) of 2
(the inset to Figure 4) is linear between 2 and 320 K. A Curie-
Weiss fit of 1/χM between 2 and 320 K yields a Weiss tempera-
ture of -4.1 K, a Curie constant of 3.062 emu K/mol, and a
corresponding effective magnetic moment of 4.95 μB, which is
close to the spin-only value. The lack of significant orbital
contribution to the magnetic moment is consistent with the
approximate trigonal-planar coordination geometry at Fe(II).
For a high-spin d6 configuration, the dz2 orbital lies lowest and
is doubly occupied, while the next highest dxz and dyz orbitals
(approximately degenerate) are each singly occupied. The
highest dx2-y2 and dxy orbitals (also approximately degenerate)
are also singly occupied. Thus, no vacant degenerate equivalent
position with the same spin exists upon rotation of these
3
dimers.46,47 The fit also indicates that the sample of 1 studied
is 98.2(1) wt % pure. Below ca. 30 K the influence of zero-
field splitting or intermolecular exchange interactions, or
both, is observed.
The magnetic properties of 2 (Figure 4) indicate that it is a
magnetically dilute high-spin iron(II) complex with S=2 and
extensive zero-field splitting as a result of the low-symmetry
(45) Muller, H.; Seidel, W.; Gorls, H. J. Organomet. Chem. 1993, 445,
133.
(46) Details of the Hamiltonian used for this fit are given in the
Supporting Information provided in ref 47.
(47) Wolf, R.; Ni, C.; Nguyen, T.; Brynda, M.; Long, G. J.; Sutton, A.
D.; Fischer, R. C.; Fettinger, J. C.; Hellman, M.; Pu, L. H.; Power, P. P.
Inorg. Chem. 2007, 46, 11277.

5016 Organometallics, Vol. 28, No. 17, 2009
Ni et al.
orbitals. As a result of this, orbital angular momentum is
quenched.48
(vbr), 7.55 (br), 28.50 (br). Anal. Calcd Ffor C54H79FeLiO3: C,
)
77.30; H, 9.49. Found: C, 77.14; H, 9.26. IR in Nujol mull (cm-1
in KBr: νCtC 2017. UV-vis (hexane, nm [ε, cm-1 M-1]): 374
(400).
Experimental Section
X-ray Crystallographic Studies. Suitable crystals of 1 and 2
were selected and covered with a layer of hydrocarbon oil under
a rapid flow of argon. They were mounted on a glass fiber
attached to a copper pin and placed in the cold N2 stream on the
diffractometer. X-ray data were collected on a Bruker SMART
1000 diffractometer at 90(2) K using Mo KR radiation (λ =
General Procedures. All manipulations were carried out using
modified Schlenk techniques under an argon atmosphere or in a
Vacuum Atmospheres HE-43 drybox. All solvents were dried
˚
over an alumina column, followed by storage over 3 A molecular
sieves overnight, and degassed three times (freeze-thaw) prior to
use. The metal halideprecursors49 and LiCtCR(R=PhortBu)50
were prepared according to literature procedures. The C and H
analyses of 1 were lower than the calculated values due to partial
desolvation. Melting points were recorded in glass capillaries
sealed under N2 and are uncorrected. UV-vis data were recorded
on a Hitachi-1200 spectrometer. 1H NMR spectra were recorded
on a Mercury 300.08 MHz spectrometer at 20 °C.
˚
0.71073 A) or on a Bruker SMART Apex II diffractometer at
˚
90(2) K with Mo KR radiation (λ = 0.71073 A). Absorption
corrections were applied using SADABS.51 The structures were
solved using direct methods and refined by the full-matrix least-
squares procedure in SHELXL.52 All non-hydrogen atoms were
refined anisotropically. Hydrogen atoms in both structures were
placed at calculated positions and included in the refinement
using a riding model.
Fe2{Ar0CC(Ph)C(Ph)CAr0} C6H14 (1 C6H14). A mixture of
3
3
Magnetic Studies. Powdered samples of 1 and 2 for magnetic
study have been sealed under N2 in a 3 mm diameter quartz tube.
The sample magnetization was measured using a Quantum
Designs MPMSXL7 superconducting quantum interference
magnetometer; in each case the sample was zero-field cooled
to 2 K and the long moment was measured upon warming to
320 K in an applied field of 0.01 T. To ensure thermal equilib-
rium between the sample in the quartz tube and the temperature
sensor, the long moment at each temperature was measured
after 44, 36, 28, 20, and 12 min intervals over the temperature
ranges 2-5, 5-10, 10-25, 25-70, and 70-320 K, respectively.
Diamagnetic corrections of -0.000737 and -0.000549 emu/
mol, obtained from tables of Pascal’s constants, were applied to
the measured susceptibility of 1 and 2, respectively.
hexanes (30 mL) and THF (2 mL) was added to a mixture of
{Ar0Fe(μ-Br)}2 (0.267 g, 0.25 mmol) and LiCtCPh (0.057 g,
0.53 mmol) at room temperature. The amber solution became
deep brown immediately. The mixture was stirred for one day,
by which time the solution had become a deep brown color with
a brown precipitate. The solution was filtered and concentrated
to ca. 10 mL, which afforded X-ray quality, black crystals of
1 after storage for several days at -18 °C. Yield: 0.114 g
(41.2%). Mp: 183-185 °C. 1H NMR (300.08 MHz, C6D6,
3
20 °C): δ 0.39 (d, JH-H =6.3 Hz, 6H, CaH(CH3)2), 0.75 (d,
3JH-H=6.3 Hz, 6H, CaH(CH3)2), 0.86 (d, 3JH-H=6.3 Hz, 6H,
CbH(CH3)2), 1.26 (d, 3JH-H=6.3 Hz, 6H, CbH(CH3)2), 1.36 (d,
3JH-H=6.3 Hz, 6H, CcH(CH3)2), 1.41 (d, 3JH-H=6.3 Hz, 6H,
CdH(CH3)2), 1.43 (d, 3JH-H=6.3 Hz, 6H, CdH(CH3)2), 1.61 (d,
br, 8H, 6H from CcH(CH3)2 and 2H from CaH(CH3)2), 2.80
3
3
Conclusion
(sept, JH-H = 6.3 Hz, 2H, CbH(CH3)2), 3.15 (sept, JH-H =
6.3 Hz, 2H, CcH(CH3)2), 3.71 (sept, JH-H = 6.3 Hz, 2H,
3
In summary, the attempted synthesis of simple Ar0FeCt
CR (R=Ph or tBu) derivatives led, in the case of R=Ph, to an
unusual binuclear 1,3-butadiene-1,4-diyl Fe(I) complex sta-
bilized by arene interactions. The formation of 1 probably
involves coupling between the Ar0 group and -CtCR
followed by oxidative coupling between the alkynes or an
alternative mechanism involving acetylide reductive inser-
tion into the Fe-Ar0 bond followed by coupling. In contrast,
for R = tBu, only the “ate” complex Ar0Fe(CtCtBu)2{Li-
(THF)2} (2) could be isolated.
3
CdH(CH3)2), 4.95 (d, JH-H = 6.6 Hz, 2H, m-Dipp), 5.09 (d,
3JH-H = 6.6 Hz, 2H, m-Dipp), 5.50 (t, JH-H = 6.6 Hz, 2H,
=
3
p-Dipp), 5.85 (d, 3JH-H=6.9 Hz, 2H, o-C6H5), 6.34 (d, 3JH-H
7.5 Hz, 2H, o-C6H5), 6.58 (m, 2H, m-C6H5), 6.69 (m, 2H,
p-C6H5), 6.77 (m, 2H, m-C6H5), 7.24 (m, 6H, C6H3 and Dipp0),
7.54 (m, 6H, C6H3 and Dipp0). Anal. Calcd for C82H98Fe2:
C, 82.39; H, 8.26. Found: C, 81.88; H, 7.95. UV-vis (hexane,
nm [ε, cm-1 M-1]): 420 (3500).
Ar0Fe(CtCtBu)2{Li(THF)2} C4H8O (2 C4H8O). A mixture
3
3
of hexanes (30 mL) and THF (2 mL) was added to a mixture of
{Ar0Fe(μ-Br)}2 (0.267 g, 0.25 mmol) and LiCtCtBu (0.089 g,
1.00 mmol) at room temperature. The amber solution became
brown in ca. 2 h. The mixture was stirred for one day, by which
time the solution had become a brown color with a brown
precipitate. The solution was filtered and concentrated to
ca. 15 mL, which afforded X-ray quality, colorless crystals of
2 after storage for several days at -18 °C. Yield: 0.282 g
(75.8%). Mp: 140-142 °C. 1H NMR (300.08 MHz, C6D6,
20 °C): δ -33.46 (br), -12.34 (vbr), -1.35 (br), 1.57 (br), 5.19
Acknowledgment. We thank the National Science
Foundation (CHE-0641020) for financial support,
Dr. James C. Fettinger for crystallographic assistance, and
Peter Klavins for magnetization measurement assistance.
Supporting Information Available: Crystallographic informa-
1
tion files (cifs) for 1 and 2 and H NMR spectra for 1 and 2.
These materials are available free of charge via the Internet at
http://pubs.acs.org.
(48) Figgis, B. N. Introduction to Ligand Fields; Wiley: New York,
1966.
(49) Sutton, A. D.; Ngyuen, T.; Fettinger, J. C.; Olmstead, M. M.;
Long, G. J.; Power, P. P. Inorg. Chem. 2007, 46, 4809.
(50) Talalaeva, T. V.; Kocheshkov, K. A. Izv. Akad. Nauk SSSR-Ser.
Khim. 1953, 392.
(51)
SADABS Version 5.0; an empirical absorption correction
program from the SAINTPlus NT; Bruker AXS: Madison, WI, 1998.
(52) SHELXL Version 5.1; Bruker AXS: Madison WI, 1998.