A basic strategy for functionalization of metal cyclopentadienyl complexes: Synthesis, characterization, and reactivity of linear, butterfly, and cubic chromium/selenium complexes containing functionally substituted cyclopentadienyl ligands

Article abstract of DOI:10.1021/om034283q

The first examples of linear, butterfly, and cubic Cr/Se complexes containing functionally substituted Cp ligands have been successfully synthesized by skeleton and functional transformations of the prefunctionalized Cp metal precursors. For example, (i) the prefunctionalized Cp metal precursors [η⁵-RC₅H₄Cr(CO)₃]₂ (1, R = MeCO; 2, R = MeO₂C) reacted with elemental selenium under the given conditions to afford linear complexes [η⁵-RC₅ H₄Cr(CO)₂]₂Se (3, R = MeCO; 4, R = MeO₂C), butterfly complexes [η⁵-RC₅ H₄Cr(CO)₂]₂Se₂ (5, R = MeCO; 6, R = MeO₂C), and cubane clusters (η⁵-RC₅ H₄)₄Cr₄Se ₄ (7, R = MeCO; 8, R = MeO₂C), whereas the linear complexes 3/4 reacted with elemental selenium under appropriate conditions to produce butterfly complexes 5/6 or cubane clusters 7/8; (ii) thermolysis of a THF solution of butterfly complex 5 or 6 gave rise to cubane cluster 7 or 8, whereas the THF solution of two butterfly complexes [CpCr(CO)₂]₂Se₂ and 6 under reflux afforded cubane clusters (η⁵-MeO₂ CC₅H₄)_nCp_4-nCr₄ Se₄ (n = 0, Cp₄Cr₄Se₄; n = 1, 9; n = 2, 10; n = 3, 11; n = 4, 8); (iii) while cluster 7 reacted with excess NaBH₄ to give secondary hydroxy derivative [η⁵- MeCH(OH)C₅H₄]₄Cr₄ Se₄ (12), it reacted with Grignard reagent MeMgI and subsequent hydrolysis of the addition intermediate to afford tertiary hydroxy derivative [η⁵- Me₂C(OH)-C₅H₄]₄Cr₄ Se₄ (13); and (iv) the functional transformation of cluster 7 under the action of Wittig reagent Ph₃P=CHPh produced cubane cluster [η⁵-PhCH=C(Me)C₅H₄]₄ Cr₄Se₄ (14), whereas the condensation reaction of 7 with 2,4-dinitrophenylhydrazine yielded phenylhydrazone derivative [η⁵-2,4-(NO₂)₂C₆H₃NHN C(Me)C₅H₄]₄Cr₄ Se₄ (15). Possible pathways for the reactions leading to functionalized cubane clusters 7-11 are suggested. Furthermore, ⁷⁷Se NMR techniques were utilized to characterize the new functionalized complexes, whereas single-crystal X-ray diffraction was employed to confirm the structures of complexes 4, 7, 8, 11, and 12.

Full text of DOI:10.1021/om034283q

1072
Organometallics 2004, 23, 1072-1080
A Ba sic Str a tegy for F u n ction a liza tion of Meta l
Cyclop en ta d ien yl Com p lexes: Syn th esis,
Ch a r a cter iza tion , a n d Rea ctivity of Lin ea r , Bu tter fly,
a n d Cu bic Ch r om iu m /Selen iu m Com p lexes Con ta in in g
F u n ction a lly Su bstitu ted Cyclop en ta d ien yl Liga n d s
Li-Cheng Song,* Hua-Wei Cheng, and Qing-Mei Hu
Department of Chemistry, State Key Laboratory of Elemento-Organic Chemistry,
Nankai University, Tianjin 300071, China
Received November 7, 2003
The first examples of linear, butterfly, and cubic Cr/Se complexes containing functionally
substituted Cp ligands have been successfully synthesized by skeleton and functional
transformations of the prefunctionalized Cp metal precursors. For example, (i) the prefunc-
tionalized Cp metal precursors [η5-RC5H4Cr(CO)3]2 (1, R ) MeCO; 2, R ) MeO2C) reacted
with elemental selenium under the given conditions to afford linear complexes [η5-RC5H4-
Cr(CO)2]2Se (3, R ) MeCO; 4, R ) MeO2C), butterfly complexes [η5-RC5H4Cr(CO)2]2Se2 (5,
R ) MeCO; 6, R ) MeO2C), and cubane clusters (η5-RC5H4)4Cr4Se4 (7, R ) MeCO; 8, R )
MeO2C), whereas the linear complexes 3/4 reacted with elemental selenium under appropri-
ate conditions to produce butterfly complexes 5/6 or cubane clusters 7/8; (ii) thermolysis of
a THF solution of butterfly complex 5 or 6 gave rise to cubane cluster 7 or 8, whereas the
THF solution of two butterfly complexes [CpCr(CO)2]2Se2 and 6 under reflux afforded cubane
clusters (η5-MeO2CC5H4)nCp4-nCr4Se4 (n ) 0, Cp4Cr4Se4; n ) 1, 9; n ) 2, 10; n ) 3, 11; n )
4, 8); (iii) while cluster 7 reacted with excess NaBH4 to give secondary hydroxy derivative
[η5-MeCH(OH)C5H4]4Cr4Se4 (12), it reacted with Grignard reagent MeMgI and subsequent
hydrolysis of the addition intermediate to afford tertiary hydroxy derivative [η5-Me2C(OH)-
C5H4]4Cr4Se4 (13); and (iv) the functional transformation of cluster 7 under the action of
Wittig reagent Ph3PdCHPh produced cubane cluster [η5-PhCHdC(Me)C5H4]4Cr4Se4 (14),
whereas the condensation reaction of 7 with 2,4-dinitrophenylhydrazine yielded phenylhy-
drazone derivative [η5-2,4-(NO2)2C6H3NHNC(Me)C5H4]4Cr4Se4 (15). Possible pathways for
the reactions leading to functionalized cubane clusters 7-11 are suggested. Furthermore,
77Se NMR techniques were utilized to characterize the new functionalized complexes, whereas
single-crystal X-ray diffraction was employed to confirm the structures of complexes 4, 7, 8,
11, and 12.
In tr od u ction
tion.7 This study focuses on organometallic complexes
and clusters containing functionally substituted cyclo-
pentadienyl ligands. It is expected that such fundamen-
tal studies in this area will ultimately achieve great
success since the parent cyclopentadienyl ligand and its
substituted derivatives are important and ubiquitous
in transition metal chemistry.
In principle, there are two basic strategies for func-
tionalization of metal-Cp compounds, the first involving
direct functionalization of the metal-Cp complexes8 and
the second being based on the transformation of pre-
functionalized Cp-metal complex precursors.3,9 Recently,
Rauchfuss and co-workers carried out a study on the
first strategy regarding direct functionalization of the
There has been increasing current interest in metal
complexes bearing ligands with an “external” function-
ality that is not ligated to the central metal. The
“external” functionality, in contrast to “internal” func-
tionality,1 is known to play an important role in the
synthesis of novel metal complexes2-4 and in the ac-
complishment of the biological function of metal en-
zymes,5,6 as well as in catalysis and molecular recogni-
* To whom correspondence should be addressed. Fax: 0086-22-
23504853. E-mail: lcsong@nankai.edu.cn.
(1) (a) Omae, I. Chem. Rev. 1979, 79, 287. (b) Gruter, G.-J . M.; van
Klink, G. P. M.; Akkerman, O. S.; Bickelhaupt, F. Chem. Rev. 1995,
95, 2405.
(2) Seyferth, D. Adv. Organomet. Chem. 1976, 14, 97.
(3) Song, L.-C.; Shen, J .-Y.; Hu, Q.-M.; Huang, X.-Y. Organometallics
1995, 14, 98.
(4) Westmeyer, M. D.; Massa, M. A.; Rauchfuss, T. B.; Wilson, S. R.
J . Am. Chem. Soc. 1998, 120, 114.
(5) (a) Holm, R. H.; Kennepohl, P.; Soloman, E. I. Chem. Rev. 1996,
96, 9. (b) Orgino, H.; Inomata, S.; Tobita, H. Chem. Rev. 1998, 98, 2093.
(6) (a) Darensbourg, M. Y.; Lyon, E. J .; Smee, J . J . Coord. Chem.
Rev. 2000, 206-207, 533. (b) Lawrence, J . D.; Li, H.; Rauchfuss, T.
B.; Benard, M.; Rohmer, M.-M. Angew. Chem. Int. Ed. 2001, 40, 1768.
(7) (a) Lehn, J .-M. Supramolecular Chemistry; VCH: Weinheim,
1995. (b)Vo¨gtle, F. Supramolecular Chemistry; Wiley: New York, 1991.
(8) Direct functionalization of cyclopentadienyl transition metal
compounds, for example see: (a) Barlow, S.; O’Hare, D. Organometal-
lics 1996, 15, 3885. (b) Saha, A. K.; Hossain, M. M. J . Organomet.
Chem. 1993, 445, 137. (c) Herberhold, M.; Biersack, M. J . Organomet.
Chem. 1990, 381, 379. (d) Balem, M. P.; Le Plouzennec, M.; Loue¨r, M.
Inorg. Chem. 1982, 21, 2573.
10.1021/om034283q CCC: $27.50 © 2004 American Chemical Society
Publication on Web 02/04/2004

Metal Cyclopentadienyl Complexes
Organometallics, Vol. 23, No. 5, 2004 1073
Sch em e 1a
Cp-metal cubane-like cluster Cp4Fe4(CO)4, based on
their initial considerations that the second strategy is
less easily applied to clusters since the functional group
on the prefunctionalized Cp ligands can be incompatible
with clusterification processes.4 To examine the suit-
ability of the two strategies for synthesizing cubane
clusters containing functionally substituted Cp ligands,
we chose to study the cubane Cr4Se4 clusters. This is
because such clusters are closely related to the active
site in biomolecules, such as high potential proteins and
ferredoxins.5 In addition, the parent compound Cp4Cr4-
Se4 of such clusters can be easily prepared.10 Now, we
have found that the second strategy is well suited for
preparing functionalized cyclopentadienyl Cr4Se4 clus-
ters from the prefunctionalized Cp-metal complex pre-
cursors, whereas the first strategy, in contrast to the
feasible case for Cp4Fe4(CO)4,4 cannot be applied to
direct functionalization of Cp4Cr4Se4 under similar
metalation and Friedel-Crafts acylation conditions to
give the corresponding cubane-like cluster complexes.
This article will mainly describe the synthesis, charac-
terization, and reactions of the functionalized Cp cubane
Cr4Se4 clusters (η5-RC5H4)nCp4-nCr4Se4 (n ) 1-4), the
functionalized Cp linear Cr2Se complexes [η5-RC5H4Cr-
(CO)2]2Se, and butterfly Cr2Se2 complexes [η5-RC5H4-
Cr(CO)2]2Se2. Furthermore, the mechanistic pathways
for production of the Cr4Se4 cubane clusters are also
described.
change to the butterfly Cr2Se2 skeleton.12-14 Either the
µ2-Se or µ2-Se2 ligand acts as a 6e donor, and the Cr
atoms in 3-6 have achieved the noble gas configuration.
Products 3-6 are the first examples of the linear and
butterfly Cr/Se complexes containing functionalized Cp
ligands, although their parent complexes [CpCr(CO)2]2Se
and [CpCr(CO)2]2Se2 were known.14-16 The IR spectra
of 3-6 showed two or three absorption bands in the
range 1999-1880 cm-1 for their terminal carbonyls and
one absorption band in the region 1717-1676 cm-1 for
their ketonic and ester carbonyls in the functionalized
1
Cp ligands. The H NMR spectra of 3-6 displayed two
singlets for the four protons in each substituted Cp ring,
one singlet at lower field being assigned to H2/H5 close
to the substituent and the other at higher field at-
tributed to H3/H4 remote from the substituent since the
substituents attached to the Cp rings are electron-
withdrawing.3
Resu lts a n d Discu ssion
Syn th esis a n d Ch a r a cter iza tion of Lin ea r , Bu t-
ter fly, a n d Cu bic Com p lexes Con ta in in g F u n c-
tion a lized Cp Liga n d s 3-6. We found that the Cr-
Cr singly bonded dimers containing functionalized Cp
ligands [η5-RC5H4Cr(CO)3]2 (1, R ) MeCO; 2, R )
MeO2C)11 reacted with 1 equiv of elemental selenium
in THF at room temperature for ca. 15 min to give the
linear Cr2Se complexes [η5-RC5H4Cr(CO)2]2Se (3, R )
MeCO; 4, R ) MeO2C) in nearly quantitative yield.
Further reaction of 3 or 4 with 1 equiv of elemental
selenium in THF at ca. 45 °C for 1.5 h and reaction of
1 or 2 with an excess amount of elemental selenium in
THF at room temperature for 16 h resulted in formation
of the butterfly Cr2Se2 complexes [η5-RC5H4Cr(CO)2]2Se2
(5, R ) MeCO; 6, R ) MeO2C) in high yield (Scheme 1).
While the linear complexes 3 and 4 could be regarded
as derived by insertion of a Se atom into the Cr-Cr
single bonds of 1 and 2 followed by loss of two CO
ligands and concomitant formation of the cumulated
CrtSe triple bonds between Cr and Se atoms, the
butterfly complexes 5 and 6 might be formally viewed
as produced from insertion of a Se atom across the
cumulated CrtSe triple bonds of 3 and 4 and concurrent
The 77Se NMR spectra of 3 and 4 each showed one
singlet for the µ2-Se atom in the highly deshielded range
from 2589 to 2605 ppm, whereas the spectra of 5 and 6
each displayed one singlet for µ2-Se2 atoms in the highly
shielded region from -257 to -267 ppm. Such 77Se NMR
data of 3-6 are comparable with the reported data
corresponding to the parent linear and butterfly com-
plexes [CpCr(CO)2]2Se and [CpCr(CO)2]2Se2, respec-
tively.17 The highly deshielding µ2-Se of 3 and 4 probably
originates from the involvement of the π-electrons of Se
in the unusual cumulated CrtSetCr linkage.18
The structure of linear complex 4 was confirmed by
a single-crystal X-ray diffraction study. The ORTEP
drawing of 4 is shown in Figure 1, whereas Table 1
presents its selected bond lengths and angles.
Figure 1 shows that complex 4 consists of an es-
sentially linear Cr-Se-Cr skeleton, two functionalized
Cp ligands η5-MeO2CC5H4, and four terminal carbonyls.
(12) Herrmann, W. A.; Rohrmann, J .; No¨th, H.; Nanila, C. K.;
Bernal, I.; Draux, M.J . Organomet. Chem. 1985, 284, 189.
(13) Herrmann, W. A. Angew. Chem., Int. Ed. Engl. 1986, 25, 56.
(14) Chen, W.; Goh, L. Y.; Sinn, E. Organometallics 1988, 7, 2020.
(15) Herrmann, W. A.; Rohrmann, J .; Scha¨fer, A. J . Organomet.
Chem. 1984, 265, C1.
(16) Goh, L. Y.; Chen, W.; Sinn, E. J . Chem. Soc., Chem. Commun.
1985, 462.
(17) Dean, P. A. W.; Goh, L. Y.; Gay, I. D.; Sharma, R. D. J .
Organomet. Chem. 1997, 533, 1.
(18) (a) Luthra, N. P.; Odom, J . D. In The Chemistry of Organic
Selenium and Tellurium Compounds; Patai, S., Rappoport, Z., Eds.;
Wiley: New York, 1986; p 189. (b) McFarlane, H. C. E.; McFarlane,
W.; In Multinuclear NMR; Mason, J ., Ed.; Plenum: New York, 1987;
p 421.
(9) Functionalization based on the prefunctionalized Cp metal
complex precursors including even alkali metal salts of functional
cyclopentadienides, for example see: (a) Macomber, D. W.; Hart, W.
P.; Rausch, M. D. Adv. Organomet. Chem. 1982, 21, 1. (b) Abbenhuis,
H. C. L.; Burckhardt, U.; Gramlich, V.; Togni, A.; Albinati, A.; Mu¨ller,
B. Organometallics 1994, 13, 4481. (c) Herberich, G. E.; Fischer, A.;
Wiebelhaus, D. Organometallics 1996, 15, 3106. (d) Song, L.-C.; Shen,
J .-Y.; Hu, Q.-M.; Wang, R.-J .; Wang, H.-G. Organometallics 1993, 12,
408.
(10) Goh, L. Y.; Mak, T. C. W. J . Organomet. Chem. 1989, 363, 77.
(11) Medina, R. M.; Masaguer, J . R.; Moran, M. Inorg. Chim. Acta
1988, 146, 115.

1074 Organometallics, Vol. 23, No. 5, 2004
Song et al.
Sch em e 2a
F igu r e 1. ORTEP drawing of 4 (30% probability ellipsoids,
H atoms are omitted).
Ta ble 1. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 4
a
The Cr-Cr bonds in the cubane cores of 7 and 8 are
omitted for clarity.
Cr(1)-C(1)
Cr(1)-C(2)
Cr(1)-Se(1)
C(1)-O(1)
1.873(9)
Cr(1A)-Se(1)
Cr(1)-C(3)
Cr(1)-C(4)
C(8)-C(3)
2.1935(16)
2.169(8)
2.189(9)
1.871(13)
2.1935(16)
1.111(10)
ferrocene or Cp4Fe4(CO)4,4,21,22 no expected functional-
ized cubane cluster complexes of [η5-MeC(O)C5H4]n-
Cp4-nCr4Se4 (n ) 1-4) and (η5-PhSC5H4)nCp4-nCr4Se4
(n ) 1-4) were obtained from the corresponding reac-
tion mixtures.
1.453(13)
Cr(1)-Se(1)-Cr(1A) 167.90(8) C(1)-Cr(1)-Se(1)
97.9(2)
153.5(6)
C(1)-Cr(1)-C(2)
C(2)-Cr(1)-C(7)
C(2)-Cr(1)-Se(1)
88.7(5)
90.9(5)
94.5(4)
C(2)-Cr(1)-C(5)
Se(1)-Cr(1)-C(5) 100.4(3)
O(1)-C(1)-Cr(1) 177.7(9)
Products 7 and 8 were fully characterized by elemen-
tal analysis, spectroscopy, and X-ray diffraction studies.
For example, the IR spectra of 7 and 8 exhibited one
absorption band in the range 1664-1716 cm-1 assigned
The bond angle around Se [167.90(8)°] in 4 is much less
than the corresponding angle in its parent complex [η5-
CpCr(CO)2]2Se [178.3(1)°], whereas the Cr-Se bond
lengths of 4 [2.1935(16) Å] are close to those of its parent
complex (2.208(1) and 2.211 Å).16 It is noteworthy that
the considerable shortening of the Cr-Se bond lengths
in comparison with the sum of the covalent radii of
chromium (rCr 1.46 Å 19) and selenium (rSe 1.17 Å 20) is
consistent with triple bonding between chromium and
selenium atoms in the linear CrtSetCr unit of complex
4. In addition, the bond length of C(8)-C(3) (1.453 (13)
Å) is much shorter than that of a normal C-C single
bond, which could be attributed to conjugation between
the π-electron systems of the substituted MeO2C and
cyclopentadienyl ring. This molecule possesses C2 sym-
metry.
Rea ction s of P r efu n ction a lized Cp P r ecu r sor s
1-6 w ith Selen iu m Lea d in g to F u n ction a lized Cp
Cu ba n e Cr 4Se4 Clu ster s 7 a n d 8. We further found
that when the Cr-Cr singly bonded dimers 1 and 2 with
excess elemental selenium, or the linear Cr2Se com-
plexes 3 and 4 with 1 equiv of selenium, or even the
butterfly Cr2Se2 complexes 5 and 6 alone were refluxed
in THF for 8 h, the corresponding functionalized cubane
clusters (η5-RC5H4)4Cr4Se4 (7, R ) MeCO; 8, R )
MeO2C) could be obtained in excellent yield (Scheme 2).
Products 7 and 8 are the first functionalized Cp
cubane Cr4Se4 clusters, which were prepared through
skeleton transformation of the prefunctionalized Cp-
metal precursors by the second synthetic strategy. It
should be noted that our attempts failed to obtain such
functionalized Cp cubane clusters by the first synthetic
strategy. For instance, when parent cubane cluster Cp4-
Cr4Se4 was treated with MeC(O)Cl/AlCl3, acetic anhy-
dride/H3PO4, or lithium diisopropylamide (LDA) fol-
lowed by treatment with (PhS)2 under conditions similar
to those of Friedel-Crafts acylation and lithiation of
1
to their ketonic and ester carbonyls, and the H NMR
spectra showed two singlets at lower and higher fields
attributed to H2/H5 and H3/H4 protons in the function-
alized Cp rings. It was previously reported17 that the
solid-state 77Se NMR spectrum of parent cluster Cp4-
Cr4Se4 (due to its insufficient solubility for a solution
NMR study) exhibited two singlets at 1018 and 1079
ppm, and it was not clear whether the two shifts
represent different Cp4Cr4Se4 molecules or different Se
environments within a single distorted molecule. How-
ever, in contrast to the case of parent cluster Cp4Cr4-
Se4, the solution 77Se NMR spectra of the functionalized
derivatives 7 and 8 displayed only one singlet in the
range 1244-1227 ppm, which implies that they possess
only one single µ3-Se environment for a single molecule.
Fortunately, this has been unambiguously confirmed by
their crystal X-ray diffraction analyses. The ORTEP
drawings of 7 and 8 are depicted in Figures 2 and 3,
while their selected bond lengths and angles are given
in Table 2.
As can be seen in Figures 2 and 3, complexes 7 and
8, similar to their methyl analogue (η5-MeC5H4)4Cr4-
Se4,23 contain a cubane-like Cr4Se4 cluster core, which
carries four substituted Cp ligands coordinated to four
Cr atoms, respectively. The cubic Cr4Se4 cluster core of
7 seems to be idealized, but that of 8 is slightly distorted,
which could be seen from their related bond lengths and
angles. For example, for 7 the bond lengths of Cr-Se
and Cr-Cr are 2.432-2.426 Å and 3.015-3.010 Å, and
the bond angles of Se-Cr-Se and Cr-Se-Cr are
102.05-101.75° and 76.76-76.57°, whereas for 8 the
bond lengths of Cr-Se and Cr-Cr are 2.394-2.376 Å
and 2.985-2.932 Å, and the bond angles of Se-Cr-Se
and Cr-Se-Cr are 102.82-100.61° and 77.52-76.02°,
(21) Ferrocenes, Togni, A., Hayashi, T. Eds. VCH: Weinheim, 1995.
(22) Massa, M. A.; Rauchfuss, T. B. Chem. Mater. 1991, 3, 788.
(23) Eremenko, I. L.; Nefedov, S. E.; Pasynskii, A. A.; Orazsakhatov,
B.; Ellert, O. G.; Struchkov, Yu. T. Yanovsky, A. I.; Zagorevsky, D. V.
J . Organomet. Chem. 1989, 368, 185.
(19) Pauling, L. The Nature of the Chemical Bond, 3rd ed.; Cornell
University Press: Ithaca, NY, 1960.
(20) Andrianov, V. G.; Biryukov, B. P.; Struchkov, Yu. T. Zh. Strukt.
Khim. 1969, 10, 1129.

Metal Cyclopentadienyl Complexes
Organometallics, Vol. 23, No. 5, 2004 1075
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 7, 8, 11, a n d 12
7
Cr(1)-C(2)
2.255(10)
2.426(2)
2.429(3)
2.432(2)
Cr(1)-Cr(1A)
Cr(1)-Cr(1B)
O(1)-C(1)
3.010(3)
3.015(3)
1.279(10)
1.503(14)
Cr(1)-Se(1A)
Cr(1)-Se(1B)
Cr(1)-Se(1)
C(1)-C(2)
C(2)-Cr(1)-Se(1A)
C(4)-Cr(1)-Se(1A)
147.1(3) Se(1B)-Cr(1)-Se(1) 101.75(6)
88.0(3) Cr(1A)-Se(1)-Cr(1C) 76.76(6)
Se(1A)-Cr(1)-Se(1B) 101.90(6) Cr(1A)-Se(1)-Cr(1)
76.57(6)
76.67(6)
119.0(18)
C(2)-Cr(1)-Se(1)
Se(1A)-Cr(1)-Se(1) 102.05(6) O(1)-C(1)-C(2)
97.5(3) Cr(1C)-Se(1)-Cr(1)
8
Cr(1)-Se(4)
Cr(1)-Se(1)
Cr(3)-Cr(4)
Cr(1)-Cr(4)
Cr(1)-Cr(3)
Cr(1)-Cr(2)
2.3761(13)
2.3824(13)
2.9848(17)
2.9326(18)
2.9521(16)
2.9669(17)
Cr(3)-Se(2)
Cr(3)-Se(4)
Cr(3)-Se(3)
Se(1)-Se(3)
Se(1)-Se(2)
C(6)-O(1)
2.3810(13)
2.3838(13)
2.3940(14)
3.6772(13)
3.7154(12)
1.338(9)
Se(4)-Cr(1)-Se(1) 102.82(5) Cr(2)-Se(1)-Cr(4) 76.60(4)
Se(4)-Cr(1)-Se(3) 102.47(5) Cr(2)-Se(1)-Cr(1) 77.14(5)
Se(4)-Cr(4)-Se(2) 100.61(5) Cr(1)-Se(1)-Se(2) 80.49(4)
F igu r e 2. ORTEP drawing of 7 (30% probability ellipsoids,
H atoms are omitted).
Se(4)-Cr(1)-Cr(4)
Se(3)-Cr(1)-Cr(4)
Se(1)-Cr(1)-Cr(3)
52.08(4) Se(3)-Se(1)-Se(2) 60.33(3)
99.62(5) Se(2)-Se(4)-Se(1) 60.35(2)
99.54(5) Cr(1)-Cr(4)-Cr(3) 59.85(4)
11
Cr(4)-Se(1)
Cr(1)-Se(1)
Cr(2)-Se(1)
Cr(2)-Se(2)
Se(2)-Cr(3)
2.4048(19)
2.396(2)
2.406(2)
2.4055(19)
2.410(2)
Cr(4)-Se(2)
Cr(4)-Se(4)
Cr(1)-C(3)
Cr(1)-Cr(4)
Cr(2)-Cr(3)
2.4140(19)
2.4135(19)
2.251(12)
2.955(3)
2.944(2)
Cr(1)-Se(1)-Cr(4)
Cr(1)-Se(1)-Cr(2)
Cr(4)-Se(1)-Cr(2)
Se(1)-Cr(1)-Se(3)
75.97(7) Se(1)-Cr(1)-Cr(3)
78.34(6) Cr(4)-Cr(1)-Cr(3)
99.96(7)
62.84(5)
76.22(7) Se(3)-Cr(2)-Se(2) 103.74(7)
99.01(7) Se(3)-Cr(2)-Cr(3)
52.11(5)
51.87(5)
62.97(6)
Se(1)-Cr(1)-Se(4) 103.69(8) Se(1)-Cr(2)-Cr(4)
Se(2)-Cr(4)-Se(4)
97.54(7) Cr(3)-Cr(2)-Cr(4)
12
Cr(1A)-Se(1)
Cr(1B)-Se(1)
Cr(1)-Se(1)
Cr(1)-Se(1A)
Se(1C)-Cr(1)
2.375(3)
Cr(1)-Cr(1A)
Cr(1)-Cr(1C)
Cr(1)-Cr(1B)
C(5)-C(6)
2.957(5)
2.384(3)
2.386(3)
2.375(3)
2.384(3)
2.969(4)
2.969(4)
1.533(10)
1.298(10)
C(6)-O(1)
Cr(1A)-Se(1)-Cr(1B) 77.19(10) Se(1A)-Cr(1)-Cr(1A) 51.77(8)
Cr(1A)-Se(1)-Cr(1)
Cr(1B)-Se(1)-Cr(1)
76.80(10) Se(1)-Cr(1)-Cr(1A) 51.43(9)
76.98(9) Se(1A)-Cr(1)-Cr(1C) 51.55(7)
F igu r e 3. ORTEP drawing of 8 (30% probability ellipsoids,
H atoms are omitted).
Se(1A)-Cr(1)-Se(1C) 101.67(10) Se(1)-Cr(1)-Cr(1C) 98.58(8)
C(1)-Cr(1)-Se(1)
Se(1A)-Cr(1)-Se(1) 101.93(10) Cr(1A)-Cr(1)-Cr(1B) 60.13(4)
86.2(6) Se(1)-Cr(1)-Cr(1B) 51.49(7)
respectively. Both C(1)-C(2) (1.503 Å) of 7 and C(5)-
C(6) (1.488 Å) of 8 are shorter than a normal C-C single
bond, due to the same reason for 4 as described above.
In addition, it is worthy of note that complexes 7 and
8, as predicated by the 18-valence-electron (18 VE) rule,
are 60-electron clusters, which contain four µ3-Se atoms
(each as a 4e donor) and six Cr-Cr single bonds.
Rea ction of P r efu n ction a lized Cp P r ecu r sor 6
w ith [Cp Cr (CO)2]2Se2 Lea d in g to Cu ba n e Cr 4Se4
Clu ster s Con ta in in g Cp a n d F u n ction a lized Cp
Liga n d s 9-11. Reaction of an equimolar quantity of
prefunctionalized Cp butterfly precursor 6 with its
parent butterfly complex [CpCr(CO)2]2Se2 in THF for 8
h produced mainly the cubane clusters containing both
Cp and functionalized Cp ligands (η5-MeO2CC5H4)n-
Cp4-nCr4Se4 (n ) 1, 9; n ) 2, 10; n ) 3, 11), along with
minor cubane clusters Cp4Cr4Se4 (n ) 0) and (η5-MeO2-
CC5H4)4Cr4Se4 (n ) 4, 8) in total 96% yield (Scheme 3).
Cubane clusters 9-11 contain both Cp and function-
alized Cp and were formed through a new type of cross-
assembled reaction,24 namely, coclusterification reaction
of two different butterfly complexes. While the IR
spectra of 9-11 showed one absorption band at ca. 1720
cm-1 for their ester’s carbonyl functionalities, the 1H
NMR spectra of 9-11 displayed one singlet for the five
protons of each Cp ring and two singlets for H2/H5 and
H3/H4 protons of each substituted Cp ring.3 It is worth
pointing out that most of the mixedCp clusters 9-11,
in contrast to parent Cp cluster Cp4Cr4Se4 and func-
tionalized Cp clusters 7 and 8, displayed 1H NMR
signals for Cp and functionalized Cp at much lower field.
1
That is, while 11 showed H NMR signals in the normal
range, the other two exhibited signals at low field up to
32 ppm, probably due to trace amounts of paramagnetic
species such as (CpCr)mSen and (RCpCr)mSen derived
from decomposition of the corresponding cubane clus-
ters.
(24) Kabashima, S.; Kuwata, S.; Ueno, K.; Shiro, M.; Hidai, M.
Angew. Chem., Int. Ed. 2000, 39, 1128.

1076 Organometallics, Vol. 23, No. 5, 2004
Song et al.
Sch em e 3a
Sch em e 4a
a
Tetramerization occurs through intermolecular coordina-
tion of Se to Cr.
apparently due to the presence of the mixed Cp ligands,
which can be seen from the bond lengths and bond
angles. For example, the values of Cr-Se (2.396-2.414
Å), Cr-Cr (2.970-2.944 Å), Se-Cr-Se (97.54-103.74°),
and Cr-Se-Cr (79.63-75.38°) are within a larger
region, respectively. However, similar to 8, this molecule
is also a 60-electron cluster, which contains four µ3-Se
4e ligands and six Cr-Cr single bonds.
a
The Cr-Cr bonds in the cubane cores of all the indicated
cubane clusters are omitted for clarity.
Rea ction P a th w a ys Lea d in g to Cu ba n e Clu ster s
7-11. The suggested pathway for production of cubic
clusters 7 and 8 is shown in Scheme 4. As can be seen
in Scheme 4, the linear complexes 3/4 and butterfly
complexes 5/6 are the intermediates for the formation
of the cubane clusters 7/8 starting from the Cr-Cr
singly bonded dimers 1/2. This is because we have
proved that (i) 1/2 could react with 1 equiv of selenium
to give 3/4 (Scheme 1); (ii) 3/4 reacted with 1 equiv of
selenium to yield 5/6 (Scheme 1); and (iii) thermolysis
of 5/6 yielded 7/8 (Scheme 2). Now, the question is how
are the cubane clusters 7/8 formed from butterfly
complexes 5/6? Initially, we thought that 7/8 might be
simply produced by dimerization of a highly unsatur-
ated species (η5-RC5H4CrSe)2 (Scheme 4, step iv), which
was generated in situ from butterfly complexes 5/6 by
loss of their CO ligands and concomitant cleavage of
their Se-Se bonds under thermolysis conditions (Scheme
4, step iii).
However, 7/8 would also be possibly produced by
tetramerization of another highly unsaturated species
η5-RC5H4CrSe (Scheme 4, step vii), which was derived
from further thermolysis of the first unsaturated species
(η5-RC5H4CrSe)2 or directly derived from 5/6 (Scheme
4, steps v and vi).
To prove which pathway is correct, we carried out a
study on the above-described cross-assembled reaction
between two butterfly complexes, 6 and [CpCr(CO)2]2Se2.
The results indicated that (i) the reaction afforded five
cubane products, Cp4Cr4Se4 and 8-11, and not three
cubane products, Cp4Cr4Se4, 8, and 10; and (ii) the
molar ratio of the five products is ca. 1:4:6:4:1. There-
fore, these observations are consistent with the combi-
natory rule of tetramerization of the two different highly
unsaturated fragments CpCrSe and η5-RC5H4CrSe,
which strongly supports the pathway involving steps v
and vi for formation of cubane clusters 7 and 8 (Scheme
4).
F igu r e 4. ORTEP drawing of 11 (30% probability el-
lipsoids, H atoms are omitted).
To examine the influence of different Cp ligands upon
77Se NMR behavior, we determined the 77Se NMR
spectra of 9-11. As a result, beyond our expectation,
they showed only one singlet (in the range 1105-1216
ppm) for their µ3-Se atoms. This implies that the
difference between Cp and the functionalized Cp is too
small to make µ3-Se environments sufficiently different
in these clusters. In addition, the 77Se chemical shifts
of (η5-MeO2CC5H4)nCp4-nCr4Se4 (n ) 1-4) increase with
the increase of number n, which is in agreement with
the fact that the methoxycarbonyl substituent is electron-
withdrawing.
The molecular structure of 11 was determined by
X-ray diffraction techniques. The ORTEP drawing of 11
is presented in Figure 4. Selected bond lengths and bond
angles are listed in Table 2. This molecule indeed
contains a cubane Cr4Se4 cluster core that carries one
Cp and three MeO2C-substituted Cp ligands coordinated
in an η5-fashion to four Cr atoms, respectively. The cubic
cluster core of 11 is more distorted than that of 8,

Metal Cyclopentadienyl Complexes
Organometallics, Vol. 23, No. 5, 2004 1077
Sch em e 5
Sch em e 6a
The possible pathway for production of cubane clus-
ters 8-11 and Cp4Cr4Se4 from the above-mentioned
cross-assembled reaction can be similarly suggested and
is shown in Scheme 5. As can be seen in Scheme 5, the
highly unsaturated species CpCrSe and η5-RC5H4CrSe
may undergo both self-tetramerization to give cubane
clusters Cp4Cr4Se4/8 and co-tetramerization to produce
cubane clusters 9-11.
It should be pointed out that in order to exclude the
possibility that the cubane clusters containing mixed
Cp ligands, namely, 9-11, were produced by ligand
exchange, we tried the reactions between two cubane
clusters, one cluster containing four Cp and the other
containing four functionalized Cp, namely, Cp4Cr4Se4
and 8. The results showed that no other cubane cluster
bearing mixed Cp ligands was formed, which further
supports the suggested pathways described in Schemes
4 and 5.
Finally, it is worthy of note that although the reaction
pathways described above appear to be reasonable and
are based on a series of experimental evidence, the
details still need to be further studied. For instance, the
supposed unsaturated species for tetramerization could
also have CO ligands such as CpCrSe(CO)n and η5-
RC5H4CrSe(CO)n (n ) 1, 2), which may lose their CO
ligands at a given stage during tetramerization.25
F u n ction a l Tr a n sfor m a tion s of Clu ster 7 Lea d -
in g to F u n ction a lized Cp Cu ba n e Clu ster s 12-15.
The second synthetic strategy directed to functionalized
Cp clusters includes not only the above-mentioned
skeleton transformations but also the functional trans-
formation reactions of the prefunctionalized Cp clus-
ters.3,22 Now, we have carried out a series of functional
transformations regarding acetyl groups of cubane
cluster 7. For instance, cluster 7 could be reduced by
excess NaBH4 in CH2Cl2/MeOH at ca. 45 °C to give the
secondary hydroxy derivative [η5-MeCH(OH) C5H4]4Cr4-
Se4 (12) in 72% yield, whereas it reacted with Grignard
reagent MeMgI in THF at room temperature followed
by hydrolysis of the addition intermediate to afford the
tertiary hydroxy derivative [η5-Me2C(OH)C5H4]4Cr4Se4
(13) in 66% yield (Scheme 6). Furthermore, cluster 7
a
The Cr-Cr bonds in the cubane cores of 7 and 12-15 are
omitted for clarity.
could also undergo olefination with excess Wittig re-
agent Ph3PdCHPh26 formed in situ from Ph3(CH2Ph)-
PBr in CHCl3/MeOH at reflux or undergo condensation
with 2,4-dinitrophenylhydrazine in refluxing CHCl3 to
produce olefin derivative [η5-PhCHdC(Me)C5H4]4Cr4Se4
(14) in 67% yield and phenylhydrazone derivative [η5-
2,4-(NO2)2C6H3NHNC(Me)C5H4]4Cr4Se4 (15) in 52% yield,
respectively (Scheme 6).
Apparently, the above-mentioned successful func-
tional transformations of cluster 7, in contrast to the
failure of direct functionalization of parent cluster Cp4-
Cr4Se4, is due to the enhanced chemical stability of the
cubic Cr4Se4 cluster core caused by functional substit-
uents and good solubility of 7 in common organic
solvents. Clusters 12-15 have been fully characterized.
For example, while the IR spectra of 12-15 displayed
absorption bands characteristic of their functionalities
such as O-H, CdC, CdN, and N-H groups, the 77Se
NMR spectra of 12-15 showed one singlet in the range
991-1275 ppm for their µ3-Se atoms. In addition, the
1H NMR spectra of 12-15 displayed two doublets or two
singlets for the four protons of each substituted Cp ring,
the downfield one being assigned to their H2/H5 protons
and the upfield one ascribed to their H3/H4 protons,
respectively. This is consistent with the reported 1H
NMR spectra of a monosubstituted cyclopentadienyl
ring in transition metal complexes, which vary greatly
in complexity such as a single resonance, an A2B2 or
A2BB′ pattern, or a multiplet pattern, all depending on
the nature of the transition metal and the substituent.27
The structure of 12 was unequivocally confirmed by
X-ray crystallography. The ORTEP drawing of 12 is
shown in Figure 5, while its selected bond lengths and
(26) Wittig, G.; Scho¨llkopf, U. Chem. Ber. 1954, 87, 1318.
(27) Song, L.-C.; Dong, Y.-B.; Hu, Q.-M.; Gao, W.-Q.; Guo, D.-S.; Liu,
P.-C.; Huang, X.-Y.; Sun, J . Organometallics 1999, 18, 2168.
(25) Band, E.; Muetterties, E. L. Chem. Rev. 1979, 98, 639.

1078 Organometallics, Vol. 23, No. 5, 2004
Song et al.
vertible functional groups and/or cubane Cr4Se4 cluster
cores closely related to the biologically active site of
some metal-containing enzymes.2-6,23
Exp er im en ta l Section
Gen er a l Com m en ts. All reactions were carried out under
an atmosphere of highly purified nitrogen using standard
Schlenk or vacuum-line techniques. Solvents for preparative
use were dried and distilled under nitrogen from Na/ben-
zophenone ketyl or CaH2 prior to use. Commercial NaBH4,
selenium powder, and 2,4-dinitrophenylhydrazine were used
as received. Ph3(CH2Ph)PBr,28 n-BuLi,29 MeMgI,30 [η5-RC5H4-
Cr(CO)3]2 (R ) MeCO, MeO2C),11 and [CpCr(CO)2]2Se2 were
16
prepared according to literature procedures. All reactions were
monitored by thin-layer chromatography (TLC) at intervals.
Column chromatography under nitrogen and preparative TLC
were carried out on a glass column (2 × 10 cm) packed with
silica gel G and glass plates (25 × 20 × 0.25 cm) coated with
silica gel H (10-40 µm), respectively. Samples for character-
ization were recrystallized in mixed dichloromethane and
hexane. IR spectra were recorded on a Nicolet 170 SX FT-IR
or Bruker Vector 22 infrared spectrophotometer. While 1H
NMR spectra were recorded on a Bruker AC-P 200 NMR
spectrometer, 77Se NMR spectra were taken from a Varian
Unity-Plus 400 NMR spectrometer with Ph2Se2 as external
standard, and chemical shifts are referenced to Me2Se (δ )
0). Elemental analysis was performed on an Elementar Vario
EL analyzer. Melting points were determined on a Yanaco MP-
500 apparatus.
F igu r e 5. ORTEP drawing of 12 (20% probability el-
lipsoids, H atoms are omitted).
angles are given in Table 2. Cluster 12 is virtually
isostructuctral with its precusor 7, except the functional
ligand acetylcyclopentadienyl in 7 being replaced by
R-hydroxyethylcyclopentadienyl. That is, the four Cd
O double bonds (for example, C(1)-O(1) ) 1.279(10) Å)
in 7 (Figure 2), after reduction with NaBH4, become four
C-O single bonds (for example, C(6)-O(1) ) 1.298 (10)
Å) in 12 (Figure 5). Particularly noteworthy is that the
four carbon atoms attached to hydroxyl groups of 12 are
chiral, among which C(6)/C(6A) possess an R configu-
ration and C(6B)/C(6C) have an S configuration (Figure
5). This molecule has an alternating 4-fold axis of
symmetry and thus is optically inactive. In addition, it
is worth noting that although the formation of such a
tetra-alcohol 12 is very interesting, we do not know, at
the present stage, how it formed and what factors made
this reduction so highly diasteroselective.
P r ep a r a tion of [η5-MeC(O)C5H4Cr (CO)2]2Se (3). A 100
mL Schlenk flask equipped with a magnetic stir-bar was
charged with 0.486 g (1.00 mmol) of [η5-MeC(O)C5H4Cr(CO)3]2,
0.079 g (1.00 mmol) of gray selenium powder, and 20 mL of
THF. The mixture was stirred at room temperature for ca. 15
min to produce an orange-red solution. After solvent was
removed under vacuum, the residue was extracted in a minium
volume of dichloromethane, which was then subjected to
column chromatography. Elution with 1:2 (v/v) CH2Cl2/
petroleum ether gave an orange red band, from which 3 was
obtained. 3: brown red solid, yield 0.490 g (0.96 mmol, 96%);
mp 90-91 °C. Anal. Calcd for C18H14Cr2O6Se: C, 42.45; H,
2.77. Found: C, 42.06; H, 2.72. IR (KBr disk): νC≡O 1954 (vs),
Su m m a r y
1914 (m), 1894 (s); νCdO 1681 (s) cm-1 1H NMR (CDCl3): δ
.
2.19 (s, 6H, 2CH3), 4.59 (s, 4H, 2H3, 2H4), 5.32 (s, 4H, 2H2,
2H5). 77Se NMR (CDCl3): δ 2589.8 (s).
We have successfully synthesized the first examples
of functionalized Cp-containing linear Cr2Se, butterfly
Cr2Se2, and cubane Cr4Se4 complexes 3-15 by a basic
strategy for functionalization of metal Cp complexes
from the corresponding prefunctionalized Cp-metal
precursors. The possible pathways for production of
cubane clusters 7-11 by skeleton transformations of the
Cr-Cr singly bonded dimers 1/2, linear complexes 3/4,
and butterfly complexes 5/6, as well as a new type of
cross-assembled reaction involving two butterfly com-
plexes 6 and [CpCr(CO)2]2Se2 have been proposed. It is
noteworthy that direct functionalization of the parent
cubane cluster Cp4Cr4Se4 with MeC(O)Cl/AlCl3 or acetic
anhydride/H3PO4 failed to give the acetyl-containing
cubane clusters [MeC(O)C5H4]nCp4-nCr4Se4 (n ) 1-4),
while the functional transformations of the acetyl-
containing cluster 7 with NaBH4, Grignard reagent
MeMgI, Wittig reagent Ph3PdCHPh, or 2,4-dinitrophe-
nylhydrazine yield the corresponding cubane cluster
derivatives 12-15. It should be noted that the various
functionalized Cr/Se complexes prepared in this article
may have potential usage not only in organometallic and
cluster chemistry but also in other areas such as
material and life sciences, since they have easily con-
P r ep a r a tion of [η5-MeO2CC5H4Cr (CO)2]2Se (4). The
same procedure as for the preparation of 3 was followed, but
0.518 g (1.00 mmol) of [η5-MeO2CC5H4Cr(CO)3]2 was employed.
4: brown red solid, yield 0.536 g (0.99 mmol, 99%); mp 80-81
°C. Anal. Calcd for C18H14Cr2O8Se: C, 39.94; H, 2.61. Found:
C, 39.62; H, 2.59. IR (KBr disk): νC≡O 1999 (s), 1958 (vs), 1925
(vs); νCdO 1715 (s) cm-1. 1H NMR (CDCl3): δ 3.71 (s, 6H, 2CH3),
4.68 (s, 4H, 2H3, 2H4), 5.32 (s, 4H, 2H2, 2H5). 77Se NMR
(CDCl3): δ 2604.6 (s).
P r epar ation of [η5-MeC(O)C5H4Cr (CO)2]2Se2 (5). Meth od
i. A mixture of 0.243 g (0.50 mmol) of [η5-MeC(O)C5H4Cr-
(CO)3]2, 0.158 g (2.00 mmol) of selenium powder, and 20 mL
of THF was stirred at room temperature for 16 h, causing a
color change from dark green to brown-green. The solvent was
removed under vacuum, and the residue was subjected to
column chromatography with 1:2 (v/v) acetone/petroleum ether
as eluent. A brown-green band was collected, from which 5
was obtained. 5: brown green solid, yield 0.241 g (0.41 mmol,
82%); mp 140-141 °C. Anal. Calcd for C18H14Cr2O6Se2: C,
(28) Grayson, M.; Keough, P. T. J . Am. Chem. Soc. 1960, 82, 3919.
(29) Gilman, H.; Moore, F. W.; Baine, O. J . Am. Chem. Soc. 1941,
63, 2479.
(30) Gilman, H.; Zoellner, E. A.; Dickey, J . B. J . Am. Chem. Soc.
1929, 51, 1576.

Metal Cyclopentadienyl Complexes
Organometallics, Vol. 23, No. 5, 2004 1079
36.75; H, 2.40. Found: C, 36.71; H, 2.50. IR (KBr disk): νC≡O
From the first band (Rf ) 0.75) was obtained 0.040 g (0.05
mmol, 24%) of (η5-MeO2CC5H4)Cp3Cr4Se4 (9) as a black solid,
mp 186-187 °C. Anal. Calcd for C22H22Cr4O2Se4: C, 31.37; H,
2.63. Found: C, 33.53; H, 2.77. IR (KBr disk): νCdO 1719 (s)
1
1954 (vs), 1890 (vs); νCdO 1676 (s) cm-1. H NMR (CDCl3): δ
2.24 (s, 6H, 2CH3), 5.02 (s, 4H, 2H3, 2H4), 5.60 (s, 4H, 2H2,
2H5). 77Se NMR (CDCl3): δ -257.4 (s).
1
cm-1. H NMR (CDCl3): δ 3.54 (s, 3H, CH3), 26.24 (s, 2H, H3,
Meth od ii. A mixture of 0.255 g (0.50 mmol) of [η5-
MeC(O)C5H4Cr(CO)2]2Se, 0.040 g (0.50 mmol) of selenium
powder, and 20 mL of THF was stirred at ca. 45 °C for 1.5 h,
resulting in a color change from brown red to brown-green.
The same workup as that in method i gave 0.209 g (0.36 mmol,
71%) of 5.
H4), 29.19 (s, 15H, 3C5H5), 31.80 (s, 2H, H2, H5). 77Se NMR
(CDCl3): δ 1105.5 (s).
From the second band (Rf ) 0.66) was obtained 0.065 g (0.07
mmol, 36%) of (η5-MeO2CC5H4)2Cp2Cr4Se4 (10) as a black solid,
mp 174-175 °C. Anal. Calcd for C24H24Cr4O4Se4: C, 32.02; H,
2.69. Found: C, 32.23; H, 2.76. IR (KBr disk): νCdO 1719 (s)
P r epa r a tion of [η5-MeO2CC5H4Cr (CO)2]2Se2 (6). Meth od
i. The same procedure as for method i for the preparation of 5
was followed, except that 0.259 g (0.50 mmol) of [η5-MeO2-
CC5H4Cr(CO)3]2 was utilized. 6: brown-green solid, yield 0.260
cm-1 1H NMR (CDCl3): δ 3.55 (s, 6H, 2CH3), 26.93 (s, 4H,
.
2H3, 2H4), 29.60 (s, 10H, 2C5H5), 32.09 (s, 4H, 2H2, 2H5). 77Se
NMR (CDCl3): δ 1161.2 (s).
g (0.42 mmol, 84%); mp 135-136 °C. Anal. Calcd for C18H14
-
From the third band (Rf ) 0.55) was obtained 0.048 g (0.05
mmol, 25%) of (η5-MeO2CC5H4)3CpCr4Se4 (11) as a black solid,
mp 193-194 °C. Anal. Calcd for C26H26Cr4O6Se4: C, 32.59; H,
2.73. Found: C, 32.53; H, 2.69. IR (KBr disk): νCdO 1718 (s)
cm-1. 1H NMR (CDCl3): δ 3.68 (s, 9H, 3CH3), 5.01 (s, 6H, 3H3,
3H4), 5.07 (s, 5H, C5H5), 5.87 (s, 6H, 3H2, 3H5). 77Se NMR
(CDCl3): δ 1215.3 (s).
From the fourth band (Rf ) 0.43) was obtained 0.013 g (0.01
mmol, 6%) of (η5-MeO2CC5H4)4Cr4Se4 (8) identified by com-
parison of its IR and 1H NMR spectra with those of the fully
characterized sample described above. The immovable base
band was collected and refluxed with 10 mL of bromobenzene
for 10 min. After cooling to room temperature, the mixture
was filtered and the filtrate was centrifuged to give a clear
centrifugate, from which 0.007 g (0.01 mmol, 5%) of Cp4Cr4-
Se4 was obtained.
Attem p ted Cp /η5-RC5H4 Liga n d Exch a n ge betw een
Cp 4Cr 4Se4 a n d [η5-RC5H4]4Cr 4Se4 (8, R ) MeO2C). A
mixture consisting of 0.078 g (0.10 mmol) of Cp4Cr4Se4 and
0.102 g (0.10 mmol) of 8 in 20 mL of THF was stirred at reflux
for 10 h. The resulting mixture was concentrated to ca. 5 mL,
which was subjected to TLC separation using 1:3:3 (v/v/v)
acetone/CH2Cl2/petroleum ether as eluent to develop only one
brown-green band. From this band 0.086 g (0.08 mmol, 84%)
of 8 was recovered, while from the immovable band 0.048 g
(0.06 mmol, 62%) of Cp4Cr4Se4 was recovered. No ligand
exchange products of [η5-MeO2CC5H4]nCp4-nCr4Se4 (n ) 1-3,
9-11) were formed.
Cr2O8Se2: C, 34.86; H, 2.28. Found: C, 34.68; H, 2.29. IR (KBr
1
disk): νC≡O 1950 (vs), 1880 (vs); νCdO 1717 (s) cm-1. H NMR
(CDCl3): δ 3.76 (s, 6H, 2CH3), 4.92 (s, 4H, 2H3, 2H4), 5.30 (s,
4H, 2H2, 2H5). 77Se NMR (CDCl3): δ -266.8 (s).
Meth od ii. The same procedure was followed as for method
ii for 5, but 0.271 g (0.50 mmol) of [η5-MeO2CC5H4Cr(CO)2]2Se
was utilized. 6: 0.232 g (0.38 mmol, 75%).
P r ep a r a tion of [η5-MeC(O)C5H4]4Cr 4Se4 (7). Meth od i.
A green suspension of 0.243 g (0.50 mmol) of [η5-MeC(O)C5H4-
Cr(CO)3]2 and 0.158 g (2.00 mmol) of selenium powder in 20
mL of THF was stirred at reflux for 8 h, and then the solvent
was removed at reduced pressure to give a brown-black
residue, which was extracted with dichloromethane. The
extracts were evaporated to dryness and then recrystallized
in CH2Cl2/petroleum ether to give product 7. 7: greenish black
solid, yield 0.224 g (0.24 mmol, 94%); mp 223-224 °C. Anal.
Calcd for C28H28Cr4O4Se4: C, 35.31; H, 2.96. Found: C, 35.33;
1
H, 3.10. IR (KBr disk): νCdO 1664 (s) cm-1. H NMR (CDCl3):
δ 2.23 (s, 12H, 4CH3), 4.95 (s, 8H, 4H3, 4H4), 5.78 (s, 8H, 4H2,
4H5). 77Se NMR (CDCl3): δ 1226.2 (s).
Meth od ii. A red suspension of 0.255 g (0.50 mmol) of [η5-
MeC(O)C5H4Cr(CO)2]2Se and 0.040 g (0.50 mmol) of selenium
powder in 20 mL of THF was stirred at reflux for 8 h to give
a brown-green mixture. The same workup as that for method
i afforded 0.226 g (0.24 mmol, 95%) of 7.
Meth od iii. A brown-green solution of 0.118 g (0.20 mmol)
of [η5-MeC(O)C5H4Cr(CO)2]2Se2 in 20 mL of THF was stirred
at reflux for 8 h, and the same workup as that for method i
gave 0.087 g (0.09 mmol, 91%) of 7.
P r ep a r a tion of (η5-MeO2CC5H4)4Cr 4Se4 (8). Meth od i.
The same procedure as for method i for the preparation of 7
was followed, but 0.259 g (0.50 mmol) of [η5-MeO2CC5H4Cr-
(CO)3]2 was employed. 8: greenish black solid, yield 0.236 g
P r ep a r a tion of [η5-MeCH(OH)C5H4]4Cr 4Se4 (12). A 100
mL Schlenk flask was charged with 0.190 g (0.20 mmol) of
[η5-MeC(O)C5H4]4Cr4Se4 in 15 mL of CH2Cl2 and 0.061 g (1.60
mmol) of NaBH4 in 15 mL of MeOH. The mixture was stirred
at ca. 45 °C for 10 h. After removal of the solvents under
reduced pressure, the residue was extracted with CH2Cl2. The
extracts were concentrated to ca. 5 mL, which was then
subjected to TLC column chromatography. Elution with ac-
etone yielded a green band, from which 12 was obtained. 12:
0.138 g (0.14 mmol, 72%), brown-green solid; mp 164-165 °C.
Anal. Calcd for C28H36Cr4O4Se4: C, 35.02; H, 3.78. Found: C,
(0.23 mmol, 93%); mp 202-203 °C. Anal. Calcd for C28H28
-
Cr4O8Se4: C, 33.09; H, 2.78. Found: C, 32.69; H, 2.73. IR (KBr
disk): νCdO 1716 (s) cm-1 1H NMR (CDCl3): δ 3.70 (s, 12H,
.
4CH3), 4.89 (s, 8H, 4H3, 4H4), 5.76 (s, 8H, 4H2, 4H5). 77Se NMR
(CDCl3): δ 1244.2 (s).
1
Meth od ii. The same procedure as for method ii for the
preparation of 7 was followed, but 0.271 g (0.50 mmol) of [η5-
MeO2CC5H4Cr(CO)2]2Se was used to afford 0.239 g (0.24 mmol,
94%) of 8.
35.16; H, 3.99. IR (KBr disk): νO-H 3371 (vs) cm-1. H NMR
(DMSO): δ 1.15 (d, J ) 3.0 Hz, 12H, 4CH3), 3.15 (s, 4H, 4CH),
4.20 (d, J ) 3.0 Hz, 4H, 4OH), 5.04 (d, 8H, 4H3, 4H4), 5.40 (s,
8H, 4H2, 4H5). 77Se NMR (CDCl3): δ 996.2 (s).
P r ep a r a tion of [η5-Me2C(OH)C5H4]4Cr 4Se4 (13). To a
deep green solution of 0.190 g (0.20 mmol) of [η5-MeC(O)C5H4]4-
Cr4Se4 in 15 mL of THF, while stirring at room temperature,
was dropwise added 2 mL (1.6 mmol) of MeMgI/diethyl ether
solution. The mixture was stirred at this temperature for 8 h,
and then 25 mL (ca. 2 mmol) of diluted HCl was added. The
mixture was stirred for an additional 20 min and then was
extracted with 3 × 10 mL of CH2Cl2. The extracts were dried
over anhydrous Na2SO4. After removal of Na2SO4, the filtrate
was concentrated to ca. 5 mL, which was subjected to TLC
separation. Elution with 1:3:3 (v/v/v) acetone/CH2Cl2/petroleum
ether afforded a brown-green band, from which 13 was
obtained. 13: 0.134 g (0.13 mmol, 66%), brown green solid;
mp 178-179 °C. Anal. Calcd for C32H44Cr4O4Se4: C, 37.81; H,
Meth od iii. The same procedure as for method iii for the
preparation of 7 was followed, but 0.124 g (0.20 mmol) of [η5-
MeO2CC5H4Cr(CO)2]2Se2 was used to give 0.094 g (0.09 mmol,
92%) of 8.
P r ep a r a tion of [η5-MeO2CC5H4]n Cp 4-n Cr 4Se4 (n ) 0,
Cp 4Cr 4Se4; n ) 4, 8; n ) 1-3, 9-11). A mixture consisting
of 0.101 g (0.20 mmol) of [CpCr(CO)2]2Se2, 0.124 g (0.20 mmol)
of [η5-MeO2CC5H4Cr(CO)2]2Se2, and 20 mL of THF was stirred
and refluxed for 8 h, resulting in a color change from brown-
green to dark green. The mixture was centrifuged to give a
clear centrifugate, which was concentrated to ca. 5 mL and
then was subjected to TLC separation using 1:2:6 (v/v/v)
acetone/CH2Cl2/petroleum ether as eluent to develop four
brown-green bands.

1080 Organometallics, Vol. 23, No. 5, 2004
Ta ble 3. Cr ysta l Da ta a n d Str u ctu r a l Refin em en t Deta ils for 4, 7, 8,11, a n d 12
Song et al.
4
7
8
11
12
empirical formula
C
18H14Cr2O8Se
C28H28Cr4O4Se4
C
28H28Cr4O8Se4
C
26H26Cr4O6Se4
C
28H36Cr4O4Se4‚
H2O
fw
541.25
952.34
1016.34
958.31
978.42
cryst syst
space group
a, Å
b, Å
c, Å
monoclinic
C2/c
10.787(6)
8.057(5)
23.448(14)
90
96.548(11)
90
2025(2)
tetragonal
I4h
10.809(6)
10.809(6)
13.197(15)
90
90
90
1542(2)
2
2.051
triclinic
P1h
triclinic
P1h
9.777(5)
10.028(6)
16.758(10)
93.260(9)
96.725(9)
111.474(9)
1509.5(15)
2
tetragonal
I4h
11.068(3)
11.068(3)
12.901(6)
90
10.036(3)
10.779(3)
16.581(5)
73.849(5)
77.721(5)
65.921(4)
1562.9(8)
2
R, deg
â, deg
90
90
γ, deg
V, Å3
1580.3(10)
2
2.056
Z
4
d(calcd), Mg/m3
abs coeff, mm-1
cryst size, mm
F(000)
1.776
2.913
2.160
6.060
2.108
6.263
6.126
5.982
0.24 × 0.12 × 0.06
0.24 × 0.20 × 0.14
0.40 × 0.25 × 0.05
0.30 × 0.20 × 0.15
0.25 × 0.15 × 0.06
1072
920
984
924
956
θ range, deg
no. of reflns
no. of indep reflns
index ranges
3.16-25.00
4419
2.44-26.34
3081
2.12-25.02
6499
1.23-25.03
6163
2.42-25.03
3261
1618 (Rint) 0.0787)
-10 e h e 12
-6 e k e 9
-27 e l e 27
1618/0/134
1546 (Rint) 0.0580)
-11 e h e 12
-3 e k e 13
-16 e l e 16
1546/6/104
5473 (Rint ) 0.041)
-11 e h e 9
-12 e k e 12
-19 e l e 14
5473/0/379
5257 (Rint)0.0343)
-8 e h e 11
-11 e k e 11
-19 e l e 19
5257/0/361
1391 (Rint) 0.1027)
-12 e h e 13
-13 e k e 11
-14 e l e 15
1391/3/93
no. of data/restraints/
params
goodness of fit on F2
final R indices
(obsd data)
1.034
R1 ) 0.0683,
0.992
R1 ) 0.0581,
0.983
R1 ) 0.0514,
1.108
R1 ) 0.0575,
0.982
R1 ) 0.0 576,
wR2 ) 0.1628
R1 ) 0.1007,
wR2 ) 0.1369
R1 ) 0.0699,
wR2 ) 0.1262
R1 ) 0.0721,
wR2 ) 0.1398
R1 ) 0.0921,
wR2 ) 0.1363
R1 ) 0.1417,
R indices
(all data)
wR2 ) 0.1799
0.993/-0.457
wR2 ) 0.1436
1.943/-1.199
wR2 ) 0.1407
1.287/ -1.883
wR2 ) 0.1545
1.267/-1.027
wR2 ) 0.1713
0.983/-0.495
largest diff peak and
hole, e Å-3
4.36. Found: C, 38.08; H, 4.46. IR (KBr disk): νO-H 3375 (vs)
4CH3), 5.15 (s, 8H, 4H3, 4H4), 5.68 (s, 8H, 4H2, 4H5), 8.31 (d,
J ) 6.6 Hz, 4H, 4H6 of benzene ring), 8.66 (d, J ) 8.5 Hz, 4H,
4H5 of benzene ring), 9.41 (s, 4H, 4H3 of benzene ring), 10.64
(s, 4H, NH). 77Se NMR (CDCl3): δ 1274.7 (s).
cm-1 1H NMR (CDCl3): δ 1.23 (s, 24H, 8CH3), 4.07 (s, 4H,
.
4OH), 5.09 (s, 8H, 4H3, 4H4), 5.94 (s, 8H, 4H2, 4H5). 77Se NMR
(CDCl3): δ 1005.7 (s).
P r ep a r a tion of [η5-P h CHdC(Me)C5H4]4Cr 4Se4 (14). A
100 mL Schlenk flask was charged with 0.190 g (0.20 mmol)
of [η5-MeC(O)C5H4]4Cr4Se4, 0.692 g (1.60 mmol) of Ph3(CH2-
Ph)PBr, 20 mL of CHCl3, and 0.640 g (16 mmol) of NaOH in
5 mL of MeOH. The mixture was stirred at reflux for 1 h,
during which time the in situ generated Wittig reagent Ph3Pd
CHPh28 had completed its reaction with [η5-MeC(O)C5H4]4Cr4-
Se4. The mixture was cooled to room temperature, and 30 mL
of H2O was added. The organic layer was separated and dried
over anhydrous Na2SO4. After removal of Na2SO4, the filtrate
was reduced to ca. 5 mL, which was subjected to TLC
separation. Elution using 1:2:3 (v/v/v) acetone/petroleum ether/
CH2Cl2 gave a brown-green band, from which 14 was obtained.
14: 0.168 g (0.13 mmol, 67%), black solid; mp 203-205 °C.
Anal. Calcd for C56H52Cr4Se4: C, 53.86; H, 4.20. Found: C,
X-r a y Cr ysta l Str u ctu r e Deter m in a tion s of 4, 7, 8, 11,
a n d 12. Single crystals of 4, 7, 8, 11, and 12 suitable for X-ray
diffraction analysis were grown by slow evaporation of a
hexane solution of 4, a hexane/CH2Cl2 solution of 7 or 8, and
a hexane/EtOH solution of 12 at room temperature and slow
diffusion of hexane into a toluene solution of 11 at room
temperature for several days, respectively. Each of the single
crystals was glued to a glass fiber and mounted on a Bruker
SMART 1000 automated diffractometer, respectively. Data
were collected at room temperature, using Mo KR graphite-
monochromated radiation (λ ) 0.71073 Å) in the ω-2θ
scanning mode. Absorption corrections were performed using
SADABS. The structures were solved by direct methods using
the SHELXTL-97 program and refined by full-matrix least-
squares techniques (SHELXL-97) on F2. Hydrogen atoms were
located by using the geometric method. All calculations were
performed on a Bruker Smart computer. Details of the crystals,
data collections, and structure refinements are summarized
in Table 3.
53.47; H, 4.09. IR (KBr disk): νCdC 1630 (s) cm-1 1H NMR
.
(CDCl3): δ 1.57 (s, 12H, 4CH3), 4.79 (s, 4H, 4CH), 5.12 (s, 8H,
4H3, 4H4), 5.67 (s, 8H, 4H2, 4H5), 7.29-7.40 (m, 20H, 4C6H5).
77Se NMR (CDCl3): δ 991.5 (s).
5
P r e p a r a t ion
of
[η -2,4-(NO2)2C6H 3NH NC(Me )-
C5H4]4Cr 4Se4 (15). To a deep green solution of 0.190 g (0.20
mmol) of [η5-MeC(O)C5H4]4Cr4Se4 in 20 mL of CHCl3 was
added 9.6 mL (ca. 1.60 mmol) of 2,4-dinitrophenylhydrazine
solution (prepared by dissolving 1.0 g of 2,4-dinitrophenylhy-
drazine in 5 mL of 98% H2SO4, 10 mL of H2O, and 35 mL of
95% EtOH). The mixture was stirred at reflux for 2 h and then
cooled to room temperature. The same workup as that for 14
produced 15. 15: 0.174 g (0.10 mmol, 52%), brown solid; mp
> 280 °C. Anal. Calcd for C52H44Cr4N16O16Se4: C, 37.34; H,
2.65; N, 13.40. Found: C, 37.00; H, 2.54; N, 13.16. IR (KBr
Ack n ow led gm en t. We are grateful to the National
Natural Science Foundation of China and the Research
Fund for the Doctoral Program of Higher Education of
China for financial support of this work.
Su p p or tin g In for m a tion Ava ila ble: An X-ray crystal-
lographic file for 4, 7, 8, 11, and 12 in CIF format. This
material is available free of charge via the Internet at
http://pubs.acs.org.
disk): νCdN 1618 (s) cm-1
.
1H NMR (CDCl3): δ 1.64 (s, 12H,
OM034283Q