Novel Rearrangement Reactions. 6. Thermal Rearrangement of Disilyl-Bridged Diiron Complexes Containing Isocyanide Ligands and Stereochemistry of the Rearranged Products

Article abstract of DOI:10.1021/om9902683

Treatment of (Me₂SiSiMe₂)[(η⁵-C₅H ₃R¹)Fe(CO)]₂(μ-CO)₂ (R¹ = H (1), R¹ = t-Bu (5)) with R²NC (R² = C₆H¹¹, t-Bu) in benzene afforded isocyanide-substituted complexes [(η⁵:η⁵-C₅H₃R ¹-Me₂SiSiMe₂C₅H₃R ¹)Fe₂(CO)(CNR²)(μ-CO)₂] (R¹ = H, R² = C₆H₁₁ (3), R² = t-Bu (4); R¹ = R² = t-Bu (6)). Further investigations indicated that the cis substrate 5c afforded only the cis product (6c), while the trans substrate 5t afforded only the trans product (6t). When 3 and 4 were heated respectively in xylene, three different rearranged products [{(Me₂Si)(η⁵-C₅H₄)-Fe(CO)L ₁}{(Me₂Si)(η⁵-C₅H ₄)Fe(CO)L₂}] (L₁ = L₂ - CO (2); L₁ = C₆H₁₁NC, L₂ = CO (7), L₂ = C₆H₁₁NC (9); L₁ = t-BuNC, L₂ = CO (8), L₂ = t-BuNC (10)) were obtained. Similarly, thermal treatment of 6t afforded three different cis rearranged products, 11c, 12c, and 13c, while treatment of 6c yielded three different trans rearranged products, 11t, 12t, and 13t. This indicated that the rearrangement still follows the reaction mechanism proposed previously on the basis of the intramolecular nature of this reaction if we only take into account the configuration of two tert-butyl groups on the Cp rings. To explain the formation of three different products, an alternative mechanism involving free ligand exchange to form three different iron-centered radical intermediates is proposed as a supplement to the previous mechanism. The complex stereochemistry in the molecules of 12 and 13 is discussed. Molecular structures of 8, 9t, 12t, and 13c have been determined by single-crystal X-ray diffraction.

Full text of DOI:10.1021/om9902683

Organometallics 1999, 18, 4493-4500
4493
Novel Rea r r a n gem en t Rea ction s. 6. Th er m a l
Rea r r a n gem en t of Disilyl-Br id ged Diir on Com p lexes
Con ta in in g Isocya n id e Liga n d s a n d Ster eoch em istr y of
th e Rea r r a n ged P r od u cts
Yongqiang Zhang, Xiuli Sun, Baiquan Wang, Shansheng Xu, and
Xiuzhong Zhou*
Department of Chemistry, State Key Laboratory of Elemento-Organic Chemistry,
Nankai University, Tianjin 300071, People’s Republic of China
Received April 14, 1999
Treatment of (Me2SiSiMe2)[(η5-C5H3R1)Fe(CO)]2(µ-CO)2 (R1 ) H (1), R1 ) t-Bu (5)) with
R2NC (R2 ) C6H11, t-Bu) in benzene afforded isocyanide-substituted complexes [(η5:η5-C5H3R1-
Me2SiSiMe2C5H3R1)Fe2(CO)(CNR2)(µ-CO)2] (R1 ) H, R2 ) C6H11 (3), R2 ) t-Bu (4); R1 ) R2
) t-Bu (6)). Further investigations indicated that the cis substrate 5c afforded only the cis
product (6c), while the trans substrate 5t afforded only the trans product (6t). When 3 and
4 were heated respectively in xylene, three different rearranged products [{(Me2Si)(η5-C5H4)-
Fe(CO)L1}{(Me2Si)(η5-C5H4)Fe(CO)L2}] (L1 ) L2 ) CO (2); L1 ) C6H11NC, L2 ) CO (7), L2 )
C6H11NC (9); L1 ) t-BuNC, L2 ) CO (8), L2 ) t-BuNC (10)) were obtained. Similarly, thermal
treatment of 6t afforded three different cis rearranged products, 11c, 12c, and 13c, while
treatment of 6c yielded three different trans rearranged products, 11t, 12t, and 13t. This
indicated that the rearrangement still follows the reaction mechanism proposed previously
on the basis of the intramolecular nature of this reaction if we only take into account the
configuration of two tert-butyl groups on the Cp rings. To explain the formation of three
different products, an alternative mechanism involving free ligand exchange to form three
different iron-centered radical intermediates is proposed as a supplement to the previous
mechanism. The complex stereochemistry in the molecules of 12 and 13 is discussed.
Molecular structures of 8, 9t, 12t, and 13c have been determined by single-crystal X-ray
diffraction.
In tr od u ction
during which one Fe-Fe bond and one Si-Si bond were
cleaved and two Si-Fe bonds were simultaneously
Extensive investigations on a variety of transition
metal complexes that activate or contain a silicon-
silicon bond revealed some unique chemical properties
such as base-induced migration,1 photoisomerization,2
and silylene elimination and rearrangement.3 We re-
cently observed that when the dinuclear iron complex
(Me2SiSiMe2)[(η5-C5H4)Fe(CO)]2(µ-CO)2 (1) was heated
at reflux in xylene, an intramolecular rearrangement
reaction between Si-Si and Fe-Fe bonds occurred,
formed (eq 1).4 On the basis of detailed investigations
* Corresponding author. Fax: 0086-22-23502458. Tel: 0086-22-
23504781. E-mail: zhouxz@public1.tpt.tj.cn.
of the rearrangement stereospecificity, reaction inter-
mediates, and crossover reaction, an alternative mech-
anism was subsequently proposed,5 which was further
confirmed by investigating thermal rearrangement
reactions of tetrahydroindenyl complexes (Me2SiSiMe2)-
[(η5-IndH4)Fe(CO)]2(µ-CO)2 and phosphite-substituted
(1) (a) Berryhill, S. R.; Sharenow, B. J . J . Organomet. Chem. 1981,
221, 143. (b) Thum, G.; Ries, W.; Malish, W. J . Organomet. Chem. 1983,
252, C67. (c) Berryhill, S. R.; Clevenger, G. L.; Burdurli, Y. P.
Organometallics 1985, 4, 1509. (d) Heal, P. C.; Gladysz, J . A. J . Am.
Chem. Soc. 1984, 106, 7636. (e) Crocco, G. L.; Gladysz, J . A. J . Chem.
Soc., Chem. Commun. 1985, 283. (f) Pannell, K. H.; Rozell, J . M.; Li,
J .; Tien-Mayr, S.-Y. Organometallics 1988, 7, 2525. (g) Pannell, K. H.;
Hernandez, C.; Cervantes, J .; Cassias, J .; Vincenti, S. Organometallics
1986, 5, 1056. (h) Crocco, J . L.; Young, C. S.; Lee, K. E.; Gladysz, J . A.
Organometallics 1988, 7, 2158. (i) Pannell, K. H. Cervantes, J .;
Parkanyi, L.; Cervantes-Lee, F. Organometallics 1990, 9, 859.
(2) (a) Pannell, K. H.; Rice, J . R. J . Organomet. Chem. 1974, 78,
C35. (b) Hernandez, C.; Sharma, H. K.; Pannell, K. H. J . Organomet.
Chem. 1993, 462, 259. (c) Pannell, K. H.; Rozell, J . M.; Hernandez, C.
J . Am. Chem. Soc. 1989, 111, 4482. (d) J ones, K. L.; Pannell, K. H. J .
Am. Chem. Soc. 1993, 115, 11336. (e) Tobita, H.; Ueno, K.; Ogino, H.
Chem. Lett. 1986, 1777. (f) Ueno, K.; Tobita, H.; Ogino, H. Chem. Lett.
1990, 369. (g) Pannell, K. H.; Wang, L.-J .; Rozell, J . M. Organometallics
1989, 8, 550.
(3) (a) Pannell, K. H.; Brun, M.-C.; Sharma, H.; J ones, K.; Sharma,
S. Organometallics 1994, 13, 1075. (b) Haynes, A.; George, M. W.;
Haward, M. T.; Poliakoff, M.; Turner, J . J .; Boag, N. M.; Green, M. J .
Am. Chem. Soc. 1991, 113, 2011. (c) Takeuchi, T.; Tobita, H.; Ogino,
H. Organometallics 1991, 10, 835. (d) Tobita, H.; Wada, H.; Ueno, K.;
Ogino, H. Organometallics 1994, 13, 2545.
(4) Sun, H.; Xu, S.; Zhou, X.; Wang, H.; Wang, R.; Yao, X. J .
Organomet. Chem. 1993, 444, C41.
(5) Zhou, X.; Zhang, Y.; Xie, W.; Xu, S.; Sun, J . Organometallics
1997, 16, 3474.
10.1021/om9902683 CCC: $18.00 © 1999 American Chemical Society
Publication on Web 10/07/1999

4494 Organometallics, Vol. 18, No. 22, 1999
Zhang et al.
complexes [(η5:η5-t-BuC5H3Me2SiSiMe2C5H3-t-Bu)Fe2-
(CO)P(OPh)3(µ-CO)2].6 More recently ruthenium and
germanium analogues have been shown to undergo
similar rearrangement.7 We report herein thermal
rearrangements of disilyl-bridged diiron complexes with
a terminal-substituted isocyanide ligand and stereo-
chemistry and structures of the rearranged products.
were refluxed in bezene to afford only the cis isocyanide-
substituted complex 6c, whereas similar treatment of
5t yielded only the trans isomer 6t (eq 3). This indicated
Resu lts a n d Discu ssion
CO-Su bstitu tion Rea ction s of (Me2SiSiMe2)[(η5-
C5H4)F e(CO)]2(µ-CO)2 (1). The replacement of carbo-
nyl groups by isocyanide ligands in diiron complex [(η5-
8
C5H5)Fe(CO)2]2 and its bridging analogues,9 either by
photolysis or themal process in benzene, was well
established. Treatment of 1 with a 3-fold excess amount
of isocyanide ligands in bezene at ambient temperature
afforded isocyanide-subsitituted complexes 3 and 4 (eq
2). The investigations indicated that only one terminal
that the CO-substitution reaction of bridged diiron
species by isocyanide ligands did not influence the
substituent configuration. Compared with the parent
complex 1, whose CO-substitution reaction could pro-
ceed facilely at room temperature, the CO-substitution
reaction of 5 was more difficult. This should be at-
tributed to substitution of bulky tert-butyl groups on the
Cp rings.
The cis isomer 6c is dark red crystals, while the trans
1
isomer 6t is green solids. In the H NMR spectrum of
6c, four chemically nonequivalent silicon methyl groups
exhibit three singlets, suggesting the overlap of two
silicon methyl proton signals, and two chemically non-
equivalent tert-butyl groups on the Cp rings indicate one
singlet. Four silicon methyl groups of 6t exhibit four
singlets, and two tert-butyl groups show two rather close
singlets. Their IR spectra give rise to only absorptions
of terminal isocyanide ligands. This indicates that only
terminal carbonyl groups were replaced by tert-butyl
isocyanide ligands.
Th er m a l Rea r r a n gem en t Rea ction s of 3 a n d 4.
Complex 3 was heated at reflux in xylene for 24 h,
surprisingly affording three different products, 2 with-
out substituted isocyanide ligands, 7 with a monosub-
stituted isocyanide ligand (the expected rearranged
product), and 9 with disubstituted isocyanide ligands.
Similar treatment of 4 also afforded three different
products: 2, 8, and 10 (eq 4). Since each iron atom in
CO group was replaced, whether at ambient tempera-
ture or in boiling bezene, which is in contrast to the case
in the nonbridged analogue [(η5-C5H5)Fe(CO)2]2. The 1H
NMR spectra of 3 and 4 exhibit two groups of cyclopen-
tadienyl proton resonance of equal intensity, each
consisting of two singlets (R and â parts of the Cp ring).
This is consistent with an asymmetric molecular struc-
ture containing two nonequivalent cyclopentadienyl
rings. The group to higher field is assigned to the
cyclopentadienyl ring bonded to the same iron atoms
as the isocyanide ligands.6b,10 Their IR spectra exhibit
absorptions of only terminal isocyanide ligands (KBr,
2105 (3) and 2110 (4) cm-1; CH2Cl2, 2112 (3) and 2115-
(4) cm-1). This indicates that 3 and 4 exist as isocyanide
terminal isomers in the solid state as well as in solution.
This also implies that the process of bridge-terminal
interchange between isocyanide ligands and carbonyl
groups, suggested as the Adams-Cotton mechanism,11
cannot occur at room temperature.
CO-Su bstitu tion Rea ction s of (Me2SiSiMe2)[(η5-
t-Bu C5H3)F e(CO)]2(µ-CO)2 (5). The cis isomer 5c and
a 3-fold excess amount of tert-butyl isocyanide ligands
(6) (a) Wang, B.; Zhang, Y.; Xu, S.; Zhou, X. Organometallics 1997,
16, 6, 4620. (b) Zhang, Y.; Xu, S.; Tian, G.; Zhou, X.; Sun, J .
Organometallics 1998, 17, 1122.
(7) (a) Zhang, Y.; Xu, S.; Zhou, X. Organometallics 1997, 16, 6017.
(b) Xie, W.; Wang B.; Xu, S.; Zhou, X. Organometallics 1998, 17, 6017.
(8) (a) Cotton, F. A.; Frenz, B. A. Inorg. Chem. 1974, 13, 253. (b)
Adams, R. D.; Cotton, F. A.; Troup, J . M. Inorg. Chem. 1974, 13, 257.
(c) Bellerby, J .; Boylan, M. J .; Ennis, M.; Manning A. R. J . Chem. Soc.,
Dalton Trans. 1978, 1185. (d) Ennis, M.; Kumar, R.; Manning A. R.;
Howell, J . A. S.; Mathur, P.; Bowan, A. J .; Stephens, F. S. J . Chem.
Soc., Dalton Trans. 1981, 1251.
(9) (a) Nakanishi, S.; Tanikia, Y.; Otsuji, Y. Bull. Chem. Soc. J pn.
1992, 65, 2309. (b) Manning, A. R.; Boss, K.; Cox, M. G.; McCabe, A.;
Soye, P.; Wade, S. C.; McArdle, D.; Cunningham, D. L. J . Organomet.
Chem. 1995, 487, 151.
(10) Haines, R. J .; DuPreez, A. L. Inorg. Chem. 1969, 8, 1459.
(11) Adams, R. D.; Cotton, F. A. J . Am. Chem. Soc. 1973, 95, 6589.

Novel Rearrangement Reactions
Organometallics, Vol. 18, No. 22, 1999 4495
F igu r e 1. ORTEP drawing of 8.
Ta ble 1. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for 8
F igu r e 2. ORTEP drawing of 9t.
Bond Distances (Å)
Fe(1)-Si(1)
Fe(1)-C(1)
Fe(2)-C(3)
C(4)-N
2.320(1)
1.733(4)
1.726(4)
1.163(4)
1.728a
Fe(2)-Si(2)
Fe(1)-C(2)
Fe(2)-C(4)
N-C(19)
2.296(1)
1.737(4)
1.810(4)
1.451(4)
1.732a
Ta ble 2. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for 9t
Bond Distances (Å)
Fe(1)-Si(1)
Fe(1)-C(2)
C(2)-N(1)
2.285(3)
1.786(7)
1.165(8)
Fe(1)-C(1)
N(1)-C(21)
Si(1)-C(11a)
1.735(9)
1.431(9)
1.885(7)
Fe(1)-Cp(1)
Fe(2)-Cp(2)
Bond Angles (deg)
132.7(2) Fe(2)-C(14)-Si(1) 128.8(2)
Fe(2)-Si(2)-C(9) 113.6(1)
99.14(9) Si(2)-Fe(2)-C(14) 100.74(9)
178.3(3) C(4)-N-C(19) 167.5(4)
Fe(1)-C(9)-Si(2)
Bond Angles (deg)
Fe(1)-Si(1)-C(14) 111.1(4)
Fe(1)-C(11)-Si(1a) 131.4(4) Fe(1)-Si(1)-C(11a) 112.9(3)
Si(1)-Fe(1)-C(9)
Fe(2)-C(4)-N
Si(1)-Fe(1)-C(11)
Fe(1)-C(2)-N(1)
100.4(2) C(1)-Fe(1)-C(2)
177.8(7) C(2)-N(1)-C(21)
95.3(4)
175.2(8)
a
Distances from the centroid of the Cp ring to the corresponding
Fe atom.
molecular framework adopts a twist-boat conformation.
This is different from the parent analogue 2,4 which has
Ci symmetry, and the corresponding six-membered ring
adopts a chair conformation. The two Fe-Si bonds
(2.320(1) and 2.296(1) Å) is different: one is much close
to that of 2 (2.315(2) Å), and the other linked with
isocyanide ligands is shorter than that of 2. This
indicates that the weaker interaction between isocya-
nide ligands and iron atoms strengthens the Fe-Si
bond. The dihedral angle between the two Cp ring
planes is 7.11°, while the two Cp rings of 2 are parallel
to each other. The Si(1) and Si(2) atoms are bent out of
the corresponding Cp rings by 0.109 and 0.226 Å,
respectively.
The ORTEP drawing of 9t is shown in Figure 2.
Selected bond distances and angles are summarized in
Table 2. The molecule consists of two (Me2Si)[(η5-C5H4)-
Fe(CO)(CNC6H11)] moieties linked to each other by two
head-to-tail Fe-Si bonds. The molecule has Ci sym-
metry, with two isocyanide ligands adopting a trans
configuration. The six-membered ring Fe1-C11-Si1a-
Fe1a-C11a-Si1 constituting the molecular framework
adopts a precise chair conformation. The cyclohexyl
group adopts a chair conformation, with the isocyanide
ligand being equitorial. The Fe-Si bond (2.285(3) Å) is
shorter than that of 2 (2.315(2) Å) and much shorter
than those in acyclic molecules (2.346-2.363 Å),12 which
accounts for greater stability of the rearranged products.
Th er m a l Rea r r a n gem en t Rea ction s of 6c a n d 6t.
As described above, thermal treatment of 6c in boiling
xylene for 24 h surprisingly afforded three different
the molecules of 9 and 10 is linked with four different
ligands, each of them can be considered as a chiral
center. Thus the isomer with two isocyanide ligands
adopting a trans configuration is meso, while the other
one with two isocyanide ligands taking a cis configura-
tion is racemic.
For complex 9 with disubstituted cyclohexyl isocya-
nide ligands, only the trans isomer 9t (meso) was
isolated, which has been determined by single-crystal
X-ray diffraction. While for complex 10, with tert-butyl
isocyanide ligands, both the cis and trans isomers 10c
(rac) and 10t (meso) were obtained. The 1H NMR
spectra of the rearranged products 7 and 8 show that
the four methyl groups on the silicon atoms are all
nonequivalent. The 13C NMR spectrum of 8 exhibits four
singlets for four silicon methyl groups, 10 singlets for
two cyclopentadienyl rings, three singlets for carbonyl
groups, and one singlet for one isocyanide ligand. The
29Si NMR signals of 8 appear at 35.5 and 35.7 ppm.
These indicate that 8 has a completely asymmetric
molecular structure, which has been confirmed by
single-crystal X-ray diffraction studies. 10c and 10t
have almost identical 1H NMR spectra except for
different silicon methyl resonances. The isomer with two
singlets for the silicon methyl groups is assigned to the
trans isomer 10t (meso) by comparing its 1H NMR
spectrum with that of 9t.
X-r a y Str u ctu r e Deter m in a tion s of 8 a n d 9t. The
ORTEP drawing of 8 is shown in Figure 1. Selected bond
distances and angles are summarized in Table 1. The
molecule is completely asymmetric, and the six-mem-
bered ring Fe1-C9-Si2-Fe2-C14-Si1 constituting the
(12) Parkanyi, L.; Pannell, K. H.; Hernadez, C. J . Organomet. Chem.
1983, 252, 127.

4496 Organometallics, Vol. 18, No. 22, 1999
Zhang et al.
Ch a r t 1
Ta ble 3. All P ossible Ster eoisom er s of 12 (L1
)
products: 11t5 (the rearranged product of 5c), 12t (the
expected rearranged product), and 13t.13 Similar treat-
ment of 6t also yielded three different products: 11c5
(the rearranged product of 5t), 12c (the expected rear-
ranged product), and 13c (eq 5, in Chart 1).14 Although
the rearrangement results became more complex when
the CO groups in diiron complexes were replaced by
isocyanide ligands, further investigations indicated that
the rearrangement reaction is still stereospecific if we
only consider the configuration of two tert-butyl groups
t-Bu NC, L2 ) CO)a
t-Bu
a1
b1
a2
trans
R(S)
R(S)
R(S)
R(S)
S(R)
S(R)
R(S)
R(S)
R(S)
S(R)
R(S)
S(R)
A(A*)
B(B*)
C(C*)
D(D*)
cis
a
A*, B*, C*, and D* mean the enantiomers of A, B, C, and D.
Ta ble 4. All P ossible Ster eoisom er s of 13 (L1 ) L2
) t-Bu NC)a
1
on the Cp rings. The H NMR spectra of 12t and 12c
show the tert-butyl group of the isocyanide ligand more
downfield than those on the Cp rings (∆δ 0.10 (12t) and
0.16 ppm (12c)). In contrast, their substrates 6c and 6t
show tert-butyl groups on the Cp rings more downfield
than that of the isocyanide ligand (∆δ 0.22 ppm for 6c
and 6t).
t-Bu
a1
b1
a2
b2
trans
R
R
R(S)
R(S)
R(S)
R(S)
S
S
S(R)
R(S)
R(S)
R(S)
R
S
R(S)
R(S)
R(S)
S(R)
S
R
R(S)
S(R)
R(S)
S(R)
E
F
G(G*)
H(H*)
I(I*)
J (J *)
cis
Ster eoch em istr y of th e Rea r r a n ged P r od u cts 12
a n d 13. In the molecules of 12 and 13, one or two CO
groups coordinated to iron atoms are replaced by iso-
cyanide ligands. This increases stereogenic centers in
these molecules, which further complicates their ster-
eochemistry. The molecules of the rearranged products
with an isocyanide ligand have three stereogenic centers
that theoretically imply eight stereomers, four pairs of
enationmers. In the molecules of the rearranged prod-
ucts with disubstituted isocyanide ligands there exist
four stereogenic centers, which imply possible existence
of 16 stereomers. However, the symmetry reduces the
number of stereomers. Thus there exist 10 stereomers,
two of which have Ci symmetry and are meso and the
remaining eight constituting four racemates, namely,
four pairs of enationmers. All possible isomers are
shown in Tables 3 and 4.15
a
G*, H*, I*, and J * mean the enantiomers of G, H, I, and J .
For the monosubstituted product 12, only two race-
mates, two pairs of enationmers, 12c and 12t, were
obtained. 12c may be assigned to isomer C(C*) by
analogy with the molecular structure of its phosphite-
substituted analogue cis-[{(Me2Si)(η5-t-BuC5H3)Fe(CO)2}-
{(Me2Si)(η5-t-BuC5H3)FeP(OPh)3(CO)}].6b 12t has the
molecular structure of A(A*), which has been confirmed
by single-crystal X-ray diffraction. For the disubstituted
product 13, only two racemates, 13c and 13t, were
isolated. The 1H NMR spectrum of 13t shows three
singlets for four silicon methyl groups and two singlets
for two tert-butyl groups on the Cp rings as well as two
singlets for two tert-butyl groups of isocyanide ligands.
This indicates that the molecule is asymmetric and its
structure cannot be assigned to be isomers E and F with
Ci symmetry. Thus 13t should have the molecular
structure of G(G*), as determined by single-crystal
X-ray diffraction (see Supporting Information). 13c has
an 1H NMR spectrum almost identical to that of 13t
(13) The trans isomers (11t, 12t, and 13t) were designated according
to the trans configuration of tert-butyl groups on the Cp rings and
without consideration of the configuration of isocyanide ligands. Thus
thermal rearrangement of the cis substrate afforded only the trans
products.
(14) The cis isomers (11c, 12c, and 13c) were designated according
to the cis configuration of tert-butyl groups on the Cp rings and without
consideration of the configuration of isocyanide ligands. Thermal
rearrangement of the trans substrate afforded only the cis products.
Therefore, the rearrangement reaction still follows the high ste-
reospecificity reported before.
(15) Although the Cp carbon atoms (1a and 1b) linked with tert-
butyl groups are not chiral centers, we consider them as chiral centers
in order to discuss stereochemistry more simply and conveniently. In
fact this designation does not influence the result of stereochemistry
in the molecules of 12 and 13.

Novel Rearrangement Reactions
Organometallics, Vol. 18, No. 22, 1999 4497
F igu r e 3. ORTEP drawing of 12t.
Ta ble 5. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for 12t
Bond Distances (Å)
F igu r e 4. ORTEP drawing of 13c.
Fe(1)-Si(1)
Fe(1)-C(1)
Fe(2)-C(3)
C(4)-N
2.317(1)
1.741(4)
1.724(4)
1.165(4)
1.722
Fe(2)-Si(2)
Fe(1)-C(2)
Fe(2)-C(4)
N-C(27)
2.303(1)
1.747(4)
1.804(4)
1.444(4)
1.727
Ta ble 6. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for 13c
Fe(1)-Cp(1)a
Fe(2)-Cp(2)a
Bond Distances (Å)
Fe(1)-Si(1)
Fe(1)-C(1)
Fe(2)-C(3)
C(2)-N(1)
C(4)-N(2)
Fe(1)-Cp(1)a
2.289(2)
1.722(5)
1.723(5)
1.158(5)
1.162(5)
1.725
Fe(2)-Si(2)
Fe(1)-C(2)
Fe(2)-C(4)
N(1)-C(27)
N(2)-C(31)
Fe(2)-Cp(2)a
2.306(2)
1.797(5)
1.798(5)
1.443(6)
1.433(6)
1.733
Bond Angles (deg)
130.2(2) Fe(2)-C(14)-Si(1) 133.7(2)
Fe(2)-Si(2)-C(9) 112.63(10)
100.64(9) Si(2)-Fe(2)-C(14) 100.00(9)
178.3(3) C(4)-N-C(27) 167.6(4)
Fe(1)-C(9)-Si(2)
Fe(1)-Si(1)-C(14) 113.1(1)
Si(1)-Fe(1)-C(9)
Fe(2)-C(4)-N
a
Distances from the centroid of the Cp ring to the corresponding
Bond Angles (deg)
Fe atom.
Fe(1)-C(9)-Si(2)
Fe(1)-Si(1)-C(16)
Si(1)-Fe(1)-C(9)
Fe(1)-C(2)-N(1)
Fe(2)-C(4)-N(2)
133.0(2)
115.2(1)
98.7(1)
177.1(4)
178.3(3)
Fe(2)-C(16)-Si(1)
133.3(2)
116.1(1)
98.7(1)
165.3(5)
164.3(6)
Fe(2)-Si(2)-C(9)
Si(2)-Fe(2)-C(16)
C(2)-N(1)-C(27)
C(4)-N(2)-C(31)
except for the difference of the proton signals on the Cp
rings. The molecular structure of 13c has been deter-
mined to be H(H*) by single-crystal X-ray diffraction.
X-r a y Str u ctu r e Deter m in a tion s of 12t a n d 13c.
The ORTEP drawing of 12t is shown in Figure 3.
Selected bond distances and angles are summarized in
Table 5. The molecule consists of one [(Me2Si)(η5-t-
BuC5H3)Fe(CO)2] moiety and one [(Me2Si)(η5-t-BuC5H4)-
Fe(CO)(CN-t-Bu)] moiety linked to each other by two
head-to-tail Fe-Si bonds. 12t is asymmetric, with two
tert-butyl groups on the Cp rings adopting a trans
configuration. The six-membered ring Fe1-C9-Si2-
Fe2-C14-Si1 constituting the molecular framework
adopts a twist-boat conformation. The two Fe-Si bonds
(2.317(1) and 2.303(1) Å) are close to that of 11t (2.3148-
(8) Å).5 The dihedral angle between the two Cp ring
planes is 5.22°, while the two Cp rings of 11t are parallel
to each other. The Si(1) and Si(2) atoms are bent out of
the corresponding Cp rings by 0.271 and 0.151 Å,
respectively. The distance from the centroid of the Cp
ring to the corresponding Fe atom (mean 1.725 Å) is
equal to that in its parent analogue 11t (1.723 Å).
The ORTEP drawing of 13c is shown in Figure 4.
Selected bond distances and angles are summarized in
Table 6. The molecule consists of two [(Me2Si)(η5-t-
BuC5H3)Fe(CO)(CN-t-Bu)] moieties linked to each other
by two head-to-tail Fe-Si bonds. 13c is also asymmetric,
with two tert-butyl groups on the Cp rings adopting a
cis configuration and two isocyanide tert-butyl groups
taking a trans configuration. The six-membered ring
Fe1-C9-Si2-Fe2-C16-Si1 constituting the molecular
framework adopts a twist-boat conformation. The two
Fe-Si bonds (2.289(2) and 2.306(9) Å) are slightly
a
Distances from the centroid of the Cp ring to the corresponding
Fe atom.
shorter than that of the parent complex 11c (mean 2.317
Å).5 The coordinated isocyanide ligands are not as
collinear as usual (C4-N2-C31 164.3(6)° and C2-N1-
C27 165.3(5)°) due to the high steric congestion of four
tert-butyl groups. The two Cp rings are almost parallel
to each other (dihedral angle 2.1°). The Si(1) and Si(2)
atoms are bent out of the corresponding Cp rings by
0.281 and 0.232 Å, respectively.
Mech a n ism . Although the stereochemistry of the
rearrangement appears rather complex when CO groups
are replaced by tert-butyl isocyanide ligands, the rear-
rangement reaction still follows the high stereospeci-
ficity reported previously (that is, the cis substrate
affords the trans product, while the trans substrate
produces the cis product) if we only take into account
the configuration of two tert-butyl groups on the Cp
rings. Therefore, the reaction mechanism proposed
previously on the basis of the intramolecular nature of
this reaction is also applied to the rearrangement of
isocyanide-substituted analogues.5,6b
However, there still remains the question of why the
thermal rearrangement exhibited such a complex ster-
eochemistry and three different rearranged products
when CO groups were replaced by isocyanide ligands.
•
It is known that Cp*Fe(CO)2 can undergo very rapid
CO exchange with free CO dissolved in the solution.16
Since isocyanide ligands are isostructural to CO groups,

4498 Organometallics, Vol. 18, No. 22, 1999
Zhang et al.
Sch em e 1
Ta ble 7. Yield s of Th er m a l Rea ction P r od u cts of 3,
4, 6c, a n d 6t
we can assume that iron-centered radical intermediates
should undergo very rapid ligand exchange with free
CO and isocyanide ligands dissolved in xylene. A pos-
sible mechanism involving free ligand exchange is
proposed as a supplement to the previously reported
mechanism (Scheme 1). The mechanism involves (i)
initial ligand exchange to form three different iron-
centered radical intermediates, and (ii) subsequent
attack of every different iron-centered radical at the Si-
Si bond by a concerted or stepwise pathway as proposed
previously.5,6b Since isocyanide ligands can freely re-
place any CO group, any isomer could possibly appear
in the reaction products. Why did we obtain only some
isomers? Simple steric factors will make some isomers
energetically favored and facilely formed. However, we
do not exclude the possibility that other isomers could
not be isolated owing to insufficient quantities .
It seems reasonable that an alternative mechanism
involves (i) the disproportionation of the starting sub-
strate to form the other two substrates which thermally
rearrange to the corresponding products or (ii) the
disproportionation of the rearranged product from the
starting substrate to form the other two products.
However, its drawback is rather evident if we carefully
investigate the rearrangement results. First, if the
rearrangement should proceed by a disproportionation
process rather than a ligand exchange process, the first
rearranged products would have the same yield as the
third ones. But all experimental results indicate that
the yields of the first products are twice or three times
as much as those of the third ones (Table 7). In addition,
IR monitoring of the rearrangement reaction of 4
indicated that the other two substrates, 1 and (Me2-
SiSiMe2)[(η5-C5H4)Fe(CN-t-Bu)]2(µ-CO)2, did not form
over the course of the rearrangement. Second, the
thermal reaction products (yield)
substrate
3
4
2 (8%)
7 (20%)
9t (4%)
2 (13%)
2 (11%)a
11t (9%)
11c (7%)
8 (27%)
10c (2%), 10t (3%)
10c (12%), 10t (6%)a
13t (3%)
8 (4%)a
6c
6t
12t (40%)
12c (30%)
13c (2%)
a
In the presence of t-BuNC (2 equiv).
assumption that the rearranged product of the starting
substrate disproportionately forms the other two prod-
ucts can be excluded by the fact that thermal treatment
of a solution of 8 in xylene for 24 h did not yield 2 and
10. Therefore, the disproportionation process is impos-
sible. Furthermore, we studied the thermal rearrange-
ment of 4 in the presence of t-BuNC. The experimental
result showed that the yield of the expected rearrange-
ment product 8, with the monosubstituted isocyanide
ligand, decreases significantly and the yield of the
product 10, with disubstituted isocyanide ligands, in-
creases evidently in the presence of 2 equiv of t-BuNC.
This indicated that the presence of excess isocyanide
ligand promoted the ligand exchange between iron-
centered radical intermediates and isocyanide ligand.
Because the starting material badly decomposed during
the thermal rearrangement and a large amount of CO
was produced, the yield of the product 2, without a
substituted isocyanide ligand, did not appear to change.
This further supported the mechanism involving free
ligand exchange during the thermal rearrangement.
In contrast, a P(OPh)3-substituted disilyl-bridged
diiron complex did not undergo scrambling of P(OPh)3
during the thermal rearrangement reaction.6b This can
be attributed to the fact that the replacement of carbo-
nyl groups by isocyanide ligands in diiron complex
occurs either by photolysis or by a themal process in
(16) Moore, B. D.; Poliakoff, M.; Turner, J . T. J . Am. Chem. Soc.
1986, 108, 1819.

Novel Rearrangement Reactions
Organometallics, Vol. 18, No. 22, 1999 4499
Ta ble 8. Su m m a r y of X-r a y Diffr a ction Da ta
8
9t
12t
13c
formula
fw
space group
cryst syst
Z
C
22H29Fe2NO3Si2
C30H44Fe2N2O2Si2
632.56
P21/c
monoclinic
2
C30H45Fe2NO3Si2
635.56
P1h
triclinic
2
C34H54Fe2N2O2Si2
690.68
P21/c
monoclinic
4
523.34
P21/n
monoclinic
4
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
volume (Å3)
14.931(5)
10.207(3)
16.508(3)
90
103.32(2)
90
2448(1)
1.420
0.20 × 0.20 × 0.40
Mo KR (0.71069)
13.04
ω/2θ
50.0
4152
3045
272
0.033
0.043
10.733(2)
9.466(1)
15.564(2)
90
98.33(1)
90
1564.5(7)
1.343
0.20 × 0.20 × 0.40
Mo KR (0.71073)
10.297
ω/2θ
46.0
2423
1284
172
0.053
0.063
12.065(3)
16.458(4)
9.296(3)
105.45(2)
93.66(2)
70.91(2)
1680.7(8)
1.256
0.20 × 0.20 × 0.30
Mo KR (0.71069)
9.62
ω/2θ
49.7
12.138(6)
20.892(9)
15.484(4)
90
98.64(3)
90
3881(2)
1.182
0.20 × 0.20 × 0.30
Mo KR (0.71069)
8.37
ω/2θ
49.9
5837
3740
380
0.040
0.050
D
calc (g‚cm-3
)
cryst size (mm)
radiation (Å3)
µ (cm-1
)
data collection method
max 2θ (deg)
total no. of observns
no. of unique data, I > 3σ(I)
final no. of variables
Ra
4657
3309
344
0.029
b
Rw
0.037
goodness of fit
1.75
2.13
1.38
1.70
a
b
2 1/2
∑||Fo| - |Fc||/∑|Fo|. [∑w(|Fo| - |Fc|)2|/∑w|Fo
] .
P r ep a r a tion of (Me2SiSiMe2)[(η5-t-Bu C5H3)2F e2(CO)-
(CN-t-Bu )](µ-CO)2 (6c a n d 6t). A solution of 0.80 g (1.38
mmol) of 5c and 0.36 g (4.14 mmol) of t-BuNC in 40 mL of
benzene was refluxed for 3 h. TLC monitoring of the reaction
indicated the disappearance of 5c. The solvent was removed
under vacuum, the dark red oil residue was chromatographed
(neutral alumina, 200-300 mesh, dichloromethane/hexane
1:1), and the products were recrystallized from dichloromethane/
hexane mixtures to give 0.65 g (74%) of dark red crystals of
6c. Mp: 149-150 °C. Anal. Calcd for C30H45Fe2NO3Si2: C,
benzene, whereas the replacement by phosphite ligands
occurs only by photolysis.
Exp er im en ta l Section
Gen er a l Con sid er a tion s. Schlenk and vacuum line tech-
niques were employed for all manipulations of air- and
moisture-sensitive compounds. Reaction solvents were distilled
from appropriate drying agents under argon before use.
Tetrahydrofuran, benzene, toluene, and xylene were distilled
from sodium/benzophenone ketyl and purged with argon
atmosphere prior to use. Isocyanide ligands C6H11NC and
t-BuNC,17 (Me2SiSiMe2)[(η5-C5H4)Fe(CO)]2(µ-CO)2 (1),4 and
(Me2SiSiMe2)[(η5-t-BuC5H3) Fe(CO)]2(µ-CO)2 (5)5 were prepared
according to literature methods. 1H, 13C, and 29Si NMR spectra
were obtained on a BRUKER AC-P 200 spectrometer using
CHCl3 (δ 7.24 ppm for 1H and 77.0 ppm for 13C) and SiMe4 as
an internal standard. Elemental analyses were performed by
1
56.70; H, 7.14; N, 2.20. Found: C, 56.48; H, 7.11; N, 2.34. H
NMR (CDCl3): δ 0.15, 0.20, 0.26 (s, s; s, 3H, 6H, 3H, SiMe2),
1.12 (s, 9H, t-BuNC), 1.34 (s, 18H, t-BuCp), 4.40, 4.52, 5.00,
5.15 (s, d, s, s, 1H, 3H, 1H, 1H, Cp). IR (νCO, cm-1): 2119(m),
1943(s), 1741(s).
Treatment similar to that of 5t as described above afforded
green solids of 6t (64%). Mp: 162-3 °C. Anal. Calcd for C30H45
-
Fe2NO3Si2: C, 56.70; H, 7.14; N, 2.20. Found: C, 56.85; H,
1
7.11; N, 2.54. H NMR (CDCl3): δ 0.12, 0.22, 0.23, 0.30 (s, s;
a
Perkin-Elmer 240C instrument. Infrared spectra were
s, s, 3H, 3H, 3H, 3H, SiMe2), 1.12 (s, 9H, t-BuNC), 1.33, 1.34
(s, s, 9H, 9H, t-BuCp), 4.26, 4.32, 4.49, 4.53, 5.01, 5.13 (s, s, s,
d, s, s, 1H, 1H, 1H, 1H, 1H, 1H, Cp). IR (νCO, cm-1): 2123(m),
2079(w,sh), 1929(s), 1746(s), 1740(s).
obtained as KBr disks and recorded on a Nicolet 5DX FT-IR
spectrometer.
P r ep a r a tion of (Me2SiSiMe2)[(η5-C5H4)2F e2(CO)(CNR)]-
(µ-CO)2 (3, R ) C6H11; 4, R ) t-Bu ). A solution of 0.60 g (1.28
mmol) of 1 and 0.21 g (1.92 mmol) of C6H11NC in 40 mL of
benzene was stirred for 11 h. TLC monitoring of the reaction
indicated the disappearance of 1. The solvent was removed
under vacuum, the dark red oil residue was chromatographed
(neutral alumina, 200-300 mesh, dichloromethane), and the
products were recrystallized from hexane to afford 0.50 g (71%)
Th er m a l Rea r r a n gem en t Rea ction s of 3 a n d 4. A
solution of 3 (0.30 g) in 25 mL of xylene was heated at reflux
for 20 h. The solvent was removed under vacuum, and the
brown residue was chromatographed (neutral alumina, 200-
300 mesh, dichloromethane/hexane, 1:5) to afford three light
yellow bands (Rf values: 0.62, 0.48, 0.34). Evaporation of
solvents afforded three different yellow crystals: 2, 20 mg (8%),
7, 60 mg (20%), and 9t, 15 mg (4%). 7: Mp: 88-90 °C. Anal.
Calcd for C24H31Fe2NO3Si2: C, 52.47; H, 5.69; N, 2.55. Found:
C, 52.66; H, 5.77; N, 2.57. 1H NMR (CDCl3): δ 0.34, 0.38, 0.41,
0.44 (s, s, s, s, 3H, 3H, 3H, 3H, SiMe2), 1.31-1.85 (3brm, 10H,
(CH2)5), 3.65 (brm, 1H, NCH), 4.70-4.89 (brm, 6H, Cp), 4.99
(s, 2H, Cp). IR (νCO, cm-1): 2113(s), 1992(vw,sh), 1908(s). 9t:
Mp: 182-4 °C. Anal. Calcd for C30H42Fe2N2O2Si2: C, 57.15;
of dark red crystals of 3. Mp: 164-6 °C. Anal. Calcd for C24H31
-
Fe2NO3Si2: C, 52.47; H, 5.69; N, 2.55. Found: C, 52.11; H,
1
5.71; N, 2.52. H NMR (CDCl3) δ: 0.24 (s, 12H, SiMe2), 1.21-
1.55 (2 brm, 10H, (CH2)5), 3.34 (brm, 1H, NCH), 4.55, 4.61,
5.15, 5.27 (s, s, s, s, 8H, Cp). IR (νCO, cm-1): 2105(m), 1944(s),
1778(m), 1729(s) (KBr); 2112(s), 1945(m), 1741(s) (CH2Cl2).
A solution of 0.60 g (1.28 mmol) of 1 and 0.33 g (3.84 mmol)
of t-BuNC in 30 mL of benzene was stirred at room temper-
ature for 20 h. Treatment similar to that described above
afforded 0.50 g (75%) of dark red crystals of 4. Mp: 113-4 °C.
Anal. Calcd for C22H29Fe2NO3Si2: C, 50.49; H, 5.59; N, 2.68.
Found: C, 50.21; H, 5.76; N, 2.84. 1H NMR (CDCl3): δ 0.24
(s, 12H, SiMe2), 1.14 (s, 9H, t-Bu), 4.53, 4.59, 5.12, 5.27 (s, s,
s, s, 8H, Cp). IR (νCO, cm-1): 2110(m), 1996(w), 1951(s), 1781-
(w), 1732(s) (KBr); 2115(s), 1950(m), 1738(s) (CH2Cl2).
1
H, 6.71; N, 4.44. Found: C, 57.25; H, 6.85; N, 4.40. H NMR
(CDCl3): δ 0.31, 0.35 (s, s, 6H, 6H, SiMe2), 1.33-1.84 (3brm,
10H, (CH2)5), 3.66 (brm, 1H, NCH), 4.66, 4.82 (s, s, 4H, 4H,
Cp). IR (νCO, cm-1): 2112(s), 1985(vw,sh), 1922(s).
(17) Schuster, R. E.; Scott, J . E.; Casanova, J . Org. Synth. 1966,
47, 75.

4500 Organometallics, Vol. 18, No. 22, 1999
Zhang et al.
A solution of 4 (0.70 g) in 30 mL of xylene was heated at
reflux for 24 h. Treatment similar to that described above
afforded four different light yellow bands. Evaporation of
solvents afforded four yellow crystals: 2, 80 mg (13%), 8, 0.19
g (27%), 10t, 15 mg (2%), and 10c, 20 mg (3%). 8: Mp: 123-4
°C. Anal. Calcd for C22H29Fe2NO3Si2: C, 50.49; H, 5.59; N, 2.68.
2H, 1H, 1H, 1H, 1H, Cp). IR (νCO, cm-1): 2106(m), 2074(m),
1985(w), 1915(s), 1900(s, sh).
Treatment similar to that of 6t (0.50 g) as described above
afforded three light yellow crystals: 11c, 30 mg (7%), 12c, 0.15
(30%), and 13c, 10 mg (2%). 12c: Mp: 145-6 °C. Anal. Calcd
for C30H45Fe2NO3Si2: C, 56.70; H, 7.14; N, 2.20. Found: C,
56.91; H, 7.03; N, 2.46. 1H NMR (CDCl3): δ 0.34, 0.35, 0.42
(s, s; s, 3H, 3H, 6H, SiMe2), 1.22, 1.23 (s, s, 9h, 9H, t-BuCp),
1.38 (s, 9H, t-BuNC), 4.52, 4.64, 4.70, 4.76, 4.87 (s, s, s, s, s,
1H, 2H, 1H, 1H, 1H, Cp). IR (νCO, cm-1): 2105(m), 2073(m),
1
Found: C, 50.57; H, 5.47; N, 2.69. H NMR (CDCl3): δ 0.35,
0.39, 0.42, 0.44 (s, s, s, s, 3H, 3H, 3H, 3H, SiMe2), 1.39 (s, 9H,
t-BuNC), 3.65 (brm, 1H, NCH), 4.98-5.02, (brm, 8H, Cp). 13C
NMR (CDCl3): δ 6.35, 6.77, 7.06, 7.22 (SiMe2), 40.0 (C(CH3)3),
57.3 (C(CH3)3), 80.8, 82.9, 83.3, 84.0, 90.6, 92.8, 92.9, 93.8 (Cp),
92.2, 98.9 (ipso Cp), 171.3 (t-BuNC), 216.1, 216.3, 218.7 (Fe-
CO). 29Si NMR (CDCl3): δ 35.5, 35.7. IR (νCO, cm-1): 2100(m),
2074(w,sh), 1983(s), 1959(w), 1920(s). 10t: Mp: 200 °C (dec).
Anal. Calcd for C26H38Fe2N2O2Si2: C, 53.99; H, 6.62; N, 4.84.
1981(s), 1920(s). 13c: Mp: 215-6 °C. Anal. Calcd for C34H54
-
Fe2N2O2Si2: C, 59.13; H, 7.88; N, 4.06. Found: C, 58.64; H,
1
7.56; N, 4.26. H NMR (CDCl3): δ 0.30, 0.34, 0.36 (s, s; s, 6H,
3H, 3H, SiMe2), 1.19, 1.25 (s, s, 9H, 9H, t-BuCp), 1.38, 1.40 (s,
s, 9H, 9H, t-BuNC), 4.41, 4.55, 4.67 (s, s, t, 2H, 3H, Cp). IR
(νCO, cm-1): 2101(m), 2062(m), 1910(s), 1897(s).
1
Found: C, 54.02; H, 6.37; N, 5.12. H NMR (CDCl3): δ 0.32,
0.35 (s, s, 6H, 6H, SiMe2), 1.38 (s, 18H, t-BuNC), 4.64, 4.70,
4.84 (s, s, s, 4H, 2H, 2H, Cp). IR (νCO, cm-1): 2103(m), 2063-
(w, sh), 1917(s), 1871(vw). 10c: Mp: 198-9 °C (dec). Anal.
Cr ysta llogr a p h ic Stu d ies. Crystals suitable for X-ray
diffraction were obtained from hexane/dichloromethane solu-
tions. All data sets were collected on Enraf-Nonius CAD-4 (9t)
or Rigaku AFC 7R (8, 12t, and 13c) diffractometers with
graphite-monochromated Mo KR radiation. The corrections for
empirical absorption were applied to intensity data. All
structures were solved by direct methods and expanded using
Fourier techniques. The non-hydrogen atoms were refined
anisotropically. All calculations for 8, 12t, and 13c were
performed using the teXsan Crystallographic Software Pack-
age of Molecular Structure Corp., while for 9t PDP11/44 and
Pentium MMX/166 computers was used. Neutral atom scat-
tering factors were taken from the tabulations of Cromer and
Waber.18 A summary of the crystallographic results is pre-
sented in Table 8.
Calcd for
C26H38Fe2N2O2Si2: C, 53.99; H, 6.62; N, 4.84.
Found: C, 54.01; H, 6.47; N, 5.11. 1H NMR (CDCl3): δ 0.34
(s, 12H, SiMe2), 1.38 (s, 18H, t-BuNC), 4.64, 4.82 (s, s, 4H,
4H, Cp). IR (νCO, cm-1): 2101(m), 2068(m), 1917(s), 1904(s).
Th er m a l Rea r r a n gem en t Rea ction s of 4 in th e P r es-
en ce of t-Bu NC. A solution of 1.14 g (2.18 mmol) of 4 and
0.37 g (4.36 mmol) of t-BuNC in 50 mL of xylene was refluxed
for 24 h. TLC monitoring of the reaction indicated the
disappearance of 4. Treatment similar to that described above
afforded four different light yellow bands. Evaporation of
solvents afforded four yellow crystals: 2, 110 mg (11%), 8, 45
mg (4%), 10t, 70 mg (6%), and 10c, 149 mg(12%).
Th er m a l Rea r r a n gem en t Rea ction s of 6c a n d 6t. A
solution of 6c (0.45 g) in 20 mL of xylene was heated at reflux
for 24 h. The solvent was removed under vacuum, and the
brown residue was chromatographed (neutral alumina, 200-
300 mesh, dichloromethane/hexane, 1:10) to afford three light
yellow bands. Evaporation of solvents afforded three different
yellow crystals: 11t, 35 mg (9%), 12t, 0.18 g (40%) and 13t,
15 mg (3%). 12t: Mp: 158-9 °C. Anal. Calcd for C30H45Fe2-
NO3Si2: C, 56.70; H, 7.14; N, 2.20. Found: C, 56.80; H, 7.10;
N, 2.40. 1H NMR (CDCl3): δ 0.25, 0.35, 0.41, 0.43 (s, s; s, s,
3H, 3H, 3H, 3H, SiMe2), 1.27 (s, 18H, t-BuCp), 1.37 (s, 9H,
t-BuNC), 4.41, 4.46, 4.61, 4.74, 4.93 (d, s, s, s, s, 1H, 1H, 2H,
1H, 1H, Cp). IR (νCO, cm-1): 2100(m), 2069(m), 1982(s), 1941-
Ack n ow led gm en t. This work was financially sup-
ported by the National Science Foundation of China and
Laboratory of Organometallic Chemistry, Shanghai
Institute of Organic Chemistry, Chinese Academy of
Science.
Su p p or tin g In for m a tion Ava ila ble: Tables of final pos-
tional and thermal parameters of the non-hydrogen atoms,
general temperature factors, and bond distances and angles
for 8, 9t, 12t, 13t, and 13c. This material is available free of
charge via the Internet at http://pubs.acs.org.
(s), 1915(s). 13t: Mp: 205 °C (dec). Anal. Calcd for C34H54
-
OM9902683
Fe2N2O2Si2: C, 59.13; H, 7.88; N, 4.06. Found: C, 58.88; H,
1
7.66; N, 4.16. H NMR (CDCl3): δ 0.24, 0.36, 0.39 (s, s, s, 6H,
(18) Cromer, D. T.; Waber, J . T. International Tables for X-ray
Crystallography; Kynoch Press: Birmingham, England, 1974; Vol. IV,
Table 2.2A.
3H, 3H, SiMe2), 1.27, 1.28 (s, s, 9H, 9H, t-BuCp), 1.36, 1.39 (s,
s, 9H, 9H, t-BuNC), 4.32, 4.42, 4.53, 4.67, 4.76 (s, s, s, s, s,