Tri-N-pyrrolylsilyl complexes of ruthenium and osmium

Article abstract of DOI:10.1021/om970044p

The development of a new, simple synthesis of tri-N-pyrrolylsilane (1) from trichlorosilane and pyrrole provides a convenient starting point for a series of interesting transition-metal complexes with the tri-N-pyrrolylsilyl ligand. Oxidative addition of 1 to M(CO)₂(PPh₃)₃ gives the six-coordinate compounds M(SiPyr₃)H(CO)₂(PPh₃)₂ (Pyr = 1-NC₄H₄; 2a, M = Ru; 2b, M = Os), whereas overall phenyl group-silyl group exchange between MPhCl(CO)(PPh₃)₂ and 1 yields the five-coordinate species M(SiPyr₃)Cl(CO)(PPh₃)₂ (3a, M = Ru; 3b, M = Os). The nitrosyl complex Os(SiPyr₃)HCl(NO)(PPh₃)₂ (4) can be prepared from OsCl(NO)(PPh₃)₃ and 1. The carbonyl groups in these compounds show relatively high C-O stretching frequencies, which fall between those found for the trihydroxysilyl and trichlorosilyl analogues. Bond lengths and angles obtained from the X-ray structure determinations of HSiPyr₃ (1) and Os(SiPyr₃)H(CO)₂(PPh₃)₂ (2b) indicate that the SiPyr₃ moiety undergoes significant changes on coordination to osmium.

Full text of DOI:10.1021/om970044p

2730
Organometallics 1997, 16, 2730-2735
Tr i-N-p yr r olylsilyl Com p lexes of Ru th en iu m
a n d Osm iu m 1
Klaus Hu¨bler,* Warren R. Roper,*,† and L. J ames Wright
Department of Chemistry, The University of Auckland,
Private Bag 92019, Auckland, New Zealand
Received J anuary 24, 1997X
The development of a new, simple synthesis of tri-N-pyrrolylsilane (1) from trichlorosilane
and pyrrole provides a convenient starting point for a series of interesting transition-metal
complexes with the tri-N-pyrrolylsilyl ligand. Oxidative addition of 1 to M(CO)2(PPh3)3 gives
the six-coordinate compounds M(SiPyr3)H(CO)2(PPh3)2 (Pyr ) 1-NC4H4; 2a , M ) Ru; 2b, M
) Os), whereas overall phenyl group-silyl group exchange between MPhCl(CO)(PPh3)2 and
1 yields the five-coordinate species M(SiPyr3)Cl(CO)(PPh3)2 (3a , M ) Ru; 3b, M ) Os). The
nitrosyl complex Os(SiPyr3)HCl(NO)(PPh3)2 (4) can be prepared from OsCl(NO)(PPh3)3 and
1. The carbonyl groups in these compounds show relatively high C-O stretching frequencies,
which fall between those found for the trihydroxysilyl and trichlorosilyl analogues. Bond
lengths and angles obtained from the X-ray structure determinations of HSiPyr3 (1) and
Os(SiPyr3)H(CO)2(PPh3)2 (2b) indicate that the SiPyr3 moiety undergoes significant changes
on coordination to osmium.
Sch em e 1
In tr od u ction
Ligands of the type PX3, where X is alkyl, alkoxy, or
halide, are often used to modify the reactivities of
transition-metal complexes due to the σ-donor and
π-acceptor abilities of the particular phosphine. In this
context Moloy and Petersen recently reported that
N-pyrrolylphosphines can act as very weak σ-donors and
possibly good π-acceptors.2 Remarkably shorter metal-
phosphorus bonding distances and significantly higher
C-O stretching frequencies relative to analogous tri-
phenylphosphine complexes were reported for transi-
tion-metal complexes of this ligand. The substantial
influence of the pyrrolyl fragments as potent electron-
withdrawing groups caused us to consider if a compa-
rable influence could be attained with N-pyrrolylsilyl
compounds. Structural characterizations have revealed
that the substituents on silicon have an important
influence on the M-Si distances.3 The observation that
electronegative groups lead to a shortening of this
parameter has frequently been explained by invoking
π-bonding, and for a few examples photoelectron spec-
troscopy has affirmed multiple-bond formation between
silicon and the metal center through participation of the
σ*-orbitals on the silyl group.4
ylpyrrole6 and, very recently, tetra-N-pyrrolylsilane7
have been reported. To our knowledge, transition-metal
complexes with N-pyrrolylsilyl ligands have not yet been
published.
The new tri-N-pyrrolylsilyl complexes reported in this
paper were prepared from tri-N-pyrrolylsilane, HSiPyr3
(1, Pyr ) 1-NC4H4). This silane has been synthesized
previously from potassium pyrrolide and trichlorosilane8
or from pyrrole and n-tetrasilane.9 However, neither
of these preparations provide easy access to large
amounts of material with high purity, and we therefore
devised a new synthesis for this useful starting material.
Resu lts a n d Discu ssion
Syn th eses. Tri-N-pyrrolylsilane (1) can easily be
prepared from trichlorosilane and pyrrole in the pres-
ence of triethylamine in tetrahydrofuran at -78 °C
(Scheme 1). After the mixture is warmed to room
temperature, addition of n-hexane causes the precipita-
tion of a solid which is removed by filtration. The
desired product can be obtained from the filtrate as a
colorless solid by reducing the volume and precipitation
with n-hexane at -40 °C. Alternatively, removal of the
solvent from the filtrate, followed by distillation under
The chemistry of N-silyl-substituted pyrrole is largely
unexplored, even though silyl functions are commonly
used as protecting groups in organic synthesis. Except
for compounds where the pyrrolyl function is part of
larger conjugated systems such as those found in
indoles, porphyrins, or tetraazaporphyrins, only the
structures of 1-silylpyrrole,5 1-[bis(trimethylsilyl)(tri-
methylsiloxy)silyl]-2,3,4-tris(1,1-dimethylethyl)-5-phen-
(5) Glidewell, C.; Robiette, A. G.; Sheldrick, G. M. J . Mol. Struct.
1971, 9, 476.
(6) Richter, H.; Arenz, S.; Michels, G.; Schneider, J .; Wagner, O.;
Regitz, M. Chem. Ber. 1988, 121, 1363.
† Telefax: (+64) 9/373 7422. E-mail: w.roper@auckland.ac.nz.
X Abstract published in Advance ACS Abstracts, May 15, 1997.
(1) Dedicated to Professor Dr. Wolfgang Beck on the occasion of his
65th birthday.
(2) Moloy, K. G.; Petersen, J . L. J . Am. Chem. Soc. 1995, 117, 7696.
(3) Clark, G. R.; Flower, K. R.; Rickard, C. E. F.; Roper, W. R.; Salter,
D. M.; Wright, L. J . J . Organomet. Chem. 1993, 462, 331.
(4) Lichtenberger, D. L.; Rai-Chaudhuri, A. J . Am. Chem. Soc. 1991,
113, 2923.
(7) Frenzel, A.; Herbst-Irmer, R.; Klingebiel, U.; Noltemeyer, M.;
Scha¨fer, M. Z. Naturforsch. 1995, B50, 1658. Allen, F. H.; Kennard,
O. 3D Search and Research Using the Cambridge Structural Database.
Chemical Design Automation News 1993, 8 (1), 31.
(8) Atwood, J . L.; Cowley, A. H.; Hunter, W. E.; Sena, S. F. Gov.
Rep. Announce. Index (U.S.) 1982, 82, 4027; Chem. Abstr. 1983, 98,
45906q.
(9) Schmidbaur, H.; Schuh, H. Z. Naturforsch. 1990, B45, 1679.
S0276-7333(97)00044-7 CCC: $14.00 © 1997 American Chemical Society

Tri-N-pyrrolylsilyl Complexes of Ru and Os
Organometallics, Vol. 16, No. 12, 1997 2731
Ta ble 1. C-O Str etch in g F r equ en cies (cm -1) for
Sch em e 2
Silyl Com p lexes of Ru th en iu m a n d Osm iu m
Ru(SiR3)-
Os(SiR3)-
Os(SiR3)-
R
Cl(CO)(PPh3)2
Cl(CO)(PPh3)2
Cl(CO)2(PPh3)2
Me
OH
Py
Cl
191115
193715
1943
189515
191916
1915
1998, 194015
2023, 196215
2041, 1967
195615
196417
194415
194617
2045, 198515
F
results in a diminished susceptibility to nucleophilic
attack, e.g. by water molecules. A mechanism has been
described for hydridosilyliridium complexes in which the
silyl ligand hydrolyzes after a reductive elimination to
give the free silane, and subsequently the resulting
hydroxysilane oxidatively adds to form a hydroxysilyl
complex.14 However, a similar reaction was not ob-
served for the oxidative addition products 2a ,b and 4,
possibly because of the strength of the metal-silicon
bond in these compounds.
The five-coordinate Os(SiPyr3)Cl(CO)(PPh3)2 (3b) adds
CO, but the reaction is easily reversed. When the six-
coordinate, almost colorless Os(SiPyr3)Cl(CO)2(PPh3)2
(5) is quickly precipitated from solution with n-hexane,
the loss of the second CO ligand after redissolution in
CDCl3 can be easily detected by a color change to yellow
or via NMR spectroscopy over a 15 min period. In the
following section a selection of IR and NMR parameters
for the new silyl compounds reported here are compared
with values for related compounds. A full list of
spectroscopic data can be found in the Experimental
Section.
high vacuum, gives the product as a colorless oil which
solidifies within a few hours. Both methods give 1 in
high purity. For further reactions, tri-N-pyrrolylsilane
can be used as a solid or, with a melting point of only
32 °C, as a liquid. Because of the sensitivity of the
compound to moisture, the latter possibility was gener-
ally more convenient. The product is stable under
nitrogen, but the solid hydrolyzes slowly in air and
much faster on dissolution in undried chloroform to give
pyrrole and unidentified silicon products.
The six-coordinate compounds M(SiPyr3)H(CO)2-
(PPh3)2 (2a , M ) Ru, 2b, M ) Os) were prepared from
10,11
M(CO)2(PPh3)3
and tri-N-pyrrolylsilane (1) in tolu-
ene. For the ruthenium complex the originally orange
mixture instantaneously turned pale yellow on addition
of 1 and after 10 min 2a was obtained as a white powder
on addition of n-hexane. The analogous osmium deriva-
tive, on the other hand, was formed only after irradia-
tion with a quartz-iodine lamp for 5 min at room
temperature, during which time the solution turned
from yellow to colorless.
IR a n d NMR Sp ectr a . The IR spectrum of the free
tri-N-pyrrolylsilane (1) shows a significant band for the
Si-H stretch at 2233 cm-1 as well as a very strong,
characteristic absorption at 1199 cm-1
. Similarly, a
Os(SiPyr3)HCl(NO)(PPh3)2 (4) was synthesized by
12
characteristic absorption for the tri-N-pyrrolylsilyl ligand
is found between 1179 and 1182 cm-1 in the IR spectra
of 2-5, which makes it very easy to identify the
presence of this ligand in a transition-metal complex.
The second important feature when one analyzes the
IR data of complexes 2-5 is the location of the C-O
stretching frequencies, which are considered to be an
indication of the electron density at the metal center.
In all tri-N-pyrrolylsilyl complexes the values of ν(CO)
are approximately 30 cm-1 higher than the frequencies
for the corresponding trialkylsilyl derivatives (see Table
1) and in each case they fall between the values found
for analogous compounds containing trihydroxysilyl or
trichlorosilyl groups. This suggests a highly electron
withdrawing nature for the tri-N-pyrrolylsilyl ligand.
In Os(SiPyr3)H(CO)2(PPh3)2 (2b), for example, ν(CO) is
1953 cm-1, whereas for the isostructural Os(SiEt3)H-
(CO)2(PPh3)2 a parameter of only 1925 cm-1 is reported.3
This can be explained in terms of either an inductive
adding air-sensitive green OsCl(NO)(PPh3)3 to a solu-
tion of tri-N-pyrrolylsilane (1) in benzene. The reaction
proceeded immediately at room temperature with the
solution changing from colorless to orange. After reduc-
tion of the solvent volume, Os(SiPyr3)HCl(NO)(PPh3)2
(4) was precipitated by addition of n-hexane.
With the phenyl compounds MPhCl(CO)(PPh3)213 and
tri-N-pyrrolylsilane (1) as starting materials, the cor-
responding five-coordinate silyl complexes M(SiPyr3)-
Cl(CO)(PPh3)2 (3a , M ) Ru; 3b, M ) Os) were formed
by irradiation with a quartz-iodine lamp in toluene for
2 h (3a ) or 10 h (3b). The reaction flasks were not
cooled, and therefore the solutions reached approxi-
mately 50 °C.
In contrast to the parent tri-N-pyrrolylsilane (1) all
tri-N-pyrrolylsilyl complexes are surprisingly stable to
moisture. They can be kept in a desiccator for months
without decomposition and are stable even in undried
solvents for days. This reduced susceptibility toward
hydrolysis has been observed for other transition-metal
silyl complexes. An explanation could be that the
electrophilicity of the silyl group is reduced because of
electron donation from the metal to the silicon.14 This
(14) Aizenberg, M.; Goikhman, R.; Milstein, D. Organometallics
1996, 15, 1075.
(15) Salter, D. M. The Synthesis and Reactivity of New Ruthenium
and Osmium Silyl Complexes. Thesis, The University of Auckland,
Auckland, New Zealand, 1993.
(16) Rickard, C. E. F.; Roper, W. R.; Salter, D. M.; Wright, L. J . J .
Am. Chem. Soc. 1992, 114, 9682.
(17) Maddock, S. M. Studies of Ruthenium and Osmium Silyl
Complexes. Thesis, The University of Auckland, Auckland, New
Zealand, 1995.
(10) Cavit, B. E.; Grundy, K. R.; Roper, W. R. J . Chem. Soc., Chem.
Commun. 1972, 60.
(11) Collins, T. J .; Grundy, K. R.; Roper, W. R. J . Organomet. Chem.
1982, 231, 161.
(12) Hill, A. F.; Roper, W. R.; Waters, J . M.; Wright, A. H. J . Am.
Chem. Soc. 1983, 105, 5939.
(13) Rickard, C. E. F.; Roper, W. R.; Taylor, G. E.; Waters, J . M.;
Wright, L. J . J . Organomet. Chem. 1990, 389, 375.
(18) (a) Hahn, T., Ed. International Tables for Crystallography, 2nd
ed.; Reidel: Dordrecht The Netherlands, 1984; Vol. A (Space-Group
Symmetry). (b) Sheldrick, G. M. SHELXTL/PC, Version 5.0; Siemens
Industrial Automation Inc., Madison, WI, 1995.

2732 Organometallics, Vol. 16, No. 12, 1997
Hu¨bler et al.
Ta ble 2. X-r a y Da ta for HSiP yr 3 (1) a n d
Os(SiP yr 3)H(CO)2(P P h 3)2‚H2O (2b‚H2O)
or mesomeric electron-withdrawing effect. The fact that
only one C-O stretching band is observed for the
compounds of the type M(SiPyr3)H(CO)2(PPh3)2 (2a , M
) Ru; 2b, M ) Os) indicates the presence of two
mutually trans carbonyl groups, and this has been
confirmed by analysis of NMR and X-ray data (see
below).
1
2b‚H2O
chem formula
fw
C12H13N3Si
227.34
C50H45N3O3OsP2Si
1016.12
cryst descripn
colorless needles
colorless blocks
0.38 × 0.28 × 0.28
triclinic,
cryst dimens (mm) 0.30 × 0.20 × 0.15
cryst syst,
space group
orthorhombic,
1
Pcab (No. 61)18a
P1h (No. 2)18a
218
In the H NMR spectrum of tri-N-pyrrolylsilane (1)
mp (°C)
a (pm)
b (pm)
c (pm)
R (deg)
â (deg)
γ (deg)
V (m3)
Z
32
the resonance for the silicon-bound hydrogen is observed
931.88(2)
974.32(2)
2647.98(4)
90
90
90
1037.7(3)
1277.8(5)
1870.6(2)
86.83(2)
89.71(2)
66.76(3)
1
at 6.14 ppm, accompanied by silicon satellites with J HSi
) 284.5 Hz, along with two pseudo triplets of an AA′XX′
pattern for R- and â-protons of the pyrrolyl rings at 6.86
and 6.47 ppm, respectively. The corresponding R- and
â-carbon atoms can be found as singlets at 113.5 and
123.6 ppm, respectively in the 13C{1H} NMR spectrum.
The 29Si NMR spectrum shows a doublet at -37.8 ppm
[2404.23(8)] × 10-30 [2275.2(11)] × 10-30
8
2
Fcalcd (kg m-3
F(000)
)
1.256 × 103
1.483 × 103
1
960
1020
with a very large J HSi coupling constant of 284.5 Hz
radiation, temp (K) Mo KR, 203(2)
Mo KR, 193(2)
2944
-12 e h e 11,
-15 e k e 0,
-22 e l e 22
1.7 e θ e 25.0
and no fine structure due to coupling with the protons
µcalcd (m-1
)
171
1
of the pyrrolyl rings. The H resonances of comparable
range of rflns
-11 e h e 11,
-10 e k e 12,
-33 e l e 32
1.5 e θ e 21.5
silanes such as triethyl- and triphenylsilane show much
1
smaller J HSi values of 177.7 and 196.8 Hz, respectively,
range of θ (deg)
no. of rflns
collected
unique
included
Fo > 4σ(Fo)
no. of params/
restraints
wR2, R1a
GOFa
and are shifted upfield to 3.68 and 5.60 ppm, respec-
tively.
8581
1372
1371
1113
197/0
8327
7932
7589
6676
536/0
The 1H NMR spectra of the six-coordinate hydride
complexes M(SiPyr3)H(CO)2(PPh3)2 (2a , M ) Ru; 2b, M
) Os) show the characteristic resonances for the hy-
drogen atoms bound to the metal center at -8.17 (2a )
and -9.32 ppm (2b) in the form of doublets of doublets
0.149, 0.073
1.29
0.168, 0.057
1.02
2
2
with coupling constants of J HPcis ) 18.7 and J HPtrans
R1 ) ∑||Fo| - |Fc||/∑|Fo|; wR2 ) {∑w(Fo - Fc2)2/∑w(Fo2)2}1/2
;
2
2
a
2
) 52.7 Hz for 2a and J HPcis ) 21.2 and J HPtrans ) 36.0
Hz for 2b. The coupling pattern clearly indicates that
the two triphenylphosphine groups are mutually cis and
that the hydride is trans to one phosphorus atom. The
presence of cis PPh3 ligands can also be seen from the
13C NMR data. Most compounds with two triphenyl-
phosphine ligands such as M(SiPyr3)Cl(CO)(PPh3)2 (3a,b)
have a trans arrangement of these two bulky groups
with resulting pseudo triplets for the ipso, ortho, and
meta carbon atoms of the phenyl rings. The 13C NMR
spectra of the six-coordinate complexes 2a and 2b,
however, show two sets of doublets for these atoms, and
this requires the existence of two chemically different
triphenylphosphine ligands.
GOF ) {∑w(Fo - Fc2)2/(n - p)}1/2
.
2
X-r a y Str u ctu r es of Com p ou n d s 1 a n d 2b. The
solid-state structures of 1 and 2b, which were deter-
mined by single-crystal X-ray studies, contain one free
tri-N-pyrrolylsilane molecule or one Os(SiPyr3)H(CO)2-
(PPh3)2 molecule accompanied by a solvate water mol-
ecule, respectively, per asymmetric unit. Crystal data
and data collection parameters are listed in Table 2, and
Figures 1 and 2 show perspective views of the two
structures. Obtaining an X-ray structure of both the
free tri-N-pyrrolylsilane and a metal complex of the
novel tri-N-pyrrolylsilyl ligand provides the opportunity
for a direct comparison to be made between the bond
lengths and angles observed for the silyl group in these
two bonding situations. Parameters within the tri-N-
pyrrolylsilyl group for both 1 and 2b are compared in
Table 3, and additional interatomic distances and angles
for complex 2b are given in Table 4.
F igu r e 1. Molecular structure of HSiPyr3 (1).
Very similar values were also found for tetra-N-pyr-
rolylsilane (N-CR, 139.3 pm; CR-Câ, 135.5 pm; Câ-
Câ′, 141.9 pm)7 and for tri-N-pyrrolylphosphine com-
plexes (N-CR, 138.7 pm; CR-Câ, 134.9 pm; Câ-Câ′,
139.5 pm).2 There are, however, differences between
the structures 1 and 2b, and the most obvious of these
are found in the interatomic distances and angles
involving silicon.
The average Si-N bond length of 172.9 pm in 1 is
comparable to the 172.5 pm found for tetra-N-pyrrolyl-
silane.7 The sum of the covalent radii for the Si-N bond
is approximately 188 pm.19 However, most of the
observed Si-N bond lengths for simple molecules (e.g.
Me3SiNHMe 172 pm;20 H3SiNMe2, 171.5 pm21) are much
The average bond lengths within the pyrrolyl rings
of 1 (N-CR, 139.2 pm, CR-Câ, 134.9 pm; Câ-Câ′. 140.3
pm) and 2b (N-CR, 138.6 pm; CR-Câ, 135.8 pm; Câ-
Câ′, 141 pm) show no significant differences (Table 3).
(19) Pauling, L.; Huggins, M. L. Z. Kristallogr. 1934, 87, 205.
(20) Roper, W. R.; Wilkins, C. J . Trans. Faraday Soc. 1962, 58, 1686.
(21) Glidewell, C.; Rankin, D. W. H.; Robiette, A. G.; Sheldrick, G.
M. J . Mol. Struct. 1970, 6, 231.

Tri-N-pyrrolylsilyl Complexes of Ru and Os
Organometallics, Vol. 16, No. 12, 1997 2733
smaller angles are found between electronegative groups
with these bonds having more p character and in turn
more s character is concentrated in bonds to electro-
positive bonding partners. An increased s character in
the Os-Si bond would also explain the much shorter
distance in 2b in comparison with the analogous tri-
ethylsilyl compound. Ab initio calculations to clarify the
influence of electronegative substituents in general and
N-pyrrolyl groups in particular on the nature of the
transition-metal-silicon bond have been undertaken.25
Fully in accord with the IR and NMR spectroscopic
data, the arrangement of the two carbonyl groups in Os-
(SiPyr3)H(CO)2(PPh3)2 (2b) is trans (C1-Os-C2, 171.6-
(4)°) and the two triphenylphosphine ligands take up
mutually cis positions (P3-Os-P4, 103.47(8)°). The tri-
N-pyrrolylsilyl ligand is located trans to one of the latter
groups, which results in a mer arrangement of the three
bulky ligands in this complex. The fourth coordination
site in this mer plane is occupied by the hydride, which
could not be found in the X-ray structure determination.
Due to the steric demands of the three bulky groups the
Si-Os-P3 angle of 153.49(8)° is much smaller than
180° and the angles between cis-positioned silyl and
phosphine ligands are much larger than 90° (101.92(8)
and 103.47(8)°), showing that Si and P3 are bent toward
the hydride position. In addition to that, two larger and
one smaller Os-Si-N angle around silicon (120.8(2),
119.3(3), and 112.4(2)°) show that one of the pyrrolyl
rings of the tri-N-pyrrolylsilyl ligand points in the
direction of the hydride. It might be expected that a
comparison of the Os-C and C-O bond lengths in
complex 2b and its triethylsilyl analogue, Os(SiEt3)H-
(CO)2(PPh3)2, would also be revealing, but unfortunately
the corresponding parameters do not differ by more than
3 times their standard deviations.3
F igu r e 2. Molecular structure of Os(SiPyr3)H(CO)2-
(PPh3)2‚H2O (2b‚H2O). All hydrogen atoms are omitted for
clarity. The solvent water molecule is not displayed.
shorter, and the mean value for 170 compounds with
silicon bound to a three-coordinate nitrogen atom22 is
174.8 pm.
The average Si-N distance in the tri-N-pyrrolylsilyl
complex 2b is 5.3 pm longer than in the free silane,
which suggests weaker bonds between silicon and the
three nitrogen atoms. An important factor in explaining
this difference lies in the special nature of the free
electron pairs on the pyrrolyl nitrogen atoms. On the
one hand, they are involved in the aromatic systems of
the five-membered rings, but on the other hand, they
can also potentially act as donors to silicon, thereby
strengthening the Si-N bonds and equalizing the
electron deficiency (via “back-donation”) at silicon which
arises from the electron-withdrawing, electronegative
nitrogen atoms. With hydrogen being the fourth sub-
stituent at silicon in compound 1, there is no alternative
to this back-donation from the pyrrolyl groups, but in
the case of complex 2b the transition-metal fragment
can partially overcome the electron deficiency at silicon
by back-bonding into a combination of the σ*-orbitals
of the SiN3 group. Consequently, the three Si-N bonds
would be weakened and the Os-Si bond strengthened.
In fact, the Os-Si distance in 2b (237.5(2) pm) is much
shorter than the one found for the analogous triethyl-
silyl compound (249.3 pm).3 While some other six-
coordinate SiR3 complexes of osmium with electron-
withdrawing groups R show similar short Os-Si
distances, for example 237.7 pm in Cl3Si-Os(CO)4-Os-
(CO)4-Os(CO)4-SiCl3, in which a second-transition
metal center is trans to the trichlorosilyl group,23 others
show much larger values, for example 246.4 pm in Os-
[Si(OH)3]Cl(CO)2(PPh3)2, in which CO is trans to sili-
con.15 This illustrates the important effect another
strong π-acceptor trans to the silyl ligand has on the
Os-Si distance.
Con clu sion s
Tri-N-pyrrolylsilane is a versatile reagent which
undergoes reactions with a number of osmium and
ruthenium complexes in different oxidation states.
Unusually short Os-Si and particularly long Si-N
distances in Os(SiPyr3)H(CO)2(PPh3)2 compared to the
parent tri-N-pyrrolylsilane as well as the lack of reac-
tivity of all the tri-N-pyrrolylsilyl complexes are signs
of a strong interaction between silicon and the metal
center, and this is probably due to back-bonding.
Relatively high CO stretching frequencies of the tri-N-
pyrrolylsilyl complexes fall between the values found
for compounds containing trihydroxysilyl or trichlorosi-
lyl groups and suggest that the tri-N-pyrrolylsilyl group
acts as a π-acceptor.
Exp er im en ta l Section
An alternative explanation arises from the discussion
of the bond angles at silicon. While the average
N-Si-N angle within the SiN3 group drops from 109.0
to 100.3° as one goes from the free silane 1 to the silyl
complex 2b, the average angle from one pyrrolyl ring
to the fourth substituent at silicon, hydrogen or osmium,
rises from 110 to 117.5°. According to Bent’s rule,24
Gen er a l Com m en ts. All reactions were carried out using
standard Schlenk techniques under a dry atmosphere of
oxygen-free dinitrogen. The solvents were carefully dried and
distilled from the appropriate drying agents prior to use.26
NMR spectra were measured at 25 °C on a Bruker DRX 400
spectrometer at 400.128 MHz (1H), 100.625 MHz (13C), or
79.495 MHz (29Si). All chemical shifts were recorded in ppm
downfield from tetramethylsilane on the δ scale. The carbon-
(22) Allen, F. H.; Kennard, O.; Watson, D. G.; Brammer, L.; Orpen,
A. G.; Taylor, R. J . Chem. Soc., Perkin Trans. 2 1987, 1.
(23) Willis, A. W.; van Bouren, G. N.; Pomeroy, R. K.; Einstein, F.
W. B. Inorg. Chem. 1983, 22, 1162.
(25) Hu¨bler, K.; Hu¨bler, U.; Roper, W. R.; Schwerdtfeger, P.; Wright,
L. J . Chemistry, in press.
(26) Perrin, D. D.; Armarego, W. L. F. Purification of Laboratory
Chemicals, 3rd ed.; Pergamon Press: New York, 1988.
(24) Bent, H. A. Chem. Rev. 1961, 61, 275.

2734 Organometallics, Vol. 16, No. 12, 1997
Hu¨bler et al.
Ta ble 3. Selected In ter a tom ic Dista n ces (p m ) a n d An gles (d eg) w ith in th e Tr i-N-p yr r olylsilyl Gr ou p
of HSiP yr 3 (1, n ) 1-3) a n d Os(SiP yr 3)H(CO)2(P P h 3)2‚H2O (2b‚H2O: n ) 5-7) Togeth er w ith Th eir
Aver a ged Va lu es
n ) 1
n ) 2
n ) 3
av
n ) 5
n ) 6
n ) 7
av
Si-Nn
171.1(4)
140.7(7)
138.4(7)
133.4(8)
134.4(9)
140.2(9)
105(2)
112.8(2)
128.7(4)
126.1(4)
105.1(5)
136(4)
173.5(4)
140.3(7)
137.1(7)
134.6(9)
135.6(8)
141.2(9)
116(2)
106.8(2)
125.0(4)
128.3(4)
106.2(5)
174.0(4)
137.3(7)
141.1(6)
136.8(8)
134.8(8)
139.5(8)
109(2)
172.9
178.8(7)
137.4(11)
138.0(11)
135.8(14)
137.3(14)
142(2)
120.8(2)
100.3(3)
125.9(6)
126.6(6)
107.4(7)
237.5(2)
178.7(7)
139.1(12)
137.7(12)
136.1(14)
134.5(14)
142(2)
119.3(3)
101.1(3)
124.0(6)
125.5(6)
107.7(7)
177.0(7)
140.6(12)
138.8(12)
134(2)
137(2)
140(2)
112.4(2)
99.5(3)b
126.0(6)
127.5(7)
104.9(8)
178.2
Nn-Cn1
Nn-Cn4
139.2
138.6
Cn1-Cn2
Cn3-Cn4
134.9
140.3
110
135.8
141
117.5
100.3
Cn2-Cn3
H/Os-Si-Nn
Nn-Si-N(n+1)
Si-Nn-Cn1
Si-Nn-Cn4
Cn1-Nn-Cn4
Si-H/Os
107.3(2)a
125.4(4)
127.4(4)
106.9(4)
109.0
126.8
106.1
125.9
106.7
a
b
N3-Si-N1. N7-Si-N5.
Ta ble 4. Ad d ition a l Bon d Len gth s (p m ) a n d
An gles (d eg) for Os(SiP yr 3)H(CO)2(P P h 3)2‚H2O
(2b‚H2O)
) 10 Hz; o-C6H5), 124.7 (s; â-C, Pyr), 110.0 (s; R-C, Pyr). IR
(Nujol): ν 1966 (CO), 1899 (RuH), 1181 cm-1 (SiPyr3). MS
(m/ e (%)): 910 (13) [M+], 654 (100) [M+ - HSiPyr3 - CO].
Anal. Calcd for C50H43N3O2SiP2Ru (909.10): C, 66.07; H, 4.77;
N, 4.62. Found: C, 66.12; H, 5.00; N, 4.30.
Os-C1
C1-O1
Os-P3
189.6(9)
116.9(11)
240.7(2)
Os-C2
C2-O2
Os-P4
188.5(9)
119.4(11)
241.1(2)
Os(SiP yr 3)H(CO)2(P P h 3)2 (2b). The yellow solution of Os-
(CO)2(PPh3)3 (130 mg, 0.126 mmol) and HSiPyr3 (69 mg, 41.6
µL, 0.304 mmol) in 20 mL of toluene turned colorless after 5
min irradiation with a quartz-iodine lamp. After a further 5
min of irradiation concentration of the solution under vacuum
to approximately 1 mL and addition of 20 mL of n-hexane leads
to a white solid which can be recrystallized out of CH2Cl2/n-
hexane to give pure 2b (96 mg, 0.096 mmol, 76%). Mp: 218
°C dec. 1H NMR (CDCl3): δ 8.0-6.5 (m, 30H; P(C6H5)3), 6.21
Si-Os-C1
Si-Os-C2
Si-Os-P3
Si-Os-P4
C1-Os-C2
P3-Os-P4
88.0(3)
83.9(3)
153.49(8)
101.92(8)
171.6(4)
103.47(8)
C1-Os-P3
C1-Os-P4
C2-Os-P3
C2-Os-P4
Os-C1-O1
Os-C2-O2
100.1(2)
88.5(3)
86.2(3)
95.5(3)
180.0(9)
174.7(8)
phosphorus coupling n/mJ CP in the triphenylphosphine ligands
n
2
2
stands for | J CP
+
mJ CP|; the hydrogen-hydrogen coupling
(t, J HH ) 1.7 Hz, 6H; R-H, Pyr), 6.11 (t, J HH ) 1.7 Hz, 6H;
n/m
n
2
J
in the pyrrolyl rings means | J HH
+
mJ HH|. Infrared
â-H, Pyr), -9.32 (dd, J HP ) 36.0 and 21.2 Hz, 1H; OsH). 13C
HH
spectra were recorded on a Perkin-Elmer Paragon 1000PC FT-
IR spectrometer. High-resolution mass spectra (fast atom
bombardment, FAB+ at 8 kV) were determined on a VG 70-
SE mass spectrometer. Melting points are reported in degrees
Celsius (uncorrected). Analytical data were obtained from the
Microanalytical Laboratory, University of Otago. Evidence of
solvation of some analytical samples was apparent from the
1H NMR spectrum (H2O, δ 1.58 (s); CH2Cl2, 5.29 (s)). Ru(CO)2-
(PPh3)3,10 Os(CO)2(PPh3)3,11 OsCl(NO)(PPh3)3,12 RuPhCl(CO)-
NMR (CDCl3): δ 188.4 (t, 2J CP ) 10 Hz; CO-C6H5), 135.5 and
1
135.0 (d, J CP ) 47 and 42 Hz; i-C6H5), 133.3 and 133.2 (d,
3
each J CP ) 10 Hz; m-C6H5), 130.1 and 130.0 (s; p-C6H5), 128.3
2
and 128.2 (d, each J C,P ) 10 Hz; o-C6H5), 124.6 (s; â-C, Pyr),
110.0 (s; R-C, Pyr). 29Si{1H} NMR (CDCl3): δ 4.9 (d, J SiPtrans
2
) 74.8 Hz). IR (Nujol): ν 2039 (OsH), 1953 (CO), 1179 cm-1
(SiPyr3). MS (m/ e (%)): 1000 (17) [M+], 263 (100) [P(Ph3)3H+].
Anal. Calcd for C50H43N3O2SiP2Os‚H2O (1016.16): C, 59.10;
H, 4.46; N, 4.14. Found: C, 59.43; H, 4.49; N, 4.03.
13
(PPh3)2,13 and OsPhCl(CO)(PPh3)2 were all prepared accord-
Ru (SiP yr 3)Cl(CO)(P P h 3)2 (3a ). After 2 h of irradiation
with a quartz-iodine lamp without cooling (50 °C) the red-
orange solution of RuPhCl(CO)(PPh3)2 (179 mg, 0.234 mmol)
and HSiPyr3 (100 µL, 166 mg, 0.730 mmol) in 20 mL of toluene
turned yellow. The crude product obtained by reducing the
volume and adding n-hexane is recrystallized out of CH2Cl2/
n-hexane to give pure 3a (175 mg, 0.191 mmol, 82%). Mp:
198 °C dec. 1H NMR (CDCl3): δ 7.7-6.9 (m, 30H; P(C6H5)3),
ing to literature procedures.
HSiP yr 3 (1). To a solution of pyrrole (8.4 mL, 120 mmol)
and triethylamine (20 mL) in 50 mL of tetrahydrofuran at -78
°C was added trichlorosilane (4.1 mL, 40 mmol) within 1 min.
After the mixture was warmed to room temperature, n-hexane
was added and the solution filtered. Reduction of the volume
of the filtrate under vacuum and distillation at 86 °C/1 Torr
2
2
leads to pure tri-N-pyrrolylsilane (25.1 g, 15.1 mL, 110.4 mmol,
6.18 (t, J HH ) 1.9 Hz, 6H; R-H, Pyr), 5.90 (t, J HH ) 1.9 Hz,
3/4
2
92%). Mp: 32 °C. 1H NMR (CDCl3): δ 6.86 (t′,
J
) 4.0
6H; â-H, Pyr). 13C NMR (CDCl3): δ 199.5 (t, J CP ) 12 Hz;
CO-C6H5), 134.8 (t′,
) 46 Hz; i-C6H5), 130.3 (s; p-C6H5), 128.2 (t′,
HH
Hz; R-H, Pyr), 6.47 (t′, 3/4J HH ) 4.0 Hz; â-H, Pyr), 6.14 (s; SiH).
13C NMR (CDCl3): δ 123.6 (s; â-C, Pyr), 113.5 (s; R-C, Pyr).
J
) 12 Hz; m-C6H5), 131.2 (t′,
J
3/5
1/3
CP
CP
2/4
J
) 10 Hz;
CP
29Si NMR (CDCl3): δ -37.8 (d, J SiH ) 284.5 Hz). IR (Nujol):
o-C6H5), 125.5 (s; â-C, Pyr), 110.4 (s; R-C, Pyr). IR (Nujol): ν
1936 (CO), 1927 (CO), 1181 cm-1 (SiPyr3). MS (m/ e): 916
[M+]. Anal. Calcd for C49H42N3OSiP2ClRu‚2.5H2O (960.49):
C, 61.28; H, 4.93; N, 4.37. Found: C, 61.48; H, 4.82; N, 4.35.
1
ν 2233 (SiH), 1199 cm-1 (SiPyr3). Because of difficulties with
the moisture sensitivity of 1, no satisfactory chemical analysis
could be obtained.
Ru (SiP yr 3)H(CO)2(P P h 3)2 (2a ). The orange solution of
Ru(CO)2(PPh3)3 (411 mg, 0.436 mmol) in 30 mL of toluene
immediately turned pale yellow when HSiPyr3 (300 µL, 498
mg, 2.19 mmol) was added. After 10 min at room temperature
the solution was concentrated to ca. 2 mL, and 10 mL of
n-hexane was added. Recrystallization from CH2Cl2/n-hexane
yields pure, white 2a (300 mg, 0.330 mmol, 76%). Mp: 225
°C dec. 1H NMR (CDCl3): δ 7.7-6.8 (m, 30H; P(C6H5)3), 6.26
Os(SiP yr 3)Cl(CO)(P P h 3)2 (3b). A solution of OsPhCl(CO)-
(PPh3)2 (315 mg, 0.368 mmol) and HSiPyr3 (100 µL, 166 mg,
0.730 mmol) in 20 mL of toluene turned reddish brown after
10 h of irradiation with a quartz-iodine lamp without cooling
(50 °C). After the volume is reduced under vacuum to
approximately 2 mL and 15 mL of n-hexane is added, the solid
obtained can be recrystallized out of CH2Cl2/n-hexane. This
yields pure 3b (286 mg, 0.285 mmol, 77%) in the form of an
orange powder. Mp: 185 °C dec. 1H NMR (CDCl3): δ 7.45-
6.90 (m, 30H; P(C6H5)3), 6.13 (t, 2J HH ) 1.9 Hz, 6H; R-H, Pyr),
2
2
(t, J HH ) 1.7 Hz, 6H; R-H, Pyr), 6.13 (t, J HH ) 1.7 Hz, 6H;
2
â-H, Pyr), -8.17 (dd, J HP ) 18.7 and 52.7 Hz, 1H; OsH). 13C
2
NMR (CDCl3): δ 202.9 (t, 2J CP ) 12 Hz; CO-C6H5), 135.6 and
5.88 (t, J HH ) 1.9 Hz, 6H; â-H, Pyr). 13C NMR (CDCl3): δ
1/3
3/5
2
3/5
135.0 (d,
J
) 38 and 39 Hz; i-C6H5), 133.2 (d,
J
) 12
182.1 (t, J CP ) 8 Hz; CO-C6H5), 134.9 (t′,
J
) 11 Hz;
CP
CP
CP
2/4
2/4
Hz; m-C6H5), 129.8 (s; p-C6H5), 128.4 and 128.3 (d, each
J
m-C6H5), 130.4 (s; p-C6H5), 128.2 (t′,
J
) 10 Hz; o-C6H5),
CP
CP

Tri-N-pyrrolylsilyl Complexes of Ru and Os
Organometallics, Vol. 16, No. 12, 1997 2735
125.3 (s; â-C, Pyr), 110.1 (s; R-C, Pyr). IR (Nujol): ν 1915 (CO),
1182 cm-1 (SiPyr3). MS (m/ e (%)): 1006 (28) [MH+], 263 (100)
[P(Ph3)3H+]. Anal. Calcd for C49H42N3OSiP2ClOs‚1.5H2O
(1031.60): C, 57.05; H, 4.40; N, 4.07. Found: C, 57.12; H, 4.42;
N, 4.08.
non-hydrogen atoms. All hydrogen atoms were refined freely
with isotropic temperature factors. Further results of the
refinement are listed in Table 2.
X-r a y Exp er im en ta l Da ta for 2b‚H2O. Suitable crystals
were obtained by diffusion of n-hexane into a chloroform
solution of the compound at room temperature. Data were
collected on an Enraf-Nonius CAD4 diffractometer. An XEMP
(SHELXTL Plus)18b absorption correction was applied. The
structure was solved by Patterson methods, and refinement
on F2 was carried out by full-matrix least-squares techniques
(SHELXTL Plus).18b Anisotropic temperature factors were
used for all non-hydrogen atoms except for the water molecule.
Hydrogen atoms were included in calculated positions with
isotropic temperature factors 20% higher than the correspond-
ing carbon atoms. Further results of the refinement are listed
in Table 2.
Os(SiP yr 3)HCl(NO)(P P h 3)2 (4). To a solution of tri-N-
pyrrolylsilane (1) (100 µL, 166 mg, 0.730 mmol) in 10 mL of
benzene was added, OsCl(NO)(PPh3)3 (184 mg, 0.177 mmol),
and the color changed instantly to orange. After 10 min of
heating under reflux the volume of the solution was reduced
under vacuum. Addition of n-hexane (10 mL) gives a crude
product; recrystallization from CH2Cl2/n-hexane leads to pure
4 in the form of a cream-colored powder (84 mg, 0.083 mmol,
48%). Mp: 178 °C dec. 1H NMR (CDCl3): δ 7.8-7.0 (m, 30H;
P(C6H5)3), 6.33 (s, 6H; R-H, Pyr), 6.12 (s, 6H; â-H, Pyr), -0.38
2
(dd, J HP ) 112.0 and 18.0 Hz, 1H; OsH). 13C NMR (CDCl3):
3
δ 134.3 and 134.0 (d, each J CP ) 10 Hz; m-C6H5), 132.0 and
1
131.2 (d, J CP ) 43 and 41 Hz; i-C6H5), 130.5 and 130.4 (s;
Ack n ow led gm en t. We thank the Alexander von
Humboldt-Stiftung for the award of a Feodor-Lynen
scholarship to K.H., Dr. C. E. F. Rickard for collecting
the data sets for the crystal structure determinations,
and The University of Auckland Research Committee
for supporting this work.
2
p-C6H5), 128.3 (d, J C,P ) 10 Hz; o-C6H5), 125.3 (s; â-C, Pyr),
110.1 (s; R-C, Pyr). IR (Nujol): ν 2083 (OsH), 1783 (NO), 1181
cm-1 (SiPyr3). MS: (m/ e (%)): 1009 (24) [MH+], 263 (100)
[P(Ph3)3H+]. Anal. Calcd for C48H43N4OSiP2ClOs‚1.6CH2Cl2
(1143.47): C, 52.10; H, 3.99; N, 4.90. Found C, 52.42; H, 4.04;
N, 4.24.
X-r a y Exp er im en ta l Da ta for 1. Crystals of 1 were grown
at -40 °C from an n-hexane solution of the compound. Data
Su p p or tin g In for m a tion Ava ila ble: Tables giving de-
scriptions of X-ray procedures and all atomic coordinates,
thermal parameters, and interatomic distances and angles (13
pages). Ordering information is given on any current mast-
head page.
were collected on a Siemens Smart CCD diffractometer.
A
SADABS absorption correction was applied. The structure
was solved by direct methods, and refinement on F2 was
carried out by full-matrix least-squares techniques (SHELXL
Plus).18b Anisotropic temperature factors were used for all
OM970044P