Lead-chromium carbonyl complexes incorporated with group 8 metals: Synthesis, reactivity, and theoretical calculations

Article abstract of DOI:10.1021/ic101560u

The trichromium-lead complex [Pb{Cr(CO)₅}₃] ^2- (1) was isolated from the reaction of PbCl₂ and Cr(CO)₆ in a KOH/MeOH solution, and the new mixed chromium-iron-lead complex [Pb{Cr(CO)₅}{Fe(CO)₄}₂]^2- (3) was synthesized from the reaction of PbCl₂ and Cr(CO)₆ in a KOH/MeOH solution followed by the addition of Fe(CO)₅. X-ray crystallography showed that 3 consisted of a central Pb atom bound in a trigonal-planar environment to two Fe(CO)₄ and one Cr(CO)₅ fragments. When complex 1 reacted with 1.5 equiv of Mn(CO)₅Br, the Cr(CO)₄-bridged dimeric lead-chromium carbonyl complex [Pb ₂Br₂Cr₄(CO)₁₈]^2- (4) was produced. However, a similar reaction of 3 or the isostructural triiron-lead complex [Pb{Fe(CO)₄}₃]^2- (2) with Mn(CO) ₅Br in MeCN led to the formation of the Fe₃Pb ₂-based trigonal-bipyramidal complexes [Fe₃(CO) ₉{PbCr(CO)₅}₂]^2- (6) and [Fe ₃(CO)₉{PbFe(CO)₄}₂]^2- (5), respectively. On the other hand, the Ru₃Pb₂-based trigonal-bipyramidal complex [Ru₃(CO)₉{PbCr(CO) ₅}₂]^2- (7) was obtained directly from the reaction of PbCl₂, Cr(CO)₆, and Ru₃(CO) ₁₂ in a KOH/MeOH solution. X-ray crystallography showed that 5 and 6 each had an Fe₃Pb₂ trigonal-bipyramidal core geometry, with three Fe(CO)₃ groups occupying the equatorial positions and two PbFe(CO)₄ or PbCr(CO)₅ units in the axial positions, while 7 displayed a Ru₃Pb₂ trigonal-bipyramidal geometry with three equatorial Ru(CO)₃ groups and two axial PbCr(CO)₅ units. The complexes 3-7 were characterized spectroscopically, and their nature, formation, and electrochemistry were further examined by molecular orbital calculations at the B3LYP level of density functional theory.

Full text of DOI:10.1021/ic101560u

Inorg. Chem. 2011, 50, 565–575 565
DOI: 10.1021/ic101560u
Lead-Chromium Carbonyl Complexes Incorporated with Group 8 Metals:
Synthesis, Reactivity, and Theoretical Calculations
Minghuey Shieh,* Yen-Yi Chu, Miao-Hsing Hsu, Wei-Ming Ke, and Chien-Nan Lin
Department of Chemistry, National Taiwan Normal University, Taipei 116, Taiwan, Republic of China
Received August 3, 2010
The trichromium-lead complex [Pb{Cr(CO)5}3]2- (1) was isolated from the reaction of PbCl2 and Cr(CO)6 in a KOH/MeOH
solution, and the new mixed chromium-iron-lead complex [Pb{Cr(CO)5}{Fe(CO)4}2]2- (3) was synthesized from the
reaction of PbCl2 and Cr(CO)6 in a KOH/MeOH solution followed by the addition of Fe(CO)5. X-ray crystallography showed
that 3 consisted of a central Pb atom bound in a trigonal-planar environment to two Fe(CO)4 and one Cr(CO)5 fragments.
When complex 1 reacted with 1.5 equiv of Mn(CO)5Br, the Cr(CO)4-bridged dimeric lead-chromium carbonyl complex
[Pb2Br2Cr4(CO)18]2- (4) was produced. However, a similar reaction of 3 or the isostructural triiron-lead complex
[Pb{Fe(CO)4}3]2- (2) with Mn(CO)5Br in MeCN led to the formation of the Fe3Pb2-based trigonal-bipyramidal complexes
[Fe3(CO)9{PbCr(CO)5}2]2- (6) and [Fe3(CO)9{PbFe(CO)4}2]2- (5), respectively. On the other hand, the Ru3Pb2-based
trigonal-bipyramidal complex [Ru3(CO)9{PbCr(CO)5}2]2- (7) was obtained directly from the reaction of PbCl2, Cr(CO)6, and
Ru3(CO)12 in a KOH/MeOH solution. X-ray crystallography showed that 5and 6each had an Fe3Pb2 trigonal-bipyramidal core
geometry, with three Fe(CO)3 groups occupying the equatorial positions and two PbFe(CO)4 or PbCr(CO)5 units in the axial
positions, while 7 displayed a Ru3Pb2 trigonal-bipyramidal geometry with three equatorial Ru(CO)3 groups and two axial
PbCr(CO)5 units. The complexes 3-7were characterized spectroscopically, and their nature, formation, and electrochemistry
were further examined by molecular orbital calculations at the B3LYP level of density functional theory.
Introduction
or main-group ligands, which can be expected to exhibit
reversible or quasi-reversible redox reactions without structural
rearrangement of their metal skeletons.1,3a,6
Cooperative bimetallic synergism is central to some of
today’s most important applications in catalysts, nanoscience,
material science, and magnetism.1-5 The cooperative proper-
ties of mixed-metal clusters are of great interest. Very few,
however, are understood in detail. One important direction in
this area is to rationalize the synthesis of symmetric metal or
mixed-metal carbonyl clusters bearing a protective shell of CO
Our research group has an ongoing interest in chromium,7
iron,8 and ruthenium9 carbonyl clusters and has recently
explored the lead-containing chromium system.10 Although
group 14-incorporated, group 6 and/or group 8 metal carbonyl
complexes have been reported, their lead-incorporated com-
plexes remain rare, mainly because of a lack of applicable
synthetic routes.2d,f,10-14 Furthermore, the effect and nature of
homo- or heteronuclear metal-metal interactions on the for-
mation of such carbonyl complexes remain little explored.15,16
*To whom correspondence should be addressed. E-mail: mshieh@ntnu.
edu.tw.
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2010 American Chemical Society
Published on Web 12/13/2010
pubs.acs.org/IC

566 Inorganic Chemistry, Vol. 50, No. 2, 2011
Shieh et al.
The study and comparison of lead-containing homo- or
heterometallic complexes are, therefore, of great interest and
are challenging in view of their cooperative chemical properties
and potential applications.
In the present study, facile routes were discovered to a series
of lead-containing homo- or heteronuclear chromium and
group 8 trigonal-planar complexes, [Et4N]2[Pb{Cr(CO)5}3]
([Et4N]2[1])11a and [Bu4N]2[Pb{Cr(CO)5}{Fe(CO)4}2]
([Bu4N]2[3]), and trigonal-bipyramidal clusters, [Et4N]2-
[Fe3(CO)9{PbFe(CO)4}2] ([Et4N]2[5]), [Et4N]2[Fe3(CO)9{PbCr-
(CO)5}2] ([Et4N]2[6]), and [Et4N]2[Ru3(CO)9{PbCr(CO)5}2]
([Et4N]2[7]), in which the mixed chromium-group 8 trigonal-
planar complexes could readily undergo coupling reactions
to give rise to their corresponding trigonal-bipyramidal com-
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Article
Inorganic Chemistry, Vol. 50, No. 2, 2011 567
the metalloplumbylene complex [(FcN)2PbCr(CO)5]
5
5
˚
[2.7157(4) A; FcN = [Fe(η -C5H5)(η -C5H3(CH2NMe2)-2)-
C,N]].11e Complex 3 is an isoelectronic analogue of 1 and 2,
which contain three unsaturated Pb-M (M = Cr, Fe) bonds
in terms of the electron-counting rule.11a,12a These three iso-
structural complexes, 1-3, thus provided good precursors for
the preparation of polynuclear clusters.
Previous studies showed that the trigonal-planar PbCr3-1
complex could react with the nucleophilic reagent PMe3 to
form its base adduct [Pb{Cr(CO)5}3(PMe3)]2- 11a
For com-
.
parison, and to explore possible metal expansion reactions,
the reactions of the trigonal-planar compounds 1-3 with
Mn(CO)5Br were studied. When complex 1 was treated with
Mn(CO)5Br at ambient temperature, a new ring complex,
[Pb2Br2Cr4(CO)18]2- (4), was produced with the elimination
of Mn2(CO)10 and [HCr2(CO)10]- (identified by IR spectro-
scopy). The results suggested that the central Pb atom was
nucleophilically attacked by Br- accompanied with the loss
of [Cr(CO)5]2-, followed by a coupling reaction to give
complex 4. Complex 4 could be further transformed to the
known tetrahedral compound [PbBr2Cr2(CO)10]2-11b via
Pb-Cr bond breakage and Pb-Br bond formation, upon
the addition of Mn(CO)5Br in a MeCN solution (Scheme 2).
Compound 4 was characterized by IR spectroscopy, ele-
mental analysis, and single-crystal X-ray diffraction. As
shown in Figure 2, the anion 4 contains an inversion center
at the center of the Pb2Cr2 plane, in which the Pb1-Cr2-
Pb1a and Cr2-Pb1-Cr2a angles are 109.79(5) and 70.21(5)ꢀ,
respectively. The Pb atom is four-coordinated but severely
distorted from the ideal tetrahedral geometry [70.21(5)-
135.81(6)ꢀ]. With respect to the bonding, complex 4 may be
considered to be composed of two [{(CO)5Cr}PbBr{Cr-
(CO)4}]- species, which are dimerized by the Pb-Cr bonding
to form a four-membered Pb2Cr2 ring due to the electron
deficiency of the Pb atoms. According to a search of the
Cambridge Crystallographic Data Centre, complex 4 is the
first example of a four-membered Pb2M2 ring in the lead-
group 6 metal system. The Pb-Cr(CO)4 distances in 4
Figure 1. ORTEP diagram of anion 3, showing 30% probability thermal
˚
ellipsoids. Selected bond lengths (A) and angles (deg): Pb1-Cr1 2.714(2),
Pb1-Fe1 2.656(2), Pb1-Fe2 2.636(2); Cr1-Pb1-Fe1 118.67(6), Cr1-
Pb1-Fe2 123.67(7), Fe1-Pb1-Fe2 117.03(7).
Scheme 1
˚
[average 2.72(1) A] are slightly longer than the Pb-Cr(CO)5
˚
distances [2.679(2) A], indicating that the Pb-Cr(CO)4 bonds
in the Pb2Cr2 ring are weaker than the pendent Pb-Cr(CO)5
bonds. As a result, complex 4 was susceptible to the attack of
Br- onto the central Pb2Cr2 ring, causing Pb-Cr bond cleav-
and the bases, as well as the concentration of the bases
applied, we have discovered a facile route to the known
lead-chromium carbonyl complex [Pb{Cr(CO)5}3]2- (1)11a
from the reaction of PbCl2 with Cr(CO)6 in a KOH/MeOH
solution. In pursuit of novel heteronuclear clusters, group 8
metals were introduced into the lead-chromium carbonyl
system. It was found that when PbCl2 was treated with Cr-
(CO)6 in a KOH/MeOH solution, followed by the addition of
Fe(CO)5, the mixed chromium-iron-lead complex [Pb{Cr-
(CO)5}{Fe(CO)4}2]2- (3) could be obtained in moderate yields
(Scheme 1). Complex 3 was quite air-sensitive and was isolated
as the salt [Bu4N]þ. Complex 3 was characterized by spectro-
scopic methods, elemental analysis, and single-crystal X-ray
diffraction analysis. An ORTEP diagram of the molecular
structure of the anion 3 is shown in Figure 1.
age to give [PbBr2Cr2(CO)10]2-
.
For comparison, an isostructural trigonal-planar complex
[Pb{Fe(CO)4}3]2- (2)12a was synthesized. The treatment of
complex 2 with Mn(CO)5Br in MeCN at 80 ꢀC led to the
formation of the trigonal-bipyramidal cluster [Fe3(CO)9-
{PbFe(CO)4}2]2- (5; Scheme 3). Complex 5 was considered
as a result of the coupling reaction of 2 via Pb-Fe and Fe-Fe
bond formation and the loss of one [Fe(CO)4]2- and three CO
units. In a similar fashion, reaction of the chromium-iron
planar complex 3 with Mn(CO)5Br in MeCN at 80 ꢀC yielded
the mixed chromium-iron trigonal-bipyramidal cluster [Fe3-
(CO)9{PbCr(CO)5}2]2- (6; Scheme 3). Likewise, cluster 6
could be regarded as a result of the dimerization of 3 via Pb-
Fe and Fe-Fe bond formation and the loss of one [Fe(CO)4]2-
and three CO units. Both clusters 5 and 6 were isolated as the
salt [Et4N]þ, and they were fully characterized by IR spectros-
copy, elemental analyses, and single-crystal X-ray diffraction.
It is of great interest that clusters 5 and 6 were interconvertible
under suitable conditions. Cluster 5 readily transformed to
cluster 6 in good yields upon treatment with Cr(CO)6 in a
The anion 3 is structurally similar to complex 111a and the
previously known triiron-lead complex 2.12a The average
˚
Pb-Fe bond length in 3 [2.65(1) A] is comparable to those
˚
in 2 [2.624(4) A] and [Et4N]2[Pb{Fe2(CO)8}{Fe(CO)4}2]
12c
˚
[2.7(1) A]
(Table 1). The Pb-Cr bond length of 3,
2.714(2) A, is close to those in 1 [average 2.729(4) A] and
˚
˚

568 Inorganic Chemistry, Vol. 50, No. 2, 2011
Shieh et al.
˚
Table 1. Average Bond Distances (A) of [PPh4]2[1], [Et4N]2[2], [Bu4N]2[3], [Et4N]2[4], [Et4N]2[5], [Et4N]2[6], [Et4N]2[7], and Related Complexes
complex
Fe-Fe
Ru-Ru
Pb-Cr
Pb-Fe
Pb-Ru
ref
[PPh4]2[1]
[Et4N]2[2]
[Bu4N]2[3]
[Et4N]2[4]
2.729(4)
11a
12a
a
2.624(4)
2.65(1)
2.714(2)
2.72(1)b
2.679(2)c
a
[Et4N]2[5]
2.83(4)
2.79(6)
2.617(5)
2.60(1)d
2.546(2)e
2.65(3)
a
[Et4N]2[6]
[Et4N]2[7]
[Et4N]2[Pb{Fe2(CO)8}{Fe(CO)4}2]
(FcN)2PbCr(CO)5
[PPh4]2[PbBr2Cr2(CO)10
Fe3(CO)9(μ3-CF)2
Fe3(CO)9[μ3-SiFeCp(CO)2]2
Fe3(CO)9(μ3-GeEt)2
Fe3(CO)9[μ3-GeFeCp(CO)2]2
Fe3(CO)9[μ3-GeRe(CO)5]2
Fe3(CO)9[μ3-GeCo(CO)4]2
Fe3(CO)9[μ3-SnRe(CO)5]2
Fe3(CO)9[μ3-SnFeCp(CO)2]2
2.67(1)
2.680(4)
a
a
2.97(1)
2.77(2)
2.7(1)
12c
11e
11b
12g
12j
12j
12j
12i
12h
12l
12k
12m
17c
17c
17a
17c
17c
17c
17c
17b
13a
13b
13c
19a
19b
20
f
2.7157(4)
2.70(2)
]
2.540(2)
2.67(2)
2.73(1)
2.73(1)
2.719(4)
2.753(6)
2.807(4)
2.792(6)
2.81
2.616(6)
2.636(6)
2.623(4)
2.688(2)
2.693(2)
2.782(2)
2.768(2)
2.75(1)
g
Fe3(CO)9[μ3-SnMn(CO)5]2
Fe3(CO)9[μ3-PCr(CO)5]2
Fe3(CO)9[μ3-PMnCp(CO)2]2
Fe3(CO)9(μ3-As)2
Fe3(CO)9[μ3-AsCr(CO)5]2
Fe3(CO)9[μ3-AsMnCp(CO)2]2
Fe3(CO)9[μ3-SbCr(CO)5]2
Fe3(CO)9[μ3-SbMnCp(CO)2]2
Fe3(CO)9(μ3-Bi)2
[PtRu5(CO)15(μ-PbPh2)(μ6-C)]
Ru(CO)2(PbPh3)(iPr-DAB)Cl
[Ru3{μ-PbR2}2(μ-CO)(CO)9]h
Ru3(CO)9(μ3-Bi)2
2.6668(5)
2.7028(8)
2.78(1)
2.92(6)
2.940(7)
2.90(3)
2.854(5)
Ru3(CO)9[μ3-GeRu(CO)2(η5-C5Me4H)]2
Ru3(CO)12
a This work. b Pb-Cr(CO)4. c Pb-Cr(CO)5. d Equatorial. e Terminal. f FcN = [Fe(η5-C5H5)(η5-C5H3(CH2NMe2)-2)-C,N]. g Estimated standard
deviations are not reported. h R = CH(SiMe3)2.
Scheme 2
and the other including apical PbFe(CO) fragments and
bisecting this plane. There is disorder across the latter plane,
leading to 50% occupancy for each equatorial Fe atom that
brings out two related orientation Fe3 triangles by rotation
of ca. 32ꢀ (see Figure S1 in the Supporting Information).
Moreover, C8 and C80, which are coordinated to the Fe4
atom, are disordered with 35% occupancy and 15% for C8a
and C8a0. Further, the O8 and O8a aoms are also disordered,
with 50% occupancy. The related trigonal-bipyramidal clus-
ters [Fe3(μ3-CF)2(CO)9],12g [Fe3{μ3-GeCo(CO)4}2(CO)9],12h
[Fe3(μ3-As)2(CO)9],17a and [Fe3(μ3-Bi)2(CO)9]17b crystallized
in the higher-symmetry space group and showed similar
disorder. Thus, cluster 5 exhibits the expected near-equilat-
eral triangle of Fe atoms with both sides capped by Pb atoms,
KOH/MeOH solution. Conversely, cluster 6 could be recon-
verted to 5 upon its reaction with Fe(CO)5/KOH/MeOH. The
in which each Pb is further bonded to an Fe(CO)4 group in a
DFT calculations also supported the observation that these
distorted tetrahedral environment and each Fe atom in the
transformations were reversible (discussed later).
The ORTEP diagram of cluster 5 is illustrated in Figure 3.
The anion lies on a site that includes two crystallographic
trigonal plane is bonded to three CO ligands.
Cluster 6 is isoelectronic and structurally similar to 5,
which consists of an equatorial Fe3(CO)9 triangular cluster with
mirror planes, one going through the equatorial Fe3 plane
both sides capped by the PbCr(CO)5 fragments (Figure 4). In
accordance with the electron-counting rule,18 three Fe-Fe bonds
(17) (a) Delbaere, L. T. J.; Kruczynski, L. J.; McBride, D. W. J. Chem.
Soc., Dalton Trans. 1973, 307–310. (b) Churchill, M. R.; Fettinger, J. C.;
Whitmire, K. H. J. Organomet. Chem. 1985, 284, 13–23. (c) Collins, B. E.;
Koide, Y.; Schauer, C. K.; White, P. S. Inorg. Chem. 1997, 36, 6172–6183. (d)
Koide, Y.; Bautista, M. T.; White, P. S.; Schauer, C. K. Inorg. Chem. 1992, 31,
3690–3692. (e) Lang, H.; Huttner, G.; Zsolnai, L.; Mohr, G.; Sigwarth, B.; Weber,
U.; Orama, O.; Jibril, I. J. Organomet. Chem. 1986, 304, 157–179. (f) Whitmire,
K. H.; Shieh, M.; Lagrone, C. B.; Robinson, B. H.; Churchill, M. R.; Fettinger,
J. C.; See, R. F. Inorg. Chem. 1987, 26, 2798–2807.
are observed for a 48-electron Fe3-based cluster in both 5 and 6.
˚
The average Pb-Fe(equatorial) bond of 5 [2.60(1) A] is slightly
˚
shorter than that in 6 [2.65(3) A], whereas the average Fe-Fe
˚
˚
bond of 5 [2.83(4) A] is comparable to that in 6 [2.79(6) A],
(18) (a) Mingos, D. M. P. Acc. Chem. Res. 1984, 17, 311–319. (b) Wade, K.
Adv. Inorg. Chem. Radiochem. 1976, 18, 1–66.

Article
Inorganic Chemistry, Vol. 50, No. 2, 2011 569
˚
Figure 2. ORTEP diagram of anion 4, showing 30% probability thermal ellipsoids. Selected bond lengths (A) and angles (deg): Pb1-Cr1 2.679(2),
Pb1-Cr2 2.732(2), Pb1-Br1 2.724(2), Pb1-Cr2a 2.716(2);Cr1-Pb1-Cr2 133.89(6), Cr1-Pb1-Cr2a 135.81(6), Cr2-Pb1-Cr2a 70.21(5), Cr1-Pb1-Br1
102.40(6), Cr2-Pb1-Br1 103.61(5), Cr2a-Pb1-Br1 105.66(5), Pb1-Cr2-Pb1a 109.79(5).
the salt [Et4N]þ (Scheme 4). Unlike the mixed chromium-
Scheme 3
iron-lead cluster 3, the analogous chromium-ruthenium-
lead trigonal-planar complex [Pb{Cr(CO)5}{Ru(CO)4}2}]2-
was not observable under similar reaction conditions, prob-
ably because of the reactive nature of the Pb-Ru bond
(discussed later).
Cluster 7 is fully structurally characterized by spectroscopic
methods, elemental analysis, and single-crystal X-ray diffrac-
tion. A diagram of the dianion 7 is shown in Figure 5. Cluster 7
is an analogue of 5 and 6, with the core geometry based on a
trigonal-bipyramidal arrangement of three equatorial Ru(CO)3
groups and two axial PbCr(CO)5 units. The average Cr-
(terminal)-Pb-Ru(equatorial) and Ru(equatorial)-Pb-Ru-
(equatorial) angles are 141.54 and 64.88ꢀ, respectively. As shown
˚
in Table 1, the average Pb-Cr length of 7 [2.680(4) A] is close to
˚
that in 6 [2.67(1) A], whereas the average Pb-Ru length of
˚
7 [2.77(2) A] is within the range of those in the reported com-
13a
˚
pounds [PtRu5(CO)15(μ-PbPh2)(μ6-C)] [2.6668(5) A], [Ru-
i
13b
˚
(CO)2(PbPh3)( Pr-DAB)Cl] [2.7028(8) A],
and [Ru3{μ-
PbR2}2(μ-CO)(CO)9] [2.78(1) A, R = CH(SiMe3)2].13c More-
˚
˚
over, the average Ru-Ru distance of 7 is 2.97(1) A, a bit longer
than those in the related Ru3 clusters [Ru3(CO)9(μ3-Bi)2]
[2.940(7) A],
probably because of the lower steric hindrance of Fe(CO)4 versus
Cr(CO)5 groups bonded to the Pb atoms (Table 1). The average
Fe(terminal)-Pb-Fe(equatorial) and Fe(equatorial)-Pb-Fe-
(equatorial) angles of 5 are 140.99 and 66.02ꢀ, respectively.
In 6, the average Cr(terminal)-Pb-Fe(equatorial) and Fe-
(equatorial)-Pb-Fe(equatorial) angles are 142.43 and 63.51ꢀ,
respectively. Although analogous E2Fe3 trigonal-bipyramidal
clusters with E = C, Si, Ge, Sn, P, As, Sb, and Bi are
known,12g-m,17 clusters 5 and 6 represent the first Pb-
capped Fe3 examples. As shown in Table 1, the average
Fe-Fe bonds in 5 [2.83(4) A] and 6 [2.79(6) A] are longer
than those in the related clusters because of the larger size
of the main-group Pb atom.
A more interesting finding was that the reaction of PbCl2
with Cr(CO)6 in a KOH/MeOH solution followed by the
addition of Ru3(CO)12 could directly yield the lead-contain-
ing mixed chromium-ruthenium trigonal-bipyramidal com-
plex [Ru3(CO)9{PbCr(CO)5}2]2- (7), which was isolated as
19a
Ru3(CO)9[μ3-GeRu(CO)2(η5-C5Me4H)]2
˚
[2.90(3) A],19b and Ru3(CO)12 [2.854(5) A],20 indicative of
the small effect of the apical atoms. A search of the Cambridge
Crystallographic Data Centre failed to yield any structurally
characterized compounds with the Cr-Pb-Fe or Cr-Pb-Ru
fragment. Clusters 6 and 7 represent the first examples of lead-
containing mixed chromium and group 8 clusters.
˚
˚
DFT Calculations. The computational method of DFT
was employed in an attempt to better understand the
nature of complexes 1-7. These calculations were carried
out using the B3LYP DFT method21,22 with LanL2DZ/
6-31G(d) basis sets. The geometries of the X-ray-
determined and proposed intermediates in this study were
fully optimized, and the natural bond order (NBO)23 and
natural population analyses (NPA)24 for complexes 1-7
are displayed in Table 2.
˚
˚
(21) (a) Becke, A. D. J. Chem. Phys. 1993, 98, 5648–5652. (b) Becke, A. D.
J. Chem. Phys. 1992, 96, 2155–2160. (c) Becke, A. D. J. Chem. Phys. 1992, 97,
9173–9177.
(22) Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. B 1988, B37, 785–789.
(23) Reed, A. E.; Curtiss, L. A.; Weinhold, F. Chem. Rev. 1988, 88, 899–926.
(24) (a) Reed, A. E.; Weinhold, F. J. Chem. Phys. 1983, 78, 4066–4073. (b)
Reed, A. E.; Weinstock, R. B.; Weinhold, F. J. Chem. Phys. 1985, 83, 735–746.
(19) (a) Hay, C. M.; Johnson, B. F. G.; Lewis, J.; Raithby, P. R.; Whitton,
A. J. J. Chem. Soc., Dalton Trans. 1988, 2091–2097. (b) Zhang, Y.; Wang, B.;
Xu, S.; Zhou, X. Organometallics 2001, 20, 3829–3832.
(20) Churchill, M. R.; Hollander, F. J.; Hutchinson, J. P. Inorg. Chem.
1977, 16, 2655–2659.

570 Inorganic Chemistry, Vol. 50, No. 2, 2011
Shieh et al.
˚
Figure 3. ORTEP diagram of anion 5, showing 30% probability thermal ellipsoids. Selected bond lengths (A) and angles (deg): Pb1-Fe1 2.546(1),
Pb1-Fe2 2.609(2), Pb1-Fe3 2.588(2), Pb1-Fe4 2.598(2), Fe2-Fe3 2.812(3), Fe3-Fe4 2.805(4), Fe4-Fe2 2.875(4); Fe3-Fe2-Fe4 59.10(9),
Fe2-Fe3-Fe4 61.6(1), Fe2-Fe4-Fe3 59.33(8).
˚
Figure 4. ORTEP diagram of anion 6, showing 30% probability thermal ellipsoids. Selected bond lengths (A) and angles (deg): Pb1-Fe1 2.653(1),
Pb1-Fe2 2.640(1), Pb1-Fe3 2.661(1), Pb1-Cr1 2.684(1), Pb2-Fe1 2.611(1), Pb2-Fe2 2.626(1), Pb2-Fe3 2.699(1), Pb2-Cr2 2.664(1), Fe1-Fe2 2.859(2),
Fe2-Fe3 2.748(2), Fe3-Fe1 2.754(2); Fe1-Fe2-Fe3 58.78(4), Fe2-Fe3-Fe1 62.63(5), Fe3-Fe1-Fe2 58.59(4).
Scheme 4
was similar to the LUMOþ1 of 2 and 3, while the
LUMOþ1 of complex 1 was similar to the LUMOs of
complexes 2 and 3. Thus, it was reasonable to propose that
the incoming Br- could interact with the Pb atom of
complex 1first,accompaniedbyafurthercouplingreaction
to give rise to complex 4. This process also postulated that
Br- attacked the positively charged Pb atom (þ0.646) of 1
followed by the loss of [Cr(CO)5]2- to give the proposed
intermediate “[BrPb{Cr(CO)5}2]-”, where the negatively
charged Cr atom (-1.443) further interacted with the Pb
atom (þ0.917) of another molecule of the intermediate,
The calculation showed that the active sites of complexes
accompanied by the release of CO units to give the dimeric
1-3 for the formation ofcomplexes4-6 couldbe relatedto
the frontier orbitals of complexes 1-3. As shown in Figure 6,
the lowest unoccupied molecular orbital (LUMO) and
LUMOþ1 of complexes 1-3had a significant contribution
from the pz or s orbital of the Pb atom, with almost the
same energy. It was noted that the LUMO of complex 1
product (Scheme 5). This assumption was supported by the
fact that the As center of the isoelectronic ClAs{Cr(CO)5}2
was susceptible to nucleophilic species.25 Further reaction
(25) von Seyerl, J.; Huttner, G. Angew. Chem., Int. Ed. Engl. 1979, 18,
233–234.

Article
Inorganic Chemistry, Vol. 50, No. 2, 2011 571
˚
Figure 5. ORTEP diagram of anion 7, showing 30% probability thermal ellipsoids. Selected bond lengths (A) and angles (deg): Pb1-Ru1 2.7715(6),
Pb1-Ru22.7452(6), Pb1-Ru32.7809(6), Pb1-Cr2 2.682(1), Pb2-Ru12.7458(6), Pb2-Ru22.8020(6), Pb2-Ru3 2.7594(6), Pb2-Cr12.677(1), Ru1-Ru2
2.9805(8), Ru2-Ru3 2.9526(8), Ru3-Ru1 2.9744(8); Ru1-Ru2-Ru3 60.17(2), Ru2-Ru3-Ru1 60.38(2), Ru3-Ru1-Ru2 59.45(2).
Table 2. Results of NBO and NPA of Complexes 1-7, the Proposed Intermediates [BrPb{Cr(CO)5}2]- and [Pb{Cr(CO)5}{Ru(CO)4}2]2-, and Ru3(CO)12
Wiberg bond index
natural charge
complex
Pb-Cr
Pb-Fe
Pb-Ru
Pb-Meq
Meq-Meq
Pb
Cr
Fe
Ru
1
2
3
0.317
0.646
0.619
0.619
0.917
0.763
-1.401
0.313
0.321
-0.554
-0.555
0.302
0.385
-1.389
-1.443
-1.068a
-1.424b
[BrPb{Cr(CO)5}2]-
4
0.258a
0.377b
5
0.340
0.270
0.131
0.492
-0.469a
-0.530b
-0.455
6
7
0.326
0.328
0.310
0.278
0.287
0.127
0.112
0.463
0.320
0.576
-1.374
-1.379
-1.389
-0.406
-0.325
-0.342
[Pb{Cr(CO)5}{Ru(CO)4}2]2-
Ru3(CO)12
0.277
0.193
a Ring. b Terminal.
of complex 4 with Mn(CO)5Br also involved the attack
of Br- on the positively charged Pb atom (þ0.763) of 4,
with Pb-Cr bond cleavage. In addition, the calculated
Wiberg bond indices (also called the bond orders) of
complex 4 reflected a weak Pb-Cr(CO)4 bond, which
could have facilitated further Br- attacks on Pb atoms,
leading to the formation of the known complex [PbBr2-
Cr2(CO)10]2- (Table 2).11b
The formation of the trigonal-bipyramidal clusters 5
and 6 from the trigonal-planar complexes 2 and 3, respec-
tively, was then examined. The highest occupied molecular
orbital (HOMO) and HOMO-1 of complex 2 were nearly
degenerate with the significant contributions from the p and
d orbitals of the Fe atoms (Figure 6). It was also found that
the HOMO of 2 was similar to the HOMO-1 of 3, while the
HOMO-1 of 2 was similar to the HOMO of complex 3. As
mentioned above, the LUMO and LUMOþ1 of complexes
2 and 3 were also close in energy with the significant contri-
bution from the s or pz orbital of the Pb atom (Figure 6).
Therefore, it is reasonable to suggest that the negatively
charged Fe atom of complex 2(-0.554) or 3(-0.555) under-
went nucleophilic attack on the positively charged Pb atom
of another molecule of complex 2 (þ0.619) or 3 (þ0.619),
with Pb-Fe and Fe-Fe bond formation and the loss of one
[Fe(CO)4]2- and three CO ligands. As shown in Table 2, it
should be mentioned that the Pb atom in complexes 5 and 6
became less positively charged (þ0.492 or þ0.463) and the
Fe atom became less negatively charged (-0.469, -0.530,
or -0.455) compared to 2 and 3, indicating the stronger
covalent character of the Pb-Fe bonds in 5 and 6. More-
over, calculations gave ΔG = -5.502 kcal/mol for the con-
version of 5 to 6, which supported the experimental results
that the conversion was reversible upon the addition of
[Cr(CO)5]2- or [Fe(CO)4]2- but was easier for the transfor-
mation of complex 5 to 6. Further NPA showed that the Pb
atom in 5 carried a positive charge of þ0.492 and the Fe
atom in the Fe(CO)4 fragment carried a charge of -0.530,
while the Pb atom in 6 carried a charge of þ0.463 and the
Cr atom in the Cr(CO)5 group carried a negative charge
of -1.374, suggestive of the larger coulomb attraction be-
tween the Pb atom and Cr(CO)5 in cluster 6.
The failure to observe the trigonal-planar intermediate
[Pb{Cr(CO)5}{Ru(CO)4}2]2- from the reaction of PbCl2,
Cr(CO)6, and Ru3(CO)12 was probably because of weak
Pb-Ru bonds. This phenomenon was supported by the
calculation that the Wiberg bond index of the Pb-Ru
bond (0.277) for the proposed intermediate “[Pb{Cr(CO)5}-
{Ru(CO)4}2]2-” was significantly smaller than those for the
Pb-Cr (0.302-0.317) and Pb-Fe (0.313-0.321) bonds
in the corresponding triangular-planar lead complexes

572 Inorganic Chemistry, Vol. 50, No. 2, 2011
Shieh et al.
Scheme 5
Table 3. DPV of 5-7, Fe3(CO)12, and Ru3(CO)12
reduction process
Epred/Va (W1/2/mVb)
complex
5
6
-1.238 (107)
-1.430 (97)
-0.440 (92)
-1.748 (132)
-0.898 (-)c
-1.550 (171)
-1.694 (150)
-0.904 (200)
-2.016 (88)
-1.106 (160)
-2.102 (110)
-2.074 (93)
-2.028 (120)
-2.244 (150)
-2.078 (104)
Fe3(CO)12
7
Ru3(CO)12
red
b
a Ep = reductive peak potential. W1/2 = width at half-height.
c Difficult to determine.
Figure 6. Spatial graphs (isovalue = 0.04-0.05) of the selected frontier
molecular orbitals of complexes 1-3.
1-3. In addition, the Wiberg bond index of the Ru-Ru
bond in cluster 7 was 0.112, smaller than that in Ru3(CO)12
(0.193) but comparable to that (0.09) for [{PPh4}2{Te2Ru4-
(CO)10Cu4Br2Cl2} THF]¥ (THF=tetrahydrofuran) in the
3
Te-Ru system.9a
Electrochemistry of 5-7. In view of the highly sym-
metric Pb2M3 (M = Fe, Ru) metal cores of the analogous
complexes 5-7, their electrochemical properties were
investigated using cyclic voltammetry (CV) and differen-
tial pulse voltammetry (DPV) in MeCN under N2, which
could be further compared with the related clusters M3-
(CO)12 (M = Fe, Ru).26 The electrochemical data for
each complex studied are listed in Tables 3 and S1 in the
Supporting Information.
Figure 7. CV (a) and DPV (b) in MeCN for [Et4N]2[5], [Et4N]2[6], and
Fe3(CO)12. Conditions: electrolyte, 0.1 M Bu4NClO4; working electrode,
glassy carbon; scan rate, 100 mV/s. Potentials are versus SCE.
The cyclic voltammograms of Fe3Pb2 trigonal-bipyr-
amidal clusters 5 and 6 exhibited three quasi-reversible
reductions (around -1.31 to -2.21 V), in which some of
the peaks were unresolved (Figure 7a). Further DPV results
revealed that 5 and 6 each had three quasi-reversible redox
reductions at -1.238, -1.550, and -2.102 V and at -1.430,
-1.694, and -2.074 V, respectively (Figure 7b). In light of
(26) Bond, A. M.; Dawson, P. A.; Peake, B. M.; Robinson, B. H.;
Simpson, J. Inorg. Chem. 1977, 16, 2199–2206.

Article
Inorganic Chemistry, Vol. 50, No. 2, 2011 573
Table 4. Reduction Potentials and Electronic Affinities of Complexes 5-7
complex
reduction potential Ea (V)
EAb (kcal/mol)
5
6
7
-1.238
-1.430
-1.748
78.13
81.57
86.09
a From DPV. b The EA can be estimated by EA ≈ Eelec(Nþ1) -
Eelec(N), where Eelec(Nþ1) and Eelec(N) represent the electronic energies
of molecules with N þ 1 and N electrons, respectively.27
the DFT calculations, the LUMO contributions of 5 and 6
predominantly came from the p and d orbitals of the equa-
torial Fe3 moieties, indicating that the reduction processes of
5 and 6 occurred in the triangular Fe3(CO)9 ring (Figure S2
in the Supporting Information). The results suggested that
complexes 5 and 6 [[Fe3(CO)9{PbM(CO)x}2]2- (M = Fe,
x = 4, 5; M = Cr, x = 5, 6)] could be reduced to form the
square-pyramidal complexes [Fe3(CO)9{PbM(CO)x}2]4-
,
with Fe-Fe bond breakage, which paralleled the chemistry
of [Fe3(μ3-Bi)2(CO)9].17f As shown in Figure 7b, Fe3(CO)12
revealed a similar pattern of three redox couples at -0.440,
-0.904, and -2.028 V. Compared with Fe3(CO)12, the
reduction potentials of clusters 5 and 6 were shifted to more
negative values, basically because of the negative charges of
the complexes. Furthermore, the first quasi-reversible reduc-
tion of complex 6 (-1.430 V) revealed a significant cathodic
shift, in contrast with complex 5 (-1.238 V), because of the
larger electron-donating ability of the apical Cr(CO)5 versus
Fe(CO)4 fragments. This result was also supported by cal-
culations that indicated that complex 6 had a smaller elec-
tron affinity, compared with complex 5 [EA ≈ Eelec(Nþ1) -
Eelec(N),27 81.57 vs 78.13 kcal/mol; Table 4].
On the other hand, as shown in Figure 8, the DPV study
of the Ru3Pb2 trigonal-bipyramidal cluster 7 exhibited three
quasi-reversible reductions (-1.748, -2.016, and -2.244 V)
that should have occurred around the equatorial Ru3(CO)9
ring, in view of the major contribution of the LUMO from
the triangular ruthenium moiety (Figure S2 in the Support-
ing Information). Similar to the case for the Fe3Pb2 trigonal-
bipyramidal clusters 5 and 6, the Ru3Pb2 complex 7 also
showed significant cathodic shifts compared with those of
Ru3(CO)12. Moreover, the first quasi-reversible reduc-
tion of 7 (-1.748 V) versus 6 (-1.430 V) revealed that 7
was more difficult to reduce than the isostructural cluster 6,
which is also supported by the smaller electron affinity
calculated for 7 compared with 6 (Table 4).
Figure 8. CV (a) and DPV (b) in MeCN for [Et4N]2[7] and Ru3(CO)12
Conditions: electrolyte, 0.1 M Bu4NClO4; working electrode, glassy
carbon; scan rate, 100 mV/s. Potentials are versus SCE.
.
study provides a new avenue to a systematic comparison of
the complicated electronic effects of mixed-metal clusters on
the basis of electrochemical and theoretical studies.
Experimental Section
All reactions were performed under an atmosphere of pure
nitrogen using standard Schlenk techniques.28 Solvents were
purified, dried, and distilled under nitrogen prior to use.
Cr(CO)6 (Strem), Fe(CO)5 (Strem), Ru3(CO)12 (Strem), Mn-
(CO)5Br (Strem), PbCl2 (Osaka), and KOH (Showa) were
used as received. The compound [Et4N]2[Pb{Fe(CO)4}3]
([Et4N]2[2]) was prepared according to the published
method.12a IR spectra were recorded on a Perkin-Elmer
Paragon 500 IR spectrometer as solutions in CaF2 cells.
Elemental analyses for C, H, and N were performed on a
Perkin-Elmer 2400 analyzer at the NSC Regional Instrumental
Center at National Taiwan University, Taipei, Taiwan. Electro-
chemicalmeasurementswereperformed atroomtemperature
under a nitrogen atmosphere and recorded using a BAS-
100W electrochemical potentiostat. A glassy carbon working
electrode, a platinum wire auxiliary electrode, and a non-
aqueousAg/Agþ electrodewereusedinathree-electrodecon-
figuration. Tetra-n-butylammonium perchlorate was used
as the supporting electrolyte, and the solute concentra-
tion was ∼10-3 M. The redox potentials were calibrated with
a ferrocenium/ferrocene (Fcþ/Fc) couple in the working solu-
tion and referenced to a saturated calomel electrode (SCE).
Synthesis of [Et4N]2[Pb{Cr(CO)5}3] ([Et4N]2[1]). To a MeOH
solution (15 mL) of Cr(CO)6 (0.68 g, 3.09 mmol) and KOH (4.21 g,
75.0 mmol) was added PbCl2 (0.28 g, 1.01 mmol) in an ice/water
bath. The resulting solution was stirred at ambient temperature for
4 h to give a reddish-brown solution. The solution was filtered
and concentrated, and a MeOH solution of [Et4N]Br (0.35 g,
Conclusion
The facile synthesis of the first examples of mixed-metal
carbonyl lead-containing trigonal-planar complex 3 and
trigonal-bipyramidal clusters [M3(CO)9{PbCr(CO)5}2]2-
(M = Fe, Ru) was demonstrated. The nature, formation,
and structural transformation of these new complexes were
systematically described and compared in terms of the
characteristicsof transition metals. In addition, three Fe3Pb2-
or Ru3Pb2-based trigonal-bipyramidal closo clusters demon-
strated a wide range of quasi-reversible redox ability. More
interestingly, pronounced cathodic shifts were observed from
the Fe3 to the Ru3 ring or as the apical fragment changed
from an Fe(CO)4 fragment to a Cr(CO)5 fragment, which
was illustrated well by the results of DFT calculations. This
(27) Lin, Y.-l.; Lee, Y.-m.; Lim, C. J. Am. Chem. Soc. 2005, 127, 11336–
11347.
(28) Shriver, D. F.; Drezdon, M. A. The Manipulation of Air-Sensitive
Compounds; Wiley-VCH Publishers: New York, 1986.

574 Inorganic Chemistry, Vol. 50, No. 2, 2011
Shieh et al.
Table 5. Crystallographic Data for [Bu4N]2[3], [Et4N]2[4], [Et4N]2[5], [Et4N]2[6], and [Et4N]2[7]
[Bu4N]2[3]
[Et4N]2[4]
[Et4N]2[5]
C33H40Fe5-
N2O17Pb2
1430.30
[Et4N]2[6]
C35H40Cr2-
Fe3N2O19Pb2
1478.62
[Et4N]2[7]
empirical formula
C45H72CrFe2-
N2O13Pb
1219.94
C34H40Br2Cr4-
N2O18Pb2
1546.89
C35H40Cr2-
Ru3N2O19Pb2
1614.31
fw
cryst syst
monoclinic
P21/n
monoclinic
P21/c
monoclinic
C2/c
0.41 ꢀ 0.24 ꢀ 0.07
28.3677(6)
10.6192(3)
17.6363(4)
monoclinic
P21/c
0.25 ꢀ 0.22 ꢀ 0.18
12.9995(2)
18.8599(3)
20.5628(4)
monoclinic
P21/n
0.20 ꢀ 0.12 ꢀ 0.10
12.1695(1)
18.2147(3)
23.5738(3)
space group
crystal dimens, mm
0.40 ꢀ 0.25 ꢀ 0.20
0.40 ꢀ 0.05 ꢀ 0.03
˚
a, A
12.281(3)
33.391(1)
13.865(4)
9.5681(2)
24.6016(6)
11.3668(3)
˚
b, A
˚
c, A
R, deg
β, deg
γ, deg
90.32(2)
101.805(1)
120.414(2)
107.506(1)
103.0966(6)
3
˚
V, A
Z
5686(3)
4
1.425
2619.1(1)
2
2.007
8.799
black, prism
4581.7(2)
4
2.074
8.926
black, prism
4807.9(1)
4
2.043
8.362
black, prism
5089.5(1)
4
2.107
7.935
red, prism
D(calcd), g/cm3
μ, mm-1
3.692
color, habit
diffractometer
radiation (λ), A
temp, K
black, prism
Nonius (CAD4)
0.710 73
298
Nonius (Kappa CCD) Nonius (Kappa CCD) Nonius (Kappa CCD) Nonius (Kappa CCD)
0.710 73
298
˚
0.710 73
200
0.710 73
298
0.710 73
298
θ range for data
collcn, deg
Tmin/Tmax
1.59-24.92
3.53-27.71
2.09-25.33
2.08-25.34
4.10-27.47
0.32/0.53 0.30/0.41
4646 (Rint = 0.0633) 4481 (Rint = 0.0928)
0.12/0.57
3521 (Rint = 0.0798)
0.17/0.20
6745 (Rint = 0.0747)
0.29/0.39
7441 (Rint = 0.0690)
no. of indep reflns
[I > 2 σ(I)]
no. of param
572
R1a/wR2a [I > 2 σ(I)] 0.060/0.138
0.165/0.179
280
0.071/0.172
0.095/0.184
286
0.057/0.144
0.072/0.165
568
0.042/0.106
0.068/0.140
568
0.045/0.082
0.089/0.094
R1a/wR2a (all data)
P
P
P
P
a The functions minimized during least-squares cycles were R1 = ||Fo| - |Fc||/ |Fo| and wR2 = [ [w(Fo2 - Fc2)2]/ [w(Fo2)2]]1/2
.
1.67 mmol) was added dropwise, precipitating the solid. The solid
was washed with deionized water in an ice/water bath several times
and dried under vacuum. The THF extract was recrystallized from
Et2O/THF to give a reddish-brown sample of [Et4N]2[1] (yield
0.29 g, 0.28 mmol, 28% based on PbCl2). IR (νCO, THF): 2010 (w),
Reaction of [Et4N]2[4] with Mn(CO)5Br. To a MeCN solution
(10 mL) of [Et4N]2[Pb2Br2Cr4(CO)18] ([Et4N]2[4]) (0.14 g, 0.09
mmol) was added Mn(CO)5Br (0.05 g, 0.18 mmol). The mixed
solution was stirred at ambient temperature for 21 h. The
solution was filtered, and the solvent was evaporated under
vacuum. The residue was extracted with CH2Cl2 to give a sample
of [Et4N]2[PbBr2Cr2(CO)10]11b (yield 0.06 g, 0.06 mmol, 33%
based on [Et4N]2[Pb2Br2Cr4(CO)18]). IR (νCO, CH2Cl2): 1990
1977 (s), 1909 (vs), 1864 (m) cm-1
.
Synthesis of [Bu4N]2[Pb{Cr(CO)5}{Fe(CO)4}2] ([Bu4N]2[3]).
A MeOH solution (20 mL) of PbCl2 (0.77 g, 2.77 mmol),
Cr(CO)6 (0.61 g, 2.77 mmol), and KOH (5.20 g, 92.7 mmol)
was stirred in an ice/water bath. The solution was stirred at
ambient temperature for 2 h, and Fe(CO)5 (0.73 mL, 5.55 mmol)
was added. The reaction solution turned brown and was allowed
to stir for 12 h. The resulting solution was filtered and concen-
trated, and an aqueous solution of [Bu4N]Br (0.70 g, 2.17 mmol)
was added dropwise, precipitating the solid. The solid was
washed with deionized water several times and dried under
vacuum. The THF extract was recrystallized from Et2O/THF
to give a reddish-brown sample of [Bu4N]2[3] (yield 1.12 g, 0.92
mmol, 33% based on PbCl2). IR (νCO, THF): 2025 (m), 1972 (s),
1957 (vs), 1910 (s), 1878 (s) cm-1. Anal. Calcd for [Bu4N]2[3]: C,
44.30; H, 5.95; N, 2.30. Found: C, 44.24; H, 6.19; N, 2.57.
Crystals of [Bu4N]2[3] suitable for X-ray diffraction were grown
from Et2O/THF. [Et4N]2[3] can be isolated by following a
similar procedure.
(m), 1953 (vs), 1893 (m), 1859 (m) cm-1
.
Synthesis of [Et4N]2[Fe3(CO)9{PbFe(CO)4}2] ([Et4N]2-
[5]). Method 1. A MeCN solution (30 mL) of [Et4N]2[Pb-
{Fe(CO)4}3] ([Et4N]2[2]) (2.02 g, 2.08 mmol) and Mn(CO)5Br
(0.86 g, 3.13 mmol) was stirred and heated at 80 ꢀC for 42 h. The
resultant yellowish-brown solution was filtered, and the solvent
was evaporated under vacuum. The residue was washed several
times with deionized water and Et2O, which was shown to
contain Mn2(CO)10 by IR spectroscopy. The CH2Cl2 extract
was recrystallized from Et2O/MeOH/CH2Cl2 to give a sample of
[Et4N]2[5] (yield 0.89 g, 0.62 mmol, 60% based on Pb). IR (νCO
,
CH2Cl2): 2011 (s), 1955 (vs), 1911 (m) cm-1. Anal. Calcd for
[Et4N]2[5]: C, 27.71; H, 2.82; N, 1.96. Found: C, 27.66; H, 2.49;
N, 2.05. Crystals of [Et4N]2[5] suitable for single-crystal X-ray
diffraction were grown from Et2O/CH2Cl2.
Method 2. To a MeCN solution (20 mL) of [Et4N]2[Fe3-
(CO)9{PbCr(CO)5}2] ([Et4N]2[6]) (0.61 g, 0.41 mmol) was added
Fe(CO)5 (0.11 mL, 0.84 mmol), KOH (4.14 g, 73.8 mmol), and
MeOH (30 mL). The mixed solution was stirred at ambient
temperature for 40 h. The solution was filtered, and the solvent
was evaporated under vacuum. The residue was washed several
times with Et2O and extracted with CH2Cl2 to give a sample of
[Et4N]2[5] (yield 0.46 g, 0.32 mmol, 78% based on Pb).
Reaction of [Et4N]2[1] with Mn(CO)5Br. To a MeCN solution
(30 mL) of [Et4N]2[1] (0.36 g, 0.34 mmol) was added Mn(CO)5Br
(0.14 g, 0.51 mmol) at ambient temperature. The resulting
solution was stirred for 30 min to give a yellow-brown solution.
The solution was filtered, and the solvent was evaporated under
vacuum. The residue was washed with Et2O, which was shown
to contain Mn2(CO)10 and [HCr2(CO)10]- by IR spectroscopy.
The residue was extracted with CH2Cl2 to give a sample of
[Et4N]2[Pb2Br2Cr4(CO)18] ([Et4N]2[4]) (yield 0.14 g, 0.09 mmol,
53% based on Pb). IR (νCO, CH2Cl2): 2036 (s), 2012 (m), 1984
(s), 1959 (m), 1943 (m), 1925 (s), 1903 (m) cm-1. Anal. Calcd for
[Et4N]2[4]: C, 26.40; H, 2.61; N, 1.81. Found: C, 26.41; H, 2.80;
N, 1.66. Crystals of [Et4N]2[4] suitable for single crystal X-ray
diffraction were grown from Et2O/CH2Cl2.
Synthesis of [Et4N]2[Fe3(CO)9{PbCr(CO)5}2] ([Et4N]2-
[6]). Method 1. To a MeCN solution (40 mL) of [Et4N]2[3]
(1.00 g, 1.00 mmol) was added Mn(CO)5Br (0.36 g, 1.31 mmol).
The mixed solution was stirred and heated to 80 ꢀC for 2 days.
The solution was filtered, and the solvent was evaporated under
vacuum. The residue was washed several times with Et2O, which
was shown by IR spectroscopy to contain Mn2(CO)10. The residue

Article
Inorganic Chemistry, Vol. 50, No. 2, 2011 575
was then extracted with CH2Cl2 to give a sample of [Et4N]2[6] (yield
0.46 g, 0.31 mmol, 62% based on Pb). IR (νCO, CH2Cl2): 2034 (s),
1949 (vs), 1918 (m), 1886 (m) cm-1. Anal. Calcd for [Et4N]2[6]: C,
28.43; H, 2.73; N, 1.89. Found: C, 28.40; H, 2.81; N, 1.86. Crystals
of [Et4N]2[6] suitable for single-crystal X-ray diffraction were
grown from Et2O/CH2Cl2.
[Et4N]2[6], and [Et4N]2[7] were refined with anisotropic tem-
perature factors. Additional crystallographic data in the form of
CIF files are available as Supporting Information.
Computational Details. All calculations reported in this study
were performed via DFT with Becke’s three-parameter (B3)
exchange functional and the Lee-Yang-Parr (LYP) correla-
tion functional (B3LYP)21,22 using the Gaussian 03 series of
Method 2. A MeOH solution (30 mL) of Cr(CO)6 (0.10 g, 0.45
mmol) and KOH (4.23 g, 0.075 mmol) was stirred in an ice/water
bath and warmed to ambient temperature. After 4 h, [Et4N]2[5]
(0.29 g, 0.20 mmol) was added to the solution, which was stirred
for another 14 h to give a yellowish-brown solution. The
solution was filtered, and the solvent was evaporated under
vacuum. The residue was washed with deionized water and Et2O
several times and dried under vacuum. The CH2Cl2 extract was
recrystallized from Et2O/MeOH/CH2Cl2 to give a sample of
[Et4N]2[6] (yield 0.18 g, 0.12 mmol, 60% based on Pb).
packages.31 The geometries of complexes 1-7, [Cr(CO)5]2-
,
[Fe(CO)4]2-, and Ru3(CO)12 and the proposed intermediates
[BrPb{Cr(CO)5}2]- and [Pb{Cr(CO)5}{Ru(CO)4}2]2- were fully
optimized with the Stuttgart/Dresden relativistic effective core
potential32 and with the LanL2DZ basis set for Pb, Br, Cr, Fe,
and Ru atoms and the 6-31G(d) basis set for C and O atoms. The
optimized geometries were further confirmed by harmonic
vibrational frequency analysis, obtained via analytical energy
second derivatives. Wiberg bond indices33 and natural charges24
were evaluated using the Weinhold NBO method.23 Graphical
representations of the molecular orbitals were obtained using
CS Chem3D 5.0.
Synthesis of [Et4N]2[Ru3(CO)9{PbCr(CO)5}2] ([Et4N]2[7]). A
MeOH solution (20 mL) of Cr(CO)6 (0.15 g, 0.68 mmol) and
KOH (5.31 g, 94.6 mmol) was stirred in an ice/water bath and
warmed to ambient temperature. After 3 h, PbCl2 (0.20 g, 0.72
mmol) was added to the solution, which was stirred for another
4 h to give a reddish-brown solution. Ru3(CO)12 (0.22 g, 0.34
mmol) was then added to the solution and stirred for 36 h
at ambient temperature to yield a brown solution, which
was filtered and concentrated, and an aqueous solution of
[Et4N]Br (0.31 g, 1.48 mmol) was added dropwise, precipitating
the solid. The solid was washed with deionized water several
times and dried under vacuum. The CH2Cl2 extract was recrys-
tallized from Et2O/MeOH/CH2Cl2 to give a reddish-brown
sample of [Et4N]2[7] (yield 0.20 g, 0.12 mmol, 35% based on
Ru). IR (νCO, CH2Cl2): 2033 (m), 1970 (vs), 1923 (m), 1887 (m)
cm-1. Anal. Calcd for [Et4N]2[7]: C, 26.04; H, 2.50; N, 1.74.
Found: C, 26.01; H, 2.71; N, 1.60. Crystals of [Et4N]2[7] suitable
for X-ray diffraction were grown from Et2O/CH2Cl2.
Acknowledgment. This work was supported by the National
Science Council of Taiwan (Grant 98-2113-M-003-006-MY3 to
M.S.). We are also grateful to the National Center for High-
Performance Computing, where the Gaussian package and
computer time were provided.
Supporting Information Available: X-ray crystallographic files
in CIF format for [Bu4N]2[3], [Et4N]2[4], [Et4N]2[5], [Et4N]2[6], and
[Et4N]2[7], CV, equatorial plane of the structure of 5, spatial graphs,
and computational details for 1-7, [Cr(CO)5]2-, [Fe(CO)4]2-, and
Ru3(CO)12 and the proposed intermediates [BrPb{Cr(CO)5}2]- and
[Pb{Cr(CO)5}{Ru(CO)4}2]2-. This material is available free of
charge via the Internet at http://pubs.acs.org.
X-ray Structural Characterization of [Bu4N]2[3], [Et4N]2[4],
[Et4N]2[5], [Et4N]2[6], and [Et4N]2[7]. Some selected crystallo-
graphic data for [Bu4N]2[3], [Et4N]2[4], [Et4N]2[5], [Et4N]2[6],
and [Et4N]2[7] are given in Table 5. All crystals were mounted on
glass fibers with epoxy cement. Data collection for [Bu4N]2[3]
was carried out using a Nonius (CAD-4) diffractometer with
graphite-monochromated Mo KR radiation at 298 K in the 2θ
range of 2.0-50ꢀ employing θ-2θ scans, and an empirical
absorption correction by azimuthal (Ψ) scans was applied.29
Data collection for [Et4N]2[4], [Et4N]2[5], [Et4N]2[6], and
[Et4N]2[7] was carried out using a Bruker-Nonius Kappa CCD
diffractometer with graphite-monochromated Mo KR radiation
at 298 K, and an empirical absorption correction by multiscans
was applied. The structures of [Bu4N]2[3], [Et4N]2[4], [Et4N]2[5],
[Et4N]2[6], and [Et4N]2[7] were refined by SHELXL packages.30
All of the non-H atoms of [Bu4N]2[3], [Et4N]2[4], [Et4N]2[5],
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Hratchian, H. P.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.;
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Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A.;
Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels,
A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.; Raghavachari,
K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.;
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€
(30) Sheldrick, G. M. SHELXL97, version 97-2; University of Gottingen:
€
Gottingen, Germany, 1997.