Reactions of phenylsilanes with iron nonacarbonyl

Article abstract of DOI:10.1021/om9505468

Reaction of equimolar amounts of Fe₂(CO)₉ and SiPhH₃ yields the triply bridged diiron complex [(OC)₃Fe]₂(μ-SiPhH)₂(μ-CO) (1a). The analogous reaction of Fe₂(CO)₉ and S

Full text of DOI:10.1021/om9505468

2604
Organometallics 1996, 15, 2604-2610
Rea ction s of P h en ylsila n es w ith Ir on Non a ca r bon yl
Richard S. Simons and Claire A. Tessier*
Department of Chemistry, University of Akron, Akron, Ohio 44325-3601
Received J uly 17, 1995X
Reaction of equimolar amounts of Fe2(CO)9 and SiPhH3 yields the triply bridged diiron
complex [(OC)3Fe]2(µ-SiPhH)2(µ-CO) (1a ). The analogous reaction of Fe2(CO)9 and SiPh2H2
provides the singly bridged diiron complex [(OC)4Fe-Fe(CO)3(SiHPh2)](µ-η2-H-SiPh2) (4).
When 4 is photolyzed for 12 h, the complex [(OC)3Fe]2(µ-η2-H-SiPh2)2 (5) is obtained. Both
4 and 5 exhibit agostic Fe-H-Si interactions. Reaction of Fe2(CO)9 or Fe(CO)5 with the
disiloxane Ph2HSi-O-SiHPh2 gives the singly bridged diiron complex [(OC)4Fe]2(µ-η2-Ph2-
1
Si-O-SiPh2) (6). All compounds have been characterized by H, 13C, and 29Si NMR and IR
spectroscopy. Compounds 4-6 have been characterized by X-ray crystallography.
In tr od u ction
choice. The photolysis or heating required to generate
Fe(CO)4 from the other binary iron carbonyls could
induce further reactions. However, for Fe3(CO)12, in-
termediates in which Fe-Fe bonds are retained have
also been proposed.6 Though few kinetic studies of
substitution processes of Fe2(CO)9 have been done due
to its low solubility, it appears that Fe2(CO)9 can also
react by way of intermediates which contain Fe-Fe
bonds.5a
The interaction of a reactive metal center with the
Si-H bond of a silane can result in either complete
oxidative addition to form M-H and M-Si bonds or a
three-center-two-electron agostic interaction (eq 1), and
often the latter is regarded as an intermediate to the
formation of the former.1 With the reactions of binary
In the reactions of binary iron carbonyls with primary
and secondary silanes, reductive elimination of H2 takes
place, presumably after the oxidative addition of the
silane. One or more of the three different types of iron-
silicon rings 1-3 can be obtained from such reactions.
iron carbonyls with silanes, it is usually assumed that
simple oxidative addition is the first step in the reaction,
though this has only been observed directly with the
tertiary silanes SiHR3 (R ) Me, Cl, Ph) with Fe(CO)5.2
The first stable agostic Si-H interaction in iron-silicon
chemistry was recently reported after this paper was
accepted.3 Such an interaction also has been suspected
in at least two compounds in the solid state and in the
gas phase for Fe+.1a,4
With the binary iron carbonyls, the nature of the
reactive iron center which interacts with the silane has
not been well-defined. Usually the reactive metal center
is believed to be Fe(CO)4. Photolysis of Fe(CO)5 and Fe3-
(CO)12, heating of Fe(CO)5, and simple dissolution of Fe2-
(CO)9 in a solvent have all been suggested as routes to
Fe(CO)4.5 If an understanding of the initial interaction
between secondary or primary silanes and Fe(CO)4 is
desired, Fe2(CO)9 would appear to be the reagent of
Corriu, Carre´, and co-workers studied the photolysis of
Fe(CO)5 with secondary silanes.7 Iron-silicon rings of
the form 1 (R ) Ph, Me; R2 ) Ph2) and 2 (R ) Ph) were
obtained. Kirillova and co-workers also obtained a
compound of structure 1 from the reaction of Fe2(CO)9
and the secondary silane 1,1-dihydro-1-silaphenalene
under unspecified conditions.8 Complexes of structure
2 may be thought of as progenitors of complexes of
structure 1 because heating or photolysis of the former
has yielded the latter.7,9 J ust recently, Ogino and co-
workers reported that the reactions of excess Fe2(CO)9
with bulky secondary silanes under reflux conditions
give the three-membered-ring products 3 (R ) Mes,
O(2,6-i-Pr2C6H3)).10 Complexes of structure 1-3 have
X Abstract published in Advance ACS Abstracts, May 1, 1996.
(1) (a) Schubert, U. Adv. Organomet. Chem. 1990, 30, 151-187. (b)
Tilley, T. D. In The Chemistry of Organosilicon Compounds; Patai, S.,
Rappoport, Z., Eds.; Wiley: New York, 1989; Chapter 24. (c) Tilley, T.
D. In The Silicon-Heteroatom Bond; Patai, S., Rappoport, Z., Eds.;
Wiley: New York, 1991; Chapter 10. (d) Schubert, U. Transition Met.
Chem. 1991, 16, 136-144.
(2) (a) J etz, W.; Graham, W. A. G. Inorg. Chem. 1971, 10, 4-9. (b)
Schroeder, M. A.; Wrighton, M. S. J . Organomet. Chem. 1977, 128,
345-358.
(3) Scharrer, E.; Chang, S.; Brookhart, M. Organometallics 1995,
14, 5686-5694.
(6) Bentsen, J . G.; Wrighton, M. S. J . Am. Chem. Soc. 1987, 109,
4530-4544.
(7) (a) Corriu, R. J . P.; Moreau, J . E. J . Chem. Soc., Chem. Commun.
1980, 278-279. (b) Carre´, F. H.; Moreau, J . J . E. Inorg. Chem. 1982,
21, 3099-3105.
(8) Kirillova, N. I.; Gusev, A. I.; Kalinina, O. N.; Afanasova, O. B.;
Chernyshev, E. A. Metalloorg. Khim. 1991, 4, 773-777.
(9) Schmid, G.; Welz, E. Z. Naturforsch. 1979, 34B, 929-933.
(10) Tobita, H.; Shinagawa, I.; Ohnuki, S.; Abe, M.; Izumi, H.; Ogino,
H. J . Organomet. Chem. 1994, 473, 187-193.
(4) Bakhtiar, R.; J acobson, D. B. Organometallics 1993, 12, 2876-
2878.
(5) (a) Shriver, D. F.; Whitmire, K. H. In Comprehensive Organo-
metallic Chemistry; Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.;
Pergamon: Oxford, U.K., 1982; Volume 4, Chapter 31.1. (b) J ordon,
R. B. Reaction Mechanisms of Inorganic and Organometallic Systems;
Oxford: New York, 1991; Chapters 5 and 7. (c) Nayak, S. K.; Farrell,
G. J .; Burkey, T. J . Inorg. Chem. 1994, 33, 2236-2242.
S0276-7333(95)00546-2 CCC: $12.00 © 1996 American Chemical Society

Reactions of Phenylsilanes with Iron Nonacarbonyl
Organometallics, Vol. 15, No. 11, 1996 2605
NMR (75 MHz, C6D6): δ 210.6 (CO); 134.6, 132.5, 130.2, 126.3
(Ar C). 29Si NMR (60 MHz, C6D6): δ 109.2.
also been obtained by using synthetic routes that involve
chlorosilanes, disilanes, or anionic iron complexes.9,11
Syn th esis of [(OC)4F e]2(η:η-P h 2Si-O-SiP h 2) (6). A.
Fe2(CO)9 (0.90 g, 2.5 mmol) and Ph2HSi-O-SiHPh2 (0.5 g, 1.3
mmol) were suspended in 60 mL of hexane. Stirring was
continued for 20 h and the mixture filtered. Removal of
solvent under vacuum provides 6 (0.10 g, 11%) as red crystals.
Anal. Calcd for C32H20O9Si2Fe2: C, 53.65; H, 2.81. Found: C,
We report herein an investigation of the reactions of
Fe2(CO)9 with phenyl-substituted silanes at room tem-
perature. We find that in addition to structure 1 two
new types of iron-silicon rings, both of which contain
agostic Si-H interactions, are formed.
53.78; H, 2.60. IR: 2094 (s), 2044 (s), 2007 (s) cm-1 1H NMR
.
(300 MHz, C6D6): δ 7.4 (m, 20H, Ar H). 13C NMR (75 MHz,
C6D6): δ 212.6, 207.9, 205.3 (CO); 141.9, 135.1, 133.8, 130.1
(Ar C). 29Si NMR (60 MHz, C6D6): δ 31.1.
B. Fe(CO)5 (0.67 mL, 5.1 mmol) and Ph2HSi-O-SiHPh2
(0.97 g, 2.5 mmol) were dissolved in 60 mL of hexane and
photolyzed for 16 h. The mixture was filtered and the solvent
was removed under vacuum to provide 6 (0.10 g, 5.6%) as red
crystals. 29Si NMR and unit cell parameters were identical
with those obtained from route A.
Exp er im en ta l Section
Gen er a l P r oced u r es. All manipulations were performed
using standard Schlenk techniques.12 All silanes were pur-
chased from Petrarch/Huls America and used without further
purification. All solvents were distilled immediately before
their use from sodium-benzophenone ketyl. Fe(CO)5 and Fe2-
(CO)9 were purchased from Aldrich and used without futher
purification. Caution! Some of the brown-black solids filtered
from the reaction mixtures of Fe2(CO)9 as well as compound
1a are pyrophoric.
1H, 13C, and 29Si NMR were recorded on a Varian 300
spectrometer at variable temperatures using a DEPT pulse
sequence for 29Si spectra.13 Elemental analyses were per-
formed by E & R Microanalytical Laboratories. The photolysis
equipment consisted of a Hanovia medium-pressure UV lamp
housed in a water-cooled fused-silica jacket.
X-r a y Cr ysta llogr a p h y. All manipulations were per-
formed on a Syntex P21 diffractometer with graphite-mono-
chromated Mo KR (λ ) 0.701 73 Å) radiation at -144 °C for 4
and 5 and 18 °C for 6. Crystal data, data collection, and data
reduction parameters are listed in Table 1. The crystals of 4
and 6 were sealed in glass capillaries under argon. The crystal
of 5 was coated with vacuum grease under an argon atmo-
sphere and mounted on
a glass fiber in air. Unit cell
parameters were obtained from the least-squares refinement
of the indices and angles of 25 centered reflections with 2θ
between 20 and 30°. All intensity data were corrected for
Lorentz and polarization effects. An empirical absorption
correction was performed by utilizing the method of ψ-scans
and applied to the intensity data. The structures of 4 and 6
were solved by direct methods and refined to convergence by
a least-squares refinement using anisotropic displacement
parameters for all non-hydrogen atoms and isotropic displace-
ment parameters for hydrogen atoms. The structure of 5 was
solved similarly, except that anisotropic displacement param-
eters were used for the iron, silicon, and oxygen atoms and
isotropic displacement parameters were used for all carbon
and hydrogen atoms. For 4 the positions of agostic and
terminal silicon hydrides were determined from a difference
map. For 5 the position of the agostic silicon hydride only
could be determined in one of the two molecules in the unit
cell.
Syn th esis of [(OC)3F e]2(µ-SiP h H)2(µ-CO) (1a ). Fe2(CO)9
(1.85 g, 5.1 mmol) was suspended in 60 mL of hexane, and
PhSiH3 (0.94 mL, 5.1 mmol) was added by syringe with
stirring. After 20 h of stirring, the reaction mixture was
filtered and the filtrate was cooled to -30 °C to provide 1a
(0.48 g, 14%) as a yellow pyrophoric powder. Anal. Calcd for
C
19H12O7Si2Fe2: C, 43.87; H, 2.33. Found: C, 43.40; H 2.68.
IR: 2129 (w), 2065 (m), 2034 (vs), 1991 (vs), 1835 (s) cm-1. 1H
NMR (300 MHz, C6D6): δ 5.8 (s, 2H, Si-H); 7.0, 7.5 (m, 10H,
Ar H). 13C NMR (75 MHz, C6D6): δ 207.1 (CO); 136.5, 136.0,
135.8, 132.2, 132.0, 128.7, 127.8 (Ar C). 29Si NMR (60 MHz,
C6D6): δ 161.71, 161.67 (J SiH ) 203.3 Hz).
Syn th esis of [(OC)4F e-F e(CO)3(SiHP h 2)](µ-η2-HSiP h 2)
(4). Fe2(CO)9 (1.85 g, 5.1 mmol) was suspended in 60 mL of
hexane, and Ph2SiH2 (0.94 mL, 5.1 mmol) was added with
stirring. After 20 h of stirring, the reaction mixture was
filtered and the filtrate was cooled to -30 °C to provide 4 (0.50
g, 37%) as red crystals. Anal. Calcd for C31H22O7Si2Fe2: C,
55.21; H, 3.29. Found: C, 55.40; H, 3.43. IR: 2085 (s), 2008
(vs) cm-1 1H NMR (300 MHz, C6D6): δ -13.2 (s, 1H, Si-H-
.
Resu lts a n d Discu ssion
Fe); 6.3 (s, 1H, Si-H); 7.5, 7.0 (m, 20H, Ar H). 13C NMR (75
MHz, C6D6): δ 214.8, 212.7, 211.6, 210.7, 210.2 (CO); 141.1,
139.7, 135.2, 134.1, 130.2, 130.0, 128.8, 128.7 (Ar C). 29Si NMR
(60 MHz, C6D6): δ 142.1 (µ-HSiPh2, J SiH ) 48.3 Hz), 15.2
(SiHPh2, J SiH ) 197.7 Hz).
A few general comments on the syntheses are ap-
propriate. The reactions involved equimolar quantities
of Fe2(CO)9 and the phenylsilane and were conducted
in hexane, a solvent in which Fe2(CO)9 has little
solubility. Reaction mixtures were stirred for about 20
h, at which time no unreacted Fe2(CO)9 was present. A
dark brown-black precipitate, which in some cases was
pyrophoric and may have contained elemental iron, was
filtered from the hexane solution. Products were iso-
lated from the hexane solution.
Syn th esis of [(OC)3F e]2(µ-HSiP h 2)2 (5). Compound 4
(0.30 g, 0.45 mmol) was dissolved in 30 mL of toluene in a
Pyrex vessel and the solution photolyzed for 12 h with a
medium-pressure mercury lamp. Removing the solvent under
vacuum and washing the precipitate with cold hexane provides
5 (0.24 g, 80%) as a yellow powder. Crystals suitable for X-ray
crystallography of 5 are obtained by cooling a saturated
toluene solution. Anal. Calcd for C30H22O6Si2Fe2: C, 55.75;
H, 3.43. Found: C, 54.74; H, 3.33. IR: 2044 (s), 2013 (s), 1980
The reaction of Fe2(CO)9 with an equimolar quantity
of PhSiH3 in hexane provides [(OC)3Fe]2(µ-SiPhH)2(µ-
CO) (1a ) in low yield as a yellow pyrophoric powder (eq
(s) cm-1 1H NMR (300 MHz, C6D6): δ -14.2 (s, 2H, Si-H-
.
Fe, J SiH ) 23.4 Hz); 8.0, 7.7, 7.5, 6.7, 6.5 (m, 20H, ArH). 13C
1
2). Complex 1a was characterized by H, 13C, and 29Si
(11) (a) Kummer, D.; Furrer, J . Z. Naturforsch. 1971, 26B, 162-
163. (b) Kerber, R. C.; Pakkanen, T. Inorg. Chim. Acta 1979, 37, 61-
65. (c) Bikovetz, A. L.; Kuzmin, O. V.; Vdovin, V. M.; Kraivin, A. M. J .
Organomet. Chem. 1980, 194, C33-C34. (d) J etz, W.; Graham, W. A.
G. J . Am. Chem. Soc. 1967, 89, 2773-2775. (e) Schmid, G.; Balk, H.-
J . J . Organomet. Chem. 1974, 80, 257-265.
(12) Shriver, D. F.; Drezdzon, M. A. The Manipulation of Air-
Sensitive Compounds, 2nd ed.; Wiley: New York, 1986.
(13) Blinka, T. A.; Helmer, B. J .; West, R. Adv. Organomet. Chem.
1984, 23, 193-218.

2606 Organometallics, Vol. 15, No. 11, 1996
Simons and Tessier
Ta ble 1. Cr ysta l Da ta , Da ta Collection a n d Red u ction , a n d Refin em en t Deta ils for Com p ou n d s 4-6
compd
4
5
6
formula
fw
C31H22Fe2O7Si2
674.4
C30H22Fe2O6Si2
626.2
C32H20Fe2O9Si2
716.4
cryst syst
space group
a (Å)
b (Å)
c (Å)
monoclinic
C2/c
29.079(6)
9.731(2)
21.113(3)
90
97.10(3)
90
5928(2)
8
1.511
1.102
triclinic
P1h
monoclinic
P21/c
17.802(4)
17.099(3)
10.919(2)
90
104.50(3)
90
3217.8(11)
4
10.018(2)
10.436(2)
14.881(3)
108.00(3)
91.46(3)
96.97(3)
1222.8(4)
2
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
d(calcd) (Mg/m3)
1.419
1.11
1.479
1.024
µ (Mo KR) (mm-1
)
cryst dimens (mm)
scan type
0.3 × 0.3 × 0.3
0.15 × 0.15 × 0.2
0.3 × 0.4 × 0.4
ω
ω
ω
scan range, (deg)
2θ range, (deg)
min, max transmissns
no. of unique data
no. of obsd data (Fo g 4σ(Fo))
no. of params
GOF
1.20
2.00
1.00
3.5-50.0
0.3150, 0.7046
5254 (Rint ) 6.84%)
3163
379
1.14
5.95
6.62
3.5-45.0
0.4796, 0.8390
3704 (Rint ) 2.80%)
1947
211
4.70
3.5-45.0
0.5779, 0.6422
4176 (Rint ) 1.53%)
2438
406
2.47
R
Rw
9.15
10.58
4.41
4.78
1
cidental equivalence of resonances, the H and 29Si{1H}
NMR are consistent with only isomer C or a 50:50
mixture of A and B.
The formation of 1a can be rationalized on the basis
of previously observed chemistry. The direct formation
of complexes of structure 1 from SiPhH3, SiPhMeH2,7
and 1,1-dihydro-1-silaphenalene8 without the observa-
tion of the presumed intermediates of structure 2 can
be explained by the lower steric hindrance of these
silanes. With the bulkier SiPh2H2 a complex of struc-
ture 2 is isolable.7 We should emphasize that 1a was
obtained in low yield. Other complexes may be present
in the reaction mixture because all the Fe2(CO)9 reacted.
On the basis of previous work and the above results,
one would predict a complex of either structure 1 or 2
from the reaction of Fe2(CO)9 and SiPh2H2. However,
when Fe2(CO)9 was reacted with an equimolar quantity
of SiPh2H2 in hexane, the complex [(OC)4Fe-Fe(CO)3-
(SiHPh2)](µ-HSiPh2) (4) was obtained as red air-sensi-
tive crystals in 37% yield (eq 3).
F igu r e 1. The three possible arrangements of the silyl
substituents of 1a . Each arrangement is drawn as a view
down the Fe-Fe bond, and all terminal CO ligands are
omitted.
NMR, IR spectroscopy, and elemental analysis. The IR
spectrum of 1a shows bands at 2129, 2065, 2034, 1994,
and 1835 cm-1
. These have been assigned to the
stretching frequencies of SisH, three terminal CtO’s,
and a bridging carbonyl, respectively.
Three isomers of 1a can be drawn and are represented
in Figure 1 as A-C. Figure 1 is drawn as a view down
the Fe-Fe bond; it omits all terminal carbonyl ligands.
Each isomer differs from the others by the relationship
of their substituents with respect to the bridging car-
bonyl. In isomers A and B the two bridging silyl
ligands are equivalent and, therefore, a single resonance
would be observed for each isomer in the 1H and the
29Si{1H} NMR spectra. In isomer C the bridging silyl
ligands are chemically inequivalent and a separate
resonance should be observed for each. In the Si-H
region of the 1H NMR 1a shows two incompletely
resolved singlets of equal intensity centered at about δ
5.8 ppm. In the 29Si{1H} NMR, 1a shows two reso-
nances of equal intensity centered at about δ 161.7 ppm.
This downfield shift for the silicon resonances is con-
sistent with those of other silicon atoms contained in
Fe2Si three-membered rings.10,11c,14 Barring any ac-
The crystal structure of 4 at -144 °C is shown in
Figure 2. Selected bond lengths and angles are listed
in Tables 2 and 3, respectively. Complex 4 consists of
a diiron moiety singly bridged by a HSiPh2 ligand. The
extremely distorted octahedral geometry of Fe(1) is
completed by four carbonyl ligands. The octahedral
geometry of Fe(2) is completed by three carbonyl
ligands, an agostic silicon hydride, and a terminal
SiPh2H ligand trans to the Fe-Fe bond. The Fe(1)-
Fe(2) (2.759(1) Å), Fe(1)-Si(1) (2.301(2) Å), and Fe(2)-
Si(1) (2.385(2) Å) bond distances are in the range found
in other complexes with Fe2Si three-membered
rings.8,14b,15 A discussion of the agostic Fe-H-Si
interaction of 4 will be presented later.
(14) (a) Kawano, Y.; Tobita, H.; Ogino, H. J . Organomet. Chem.
1992, 428, 125-143. (b) Pannell, K. H.; Sharma, H. Organometallics
1991, 10, 954-959. (c) Ueno, K.; Hamashima, N.; Ogino, H. Organo-
metallics 1991, 10, 959-962.
As shown in Scheme 1, compound 4 could be thought

Reactions of Phenylsilanes with Iron Nonacarbonyl
Organometallics, Vol. 15, No. 11, 1996 2607
Sch em e 1
F igu r e 2. Thermal ellipsoid diagram of [(OC)4Fe-Fe(CO)3-
(SiPh2H)](µ-HSiPh2) (4). The thermal ellipsoids are drawn
at the 50% probability level, and hydrogen atoms on phenyl
substituents have been omitted for clarity.
from Fe2(CO)9 has not been determined.10 Loss of CO
from 3a followed by reaction with additional SiPh2H2
would give 4. In order to test whether Scheme 1 is a
reasonable route to 4, a reaction of 2 molar equiv of
Fe2(CO)9 and 1 molar equiv of Ph2SiH2, under otherwise
the same conditions as used for 4, was carried out. The
anticipated product 3a was not isolated. Instead, an
Ta ble 2. Selected Bon d Len gth s (Å) for 4
Non-Hydrogen Atoms
Fe(1)-Fe(2)
Fe(1)-Si(1)
Fe(1)-C(1)
Fe(1)-C(2)
Fe(1)-C(3)
Fe(1)-C(4)
Fe(2)-Si(1)
Fe(2)-Si(2)
Fe(2)-C(5)
Fe(2)-C(6)
Fe(2)-C(7)
2.759(1)
2.301(2)
1.781(8)
1.819(8)
1.798(7)
1.813(7)
2.385(2)
2.365(2)
1.798(8)
1.794(7)
1.785(7)
Si(1)-C(8)
Si(1)-C(14)
Si(2)-C(20)
Si(2)-C(26)
O(1)-C(1)
O(2)-C(2)
O(3)-C(3)
O(4)-C(4)
O(5)-C(5)
O(6)-C(6)
O(7)-C(7)
1.873(7)
1.887(7)
1.866(8)
1.865(7)
1.136(10)
1.131(10)
1.134(9)
1.139(9)
1.136(9)
1.140(8)
1.157(9)
1
oil was obtained whose H NMR showed the presence
of 4 and other species which contained terminal Fe-H
and Si-H. If 3a was present, we were unable to detect
it. These results suggest either that a mechanism which
does not involve 3a as an intermediate is operative or
that 3a is too reactive to be isolated.
An unresolved question is why complexes of structure
1 or 2 were not obtained as the products from the
reaction of Fe2(CO)9 and SiPh2H2, as they were from
the reaction of Fe(CO)5 and SiPh2H2. The lack of
products of structure 1 or 2 suggests that an intermedi-
ate other than Fe(CO)4 was involved in the production
of 4 or that UV irradiation used with Fe(CO)5 allows
for other processes to take place.
Silicon Hydridesa
Fe(2)-H(1)
1.66
Si(1)-H(1)
Si(2)-H(2)
1.66
1.43
a
See ref 16.
Ta ble 3. Selected Bon d An gles (d eg) for 4
Non-Hydrogen Atoms
Fe(2)-Fe(1)-Si(1)
55.4(1) C(2)-Fe(1)-C(4)
153.1(2) C(3)-Fe(1)-C(4)
97.9(2) Fe(1)-Fe(2)-Si(1)
88.1(2) Fe(1)-Fe(2)-Si(2)
86.8(2) Si(1)-Fe(2)-Si(2)
93.2(3) Fe(1)-Fe(2)-C(5)
82.0(2) Si(1)-Fe(2)-C(5)
86.6(2) Si(2)-Fe(2)-C(5)
95.1(3) Fe(1)-Fe(2)-C(6)
170.0(3) Si(1)-Fe(2)-C(6)
103.7(2) Si(2)-Fe(2)-C(6)
159.1(2) C(5)-Fe(2)-C(6)
103.0(3) Fe(1)-Fe(2)-C(7)
91.0(2) Fe(2)-Si(1)-C(8)
92.9(3)
When complex 4 is photolyzed in toluene for 12 h,
[(OC)3Fe]2(µ-HSiPh2)2 (5) is obtained as a yellow air-
sensitive powder in high yield (eq 4). (As will be
Fe(2)-Fe(1)-C(1)
Si(1)-Fe(1)-C(1)
Fe(2)-Fe(1)-C(2)
Si(1)-Fe(1)-C(2)
C(1)-Fe(1)-C(2)
Fe(2)-Fe(1)-C(3)
Si(1)-Fe(1)-C(3)
C(1)-Fe(1)-C(3)
C(2)-Fe(1)-C(3)
Fe(2)-Fe(1)-C(4)
Si(1)-Fe(1)-C(4)
C(1)-Fe(1)-C(4)
Si(1)-Fe(2)-C(7)
Si(2)-Fe(2)-C(7)
C(5)-Fe(2)-C(7)
C(6)-Fe(2)-C(7)
Fe(1)-Si(1)-Fe(2)
Fe(1)-Si(1)-C(8)
90.6(3)
52.5(1)
175.8(1)
131.0(1)
96.0(2)
98.5(2)
81.4(2)
81.3(2)
133.4(2)
95.4(2)
91.8(3)
102.0(2)
117.7(2)
discussed below, resonance forms other than that drawn
in eq 4 can be drawn for 5.) Apparently photolysis of 4
promotes the loss of a carbonyl ligand to provide a 16-
electron iron center to which the terminal silyl ligand
may coordinate. Mild photolysis conditions (light was
filtered by Pyrex) were purposely chosen in order to
selectively effect loss of carbon monoxide without also
inducing loss of hydrogen.
The crystal structure of 5 at -144 °C is shown in
Figure 3. The unit cell of 5 contains two independent
molecules. The bond lengths and angles for each
molecule are essentially the same. Selected bond
lengths and angles for one of the molecules are listed
in Tables 4 and 5, respectively. The structure of 5
consists of a diiron moiety doubly bridged by two silyl
ligands, giving a planar four-membered ring. The two
Fe-Si bonds are bridged by an agostic hydride (see
below). The distorted-octahedral geometry at each iron
atom is completed by one equatorial and two apical
80.6(2) Fe(1)-Si(1)-C(14) 120.1(2)
161.8(3) Fe(2)-Si(1)-C(14) 121.1(2)
92.9(3) C(8)-Si(1)-C(14)
105.4(3)
72.1(1) Fe(2)-Si(2)-C(20) 113.3(2)
118.3(2) Fe(2)-Si(2)-C(26) 110.1(2)
C(20)-Si(2)-C(26) 109.3(3) Fe(2)-C(7)-O(7)
177.7(6)
176.5(7)
178.7(6)
177.2(6)
Fe(1)-C(1)-O(1)
Fe(1)-C(2)-O(2)
Fe(1)-C(3)-O(3)
177.5(6) Fe(1)-C(4)-O(4)
177.4(7) Fe(2)-C(5)-O(5)
177.0(6) Fe(2)-C(6)-O(6)
Agostic Hydridea
92
Fe(2)-H(1)-Si(1)
a
See ref 16.
of as being derived from the reaction of SiPh2H2 with a
complex of structure 3, which will be referred to as 3a .
The mechanism by which compounds of type 3 form
(15) (a) Sheldrick, W. S. In The Chemistry of Organic Silicon
Compounds; Patai, S., Rappoport, Z., Eds.; Wiley: New York, 1989;
Vol. 1, Chapter 3. (b) Lukevics, E.; Pudova, O.; Struckovich, R.
Molecular Structure of Organosilicon Compounds; Wiley: New York,
1989.

2608 Organometallics, Vol. 15, No. 11, 1996
Simons and Tessier
agostic hydride and M-H distances are longer than
those of typical covalent bonds.1a Several structural
features of 4 and 5 indicate that they both contain
agostic hydride interactions.16 For complex 4, H(1) was
located in the difference map at 1.66 Å from both Fe(2)
and Si(1) with an Fe(2)-H(1)-Si(1) angle of 92°. As
expected, the agostic Si(1)-H(1) distance of 4 is con-
siderably longer than the terminal Si(2)-H(2) distance
of 1.43 Å. In addition, there is a lengthening of the
Fe(2)-Si(1) bond distance as compared to the distance
of Fe(1)-Si(1). For each molecule of complex 5, two
separate pairs of Fe-Si bond distances exist (2.358(6)
and 2.406(6) Å). An agostic hydride was located in the
difference map at distances 1.57 and 2.10 Å from the
Fe(1) and Si(1a) atoms, respectively, but for only one of
the two independent molecules of 5. The Fe-H-Si
angle is 81°.
F igu r e 3. Thermal ellipsoid diagram of one of the two
independent molecules of [(OC)4Fe]2(µ-SiPh2H)2 (5). The
thermal ellipsoids are drawn at the 50% probability level,
and hydrogen atoms on phenyl substituents have been
omitted for clarity.
The crystallographic evidence for agostic Fe-Si-H
interactions for 4 and 5 has been corroborated by NMR
data. In the 1H NMR for 4, resonances are observed
for the terminal Si-H proton at δ 6.3 and the agostic
Fe-H-Si proton at δ -13.2. A signal similar to this
latter resonance would be expected for the two equiva-
Ta ble 4. Selected Bon d Len gth s (Å) for On e of th e
In d ep en d en t Molecu les of 5
1
lent agostic hydrogen atoms of 5. However, in the H
Non-Hydrogen Atoms
Fe(1)-Si(1)
Fe(1)-C(1)
Fe(1)-C(2)
Fe(1)-C(3)
Fe(1)-Fe(1A)
Fe(1)-Si(1A)
2.358(6)
1.84(2)
1.82(2)
1.73(2)
2.759(6)
2.406(6)
Si(1)-C(12)
Si(1)-C(18)
O(1)-C(1)
O(2)-C(2)
O(3)-C(3)
1.89(2)
1.91(2)
1.11(3)
1.14(2)
1.18(3)
NMR of 5 at 23 °C, a broad, barely visible resonance at
about -14.2 ppm is observed. The variable-temperature
1H NMR of 5 was investigated from -60 to +60 °C.
Compound 5 is fluxional on the 1H NMR time scale
down to -40 °C. At -40 °C a single sharp resonance is
observed at δ -14.2 ppm with satellite peaks due to
weak coupling with 29Si (J ) 23.4 Hz). The fluxionality
of 5 can be explained by the facile complexation-
decomplexation of the Si-H bond to the iron center.17
From the coalescence temperature of the Fe-H-Si
resonance, ∆Gq for this process is calculated to be 22 (
1 kcal mol-1 at both -10 and 23 °C.18 In contrast to 5,
4 displays no fluxional behavior at 23 °C.
In the 29Si NMR, the bridging silyl ligand in com-
pound 4 is observed at δ 142.1 ppm, whereas the
terminal silyl ligand of 4 is observed at δ 15.2. The
Si-H (1.67 Å) bond distance and the silicon-hydrogen
coupling constant of 48.3 Hz for the bridging silyl ligand
of 4 are parameters expected for “normal” agostic
M-H-Si interactions, whereas the Si-H bond distance
of 1.44 Å for the nonbridging silyl ligand and the
silicon-hydrogen coupling constant of 197.7 Hz are
consistent with parameters for terminal silyl hy-
drides.15,19 The room-temperature 29Si NMR spectrum
for 5 was featureless. However, at -40 °C, the 29Si
NMR spectrum of 5 shows a sharp singlet at δ 109.2
ppm with a silicon-hydrogen coupling constant of 23.4
Hz. The silicon-hydrogen coupling constant for 5 is at
the lower limit (20-136 Hz1a,20 ) of values reported for
other compounds with M-H-Si agostic hydrides. Cor-
respondingly the Si-H distance (2.10 Å) for 5 is at the
upper limit of values reported for other compounds with
Agostic Hydridea
1.57 Si(1)-H(1)
Fe(1)-H(1)
2.10
a
See ref 16.
Ta ble 5. Selected Bon d An gles (d eg) for On e of th e
In d ep en d en t Molecu les of 5
Non-Hydrogen Atoms
88.3(7) Fe(1A)-Fe(1)-Si(1A) 53.8(2)
Si(1)-Fe(1)-C(1)
Si(1)-Fe(1)-C(2)
C(1)-Fe(1)-C(2)
Si(1)-Fe(1)-C(3)
C(1)-Fe(1)-C(3)
C(2)-Fe(1)-C(3)
87.1(7) Fe(1)-Si(1)-C(12)
170.1(9) Fe(1)-Si(1)-C(18)
103.8(8) C(12)-Si(1)-C(18)
84.7(10) Fe(1)-Si(1)-Fe(1A)
116.3(5)
116.9(7)
108.7(8)
70.8(2)
87.9(9) C(12)-Si(1)-Fe(1A) 118.8(6)
Si(1)-Fe(1)-Fe(1A) 55.4(2) C(18)-Si(1)-Fe(1A) 121.1(6)
C(1)-Fe(1)-Fe(1A)
C(2)-Fe(1)-Fe(1A)
92.3(7) Fe(1)-C(1)-O(1)
92.3(6) Fe(1)-C(2)-O(2)
175.9(18)
176.0(18)
178.0(10)
124.8(13)
118.3(16)
117.8(12)
121.3(15)
C(3)-Fe(1)-Fe(1A) 159.2(8) Fe(1)-C(3)-O(3)
Si(1)-Fe(1)-Si(1A) 109.2(2) Si(1)-C(12)-C(7)
C(1)-Fe(1)-Si(1A)
C(2)-Fe(1)-Si(1A)
94.3(7) Si(1)-C(12)-C(11)
95.5(6) Si(1)-C(18)-C(13)
C(3)-Fe(1)-Si(1A) 146.9(8) Si(1)-C(18)-C(17)
Agostic Hydridea
81
Fe(1)-H(1)-Si(1A)
a
See ref 16.
carbonyl ligands. It is interesting that the Fe-Fe bond
distance (2.759(6) Å) of 5 is equal, within experimental
error, to that found in 4. Presumably the planarity of
the Fe2Si2 core alleviates any steric congestion which
can be associated with the addition of another bridging
ligand.
The M-Si, M-H, and Si-H bond distances combined
with the NMR silicon-hydrogen coupling constants are
most useful for identifying the agostic hydride interac-
tions. In general, the weakened agostic Si-H interac-
tion is distinguished from a terminal Si-H by an
increase in the Si-H bond distance and a decrease in
the silicon-hydrogen coupling constant. In addition,
the M-Si bond distances increase when bridged by an
(16) The esd values for hydrogen atoms appeared to underestimate
their error and have been omitted. Instead, parameters for hydrogen
atoms have been truncated by one significant figure.
(17) Wang, W. D.; Eisenberg, R. J . Am. Chem. Soc. 1990, 112, 1833-
1841.
(18) Sandstro¨m, J . Dynamic NMR Spectroscopy; Academic: New
York, 1982; pp 78, 96.
(19) Kupce, E.; Lukevics, E. In Isotopes in the Physical and Biomedi-
cal Sciences, Buncel, E., J ones, J . R., Eds.; Elsevier: Amsterdam, 1991;
Vol 2, pp 213-295.
(20) Driess, M.; Reigys, M.; Pritzkow, H. Angew. Chem., Int. Ed.
Engl. 1992, 31, 1510-1513.

Reactions of Phenylsilanes with Iron Nonacarbonyl
Organometallics, Vol. 15, No. 11, 1996 2609
M-H-Si agostic hydrides.1a Both NMR and crystal-
lographic data indicate that the agostic Fe-H-Si
interactions of 5 are weak. The only other known
agostic Fe-H-Si interaction, in the cationic complex
[Cp(CO)(PEt3)Fe(η2-H-SiEt3)][B(3,5-(CF3)2C6H3)4], has
been characterized by a silicon-hydrogen coupling con-
stant of 62.4 Hz.3
Infrared data have been seldom used to characterize
agostic M-H-Si interactions. The position of the broad
M-H-Si band has been reported as high as 1890 cm-1
for a mononuclear complex and in the range 1790-1650
cm-1 for dinuclear complexes, and this band appears to
be easier to detect by Raman rather than IR spectros-
copy.21,22 No band in the 1900-1600 cm-1 region of the
IR spectrum was observed for either 4 or 5. We assign
the strong, sharp band at 2085 cm-1 in the spectrum of
4 to the terminal Si-H stretch. Other bands of 4 and
all bands of 5 in the 2100-1600 cm-1 region are
assigned to carbonyl stretching modes.
F igu r e 4. Thermal ellipsoid diagram of [(OC)4Fe]2(η:η-Ph2-
Si-O-SiPh2) (6). The thermal ellipsoids are drawn at the
50% probability level, and hydrogen atoms have been
omitted for clarity.
Ta ble 6. Selected Bon d Len gth s (Å) for 6
As shown in eq 5, the complex [(OC)4Fe]2(η:η-Ph2Si-
O-SiPh2) (6) can be isolated by three different routes.
Fe(1)-Fe(2)
Fe(1)-Si(1)
Fe(1)-C(1)
Fe(1)-C(2)
Fe(1)-C(3)
Fe(1)-C(4)
Si(1)-O(9)
Si(1)-C(9)
Si(1)-C(15)
Si(2)-O(9)
Si(2)-C(21)
Si(2)-C(27)
O(1)-C(1)
2.875(2)
2.412(2)
1.822(9)
1.804(9)
1.809(9)
1.766(10)
1.638(6)
1.854(8)
1.869(7)
1.641(5)
1.873(8)
1.879(9)
1.135(12)
Fe(2)-Si(2)
Fe(2)-C(5)
Fe(2)-C(6)
Fe(2)-C(7)
Fe(2)-C(8)
O(2)-C(2)
O(3)-C(3)
O(4)-C(4)
O(5)-C(5)
O(6)-C(6)
O(7)-C(7)
O(8)-C(8)
2.426(2)
1.807(10)
1.782(10)
1.782(11)
1.793(10)
1.134(11)
1.134(10)
1.149(12)
1.155(12)
1.142(12)
1.128(14)
1.147(12)
Ta ble 7. Selected Bon d An gles (d eg) for 6
Red crystalline complex 6 was first isolated in about 2%
yield by conducting the photolysis of 4 without full
exclusion of air. In this novel reaction, the product 6
has one more carbonyl ligand than the reagent 4.
Therefore, some of complex 4 serves as a sacrificial
source of the extra carbonyl ligand. It seemed reason-
able to expect higher yields of 6 from reagents which
already have at least four carbonyl ligands per iron.
With this in mind, the reaction of Ph2HSi-O-SiHPh2
with Fe(CO)5 under photolytic conditions and the room-
temperature reaction of Ph2HSi-O-SiHPh2 with Fe2-
(CO)9 were examined. In both cases the yield of 6 was
better than when it was prepared from 4 (5.6% and 11%,
respectively), but only marginally. The photolysis of
Fe(CO)5 with HMe2Si-O-SiMe2H has been reported to
give a 55% yield of the related complex [(OC)4Fe]2(η:η-
Me2Si-O-SiMe2).23 No evidence for a monoiron com-
plex such as H2Fe(CO)3(Ph2Si-O-SiPh2) or HFe(CO)4-
(Ph2Si-O-SiPh2H) was obtained, even though mono-
nuclear rather than dinuclear complexes are usually
obtained when a disiloxane adds to a metal.24
Fe(2)-Fe(1)-Si(1)
91.1(1) Si(2)-Fe(2)-C(8)
89.0(3) C(5)-Fe(2)-C(8)
173.8(3) C(6)-Fe(2)-C(8)
76.7(3) C(7)-Fe(2)-C(8)
87.6(3) Fe(1)-Si(1)-O(9)
98.5(4) Fe(1)-Si(1)-C(9)
93.9(3) O(9)-Si(1)-C(9)
79.4(3)
Fe(2)-Fe(1)-C(1)
Si(1)-Fe(1)-C(1)
Fe(2)-Fe(1)-C(2)
Si(1)-Fe(1)-C(2)
C(1)-Fe(1)-C(2)
Fe(2)-Fe(1)-C(3)
Si(1)-Fe(1)-C(3)
C(1)-Fe(1)-C(3)
C(2)-Fe(1)-C(3)
Fe(2)-Fe(1)-C(4)
Si(1)-Fe(1)-C(4)
C(1)-Fe(1)-C(4)
C(2)-Fe(1)-C(4)
C(3)-Fe(1)-C(4)
Fe(1)-Fe(2)-Si(2)
Fe(1)-Fe(2)-C(5)
Si(2)-Fe(2)-C(5)
Fe(1)-Fe(2)-C(6)
Si(2)-Fe(2)-C(6)
C(5)-Fe(2)-C(6)
Fe(1)-Fe(2)-C(7)
Si(2)-Fe(2)-C(7)
C(5)-Fe(2)-C(7)
C(6)-Fe(2)-C(7)
Fe(1)-Fe(2)-C(8)
94.3(4)
166.9(4)
93.6(5)
107.5(2)
113.3(3)
108.9(3)
81.1(3) Fe(1)-Si(1)-C(15) 115.0(2)
92.7(4) O(9)-Si(1)-C(15)
165.2(4) C(9)-Si(1)-C(15)
167.7(3) Fe(2)-Si(2)-O(9)
87.9(3) Fe(2)-Si(2)-C(21) 113.5(3)
93.2(4) O(9)-Si(2)-C(21) 110.0(3)
91.0(4) Fe(2)-Si(2)-C(27) 112.9(2)
98.1(4) O(9)-Si(2)-C(27) 105.6(3)
87.9(1) C(21)-Si(2)-C(27) 108.2(4)
88.9(3) Si(1)-O(9)-Si(2)
172.7(4) Fe(1)-C(1)-O(1)
76.4(3) Fe(1)-C(2)-O(2)
89.6(3) Fe(1)-C(3)-O(3)
96.1(5) Fe(1)-C(4)-O(4)
169.3(3) Fe(2)-C(5)-O(5)
89.1(3) Fe(2)-C(6)-O(6)
95.2(4) Fe(2)-C(7)-O(7)
93.4(5) Fe(2)-C(8)-O(8)
95.9(3)
106.7(3)
105.1(3)
106.4(2)
134.0(3)
174.4(8)
173.4(9)
176.5(8)
176.5(7)
177.6(9)
174.4(8)
176.3(10)
176.6(8)
Complex 6 has been characterized by spectroscopy
and by X-ray crystallography. The 29Si NMR chemical
shift of 6 occurs at δ 31.1 ppm, which is considerably
upfield from the chemical shift of silicon atoms con-
tained in the three-membered rings of 4 and 5. The
crystal structure of 6 is shown in Figure 4. Selected
bond lengths and angles are listed in Tables 6 and 7,
respectively. The structure of 6 consists of a diiron
moiety singly bridged by the disiloxane Ph2Si-O-SiPh2.
The octahedral geometry at each iron atom is completed
by four carbonyl ligands. The Fe-Fe (2.875(2) Å) bond
distance is long15 but not unreasonable, considering the
steric requirements of the bridging disiloxane. The
Fe(1)-Si(1) (2.412(2) Å) and the Fe(2)-Si(2) (2.426(2)
Å) bond distances are long but are in the range of other
(21) Andrews, M. A.; Kirtley, S. W.; Kaesz, H. D. In Transition Metal
Hydrides; Bau, R., Ed.; Advances in Chemistry 167; American Chemi-
cal Society: Washington, DC, 1978; pp 215-231.
(22) (a) Auburn, M.; Ciriano, M.; Howard, J . A. K.; Murray, M.;
Pugh, N. J .; Spencer, J . L.; Stone, F. G. A. J . Chem. Soc., Dalton Trans.
1980, 659-666. (b) Takao, T.; Suzuki, H. Organometallics 1994, 13,
2554-2556.
(23) Greene, J .; Curtis, M. D. Inorg. Chem. 1978, 17, 2324-2326.
(24) Chralovsky, V. In The Chemistry of Inorganic Homo and
Heterocycles; Haiduc, I., Sowerby, D. B., Eds.; Academic: London, 1987;
Vol. 1, Chapter 10.

2610 Organometallics, Vol. 15, No. 11, 1996
Simons and Tessier
Fe-Si bond distances.15 The disiloxane retains typical
Si-O (1.638(6) and 1.640(5) Å) bond distances, but the
Si-O-Si angle (134.0(3)°) is smaller than in free
disiloxanes with similar substituents.15 The crystal
structure of the free ligand Ph2HSi-O-SiHPh2 has
been found to be disordered. An asymmetric Si-O-Si
fragment with Si-O bond distances of 1.56 and 1.69 Å
and an apparent Si-O-Si bond angle of 160° were
reported.25 An interesting structural feature is the
approximate staggered relationship of the carbonyls on
Fe(1) with respect to the carbonyls on Fe(2). Presum-
ably this “twisting” of the Fe-Fe bond is a result of the
steric crowding caused by the phenyl substituents on
Si(1) and Si(2).
silicon stoichiometry and different conditions for the
photolyses: a medium-pressure bulb and a Pyrex ap-
paratus for the former and a high-pressure bulb in a
fused-silica apparatus for the latter. With Fe3(CO)12
different chemistries are observed at different wave-
lengths.6 The reaction of Ph2HSi-O-SiHPh2 with
either Fe2(CO)9 or Fe(CO)5 provides 6, a diiron complex
bridged by a disiloxane. The exact mechanism by which
the formation of 1a , 4, and 6 from Fe2(CO)9 and the
appropriate phenylsilane proceed is difficult to assess
from the experiments described herein, and more than
one mechanism could be operating simultaneously. The
products 1a , 4, and 6 can be rationalized by mechanisms
involving either Fe2(CO)n and/or Fe(CO)4 as the initial
iron carbonyl species.
Su m m a r y
Ack n ow led gm en t. We thank Wiley Youngs and
Peter Rinaldi for useful discussions and J ames Howe
(deceased) for library research. This work was sup-
ported by the National Science Foundation (Grant No.
CHE-9309160) and by the State of Ohio Board of
Regents Research Challenge.
In conclusion, this study has demonstrated that
phenylsilanes oxidatively add to reactive iron carbonyl
species to give dinuclear iron-silicon complexes, all of
which contain Fe-Fe bonds. With the primary silane
SiPhH3, the reductive elimination of the elements of 1
mol of dihydrogen for each of the two silyl ligands
provides a complex of structure 1. As with the primary
silane, 2 mol of the secondary silane SiPh2H2 adds to a
diiron fragment. However, with SiPh2H2, only 1 mol of
dihydrogen is lost in the addition of the two ligands,
giving the complex 4. The silyl ligands of 4 each still
contain a hydride, one as a terminal ligand and one
involved in an agostic interaction. Photolysis of 4
promotes the loss of one carbonyl ligand to give a 16-
electron iron center, to which the remaining terminal
silyl ligand oxidatively adds to provide 5. The products
obtained from the reaction of Fe2(CO)9 and SiPh2H2 and
subsequent photolysis are very different from the prod-
ucts of the photolysis of Fe(CO)5 and SiPh2H2.7,26 The
difference may be partially due to differences in iron to
Su p p or tin g In for m a tion Ava ila ble: Tables of data col-
lection and structure solution details, fractional atomic coor-
dinates and equivalent isotropic displacement parameters,
bond distances and angles, and anisotropic and isotropic
displacement parameters for the crystal structures of 4-6 (24
pages). This material is contained in many libraries on
microfiche, immediately follows this article in the microfilm
version of the journal, can be ordered from the ACS, and can
be downloaded from the Internet; see any current masthead
page for ordering information and Internet access instructions.
OM9505468
7
(26) We considered the possibility that [(OC)4FeSiPh2]2 may have
been misidentified because it has a 29Si NMR chemical shift (δ 109 or
111 ppm) which is identical with that of 5 (δ 109 ppm). The lack of
fluxionality of [(OC)4FeSiPh2]2 and other data (see following references)
indicate that [(OC)4FeSiPh2]2 and 5 are different compounds: (a)
Corriu, R. J . P.; Lanneau, G. F.; Chauhan, B. P. S. Organometallics
1993, 12, 2001-2003. (b) Chauhan, B. P. S.; Corriu, R. J . P.; Lanneau,
G. F.; Priou, C.; Auner, N.; Handwerker, H.; Herdtweck, E. Organo-
metallics 1995, 14, 1657-1666.
(25) Wojnowski, W.; Peters, K.; Peters, E.-M.; Meyer, T.; von
Schnering, H. G. Z. Anorg. Allg. Chem. 1986, 537, 31-39.