Similarities and contrasts between silyl and stannyl derivatives of ruthenium and osmium

Article abstract of DOI:10.1021/om060526d

Silyl and stannyl complexes of ruthenium and osmium bearing halogen substituents on the silicon and tin atoms undergo many interesting reactions. While there are formal similarities, there are also marked differences between these silyl and stannyl derivatives. This review first surveys the synthetic approaches we have developed to the silyl and stannyl complexes that involve oxidative addition of halogenated silanes coupled with reductive elimination for the preparation of the silyl complexes L_nM(SiR_nX _3-n) (M = Ru, Os) and reaction between L_nMH and the vinylstannane R₃SnCH=CH₂ to give first the triorganostannyl complexes L_nM(SnR₃) (M = Ru, Os), which are then functionalized by redistribution reactions to give L _nM(SnR_nX_3-n) (M = Ru, Os). Among the unusual compounds derived from these halogenated silyl and stannyl complexes are derivatives with the following novel ligands: Si(OH)₃, Sn-(OH) ₃, silatranyl, stannatranyl, SnH₃, and SnMe ₂SnPh₃. A contrast between the osmasilanol L _nOs(SiMe₂-OH) and the osmastannol L _nOs(SnMe₂OH) is that the former deprotonates to a silanolate anion, [L_nOs(SiMe₂O)]^-, while the latter, when treated with base, ortho-stannylates a triphenylphosphine ligand. Another contrast is provided by the ease with which osmium trimethylstannyl complexes undergo α-methyl migration reactions.

Full text of DOI:10.1021/om060526d

4704
Organometallics 2006, 25, 4704-4718
ReViews
Similarities and Contrasts between Silyl and Stannyl Derivatives of
Ruthenium and Osmium
Warren R. Roper* and L. James Wright
Department of Chemistry, The UniVersity of Auckland, Auckland, New Zealand
ReceiVed June 16, 2006
Silyl and stannyl complexes of ruthenium and osmium bearing halogen substituents on the silicon and
tin atoms undergo many interesting reactions. While there are formal similarities, there are also marked
differences between these silyl and stannyl derivatives. This review first surveys the synthetic approaches
we have developed to the silyl and stannyl complexes that involve oxidative addition of halogenated
silanes coupled with reductive elimination for the preparation of the silyl complexes LnM(SiRnX3-n) (M
) Ru, Os) and reaction between LnMH and the vinylstannane R3SnCHdCH2 to give first the
triorganostannyl complexes LnM(SnR3) (M ) Ru, Os), which are then functionalized by redistribution
reactions to give LnM(SnRnX3-n) (M ) Ru, Os). Among the unusual compounds derived from these
halogenated silyl and stannyl complexes are derivatives with the following novel ligands: Si(OH)3, Sn-
(OH)3, silatranyl, stannatranyl, SnH3, and SnMe2SnPh3. A contrast between the osmasilanol LnOs(SiMe2-
OH) and the osmastannol LnOs(SnMe2OH) is that the former deprotonates to a silanolate anion,
[LnOs(SiMe2O)]-, while the latter, when treated with base, ortho-stannylates a triphenylphosphine ligand.
Another contrast is provided by the ease with which osmium trimethylstannyl complexes undergo R-methyl
migration reactions.
of these five- and six-coordinate complexes are shown in
Scheme 1. A divergence between the ruthenium and osmium
complexes is that whereas the osmium complexes, e.g., 3, take
up CO to form the stable dicarbonyl complexes 4, the ruthenium
complexes, e.g., 1, take up CO to give the six-coordinate
complexes 2a, which in solution are in dynamic equilibrium
with the η2-acyl complexes 2b. The position of this equilibrium
depends on steric3 and electronic4 factors associated with both
the aryl group and the halide on the metal.
The coordinative unsaturation of complexes such as 3 opened
pathways to exotic organometallics such as the stable and
structurally characterized methylene complex 5 5 (Scheme 2).
A related observation is that the trichloromethyl complex 6
spontaneously rearranges to the dichlorocarbene complex 7. This
rearrangement is driven by a combination of coordinative
unsaturation at osmium and the presence of a good leaving group
on the metal-bound carbon atom. The dichlorocarbene complex
7, in turn, opens the way to complexes bearing the complete
set of chalcocarbonyl ligands, 8 6 (Scheme 3), and the five-
coordinate carbyne complex 97 (Scheme 3). The key to the
formation of 8 and 9 is the dichlorocarbene complex 7, and
dihalocarbene complexes in general undergo many other
interesting reactions dependent upon the presence of good
I. Introduction
This review, which summarizes our research on ruthenium
and osmium silyl and stannyl complexes over the past 16 years,
begins with a short introductory section that highlights some
of our earlier results involving the synthesis and study of
coordinatively unsaturated organometallic derivatives of ruthe-
nium and osmium. This early organometallic work emphasized
the extraordinary opportunities afforded by coordinative unsat-
uration at the metal center, together with the presence of good
leaving groups on a carbon donor atom, for the synthesis of
unusual products. In an extension of this work, coordinatively
unsaturated (as well as saturated) silyl and stannyl complexes
of ruthenium and osmium that bear good leaving groups on the
silicon or tin donor atoms have been synthesized. Studies have
shown that these compounds are versatile precursors to com-
plexes with novel silicon and tin ligands, and in addition, the
results have allowed interesting comparisons to be made between
the silyl and stannyl complexes.
A. Haloalkyl and Dihalocarbene Complexes. A valuable
development in the organometallic chemistry of ruthenium and
osmium was the discovery that five-coordinate, coordinatively
unsaturated, σ-aryl derivatives, MRCl(CO)(PPh3)2 (M ) Ru,
Os; R ) aryl), were easily accessible from reaction between
MHCl(CO)(PPh3)3 and HgR2.1 In the solid state these colored
compounds (red or orange) proved to have tetragonal-pyramidal
geometry2 and in solution readily take up a variety of small
ligands to form colorless six-coordinate complexes. Examples
(3) Roper, W. R.; Taylor, G. E.; Waters, J. M.; Wright, L. J. J.
Organomet. Chem. 1979, 182, C46.
(4) Clark, G. R.; Roper, W. R.; Wright, L. J.; Yap, V. P. D. Organo-
metallics 1997, 16, 5135.
(5) Bohle, D. S.; Clark, G. R.; Rickard, C. E. F.; Roper, W. R.; Shepard,
W. E. B. Wright, L. J. J. Chem. Soc., Chem. Commun. 1987, 563.
(6) Clark, G. R.; Marsden, K.; Roper, W. R.; Wright, L. J. J. Am. Chem.
Soc. 1980, 102, 1206.
(7) Clark, G. R.; Marsden, K.; Roper, W. R.; Wright, L. J. J. Am. Chem.
Soc. 1980, 102, 6570.
(1) Roper, W. R.; Wright, L. J. J. Organomet. Chem. 1977, 142, Cl.
(2) Rickard, C. E. F.; Roper, W. R.; Taylor, G. E.; Waters, J. M.; Wright,
L. J. J. Organomet. Chem. 1990, 389, 375.
10.1021/om060526d CCC: $33.50 © 2006 American Chemical Society
Publication on Web 09/02/2006

Organometallics, Vol. 25, No. 20, 2006 4705
Scheme 1
Figure 1.
B. From Compounds with M-C Bonds to Compounds
with M-B, M-Si, and M-Sn Bonds (M ) Ru, Os). Looking
beyond organometallic chemistry to “inorganometallic” chem-
istry, the remarkable chemistry associated with halogenated alkyl
ligands sketched above suggested to us that it would be
worthwhile to explore analogous complexes with transition-
metal-boron, -silicon, and -tin bonds. Therefore, we decided
to synthesize both coordinatively unsaturated boryl, silyl, and
stannyl complexes of ruthenium and osmium and their coordi-
natively saturated analogues, especially those which bear at least
one good leaving group on the main-group element. Accord-
ingly, the complexes 13-18 (Figure 1) became target molecules.
This work began about 16 years ago, and the metal-boron
results have been reviewed.10,11 In this review article we
summarize our results on the silyl and stannyl derivatives,
focusing particularly on the similarities and contrasts between
the two classes of compounds.
Scheme 2
Scheme 3a
II. Methods for the Preparation of Transition-Metal
Silyl Complexes
Most transition-metal silyl complexes have been made by
either oxidative addition of a Si-element bond (most commonly
Si-H) or through attack of transition-metal anions at an
electrophilic silicon center (or less commonly the inverse
reaction, attack of silicon anions at a transition-metal center).12
Reactions with transition-metal anions are not appropriate for
the preparation of compounds with halogen-substituted silyl
ligands. Since chlorosilanes are readily available, the oxidative
addition approach to the target molecules 14 with a halosilyl
ligand (i.e., with n ) 0-2; see Figure 1) is at first sight
attractive. However, reactive zerovalent ruthenium and osmium
complexes (e.g., M(CO)2(PPh3)3) are usually incompatible with
compounds containing Si-X (X ) halogen) bonds, because of
the difficulty of preventing the formation of trace amounts of
HX, which bring about rapid protonation of zerovalent com-
plexes. Simple oxidative addition reactions to these zerovalent
complexes were therefore limited to organosilanes without Si-X
bonds.
a The asterisk denotes the proposed intermediate from the reaction
between OsHCl(CO)(PPh3)3 and Hg(CCl3)2.
Scheme 4
(9) Headford, C. E. L.; Roper, W. R. J. Organomet. Chem. 1983, 244,
C53.
(10) Irvine, G. J.; Lesley, M. J. G.; Marder, T. B.; Norman, N. C.; Rice,
C. R.; Robins, E. G.; Roper, W. R.; Whittell, G. R.; Wright, L. J. Chem.
ReV. 1998, 98, 2685.
leaving groups on the carbene carbon atom.8 Even coordinatively
saturated haloalkyl complexes related to 6 (see complex 11 in
Scheme 4) exhibit interesting nucleophilic substitution reactions
at the metal-bound carbon.9
(11) Clark, G. R.; Irvine, G. J.; Rickard, C. E. F.; Roper, W. R.;
Williamson, A.; Wright, L. J. In Contemporary Boron Chemistry; Davidson,
M. G., Hughes, A. K., Marder, T. B., Wade, K., Eds.; Royal Society of
Chemistry: Cambridge, U.K., 2000; pp 379-385.
(12) Tilley, T. D. In The Chemistry of Organic Silicon Compounds; Patai,
S., Rappoport, Z., Eds.; Wiley: New York, 1989; Chapter 24.
(8) Brothers, P. J.; Roper, W. R. Chem. ReV. 1988, 88, 1293.

4706 Organometallics, Vol. 25, No. 20, 2006
Scheme 5
Scheme 7
Scheme 6
compounds Os(SiR3)H3(PH3)3 (R ) H, NH2, NC4H4), allowed
the recognition of a unique kind of bonding in 20-22, in which
the silicon atom interacts with all three equivalent hydrogen
atoms. The hydride ligands are in bridging positions, as shown
in Scheme 6, and three partial Si‚‚‚H-Os three-center bonds
are formed.16 An alternative description of this bonding has been
discussed.19 Crystal structures have been determined for both
21 and 22. The Os-Si bond in 21 is 2.293(3) Å, and the
corresponding distance in 22 is 2.3442(8) Å. These are both
short distances when they are compared with typical values for
octahedral osmium complexes, and the value for 21 is almost
as short as those found in the five-coordinate trihalosilyl
complexes Os(SiF3)Cl(CO)(PPh3)2 (2.254(2) Å) and Os(SiCl3)-
Cl(CO)(PPh3)2 (2.273(6) Å) (see section IVB below). The
marked difference between the Os-Si bond distances for 21
and 22 is a reflection of the powerful electron-withdrawing effect
of the N-pyrrolyl substituents on silicon. This effect is also
evident from the theoretical calculations.16 In the crystal structure
of 22 the hydrides are located and the measured Os-H distances
are 1.52(3), 1.66(3), and 1.57(3) Å. The calculated distances
between silicon and hydrogen are Si‚‚‚H(1) ) 2.06(4) Å, Si‚‚
‚H(2) ) 2.00(4) Å, and Si‚‚‚H(3) ) 1.96(3) Å. These numbers
are indicative of very weak Si‚‚‚H interactions in complex 22.
Nevertheless, the measured Si-H coupling constants in 20 and
21 are 47.4 and 29.2 Hz, respectively. The three compounds
20-22 represent new examples of nonclassical interligand
interactions between one silyl group and three hydride ligands.19
III. Synthesis of Six- and Seven-Coordinate Silyl
Complexes via Oxidative Addition of Si-H Bonds to
Reactive Complexes of Ruthenium and Osmium
A. Oxidative Addition to Os(CO)2(PPh3)3. As illustrated
in Scheme 5, the zerovalent osmium complex Os(CO)2(PPh3)3
reacts with a range of organosilanes to give the octahedral silyl
complexes 19.13-15 These products sometimes exist as a mixture
of geometrical isomers, with the isomer depicted in 19 usually
predominating and confirmed crystallographically for OsH-
(SiEt3)(CO)2(PPh3)213 and OsH[Si(NC4H4)3](CO)2(PPh3)2.14 The
fact that the osmium is coordinatively saturated in these
complexes and especially that the silyl substituents do not
include good leaving groups means that these complexes cannot
readily be further modified and therefore do not offer a route
to the target molecules 14, 15, 17, and 18 (see Figure 1). The
solution to this problem lay in using not a zerovalent complex
of osmium but a five-coordinate phenyl derivative of osmium-
(II), OsPhCl(CO)(PPh3)2, as a substrate for oxidative addition
reactions with silanes, as described below in section IV. Before
we describe this approach, we summarize other interesting silyl
derivatives of Ru(IV) and Os(IV) prepared from oxidative
addition reactions.
B. Oxidative Addition to either RuH2(PPh3)4 or OsH4-
(PPh3)3. As shown in Scheme 6, the seven-coordinate silyl
trihydride complexes Ru[Si(NC4H4)3]H3(PPh3)3 (20)16 and Os-
(SiR3)H3(PPh3)3 (21, R ) NC4H4;16 22, SiR3 ) silatranyl15) are
prepared through treatment of either RuH2(PPh3)4 or OsH4-
(PPh3)3 with the appropriate silane. Compounds of this general
structural type are well-known for both iron (Fe(SiR3)H3L3)17
and ruthenium (Ru(SiR3)H3L3).18 However, there was neither
good structural data with location of the hydride ligands nor
extensive NMR data, particularly Si-H coupling constant
measurements for this class of compounds, until the ruthenium
and osmium complexes 20-22 were reported. The new
information, together with ab initio calculations on the model
IV. Five-Coordinate Ruthenium and Osmium Silyl
Complexes
A. Synthesis. As shown in Scheme 7, the reaction between
the red, coordinatively unsaturated complex OsPhCl(CO)-
(PPh3)2, and excess trichlorosilane proceeds under mild condi-
tions and in high yield to give the yellow complex Os(SiCl3)-
Cl(CO)(PPh3)2 (23).20 This reaction probably involves initial
oxidative addition of the Si-H bond followed by favorable
reductive elimination of benzene. Complex 23 is a member of
the class of compounds represented by 14 in Figure 1 and is a
versatile starting material because of the three reactive Si-Cl
bonds, the coordinative unsaturation at the osmium center, and
the lability of the Os-Cl bond. Moreover, the transformation
of the five-coordinate phenyl complex to the corresponding five-
coordinate silyl complex is equally effective with the ruthenium
analogue RuPhCl(CO)(PPh3)2,21 with silanes bearing either one
(13) 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.
(14) Hu¨bler, K.; Roper, W. R.; Wright, L. J. Organometallics 1997, 16,
2730.
(15) Rickard, C. E. F.; Roper, W. R.; Woodgate, S. D.; Wright, L. J. J.
Organomet. Chem. 2000, 609, 177.
(16) Hu¨bler, K.; Hu¨bler, U.; Roper, W. R.; Schwerdtfeger, P.; Wright,
L. J. Chem. Eur. J. 1997, 3, 1608.
(17) Schubert, U.; Gilbert, S.; Mock, S. Chem. Ber. 1992, 125, 835.
(18) (a) Kono, H.; Wakao, N.; Ito, K.; Nagai, Y. J. Organomet. Chem.
1997, 132, 53. (b) Haszeldine, R. N.; Malkin, L. S.; Parish, R. V. J.
Organomet. Chem. 1979, 182, 323.
(19) Nikonov, G. I. Angew. Chem., Int. Ed. 2001, 40, 3353.
(20) Hu¨bler, K.; Hunt, P. A.; Maddock, S. M.; Rickard, C. E. F.; Roper,
W. R.; Salter, D. M.; Schwerdtfeger, P.; Wright, L. J. Organometallics 1997,
16, 5076.
(21) Clark, G. R.; Rickard, C. E. F.; Roper, W. R.; Salter, D. M.; Wright,
L. J. Pure Appl. Chem. 1990, 62, 1039.

Organometallics, Vol. 25, No. 20, 2006 4707
Scheme 8
Figure 2. Structural data for the five-coordinate osmium complexes
Os(SiR3)Cl(CO)(PPh3)2 (R ) F, Cl, OH, Me). In addition to a
strengthening of the Os-Si bond due to ionic contributions,
calculations reveal the importance of increasing π-bonding in the
order SiMe3 < Si(OH)3 < SiCl3 < SiF3.
d orbitals with a suitable linear combination of either Si-F or
Si-Cl σ* orbitals. In Os(SiF3)Cl(CO)(PPh3)2 the SiF3 ligand
was estimated to have almost half the π-acceptor ability of the
CO ligand in the same molecule. In a related observation, a
photoelectron spectral study established that the SiCl3 ligand
in CpFe(SiCl3)(CO)2 is an effective π-acceptor ligand.28 The
ν(CO) values for Os(SiR3)Cl(CO)(PPh3)2 (R ) F, Cl, OH, Me)
measured in the IR spectra and presented in Figure 2 are
consistent with this picture of the bonding.
C. Reactions at Osmium. The silyl ligand, once introduced
into a five-coordinate ruthenium or osmium complex, can in
some cases undergo an exchange process with a differently
substituted silane; e.g., Os[Si(OH)3]Cl(CO)(PPh3)2 when treated
with HSiMe2Cl affords Os(SiMe2Cl)Cl(CO)(PPh3)2 in good
yield.
An illustration of the usefulness of the labile halide on
osmium in the five-coordinate silyl complexes 14 (see Figure
1) is depicted in Scheme 8, where Os[Si(OEt)3]Cl(CO)(PPh3)2
(25) (from OsPhCl(CO)(PPh3)2 and HSi(OEt)3) undergoes a
reaction with PhLi to replace the chloride and form an Os-
phenyl bond in Os[Si(OEt)3]Ph(CO)(PPh3)2 (26). Both 25 and
26 take up CO to form the six-coordinate complexes Os[Si-
(OEt)3]Cl(CO)2(PPh3)2 (27) and Os[Si(OEt)3]Ph(CO)2(PPh3)2
(28), respectively. Interestingly, the formation of 27 is reversible,
and on heating in solution CO is lost and complex 25 is
reformed. Most bis(triphenylphosphine) dicarbonyl complexes
of osmium(II) resist loss of CO. We have observed one other
osmium silyl complex to behave similarly, Os[Si(NC4H4)3]Cl-
(CO)2(PPh3)2, which loses CO in solution even at room
temperature within minutes.14 It is interesting that in complex
26, where there are two ligands (phenyl and silyl), both of
recognized strong σ bonding/trans influence character, it is the
silyl ligand which dominates and which adopts the apical site
of the tetragonal pyramid, as revealed by crystal structure
determination. Complexes 26 and 28, with adjacent silyl and
aryl ligands, are models for the kind of metal complex
intermediates postulated to facilitate silicon-carbon bond
formation through reductive elimination in metal-catalyzed
processes such as hydrosilation.29 However, both 26 and 28 are
remarkably robust compounds which resist thermal decomposi-
tion at elevated temperatures over long periods of time, and
PhSi(OEt)3 is not observed among the decomposition products
that eventually form.23 These observations are in marked contrast
to the reactivity of the analogous boryl complex Os(Bcatecho-
late)(o-tolyl)(CO)2(PPh3)2, which at room temperature readily
undergoes reductive elimination to form o-tolylBcatecholate.30,31
D. Insertion Reactions into the Ru/Os-Si Bond. Another
reflection of the low reactivity of the Os-Si bonds in both the
or two chlorine substituents, viz., H-SiR2Cl and H-SiRCl2,
with silanes bearing other electronegative substituents such as
H-Si(NC4H4)3, H-Si(OEt)3, and H-Si(OC2H4)3N,14,22-24 and
even with trimethyl- and triethylsilane. However, in an atypical
reaction, trimethylsilane with OsPhCl(CO)(PPh3)2 gives the
osmium(IV) complex OsH3(SiMe3)(CO)(PPh3)2 (24) (see Scheme
7) rather than the expected Os(SiMe3)Cl(CO)(PPh3)2.25 The
formation of this product must involve multiple oxidative
addition and reductive elimination steps. Complex 24 is clearly
related to the trihydride silyl complexes MH3(SiR3)(PPh3)3 (M
) Ru, Os), which have been discussed in section IIIB, above.
B. Structure and Bonding. The tetragonal-pyramidal ge-
ometry of the five-coordinate silyl complexes represented by
14 in Figure 1 has been confirmed by numerous X-ray crystal
structure determinations. In all of these structures the silyl ligand
is located in the apical site. It is worth noting here that the related
five-coordinate boryl complexes of ruthenium and osmium also
adopt this structure with the boryl ligand apical, as do the five-
coordinate stannyl derivatives to be discussed below.26,27
Structural data for the set of five-coordinate osmium complexes
Os(SiR3)Cl(CO)(PPh3)2 (R ) F, Cl, OH, Me) (see Figure 2)
confirm other observations that the transition-metal-silicon
distance becomes shorter as the electronegativity of the sub-
stituents on silicon becomes greater.12 The measured distances
are Os-SiR3 ) 2.254(2), 2.273(6), 2.319(2), and 2.374(2) Å
for R ) F, Cl, OH, Me, respectively.20 These very short
distances lie at the short end of the range of 75 observations
for Os-Si distances recorded in the Cambridge Crystallographic
Data Base, and indeed, the value of 2.254(2) Å remains the
shortest Os-Si distance ever reported. A computational study
of this same set of four isostructural compounds20 shows that,
in addition to the expected strengthening of the Os-Si σ bond
as the ionic contributions increase, there is at least for the SiF3
and SiCl3 ligands a significant contribution to the bonding from
an Os-Si π bond formed from overlap of appropriate osmium
(22) Kwok, W.-H.; Lu, G.-L.; Rickard, C. E. F.; Roper, W. R.; Wright,
L. J. J. Organomet. Chem. 2004, 689, 2511.
(23) Albrecht, M.; Rickard, C. E. F.; Roper, W. R.; Williamson, A.;
Woodgate, S. D.; Wright, L. J. J. Organomet. Chem. 2001, 625, 77.
(24) Attar-Bashi, M. T.; Rickard, C. E. F.; Roper, W. R.; Wright, L. J.;
Woodgate, S. D. Organometallics 1998, 17, 504.
(25) Mo¨hlen, M.; Rickard, C. E. F.; Roper, W. R.; Salter, D. M.; Wright,
L. J. J. Organomet. Chem. 2000, 593-594, 458.
(26) Irvine, G. J.; Roper, W. R.; Wright, L. J. Organometallics 1997,
16, 2291.
(28) Lichtenberger, D. L.; Rai-Chaudhuri, A. J. Am. Chem. Soc. 1991,
113, 2923.
(29) Schubert, U. Angew. Chem., Int. Ed. Engl. 1994, 33, 419.
(27) Rickard, C. E. F.; Roper, W. R.; Williamson, A.; Wright, L. J.
Organometallics 1998, 17, 4869.

4708 Organometallics, Vol. 25, No. 20, 2006
Scheme 9
Scheme 11
Scheme 10
nation. A similar migration occurs with the corresponding
silatranyl complex.24 It is well-established that insertion reactions
involving the thiocarbonyl ligand are much more facile than
the corresponding carbonyl insertion reactions.10,35
Before discussing in detail the nucleophilic substitution
reactions undergone by the halosilyl complexes introduced
above, which are examples of target molecules 14 and 17 (Figure
1), we describe the preparation of the corresponding stannyl
complexes 15 and 18, in order that the reactions of the silyl
and stannyl complexes can be discussed together, drawing
attention to similarities and contrasts between them.
five- and six-coordinate silyl complexes discussed above is that
no insertion reactions with alkynes have been observed.
However, the analogous ruthenium complexes readily undergo
insertion reactions with ethyne, as shown in Scheme 9.32 The
orange, five-coordinate, silyl-substituted vinyl derivatives 30 (R3
) Me3, Et3, Me2OEt) are formed when the corresponding five-
coordinate silyl complexes 29 are placed under ethyne at a
pressure of 0.8 atm and at room temperature for several hours.
In the special case when R3 ) Me2OH, the isomer with cis
geometry about the double bond is trapped by the OH group
coordinating to the ruthenium to form the stable chelated
complex 31. The presence of this five-membered ring was
confirmed by a crystal structure determination of a derivative
of 31. This chemistry parallels the ethyne insertion into the
Ru-B bond in Ru(Bcatecholate)Cl(CO)(PPh3)2, where a related
Ru-O donor bond from an oxygen of the catecholate group
forms a similar five-membered ring.33
V. Methods for the Preparation of Transition-Metal
Stannyl Complexes
The methods detailed above in section II for the synthesis of
transition-metal silyl complexes are generally applicable also
to the synthesis of transition-metal stannyl complexes.36 Restric-
tions are that, once again, reactions with transition-metal anions
are not appropriate for the preparation of compounds with
halogen-substituted stannyl ligands and there are fewer available
stable stannanes, particularly those bearing both hydrogen and
halogen substituents. Nevertheless, the oxidative addition of
simple organostannanes to low-oxidation-state complexes of the
platinum-group metals has been widely used as a method of
preparing compounds containing metal-tin bonds.37
While the insertion reactions described above are limited to
ruthenium, one insertion reaction which did proceed readily with
an osmium complex involved insertion of a thiocarbonyl ligand
into an Os-Si bond. This is depicted in Scheme 10, where the
five-coordinate ruthenium and osmium thiocarbonyl complexes
32 take up CO to give the six-coordinate complexes 33, which
then immediately rearrange at room temperature to the red η2-
silathioacyl complexes 34.34 The structure of the ruthenium
complex was confirmed by an X-ray crystal structure determi-
VI. Synthesis of Six-Coordinate Stannyl Complexes via
Oxidative Addition to Zerovalent Complexes of
Ruthenium and Osmium
Stannanes can replace silanes in oxidative addition to the
zerovalent osmium complexes Os(CO)2(PPh3)3 and OsCl(NO)-
(PPh3)3, as shown in Scheme 11, to give the octahedral stannyl
complexes 3538 and 36.39 Like the silyl complexes, these
(30) Rickard, C. E. F.; Roper, W. R.; Williamson, A.; Wright, L. J.
Angew. Chem., Int. Ed. 1999, 38, 1110.
(31) Rickard, C. E. F.; Roper, W. R.; Williamson, A.; Wright, L. J.
Organometallics 2000, 19, 4344.
(35) (a) Collins, T. J.; Roper, W. R. J. Chem. Soc., Chem. Commun.
1976, 1044. (b) Roper, W. R.; Town, K. G. J. Chem. Soc., Chem. Commun.
1977, 781. (c) Clark, G. R.; Collins, T. J.; Marsden, K.; Roper, W. R. J.
Organomet. Chem. 1978, 157, C23.
(32) Maddock, S. M.; Rickard, C. E. F.; Roper, W. R.; Wright, L. J.
Organometallics 1996, 15, 1793.
(33) Clark, G. R.; Irvine, G. J.; Roper, W. R.; Wright, L. J. Organome-
tallics 1997, 16, 5499.
(36) Holt, M. S.; Wilson, W. L.; Nelson, J. H. Chem. ReV. 1989, 89, 11.
(37) Mackay, K. M.; Nicholson, B. K. In ComprehensiVe Organometallic
Chemistry; Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.; Pergamon:
Oxford, U.K., 1982; Vol. 6, p 1043.
(34) Rickard, C. E. F.; Roper, W. R.; Salter, D. M.; Wright, L. J.
Organometallics 1992, 11, 3931.
(38) Rickard, C. E. F.; Roper, W. R.; Whittell, G. R.; Wright, L. J. J.
Organomet. Chem. 2004, 689, 605.

Organometallics, Vol. 25, No. 20, 2006 4709
Scheme 12
Scheme 13
products sometimes exist as a mixture of geometrical isomers,
with the isomer depicted in 35 usually predominating. It is worth
noting that OsH(SnMe3)(CO)2(PPh3)2 exists as mixture of four
isomers, each of which has been characterized by multinuclear
NMR spectroscopy. However reaction between the isomeric
mixture of OsH(SnMe3)(CO)2(PPh3)2 and SnI4 results in re-
placement of two of the methyl groups on tin to form OsH-
(SnMeI2)(CO)2(PPh3)2, which remarkably exists as only one
isomer, that with mutually trans triphenylphosphine ligands and
mutually trans CO ligands. Further reaction with I2 cleaves the
Os-H bond to give OsI(SnMeI2)(CO)2(PPh3)2, which retains
the same arrangement of CO and PPh3 ligands, as revealed by
an X-ray crystal structure determination. The nitrosyl complex
36 has only one detectable isomer, that with mutually cis
triphenylphosphines and trans chloride and nitrosyl ligands (see
Scheme 11). The reaction of 36 with CO brings about a formal
reduction of the osmium and formation of the five-coordinate
mono(triphenylphosphine) complex Os[Sn(p-tolyl)3](CO)2(NO)-
(PPh3) (37). Once again, this preparative route involving
oxidative addition to zerovalent complexes is not productive in
leading to coordinatively unsaturated stannyl complexes and
attention was therefore directed to other possible routes to the
target molecule 15 in Figure 1.
Scheme 14
release of C2H4. There is precedent for reversible insertion of
C2H4 into an Fe-SiMe3 bond.42 For this reaction strategy to be
successful for the introduction of stannyl ligands to ruthenium
and osmium, both vinyl insertion into M-H and subsequent
â-stannyl elimination must be viable. The vinyl insertion seemed
quite plausible for RuHCl(CO)(PPh3)3, but we were doubtful
about this step for OsHCl(CO)(PPh3)3, in view of the strength
of the Os-H bond and the relative inertness of OsHCl(CO)-
(PPh3)3 toward triphenylphosphine dissociation. Remarkably,
as shown in Scheme 13, the reaction works well for both
ruthenium and osmium to give the five-coordinate triorga-
nostannyl derivatives 39.43 These compounds have the same
geometry as the silyl analogues: i.e., a tetragonal pyramid with
the stannyl ligand in the apical position. This was verified by a
crystal structure determination of Ru(SnMe3)Cl(CO)(PPh3)2.43
While the ruthenium trimethylstannyl and tributylstannyl com-
plexes have good solution stability, it is interesting that even at
room temperature the ruthenium tri-p-tolylstannyl derivative
undergoes a slow transformation to the σ-p-tolyl derivative 40
(see Scheme 14). This process most likely involves an R-elim-
ination reaction with release of the stannylene fragment “SnR2”,
but the nature of the organotin product was not determined.
Further discussion of R-elimination reactions involving stannyl
ligands will be presented in section VIIIF.
The five-coordinate trimethylstannyl derivative of osmium
Os(SnMe3)Cl(CO)(PPh3)2 (41) is a relatively unstable com-
pound, and thermal reactions of this compound will be discussed
below. However, introduction of a sixth ligand to form the
coordinatively saturated derivatives Os(SnMe3)Cl(CO)2(PPh3)2
(42), Os(SnMe3)Cl(CO)(CN-p-tolyl)(PPh3)2 (43), and Os(S-
nMe3)(κ2-S2CNMe2)(CO)(PPh3)2 (44) proceeds smoothly, and
these products have high stability (see Scheme 15).44,45 The
corresponding coordinatively saturated ruthenium complexes are
also easily prepared.44
VII. Five-Coordinate Ruthenium and Osmium Stannyl
Complexes
A. Synthesis. In attempting to extend the successful synthetic
route for five-coordinate silyl complexes detailed in Schemes
7 and 9, a serious limitation is that suitable compounds with
Sn-H bonds are restricted to stannanes of the formula R3SnH,
which have moderate stability and are readily available. Stan-
nanes of the formula R2SnHX are much less stable, decomposing
at room temperature mainly to distannanes R2XSnSnXR2 and
40
H2 or the oligostannanes (R2Sn)n and clearly would not
withstand thermal reaction with OsPhCl(CO)(PPh3)2. Accord-
ingly, the reaction was investigated with HSnMe3.13 Like the
reaction between HSiMe3 and OsPhCl(CO)(PPh3)2, which led
to the osmium(IV) hydride OsH3(SiMe3)(CO)(PPh3)2, the reac-
tion with HSnMe3 also led to an osmium(IV) hydride. However,
this was not “OsH3(SnMe3)(CO)(PPh3)2” but, rather, the dihy-
dride OsH2(SnMe3)2(CO)(PPh3)2 (38) (see Scheme 12). Com-
plex 38 is a classical hydride of very high thermal stability,
showing no tendency to undergo reductive elimination of either
H2 or HSnMe3. Clearly, a quite different synthetic approach to
coordinatively unsaturated stannyl complexes of the type
illustrated by 15 in Figure 1 was needed.
A clue was provided by the observation of Wakatsuki et al.41
that trimethylvinylsilane reacts with RuHCl(CO)(PPh3)3 (see
Scheme 13) to give the five-coordinate trimethysilyl complex
Ru(SiMe3)Cl(CO)(PPh3)2.21 This reaction probably proceeds via
initial insertion of the vinyl double bond into the Ru-H bond
and subsequent â elimination of the trimethylsilyl group with
B. Functionalization of Stannyl Ligands. Having developed
a successful and reasonably general route to these five- and six-
coordinate triorganostannyl complexes, it remained only for us
(42) Randolph, C. L.; Wrighton, M. S. J. Am. Chem. Soc. 1986, 108,
3366.
(39) Clark, A. M.; Rickard, C. E. F.; Roper, W. R.; Wright, L. J. J.
Organomet. Chem. 1997, 543, 111.
(40) Davies, A. G. Organotin Chemistry, 2nd ed.; Wiley-VCH: Wein-
heim, Germany, 2004.
(43) Clark, G. R.; Flower, K. R.; Roper, W. R.; Wright, L. J. Organo-
metallics 1993, 12, 259.
(44) Craig, P. R.; Flower, K. R.; Roper, W. R.; Wright, L. J. Inorg. Chim.
Acta 1995, 240, 385.
(41) Wakatsuki, Y.; Yamazaki, H.; Nakano, M.; Yamamoto, Y. J. Chem.
Soc., Chem. Commun. 1991, 703.
(45) Clark, A. M.; Rickard, C. E. F.; Roper, W. R.; Woodman, T. J.;
Wright, L. J. Organometallics 2000, 19, 1766.

4710 Organometallics, Vol. 25, No. 20, 2006
Scheme 15
Scheme 17
mild conditions. An early recognition of this type of reaction is
discussed by Kummer and Graham.48 The efficiency of this
approach is well-illustrated in Scheme 17, where it can be seen
that Os(SnMe3)(κ2-S2CNMe2)(CO)(PPh3)2 (44, which with
iodine loses the stannyl ligand) is cleanly transformed by
reaction with excess SnI4 into Os(SnI2Me)(κ2-S2CNMe2)(CO)-
(PPh3)2 (48).45 The last methyl group in 48 is cleanly removed
through reaction with iodine without affecting the Os-Sn bond,
to give Os(SnI3)(κ2-S2CNMe2)(CO)(PPh3)2 (49). In yet another
high-yielding reaction, 44 when treated with SnCl2Me2 gives
Os(SnClMe2)(κ2-S2CNMe2)(CO)(PPh3)2 (50) (see Scheme 17).49
The redistribution reaction is even effective between two stannyl
complexes: e.g., Os(SnI2Me)(κ2-S2CNMe2)(CO)(PPh3)2 and Os-
(SnMe3)(κ2-S2CNMe2)(CO)(PPh3)2 give Os(SnIMe2)(κ2-S2-
CNMe2)(CO)(PPh3)2.45 The halostannyl complexes 46-50,
prepared as described above, are all examples of the target
molecule 18 (Figure 1), and all were suitable for the study of
nucleophilic substitution reactions at the tin center.
Scheme 16
to find ways to functionalize the tin center to reach the target
molecules represented by 15 and 18 in Figure 1. Initial attempts
were focused on selective iodine cleavage of Sn-C bonds, under
mild conditions. This is successful in some cases. In Scheme
16 it can be seen that Os(SnMe3)Cl(CO)(CN-p-tolyl)(PPh3)2 (43)
is cleanly converted to Os(SnIMe2)Cl(CO)(CN-p-tolyl)(PPh3)2
(47) through reaction with iodine and the stereochemistry at
osmium is retained in this process.46 However, not all iodine
cleavages proceed in such a straightforward manner. When the
ruthenium analogue of 43, Ru(SnMe3)Cl(CO)(CN-p-tolyl)-
(PPh3)2 (45), is treated with iodine, one methyl group is cleaved
from tin but the intriguing and unexpected product is Ru-
(SnClMe2)I(CO)(CNp-tolyl)(PPh3)2 (46), in which the CO and
CN-p-tolyl ligands are now mutually trans, as are the iodide
and stannyl ligands (see Scheme 16).46 A possible rationale for
this transformation is that the initial Sn-C bond cleavage
produces a tin ligand with some “stannylene” character and rapid
intramolecular migration of chloride from ruthenium generates
the chlorodimethylstannyl ligand in the intermediate “[Ru-
(SnClMe2)(CO)(CN-p-tolyl)(PPh3)2]+”. When iodide finally
coordinates to ruthenium in this cation, it is directed to the site
trans to this stannyl ligand, thus producing 46.
Another unsatisfactory reaction with iodine is that attempted
selective Sn-C bond cleavage in Os(SnMe3)(κ2-S2CNMe2)-
(CO)(PPh3)2 (41) leads mainly to complete removal of the
stannyl ligand from osmium.45 Clearly, a more predictable and
controllable process for replacing organic substituents on tin
with halide substituents was required. The venerable Kochesh-
kov reaction is the answer.47 This redistribution of alkyl and
halogen groups on tin works extremely well for organotin
compounds bearing a metal substituent, LnM-SnR3. It appears
that the metal has an activating effect on this process, since
these redistributions involving stannyl ligands occur under very
VIII. Special Silyl and Stannyl Ligands Derived from
Ligand Reactions at Silicon and Tin, Respectively
A. Trihydroxysilyl (-Si(OH)3) and Trihydroxystannyl
(-Sn(OH)3) Ligands. A characteristic property of both orga-
nosilicon halides50 and organotin halides40 is their ready
hydrolysis, which is usually followed rapidly by condensation
reactions to give complex oligomeric or polymeric materials.
Several organosilanetriols with very bulky organo substituents
have been characterized, but in the solid state even these
compounds show extensive intermolecular hydrogen bonding.51
However, organosilicon halides bearing a metal-ligand frag-
ment as a substituent frequently show much reduced susceptibil-
ity toward hydrolysis, particularly when the metal fragment is
very electron releasing toward the silicon atom.52 This relative
inertness of chlorosilyl ligands toward hydrolysis has led to the
development of alternative synthetic approachs to metallasil-
anols, such as the reaction between dimethyldioxirane and a
ligated Si-H function.53 Nevertheless, as shown in Scheme 18,
(48) Kummer, R.; Graham, W. A. G. Inorg. Chem. 1968, 7, 1208.
(49) Lu, G.-L.; Mo¨hlen, M. M.; Rickard, C. E. F.; Roper, W. R.; Wright,
L. J. Inorg. Chim. Acta 2005, 358, 4145.
(50) Corey, J. Y. In The Chemistry of Organic Silicon Compounds; Patai,
S., Rappoport, Z., Eds.; Wiley: New York, 1989; Chapter 1.
(51) (a) Ishida, H.; Koenig, J. L.; Gardner, K. C. J. Chem. Phys. 1982,
77, 5748. (b) Al-Juaid, S. S.; Buttrus, N. H.; Damja, R. I.; Derouiche, Y.;
Eaborn, C.; Hitchcock, P. B.; Lickiss, P. D. J. Organomet. Chem. 1989,
371, 287.
(52) Malisch, W.; Schmitzer, S.; Kaupp, G.; Hindahl, K.; Ka¨b, H.;
Wachtler, U. In Organosilicon Chemistry, From Molecules to Materials;
Auner, N., Weis, J., Eds.; VCH: Weinheim, Germany, 1994; p 185.
(53) Mo¨ller, S.; Fey, O.; Malisch, W.; Seelbach, W. J. Organomet. Chem.
1996, 507, 239.
(46) Clark, G. R.; Flower, K. R.; Roper, W. R.; Wright, L. J. Organo-
metallics 1993, 12, 3810.
(47) Kocheshkov, K. A. Ber. Dtsch. Chem. Ges. 1926, 62, 996.

Organometallics, Vol. 25, No. 20, 2006 4711
Scheme 18
Scheme 19
Scheme 20
the coordinatively unsaturated trichlorosilyl complex Os(SiCl3)-
Cl(CO)(PPh3)2 (23) is readily hydrolyzed to the corresponding
trihydroxysilyl complex Os[Si(OH)3]Cl(CO)(PPh3)2 (51), which
is a stable crystalline material showing no tendency to further
self-condensation. Remarkably, a crystal structure of 51 reveals
the absence of any intra- or intermolecular hydrogen bonding,
the trihydroxysilyl ligand remaining as a completely discrete
ligand.54 The steric protection offered by the two triphenylphos-
phine ligands may contribute to the absence of hydrogen
bonding, but other factors must also be important, since the
structures of related complexes such as Os[B(OH)2]Cl(CO)-
(PPh3)2, where steric factors are comparable, are dimeric with
substantial hydrogen-bonding interactions.55
In striking contrast to the facile hydrolysis of Os(SiCl3)Cl-
(CO)(PPh3)2, the coordinatively saturated trichlorosilyl complex
Os(SiCl3)(κ2-S2CNMe2)(CO)(PPh3)2 (52) is completely resistant
to hydrolysis, even under very forcing conditions (see Scheme
18).56 It is difficult to believe that the steric environment about
the silicon differs significantly in these two compounds, and
the dramatic difference in reactivity must be because a different
mechanism of hydrolysis is available to the coordinatively
unsaturated complex 23. A plausible interpretation is that the
facile hydrolysis of coordinatively unsaturated Os(SiCl3)Cl(CO)-
(PPh3)2 occurs because the nucleophile, hydroxide, attacks at
the osmium to form an anionic complex, [Os(SiCl3)Cl(OH)(CO)-
(PPh3)2]-, and the ensuing hydrolysis becomes intramolecular.
Support for this anionic intermediate is that the closely related
anion [Os(SiCl3)Cl2(CO)(PPh3)2]- has been characterized.56 This
same contrast in reactivity toward hydroxide is also shown by
the two chlorodimethylsilyl complexes Os(SiMe2Cl)Cl(CO)-
(PPh3)2 and Os(SiMe2Cl)(κ2-S2CNMe2)(CO)(PPh3)2; the first of
these two is readily hydrolyzed, but the six-coordinate complex
is not.57
Although the simple hydrolysis of Os(SiCl3)Cl(CO)(PPh3)2
(23) with excess hydroxide gives only Os[Si(OH)3]Cl(CO)-
(PPh3)2 (51), a condensation product is formed when Os(SiCl3)-
Cl(CO)(PPh3)2 (23) is treated with Os[Si(OH)3]Cl(CO)(PPh3)2
(51) in the presence of water (see Scheme 19).54 The product,
complex 53, has an unusual bridging -Si(OH)2OSi(OH)2-
ligand, and a crystal structure determination again reveals the
absence of any intermolecular hydrogen bonding, but there is a
weak intramolecular hydrogen bond to an osmium-bound
chloride ligand, as depicted in Scheme 19.
Other five-coordinate chlorosilyl complexes such as M(SiMe-
Cl2)Cl(CO)(PPh3)2 (54; M ) Ru, Os), as shown in Scheme 20,
readily undergo similar hydrolysis reactions to the corresponding
hydroxysilyl complexes M[SiMe(OH)2]Cl(CO)(PPh3)2 (55; M
) Ru, Os) and also related reactions with ethanol to give the
ethoxysilyl complexes M[SiMe(OEt)2]Cl(CO)(PPh3)2 (56; M )
Ru, Os).22 An interesting feature associated with Os[SiMe(OEt)2]-
Cl(CO)(PPh3)2 is that there are structural data for this compound
and for the corresponding CO adduct Os[SiMe(OEt)2]Cl(CO)2-
(PPh3)2. The Os-Si distance in the five-coordinate complex is
2.3196(11) Å, whereas with CO trans to the silyl ligand in the
six-coordinate complex the Os-Si distance increases to 2.4901-
(8) Å. In conjunction with this lengthening of the Os-Si bond,
the Os-CO distance for the carbonyl trans to the silyl ligand is
2.024(4) Å, whereas the Os-CO distance for the carbonyl trans
to the chloride ligand is 1.887(3) Å. Clearly, the silyl and CO
ligands, when located mutually trans, have a pronounced bond
lengthening effect on each other.22
Further examples of nucleophilic attack at chlorosilyl ligands,
involving both oxygen and nitrogen nucleophiles, are illustrated
in Scheme 21. Here it can be seen that 2-hydroxypyridine,
2-aminopyridine, and acetate all give rise to mono(triph-
enylphosphine) complexes with tethered silyl ligands, each
forming a five-membered chelate ring, in complexes 58-60,
respectively.58
While the trichlorosilyl ligand in the coordinatively saturated
trichlorosilyl complex Os(SiCl3)(κ2-S2CNMe2)(CO)(PPh3)2 (52)
is spectacularly inert, as discussed above, the related coordi-
natively saturated triiodostannyl complex Os(SnI3)(κ2-S2CNMe2)-
(CO)(PPh3)2 (49) readily undergoes a hydrolysis reaction, at
room temperature within minutes, with hydroxide ion (see
Scheme 22).45 This was the first trihydroxystannyl complex
reported and, remarkably, shows no tendency to condense to
more complex products. More recently a trihydroxystannyl
(54) Rickard, C. E. F.; Roper, W. R.; Salter, D. M.; Wright, L. J. J. Am.
Chem. Soc. 1992, 114, 9682.
(55) Clark, G. R.; Irvine, G. J.; Roper, W. R.; Wright, L. J. J. Organomet.
Chem. 2003, 680, 81.
(56) Kwok, W.-H.; Lu, G.-L.; Rickard, C. E. F.; Roper, W. R.; Wright,
L. J. J. Organomet. Chem. 2006, 691, 2593.
(57) Albrecht, M.; Kwok, W.-H.; Lu, G.-L.; Rickard, C. E. F.; Roper,
W. R.; Salter, D. M.; Wright, L. J. Inorg. Chim. Acta 2005, 358, 1407.
(58) Kwok, W.-H.; Lu, G.-L.; Rickard, C. E. F.; Roper, W. R.; Wright,
L. J. J. Organomet. Chem. 2004, 689, 2979.

4712 Organometallics, Vol. 25, No. 20, 2006
Scheme 21
Scheme 23
Scheme 24
Scheme 22
distance (3.242(3) Å) is observed in the osmium(IV) silatranyl
complex Os[Si(OC2H4)3N]H3(PPh3)3 (see section IIIB), and this
complex has also been protonated and methylated at nitrogen.15
A graphic illustration of the unique influence the metal has
on the shape of the silatrane cage is that when the thiocarbonyl
analogue of 63 is treated with CO, a migratory insertion reaction
occurs to form the η2-thioacyl complex 66 (replacing the Si-
Os bond with a Si-C bond), and in this complex the
characteristic architecture of the silatrane is reestablished with
a Si-N distance of 2.086(6) Å (see Scheme 23).
ligand has been recognized bridging a trinickel cluster.59 Other
halostannyl ligands in coordinatively saturated complexes readily
undergo nucleophilic substitution reactions. For example, the
SnI2Me ligand in complex 48 reacts with catechol in the
presence of base to form the elaborate stannyl ligand depicted
in complex 62 (see Scheme 22). Other examples of facile
nucleophilic substitution reactions, and of stannyl complexes
that retain electrophilicity at the tin, where the silicon analogues
do not, will be discussed in detail in subsequent sections.
B. Silatranyl and Stannatranyl Complexes. Silatranes,
cyclic organosilicon ethers of tris(2-oxyalkylamine), are a special
class of hypervalent silicon compounds with a cage structure
characterized by a variable transannular N-Si bonding interac-
tion. It is straightforward to incorporate a silatranyl ligand into
an osmium complex utilizing the synthetic approach given in
Scheme 7: i.e., reaction between OsPhCl(CO)(PPh3)2 and the
silatrane HSi(OC2H4)3N (see Scheme 23).24 The coordinatively
unsaturated silatranyl complex 63 can be made with either
carbonyl or thiocarbonyl as accompanying ligand. The structure
of the complex bearing the carbonyl ligand reveals that the
silatrane cage is opened to the extent that the distance between
the nitrogen atom and the silicon atom is 3.000(7) Å, while the
Os-Si distance remains essentially the same as the value for
Os[Si(OH)3]Cl(CO)(PPh3)2. The silicon-nitrogen separation in
silatranes is generally in the range 2.00-2.26 Å. The observed
elongation in 63 results in the geometry about the nitrogen atom
becoming planar. A consequence of this is that the nitrogen
atom can be quaternized by reaction either with MeI or with
triflic acid, reactions previously unobserved for silatranes. An
even greater elongation of the silicon-nitrogen interatomic
The established reactivity of Os(SnI3)(κ2-S2CNMe2)(CO)-
(PPh3)2 (46) toward hydrolysis suggested that a direct route to
the unknown stannatranyl complexes could be the reaction
between 46 and triethanolamine. This approach works beauti-
fully, as shown in Scheme 24, to give Os[Sn(OC2H4)3N](κ2-
S2CNMe2)(CO)(PPh3)2 (68).60 Indeed, the reaction is also
successful with nitrilotriacetic acid to give the first example of
a metal-substituted stannatranone, Os[Sn(OC{O}CH2)3N](κ2-
S2CNMe2)(CO)(PPh3)2.45 For a direct structural comparison of
silatranyl and stannatranyl ligands in the same coordination
environment, the silicon analogue of 68 was prepared by treating
63 with dimethyldithiocarbamate to produce the silatranyl
complex Os[Si(OC2H4)3N](κ2-S2CNMe2)(CO)(PPh3)2 (67) (see
Scheme 24).
There is a telling contrast between the structures of the two
cage ligands. Whereas the silatranyl ligand in 67 shows the
expanded cage structure observed for the other silatranyl
complexes (a silicon-nitrogen separation of 3.176(6) Å), the
stannatranyl ligand in 68 has a Sn-N bond distance of 2.422-
(4) Å,60 which is quite comparable to the distance found in non-
metal-substituted stannatranes such as MeSn(OC2H4)3N (2.28(1)
Å).61 Clearly, attachment of the stannyl ligand to osmium does
(60) Rickard, C. E. F.; Roper, W. R.; Woodman, T. J.; Wright, L. J.
Chem. Commun. 1999, 837.
(59) Simo´n-Manso, E.; Kubiak, C. P. Angew. Chem., Int. Ed. 2005, 44,
1125.
(61) Swisher, R. G.; Day, R. O.; Holmes, R. R. Inorg. Chem. 1983, 22,
3692.

Organometallics, Vol. 25, No. 20, 2006 4713
Scheme 25
Scheme 27
Ru[Sn(OH)Me2]I(CO)(CNR)(PPh3)2 (72), which is derived from
Ru(SnClMe2)I(CO)(CNR)(PPh3)2 (46; see Scheme 16) through
reaction with aqueous KOH, when treated with H2S forms the
unprecedented thiohydroxystannyl complex Ru[Sn(SH)Me2]I-
(CO)(CNR)(PPh3)2 (73).46 This compound is quite stable and
once again shows a reluctance to undergo a self-condensation
reaction or disproportionation. Other molecules containing the
Sn-S-H moiety are usually unstable and disproportionate to
the ditin sulfides and H2S,40 unless very bulky substituents such
as tert-butyl are present on the tin atom, as in (But)3SnSH.62
In a more straightforward reaction the methyldiiodostannyl
complex Os(SnMeI2)(κ2-S2CNMe2)(CO)(PPh3)2 (48) reacts with
ethanedithiol in the presence of the base triethylamine to give
the sulfur-substituted stannyl complex 74 (see Scheme 26).45
Scheme 26
D. SnH3 and Related Ligands from Reactions with
Hydride Nucleophiles. It is well-established that complexes
with halostannyl ligands such as Cp(CO)2FeSnR2I can undergo
nucleophilic substitution at tin with hydridic reagents such as
K[BHEt3] to give a corresponding stannyl complex containing
a Sn-H bond, Cp(CO)2FeSnR2H (R ) CH(SiMe3)2).63 The
demonstrated ease with which all three iodides can be displaced
from Os(SnI3)(κ2-S2CNMe2)(CO)(PPh3)2 (49; see section VIIIA)
suggested that this complex could be used in the synthesis of
the SnH3 complex Os(SnH3)(κ2-S2CNMe2)(CO)(PPh3)2 (75).
Stable examples of SnH3 complexes were previously unknown.
The reaction as drawn in Scheme 27, using NaBH4, proceeds
in high yield, and complex 75 has been isolated as a stable
crystalline solid. Complex 75 was characterized by multinuclear
NMR spectroscopy and by an X-ray crystal structure determi-
nation, which located the hydrogen atoms.64 In the IR spectrum
of 75 bands at 1763, 1750, and 1735 cm-1 are attributed to
ν(SnH). These values are lower than in the simple organostan-
not significantly reduce the electrophilicity of the tin atom. This
is very different from the situation with the corresponding silyl
ligands and must be related to the greater ability of the tin atom
to attain higher coordination numbers.
C. Unusual Silyl and Stannyl Ligands from Reactions with
Nitrogen and Sulfur Nucleophiles. In Scheme 21 it has been
shown that a monochlorosilyl ligand reacts with a nitrogen
nucleophile in the form of 2-aminopyridine to form complex
59, which has a tethered silyl ligand containing a Si-N bond.
An extension of this reaction is depicted in Scheme 25, where
the dichlorosilyl complex Os(SiMeCl2)Cl(CO)(PPh3)2 (54) reacts
with 2-aminopyridine to form complex 69, which contains a
novel tridentate κ3N,N,Si-silyl ligand.22 Complexes 59 and 69
both contain five-membered chelate rings associated with the
tethering arms. When the coordinatively unsaturated complexes
M(SiMeCl2)Cl(CO)(PPh3)2 (54; M ) Ru, Os) are treated with
8-aminoquinoline, the reaction follows a different course. The
unusual products M(SiMeCl2)Cl(CO)(PPh3)(κ2N,N-NC9H6NH2-
8) (70; M ) Ru, Os) have the 8-aminoquinoline bound as simple
chelate ligands that utilize both the quinoline nitrogen and the
NH2 nitrogen as donor atoms with displacement of a triphen-
ylphosphine ligand (see Scheme 25). Remarkably, a crystal
structure determination reveals that the NH2 function is coor-
dinated adjacent to the unchanged SiMeCl2 ligand. A condensa-
tion reaction between NH2 and SiMeCl2 would result in
formation of a six-membered ring. This less favorable chelate
ring size must be a factor contributing to the lack of reactivity
of the adjacent NH2 and SiMeCl2 functions. The Si-Cl bonds
do, however, show reactivity toward ethanol, and at room
temperature in contact with ethanol complex 70 is rapidly
converted to complex 71 (see Scheme 25).
nane Si(CH2CH2SnH3)4, where ν(SnH) is found at 1852 cm-1 65
.
A similar observation has been made for another transition-
metal-substituted stannane, Cp2Hf(SnHMes2)Cl, where ν(SnH)
is 1728 cm-1, whereas the value for Mes2SnH2 is 1864 cm-1 66
.
1
In the H NMR the SnH3 protons are seen as a triplet at 2.86
ppm through coupling to two equivalent phosphorus atoms (3JPH
1
1
117
119
) 3.2 Hz) with Sn satellites ( J
) 1348, J
) 1288
SnH
SnH
Hz). These one-bond Sn-H coupling constants are conspicu-
ously lower than those observed in simple organostannanes,
(62) Ha¨nssgen, D.; Reuter, P.; Do¨llein, G. J. Organomet. Chem. 1986,
317, 159.
(63) Lappert, M. F.; McGeary, M. J.; Parish, R. V. J. Organomet. Chem.
1989, 373, 107.
(64) Mo¨hlen, M. M.; Rickard, C. E. F.; Roper, W. R.; Whittell, G. R.;
Wright, L. J., Inorg. Chim. Acta, in press.
(65) Schumann, H.; Wassermann, B. C.; Frackowiak, M.; Omotowa, B.;
Schutte, S.; Velder, J.; Mu¨hle, S. H.; Krause, W. J. Organomet. Chem.
2000, 609, 189.
In unusual reactions, depicted in Scheme 26, it is possible to
use ligand reactions at a metal-bound stannyl ligand to form
new stannyl ligands containing Sn-S bonds. The ruthenastannol
(66) Neale, N. R.; Tilley, T. D. J. Am. Chem. Soc. 2002, 124, 3802.

4714 Organometallics, Vol. 25, No. 20, 2006
salt of the complex anion [Os(SiMe3)Me2(CO)(PPh3)2]- (78).
When this salt is in contact with ethanol, methane is liberated
and the red complex Os(SiMe3)Me(CO)(PPh3)2 (79) is formed.69
Addition of CO to complex 79 gives the more stable, saturated
complex Os(SiMe3)Me(CO)2(PPh3)2 (80).
Scheme 28
Before describing the thermal reactions of the trimethylsilyl
methyl complex Os(SiMe3)(Me)(CO)(PPh3)2 (79), it is relevant
to consider the thermal reaction of the trimethylsilyl chloride
complex Os(SiMe3)Cl(CO)(PPh3)2. This latter compound is very
stable, and it is only after heating in molten triphenylphosphine
at 160 °C for 2 h that decomposition occurs, the major products
being the ortho-metalated complex Os(κ2C,P-C6H4PPh2)Cl(CO)-
(PPh3)270 and OsHCl(CO)(PPh3)3, both products involving loss
of the silyl ligand. In marked contrast to the stability of Os-
(SiMe3)Cl(CO)(PPh3)2, the corresponding trimethylsilyl methyl
complex Os(SiMe3)(Me)(CO)(PPh3)2 (79) shows solution in-
stability and, as depicted in Scheme 28, readily undergoes a
thermal reaction (toluene reflux, 1 h) in the presence of
triphenylphosphine, to give as the major product the ortho-
silylated as well as ortho-metalated complex Os(κ2Si,P-
SiMe2C6H4PPh2)(κ2C,P-C6H4PPh2)(CO)(PPh3) (81). This un-
usual product, which retains the Os-Si bond, has also been
observed from the thermal reaction of OsHCl(CO)(PPh3)3 and
Hg(SiMe3)2.21 The same ortho-silylated ligand, κ2Si,P-SiMe2C6H4-
PPh2, has been described by others in the thermal reaction of a
base-stabilized silylene triphenylphosphine complex of ruthe-
nium(II).71 This suggests the possibility that a dimethylsilylene
intermediate is involved in the formation of complex 81. Such
an intermediate could arise from a migration of a methyl group
from the trimethylsilyl ligand to osmium. There is precedent
for this sort of process on osmium, in that a methyl group has
been observed to migrate to osmium from a bound trimethyl-
stannyl ligand (see section VIIIF below). However, the details
of the mechanism are unknown and the reaction must be of
some complexity, since an ortho-metalated triphenylphosphine
ligand is also formed. An interesting aside is that when complex
81 reacts with tris(pyrrolyl)phosphine the product is Os(κ2Si,P-
SiMe2C6H4PPh2)(κ2C,P-C6H4PPh2)(CO)[P(NC4H4)3], where only
the triphenylphosphine trans to silicon is replaced. The effect
of introducing the very good π-accepting ligand tris(pyrrolyl)-
phosphine is to lengthen the Os-Si distance from 2.4716(13)
Å in 81 to 2.5110(8) Å in Os(κ2Si,P-SiMe2C6H4PPh2)(κ2C,P-
C6H4PPh2)(CO)[P(NC4H4)3]. This is the longest recorded Os-
Si distance for an octahedral osmium silyl complex.69
A minor product from the thermal reaction of Os(SiMe3)-
(Me)(CO)(PPh3)2 (79) in the presence of triphenylphosphine
involves loss of the trimethylsilyl ligand and the methyl ligand,
giving eventually Os(κ2C,P-C6H4PPh2)2(CO)(PPh3) (82), which
contains two ortho-metalated triphenylphosphine ligands (see
Scheme 28).
F. R-Methyl Migration Reactions in Trimethystannyl
Complexes and Thermal Reactions of the Coordinatively
Unsaturated Trimethystannyl Complex Os(SnMe3)Cl(CO)-
(PPh3)2. In section VIIA the facile transformation of the
coordinatively unsaturated complex Ru[Sn(p-tolyl)3]Cl(CO)-
(PPh3)2 to Ru(p-tolyl)Cl(CO)(PPh3)2 was described. This must
involve as an initial step an R-p-tolyl migration reaction, and
in this section we describe several other examples of this same
process involving stannyl complexes of osmium. It can be noted
that the zirconium and hafnium triphenylstannyl complexes
RnSnH4-n (n ) 1-3), which are typically 1900-1600 Hz.65,67
Even lower values, 961 and 918 Hz, have been recorded for
Cp2Hf(SnHMes2)Cl.66 These reduced values have been attributed
to the presence of the transition metal as a substituent on tin of
very low effective electronegativity.68 The Sn-H distances in
75 are Sn-H(1) ) 1.79(5) Å, Sn-H(2) ) 1.68(5) Å, and Sn-
H(3) ) 1.81(5) Å. The average of these values (1.76 Å) is long
compared with the average for the Sn-H bonds in Si(CH2CH2-
SnH3)4, which is 1.60(7) Å [10].65 This bond lengthening is
consistent with the reduced ν(SnH) and JSnH values in 75.
As expected, the Sn-H bonds are quite reactive, and
dissolution in chloroform converts 75 to the corresponding
trichlorostannyl complex Os(SnCl3)(κ2-S2CNMe2)(CO)(PPh3)2
(76), while reaction with HF gives the corresponding trifluo-
rostannyl complex Os(SnF3)(κ2-S2CNMe2)(CO)(PPh3)2 (77) (see
Scheme 27). The Os-Sn distances in 76 and 77 are almost
identical at 2.5969(5) and 2.5934(3) Å, respectively, and these
are the shortest Os-Sn distances recorded in the Cambridge
Crystallographic Data Base for six-coordinate osmium and four-
coordinate tin. In closely related reactions with complexes
containing appropriate mixed methyl/halostannyl ligands, Os-
(SnH2Me)(κ2-S2CNMe2)(CO)(PPh3)2 and Os(SnHMe2)(κ2-S2-
CNMe2)(CO)(PPh3)2 have also been isolated.64
E. Coordinatively Unsaturated Os(SiMe3)Me(CO)(PPh3)2
from Reaction of Os(SiCl3)Cl(CO)(PPh3)2 with MeLi and
the Thermal Reactions of this Complex. At an earlier point
in this review, section IVC, the complex Os[Si(OEt)3]Ph(CO)-
(PPh3)2 (26) was described as the product of reaction between
Os[Si(OEt)3]Cl(CO)(PPh3)2 (25) and PhLi (see Scheme 8).
Complex 26 proved to be remarkably resistant to reductive
elimination of PhSi(OEt)3, and to explore whether an analogous
complex with the simpler trimethylsilyl ligand might behave
differently, the complex Os(SiMe3)Me(CO)(PPh3)2 (79) was
prepared. As shown in Scheme 28, treatment of Os(SiCl3)Cl-
(CO)(PPh3)2 (23) with an excess of methyllithium in an ether/
toluene mixture led to the precipitation of the colorless lithium
(69) Clark, G. R.; Lu, G.-L.; Rickard, C. E. F.; Roper, W. R.; Wright,
L. J. J. Organomet. Chem. 2005, 690, 3309.
(67) Maddox, M. L.; Flitcroft, N.; Kaesz, H. D. J. Organomet. Chem.
1965, 4, 50.
(68) Aylett, B. J. J. Organomet. Chem., Libr. 1980, 9, 327.
(70) Bennett, M. A.; Clark, A. M.; Contel, M.; Rickard, C. E. F.; Roper,
W. R.; Wright, L. J. J. Organomet. Chem. 2000, 601, 299.
(71) Wada, H.; Tobita, H.; Ogino, H. Organometallics 1997, 16, 3870.

Organometallics, Vol. 25, No. 20, 2006 4715
Scheme 29
Figure 3.
Scheme 31
Scheme 30
CpCp*M(SnPh3)Cl (M ) Zr, Hf) can be induced to form
CpCp*M(Ph)Cl72,73 in reactions similar to that undergone by
Ru[Sn(p-tolyl)3]Cl(CO)(PPh3)2, but under much more vigorous
conditions.
It is shown in Scheme 29 that the five-coordinate trimeth-
ylstannyl complex Os(SnMe3)Cl(CO)(PPh3)2 (41) undergoes the
expected reaction with CO to form the six-coordinate complex
Os(SnMe3)Cl(CO)2(PPh3)2 (42). However, quite unexpectedly
the reaction of 41 with pyridine at room temperature leads to
the rearranged pyridine adduct Os(SnMe2Cl)(Me)(CO)(pyridine)-
(PPh3)2 (83), where a methyl group has migrated to osmium
and a chloride has migrated from osmium to tin. Even more
unexpectedly, when 83 is treated with CO at room temperature,
these migrations are reversed and the trimethylstannyl complex
Os(SnMe3)Cl(CO)2(PPh3)2 (42) is formed in good yield.74
Methyl migration to osmium is also promoted by the addition
of acetate to Os(SnMe3)Cl(CO)(PPh3)2 (41) to form 84, where
acetate bridges the Os-Sn bond (see Scheme 29). The same
product is also formed when 83 is treated with acetate. Both
83 and 84 have been structurally characterized.74
The coordinatively saturated complex Os(SnMe3)Cl(CO)2-
(PPh3)2 (42) is much more stable than 41, but under forcing
conditions it too undergoes a methyl migration from tin to
osmium to form the dimethylchlorostannyl complex Os(SnMe2-
Cl)(Me)(CO)2(PPh3)2 (85), as depicted in Scheme 30.
These observations can be rationalized if the coordinatively
unsaturated trimethylstannyl complex 41 is in equilibrium with
the transient stannylene species A and C, depicted in Figure 3.
Further support for the intermediacy of stannylene complexes
is provided by the thermal reactions of Os(SnMe3)Cl(CO)(PPh3)2
(41) shown in Scheme 31.
understood by invoking the intermediacy of the transient
stannylene complex C in Figure 3. Complex 87 is converted to
complex 86 by a redistribution reaction with SnMe2Cl2. These
complexes are analogues of the silicon-containing complex 81
in Scheme 28. In the formation of these compounds there are
parallels with electrophilic carbene and silylene ligands attacking
the ortho position of a phenyl ring in a PPh3 ligand.71,76
G. The Very Different Reactions of an Osmasilanol
(LnOs-SiMe2OH) and an Osmastannol (LnOs-SnMe2OH)
with Strong Base. Metallasilanols (LnM-SiR2OH)52 are likely
to be valuable synthetic intermediates, as are the nonmetalated
analogues. Although these compounds are now well-established,
the chemical reactivity associated with M-Si-OH linkages has
been mostly unexplored. Significant reports include the conver-
sion of metallasilanols to both dimetalladisiloxanes (through
condensation)54 and to metalladisiloxanes.52 In one instance, the
conversion of a metallasilanol to an isolated lithium metallasi-
lanolate (LnM-SiR2OLi) has been reported, and this was shown
to be a dimer in the solid state.77
The five- and six-coordinate (dimethylchlorosilyl)osmium-
(II) complexes Os(SiMe2Cl)Cl(CO)(PPh3)2 and Os(SiMe2Cl)-
(κ2-S2CNMe2)(CO)(PPh3)2 provide the opportunity to access,
through hydrolysis, the corresponding silanol complexes. The
accompanying set of ligands in these compounds constitute
rather inert groupings that allow focus on reactions at the Si
centers. As shown in Scheme 32, the osmasilanol Os(SiMe2-
OH)Cl(CO)(PPh3)2 (88), which is readily obtained by hydrolysis
of Os(SiMe2Cl)Cl(CO)(PPh3)2, is conveniently deprotonated by
tBuLi to give the solid lithium silanolate complex Os(SiMe2-
Heating complex 41 in solution, in the presence of triph-
enylphosphine, induces an ortho stannylation of one phenyl
group of a triphenylphosphine ligand and an ortho metalation
of another triphenylphosphine ligand, to produce the metalla-
cyclic complexes Os(κ2Sn,P-SnMeClC6H4PPh2)(κ2C,P-C6H4-
PPh2)(CO)(PPh3) (86) and Os(κ2Sn,P-SnMe2C6H4PPh2)(κ2C,P-
C6H4PPh2)(CO)(PPh3) (87).75 The formation of 86 can be
(75) Lu, G.-L.; Rickard, C. E. F.; Roper, W. R.; Wright, L. J. J.
Organomet. Chem. 2005, 690, 4114.
(76) Hoskins, S. V.; Rickard, C. E. F.; Roper, W. R. J. Chem. Soc., Chem.
Commun. 1984, 1000.
(77) Goikhman, R.; Aizenberg, M.; Kraatz, H.-B.; Milstein, D. J. Am.
Chem. Soc. 1995, 117, 5865.
(72) Woo, H.-G.; Freeman, W. P.; Tilley, T. D. Organometallics 1992,
11, 2198.
(73) Neale, N. R.; Tilley, T. D. J. Am. Chem. Soc. 2005, 127, 14745.
(74) Rickard, C. E. F.; Roper, W. R.; Woodman, T. J.; Wright, L. J.
Chem. Commun. 1999, 1101.

4716 Organometallics, Vol. 25, No. 20, 2006
Scheme 32
Scheme 35
Scheme 33
the structurally characterized cyclic complex Os(κ2Sn,P-
SnMe2C6H4PPh2)(κ2-S2CNMe2)(CO)(PPh3) (97), in which the
Sn-O bond has been ruptured and one of the phenyl rings of
a triphenylphosphine ligand is “ortho-stannylated”.49 The yield
of 97 is maximized (79%) when 2 equiv of tBuLi is used. Use
of only 1 equiv of tBuLi leaves unreacted starting material and
complex 97 is formed in reduced yield. No information is
available on the mechanism of this reaction, but the observed
product is compatible with the intermediacy of an electrophilic
stannylene complex.
Scheme 34
The novel cyclic complex 97 is selectively functionalized at
the tin atom by reaction with SnMe2Cl2, which exchanges one
methyl group for chloride, giving Os(κ2Sn,P-SnMeClC6H4-
PPh2)(κ2-S2CNMe2)(CO)(PPh3) (98) as a mixture of diastere-
omers. Complex 98 undergoes facile nucleophilic substitution
reactions at the Sn-Cl bond, and reaction with hydroxide ion
gives the osmastannol complex Os(κ2Sn,P-SnMeOHC6H4-
PPh2)(κ2-S2CNMe2)(CO)(PPh3), while reaction with sodium
borohydride gives the corresponding tin hydride complex Os-
(κ2Sn,P-SnMeHC6H4PPh2)(κ2-S2CNMe2)(CO)(PPh3), as ex-
pected.49
H. The Special Case of a (Dimethylamino)dimethylsilyl
Ligand Leading to Dimethylamino-Bridged Bis(silylene)
Complexes. Despite the versatility of the preparative procedure
shown in Scheme 7 for the synthesis of variously substituted
silyl complexes of ruthenium and osmium, when the procedure
was applied to the use of (dimethylamino)dimethylsilane,
HSiMe2NMe2, the ensuing reaction followed a completely
different course. As shown in Scheme 35, treatment of MRCl-
(CO)(PPh3)2 with an excess of HSiMe2NMe2 produces three
compounds for M ) Ru: the dimethylamino-bridged bis-
(dimethylsilylene) complexes 99 and 101, together with the
unusual diruthenium complex 103 (formed in low yield). For
M ) Os, only two compounds are formed: the dimethylamino-
bridged bis(dimethylsilylene) complexes 100 and 102.78 The
reaction proceeds for R ) Ph, SiEt3, SiMe2Cl. However, yields
were best for R ) SiMe2Cl, and since M(SiMe2Cl)Cl(CO)-
(PPh3)2 (M ) Ru, Os) can both be prepared directly in high
yield from MHCl(CO)(PPh3)3 and HSiMe2Cl, M(SiMe2Cl)Cl-
(CO)(PPh3)2 were the starting materials of choice. It is likely
that the first step in the reaction is an exchange of silyl ligand
(see section IVC) to give M[SiMe2(NMe2)]Cl(CO)(PPh3)2, but
OLi)Cl(CO)(PPh3)2 (89).57 Complex 89 reacts with either Me3-
SiCl or Me3SnCl to give the corresponding osmadisiloxane
Os(SiMe2OSiMe3)Cl(CO)(PPh3)2 (90) or osmastannasiloxane
Os(SiMe2OSnMe3)Cl(CO)(PPh3)2 (91), respectively. As already
mentioned in section VIIIA, the hydrolysis of the coordinatively
saturated Os(SiMe2Cl)(κ2-S2CNMe2)(CO)(PPh3)2 (93) (see
Scheme 33) is not effected by KOH but can be achieved by
chromatography on silica gel. The resulting osmasilanol Os-
(SiMe2OH)(κ2-S2CNMe2)(CO)(PPh3)2 (94) is also deprotonated
t
with BuLi, and subsequent treatment with Me3SiCl gives the
expected osmadisiloxane Os(SiMe2OSiMe3)(κ2-S2CNMe2)(CO)-
(PPh3)2 (95).57
The chemistry described above for the osmasilanols 88 and
94 is predictable and expected. However, the behavior of the
corresponding osmastannol Os(SnMe2OH)(κ2-S2CNMe2)(CO)-
(PPh3)2 (96), prepared by the ready hydrolysis of Os(SnMe2-
Cl)(κ2-S2CNMe2)(CO)(PPh3)2 (50; see Scheme 34), is com-
pletely unexpected. Treatment of the osmastannol 96 with tBuLi
does not produce an isolable osmastannolate but rather gives
(78) Choo, T. N.; Kwok, W.-H.; Rickard, C. E. F.; Roper, W. R.; Wright,
L. J. J. Organomet. Chem. 2002, 645, 235.

Organometallics, Vol. 25, No. 20, 2006 4717
Scheme 36
Figure 4.
the subsequent steps can only be speculated upon. Nevertheless,
the dimethylamino-bridged bis(dimethylsilylene) complexes are
formed in reasonable yield and preference for either the chloride
products 99 and 100 or the hydride products 101 and 102 can
be controlled by varying the experimental conditions. Structural
data reveal that the RuSiNSi and OsSiNSi rings of the
bis(silylene) ligand system are folded at the Si atoms and the
Ru-Si and Os-Si distances are short, while Si-N distances
are long. These structural data suggest some multiple-bond
character in the metal-silicon bonds, and this is further
2.8236(6) Å, while the corresponding distance in Os(SnMe2-
SnPh3)Cl(CO)2(PPh3)2 is 2.8367(2) Å. These distances lie
between those found in simple organopolystannanes, e.g., Ph6-
Sn2 (2.770(4) Å),83 and the distance found in Br2Sn2[Mn(CO)5]4
(2.885(1) Å).84
supported by the downfield chemical shifts observed in the 29
-
Si NMR spectra of these compounds. Overall, the bonding in
these compounds can be represented by the valence bond
structures D and E, shown in Figure 4. Closely related bis-
(dimethylsilylene) complexes bridged with a methoxy function
have been derived through rearrangement of intermediate
disilanyl complexes of the type LnM-SiMe2SiMe2OMe.79
The diruthenium complex 103 has a short Ru-Ru bond
(2.7557(2) Å) that is bridged by chloride and two dimethyl-
silylene ligands. One ruthenium retains the dimethylamino-
bridged bis(dimethylsilylene) ligand system and a CO, while
the other has CO, PPh3, and two hydride ligands. Structural
evidence indicates that each of the bridging dimethylsilylene
ligands is involved in a three-center bonding situation (RuSiH),
as depicted in Scheme 35.
The complexes give beautifully resolved 119Sn NMR spectra
which allow direct measurement of both 119Sn-119Sn and
119Sn-117Sn one-bond Sn-Sn coupling constants. As an
example, we discuss in detail the 119Sn NMR spectrum of Os-
(SnMe2SnMe3)(κ2-S2CNMe2)(CO)(PPh3)2. In this compound
both the R-Sn and â-Sn resonances, at -283.3 and -170.8 ppm,
respectively, are observed as triplets through coupling to
phosphorus. The two-bond coupling of the R-Sn is 88 Hz, and
the three-bond coupling of the â-Sn is 9 Hz. Each of these
triplets shows two sets of satellites arising through one-bond
Sn-Sn coupling to the adjacent tin atom, when present as either
the 117Sn isotope or the 119Sn isotope. The satellite signals are
not symmetrically distributed about the central triplet signal,
because the chemical shift of the 119Sn resonance changes
according to whether the adjacent isotope is 117Sn or 119Sn. The
assignments of the appropriate pairs of satellite triplets, for
determination of the coupling constants, are based upon the
I. Osmium Complexes with Distannyl Ligands (LnOsSnMe2-
-
SnR3) from Reaction between LnOs(SnMe2Cl) and SnR3
.
Disilanyl complexes of the type LnM-SiR2SiR3 are reasonably
easily accessible from appropriately substituted disilanes by
introducing the metal either as an anion or through an elimina-
tion reaction.80 On the other hand, distannyl complexes of the
type LnM-SnR2-SnR3 are quite rare, with the best previously
characterized example being CpCp*ClHf(SnPh2SnHMes2) (which
was spectroscopically but not structurally characterized) from
the complicated and unexpected reaction of CpCp*ClHf-
(SnHMes2) with Ph2SnH2.81 In view of the demonstrated
reactivity of Sn-Cl bonds in chlorostannyl ligands bound to
ruthenium and osmium (see section VIIIA-D,F,G) it seemed
likely that reaction between LiSnR3 and a halostannyl complex,
LnM-SnR2X, could offer a general and direct route to the
distannyl complexes LnM-SnR2SnR3. Accordingly, the reac-
tions shown in Scheme 36 were studied.82 These reactions
proceed cleanly in good yield to give the stable crystalline
distannyl complexes Os(SnMe2SnMe3)(κ2-S2CNMe2)(CO)-
(PPh3)2 (104; R ) Me) and Os(SnMe2SnPh3)(κ2-S2CNMe2)-
(CO)(PPh3)2 (104; R ) Ph). The reaction is equally effective
with Os(SnMe2Cl)Cl(CO)2(PPh3)2 as substrate, the reaction with
KSnPh3 giving the distannyl complex Os(SnMe2SnPh3)Cl(CO)2-
(PPh3)2. The X-ray crystal structures of Os(SnMe2SnPh3)(κ2-
S2CNMe2)(CO)(PPh3)2 (104; R ) Ph) and Os(SnMe2SnPh3)-
Cl(CO)2(PPh3)2 have been determined. The Os-Sn distances
are unremarkable, and the Sn(1)-Sn(2) distance in 104 is
119Sn119
119Sn117Sn
is the same as
requirement that the ratio J
Sn/J
magnetogyric ratio for 119Sn/117Sn: that is, 1.0462.40 The
coupling constants so measured for the R-Sn in Os(SnMe2-
1
SnMe3)(κ2-S2CNMe2)(CO)(PPh3)2 are J
) 2333 and
) 2332
117Sn119Sn
1
1J
) 2442 Hz and for the â-Sn are J
119Sn119Sn
117Sn119Sn
and 1J
Sn ) 2441 Hz. These coupling constants are far less
119Sn119
than that reported for Me3SnSnMe3 (1J
) 4404 Hz).40
119Sn119Sn
Two other transition-metal distannyl complexes where the one-
bond Sn-Sn coupling constants have been measured are
CpCp*ClHfSnPh2SnHMes2, for which 1J Sn is 185 Hz,81
117/119Sn119
and Cp[P(OPh)3]2FeSn(SnMe3)3,85 for which a value near zero
was measured by a heteronuclear double-resonance experiment.
It is clear that the presence of a transition metal and associated
ligands as a substituent on a ditin fragment has the effect of
reducing the one-bond Sn-Sn coupling constant.
An interesting feature of the reactivity of the osmium
distannyl complexes is that it is possible to carry out selective
functionalization at the osmium-bound tin atom (the R-Sn) while
maintaining the integrity of the Sn-Sn bond (see Scheme 36).
This can be achieved through a redistribution reaction either
with SnMe2Cl2 or even with molecular iodine.82 It should be
(82) Mo¨hlen, M. M.; Rickard, C. E. F.; Roper, W. R.; Whittell, G. R.;
Wright, L. J. J. Organomet. Chem. 2006, 691, 4065.
(83) Preut, H.; Haupt, H. J.; Huber, F. Z. Anorg. Allg. Chem. 1973,
396, 81.
(84) Spek, A. L.; Bos, K. D.; Bulten, E. J.; Noltes, J. G. Inorg. Chem.
1976, 15, 339.
(79) (a) Ueno, K.; Tobita, H.; Shimoi, M.; Ogino, H. J. Am. Chem. Soc.
1988, 110, 4092. (b) Takeuchi, T.; Tobita, H.; Ogino, H. Organometallics
1991, 10, 835.
(80) (a) Sharma, H. K.; Pannell, K. H. Chem. ReV. 1995, 95, 1351. (b)
Okazaki, M.; Tobita, H.; Ogino, H. Dalton Trans. 2003, 493.
(81) Neale, N. R.; Tilley, T. D. Tetrahedron 2004, 60, 7247.
(85) Mitchell, T. N.; Walter, G. J. Chem. Soc., Perkin Trans. 2
1977, 1842.

4718 Organometallics, Vol. 25, No. 20, 2006
noted that iodine cleaves a methyl group from the R-Sn more
rapidly than it cleaves either the Sn-Sn bond or the Sn-phenyl
bonds on the â-Sn. The activating effect of the LnOs substituent
on redistribution reactions at the osmium-bound tin atom has
been remarked upon in section VIIB.
ligand are resistant to hydrolysis. In contrast, the corresponding
coordinatively saturated trihalostannyl complexes are readily
hydrolyzed. This reduced electrophilicity of the silicon atom
when bound to an electron-rich saturated metal center is also
reflected in very different structures for silatranyl and stan-
natranyl complexes. The high reactivity of Sn-halogen bonds
in substituted stannyl complexes makes it possible to access
unusual derivatives such as an SnH3 complex and distannyl
(SnR2SnR3) complexes. Another difference is that trimethyl-
stannyl complexes of osmium often undergo reversible reactions
in which a methyl group migrates from tin to osmium, whereas
trimethylsilyl complexes of osmium do not.
IX. Concluding Remarks
The five-coordinate silyl and stannyl derivatives of ruthenium-
(II) and osmium(II) all exhibit tetragonal-pyramidal geometry
with the silicon or tin atoms at the apical position. The six-
coordinate silyl and stannyl derivatives of ruthenium(II) and
osmium(II) are all octahedral. However, apart from these
structural similarities, in other aspects of the chemistry of these
complexes marked differences emerge. These begin with
synthesis, where the oxidative addition of silanes to MPhCl-
(CO)(PPh3)2 (M ) Ru, Os) leads directly to coordinatively
unsaturated silyl derivatives. This is not a viable route to the
corresponding stannyl complexes, and these are prepared from
vinylstannanes and MHCl(CO)(PPh3)3 (M ) Ru,Os). The
reactivities of halosilyl and halostannyl ligands are often quite
different. For example, coordinatively unsaturated complexes
containing the trichlosilyl ligand are easily hydrolyzed but
coordinatively saturated complexes containing the trichlosilyl
Acknowledgment. We are very appreciative of the excellent
efforts of all our co-workers, whose names appear in the
references. Financial support for this work is gratefully ac-
knowledged from the Marsden Fund administered by the Royal
Society of New Zealand, the Research committee of The
University of Auckland, the Royal Society of London, the
Alexander von Humboldt Foundation, and the Croucher Foun-
dation of Hong Kong.
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