A new method for introducing tin ligands into tetrairidium dodecacarbonyl

Article abstract of DOI:10.1021/om1012083

The reaction of Ph₃SnOH with Ir₄(CO)₁₂ in the presence of [Bu₄N]OH in methanol solvent gave two products, [Bu₄N][Ir₄(CO)₁₁(SnPh₃)] (1; 45% yield) and [Bu₄N][Ir₄(CO)₁₀(SnPh ₃)₂(μ-H)] (2; 5.5% yield), and the reaction of Ir ₄(CO)₁₁(PPh₃) with Ph₃SnOH in the presence of [Bu₄N]OH gave the complex Ir₄(CO) ₁₀(SnPh₃)(PPh₃)(μ-H) (3) in 44% yield. It is proposed that the reactions occur by the addition of the anion [OSnPh ₃]^- generated in situ to a CO ligand of the Ir ₄(CO)₁₂ to form a stannyl-substituted metallocarboxylate ligand that subsequently loses CO₂ and transfers the SnPh₃ group to a metal atom.

Full text of DOI:10.1021/om1012083

Organometallics 2011, 30, 661–664 661
DOI: 10.1021/om1012083
A New Method for Introducing Tin Ligands into Tetrairidium
Dodecacarbonyl
Richard D. Adams,* Mingwei Chen, Eszter Trufan, and Qiang Zhang
Department of Chemistry and Biochemistry, University of South Carolina, Columbia, South Carolina 29208,
United States
Received December 29, 2010
Scheme 1
Summary: The reaction of Ph3SnOH with Ir4(CO)12 in the
presence of [Bu4N]OH in methanol solvent gave two products,
[Bu4N][Ir4(CO)11(SnPh3)] (1; 45% yield) and [Bu4N][Ir4-
(CO)10(SnPh3)2(μ-H)] (2; 5.5% yield), and the reaction of
Ir4(CO)11(PPh3) with Ph3SnOH in the presence of [Bu4N]OH
gave the complex Ir4(CO)10(SnPh3)(PPh3)(μ-H) (3) in 44%
yield. It is proposed that the reactions occur by the addition of
the anion [OSnPh3]- generated in situ to a CO ligand of the
Ir4(CO)12 to form a stannyl-substituted metallocarboxylate
ligand that subsequently loses CO2 and transfers the SnPh3
group to a metal atom.
It has been known for many years that tin is an important
modifier for both homogeneous1 and heterogeneous2-4
transition-metal catalysts. Tin has been shown to improve
the selectivity of certain types of catalytic hydrogenation
reactions.5-9 When it is combined with platinum, it can even
increase catalytic activity.3,4 Recent studies have shown that
supported multimetallic nanocluster catalysts can be prepared
with almost stoichiometric precision when they are created by
using multimetallic cluster complexes as catalyst precursors.5-9
Iridium is known to exhibit interesting catalytic properties;10
however, due to its low reactivity it is difficult in introduce tin
ligands in tetrairidium dodecacarbonyl. Some tin-substituted
tetrairidium complexes have been obtained from the more
reactive anion [Ir4(CO)11Br]-.11,12 We have recently shown
that the triiridum complex Ir3(CO)6(μ-SnPh2)3(SnPh3)3 is
formed in low yield from the reaction of Ir4(CO)12 with HSnPh3
at 125 °C (eq 1), but this reaction leads to degradation of the
tetrairidium cluster.13 In an effort to find a more convenient
route to tetrairidium-tin carbonyl complexes, we have exam-
ined the reactions of Ir4(CO)12 and Ir4(CO)11(PPh3) with
Ph3SnOH under basic conditions.
*To whom correspondence should be addressed. E-mail: Adams@chem.
sc.edu.
(1) Holt, M. S.; Wilson, W. L.; Nelson, J. H. Chem. Rev. 1989, 89,
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(5) Adams, R. D.; Trufan, E. Philos. Trans. R. Soc. 2010, 368, 1473–
1493.
The two products [Bu4N][Ir4(CO)11(SnPh3)] (1; 45% yield)
and [Bu4N][Ir4(CO)10(SnPh3)2(μ-H)] (2; 5.5% yield) were
obtained from the reaction of Ir4(CO)12 with an excess of
Ph3SnOH in the presence of [Bu4N]OH in methanol solvent
at reflux for 30 min (see Scheme 1). Note that these products
are not obtained in the absence of base.
Compound 2 can be obtained from 1 in 18% yield by
treatment with an excess of Ph3SnOH in methanol solvent in
the presence of [Bu4N]OH at 25 °C over 15 h. The structures
of the complex anions of 1 and 2 were established by a
combination of IR, 1H NMR, negative ion mass spectra, and
single-crystal X-ray diffraction analyses of their [Et4N]þ and
[Bu4N]þ salts, respectively. An ORTEP diagram of the
structure of the anion of 1 is shown in Figure 1. The anion
consists of a tetrahedral cluster of four iridium atoms with 1
SnPh3 ligand and 11 carbonyl ligands. Three of the carbonyl
(6) Thomas, J. M.; Adams, R. D.; Boswell, E. M.; Captain, B.;
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Gronbeck, H.; Raja, R. Faraday Discuss. 2008, 138, 301–315.
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Int. Ed. 2006, 45, 4782–4785.
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Midgley, P. A.; Raja, R.; Thomas, J. M. Angew. Chem., Int. Ed. 2007,
46, 8182–8185.
(9) Adams, R. D.; Blom, D. A.; Captain, B.; Raja, R.; Thomas, J. M.;
Trufan, E. Langmuir 2008, 24, 9223–9226.
(10) (a) Gates, B. C. Chem. Rev. 1995, 95, 511–522. (b) Argo, A. M.;
Odzak, J. F.; Goellner, J. F.; Lai, F. S.; Xiao, F.-S.; Gates, B. C. J. Phys.
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Moura, F. C. C.; dos Santos, E. N.; Lago, R. M.; Vargas, M. D.; Araujo, M. H.
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r
2011 American Chemical Society
Published on Web 01/21/2011
pubs.acs.org/Organometallics

662 Organometallics, Vol. 30, No. 4, 2011
Adams et al.
Figure 2. ORTEP diagram of the molecular structure of
[HIr4(CO)10(SnPh3)2]- (2), showing 30% probability thermal
ellipsoids. The hydrogen atoms on the phenyl rings are omitted
˚
for clarity. Selected interatomic bond distances (A) and angles
Figure 1. ORTEP diagram of the molecular structure of the
anion [Ir4(CO)11(SnPh3)]- of 1-Et, showing 30% probability
thermal ellipsoids. The hydrogen atoms on the phenyl rings are
(deg): Ir1-Ir3 = 2.7122(6), Ir1-Ir4 = 2.7184(6), Ir1-Ir2 =
2.8608(6), Ir2-Ir4 = 2.7074(7), Ir2-Ir3 = 2.7225(7), Ir1-
H1 = 1.75(2), Ir1-Sn1 = 2.6449(9), Ir2-Sn2 = 2.6626(10),
Ir2-H1 = 1.74(2), Ir3-Ir4 = 2.7206(7); Sn1-Ir1-Ir4 =
165.75(3), Sn2-Ir2-Ir3 = 163.86(3).
˚
omitted for clarity. Selected interatomic bond distances (A) and
angles (deg) of compound 1: Ir1-Ir2 = 2.7610(3), Ir1-Ir3 =
2.7616(4), Ir1-Ir4=2.7435(4), Ir2-Ir3=2.7061(4), Ir2-Ir4=
2.7210(4), Ir3-Ir4=2.7240(4), Ir1-Sn1=2.6358(4); Sn1- Ir1-
Ir2=107.660(13), Ir4-Ir1-Sn1=164.246(15).
For comparison, we have also investigated the reaction of
the PPh3 derivative of Ir4(CO)11(PPh3)17 with Ph3SnOH.
The new tin complex Ir4(CO)10(SnPh3)(PPh3)(μ-H) (3) was
isolated by TLC in 44% yield after stirring a solution of an
excess of Ph3SnOH with Ir4(CO)11(PPh3) and [Bu4N]OH for
16 h at 25 °C. An ORTEP diagram of the molecular structure
of 3 is shown in Figure 3. In the solid state, there are two
independent molecules of 3 in the asymmetric crystal unit.
Both molecules are structurally similar and contain one PPh3
ligand and one SnPh3 ligand. The PPh3 and SnPh3 ligands
are disordered in both molecules; thus, the Ir-Sn/P distances
measured here are not of high accuracy, but the structural
analysis does confirm the gross structure of the molecule.
The tetrahedral arrangement of iridium atoms is not dis-
ordered; therefore, the Ir-Ir distances are reliable. The Ir-Ir
bond between the PPh3 and SnPh3 ligands contains a brid-
ging hydrido ligand and this Ir-Ir distance, Ir1-Ir2 =
ligands are edge-bridging ligands about the Ir(1)-Ir(2)-Ir-
(3) triangular group of metal atoms. All the others are linear
terminal carbonyl ligands. The Ir-Ir bond distances range
˚
from 2.7061(4) to 2.7610(3) A. These values are slightly
˚
longer than the Ir-Ir distances of 2.692 A found in Ir4-
(CO)12, which has a disordered structure in the solid state.14
The SnPh3 ligand lies approximately trans to the Ir1-Ir4 bond:
Ir4-Ir1-Sn1 = 164.246(15)o. The Ir1-Sn1 distance, 2.6358-
˚
(4) A, is significantly shorter than the Ir-Sn distances to the
SnPh3 ligands found in the crowded triiridium cluster complex
Ir3(CO)6(SnPh3)3(μ-SnPh2)3 (2.6736(9)-2.6981(11) A),13 but it
˚
˚
is similar to the Ir-Sn distance of 2.6216(5) A found in the less
crowded monoiridium complex Ir(COD)(CO)2SnPh3.15
An ORTEP diagram of the structure of the anion of 2 is
shown in Figure 2. The anion consists of a tetrahedral cluster
of four iridium atoms with two SnPh3 ligands on different
iridium atoms, Ir(1) and Ir(2). Each tin-substituted iridium
atom contains two linear terminal carbonyl ligands; the
other two iridium atoms have three carbonyl ligands. There
is a bridging hydrido ligand across the Ir(1)-Ir(2) bond:
δ -19.69 (2JSn-H = 9.51 Hz) in the H NMR spectrum. As
˚
˚
2.8851(5) A for molecule 1 and Ir5-Ir6 = 2.8730(5) A for
molecule 2, is significantly longer than the other Ir-Ir dis-
tances, which range from 2.7012(5) to 2.7159(5) A. The
16
˚
hydride ligand exhibits the usual upfield shift: δ -18.37. The
phosphine ligand exhibits a typical 31P resonance shift:
δ -15.18 ppm.
expected,16 the hydride-bridged Ir-Ir distance, 2.8609(6) A,
˚
Although 3 is an uncharged, neutral molecule, we have not
yet been able to isolate any uncharged forms of the two
anions of 1 and 2 by acidification with protic acids. This may
simply be due to the relative differences in basicity of the
corresponding anions. Because of the presence of the PPh3
ligand, a deprotonated form of 3 would be considerably
more basic than that of 1 and thus would be more stable in its
protonated form. These studies are still in progress.
is significantly longer than the unbridged Ir-Ir distances,
˚
which range from 2.7074(7) to 2.7225(7) A. The Ir-Sn
˚
bond distances, Ir1-Sn1 = 2.6449(9) A and Ir2-Sn2 =
2.6625(10) A, are similar to those found in 1. Each of the
metal atoms in 1 and 2 has an 18-electron configuration.
˚
(14) Churchill, M. R.; Hutchinson, J. P. Inorg. Chem. 1978, 17, 3528–
3535.
(15) Adams, R. D.; Trufan, E. Organometallics 2010, 29, 4346–4353.
(16) (a) Bau, R.; Drabnis, M. H. Inorg. Chim. Acta 1997, 259, 27–50.
(b) Teller, R. G.; Bau, R. Struct. Bonding 1981, 41, 1–82.
(17) Ros, R.; Scrivanti, A.; Albano, V. G.; Braga, D.; Garlaschelli, L.
J. Chem. Soc., Dalton Trans. 1986, 2411–2421.

Communication
Organometallics, Vol. 30, No. 4, 2011 663
Figure 3. ORTEP diagram of the molecular structure of HIr4(CO)10(SnPh3)(PPh3) (3), showing 30% probability thermal ellipsoids
(the disorder between Sn and P is not shown). The hydrogen atoms on the phenyl rings are omitted for clarity. Selected interatomic
˚
bond distances (A) and angles (deg): molecule 1, Ir1-Ir2 = 2.8851(5), Ir2-Ir3 2.7095(5), Ir2-Ir4 = 2.7135(5), Ir1-Sn1(P2) =
2.5212(10), Ir1-Ir3 = 2.7100(5), Ir1-Ir4 = 2.7142(5), Ir3-Ir4 = 2.7012(5), Ir1-H1 = 1.76(5), Ir2-P1(Sn2) = 2.5126(10), Ir2-
H1 = 1.79(6), Sn1(P1)-Ir1-Ir2 = 113.17(3), P1(Sn2)-Ir2-Ir1 = 112.69(3); molecule 2, Ir5-Ir6 = 2.8730(5), Ir5-Ir7 = 2.7149(6),
Ir5-Ir8 = 2.7159(5), Ir6-Ir7 = 2.7054(5), Ir6-Ir8 = 2.7109(5), Ir7-Ir8 = 2.7058(6), Ir5-H2 = 1.78(7), Ir5-P3(Sn4) = 2.4491(14),
Ir6-Sn3(P4) = 2.6079(9), Ir6-H2 = 1.78(7), Sn3(P4)-Ir6-Ir5 = 113.14(2), P3(Sn4)-Ir5-Ir6 = 109.39(3).
Scheme 2
It is worthwhile to consider possible mechanisms for the
formation of the anions 1 and 2 and the neutral molecule 3. A
number of years ago, Garlaschelli et al. showed that alk-
oxides add to the carbonyl ligands of Ir4(CO)12 to form
metallocarboxylate ligands.18 For the basic media used here-
in, it is proposed that a similar process involving [OSnPh3]-,
generated in situ, could lead to a similar triphenylstannyl-
substituted metallocarboxylate, such as A (see Scheme 2).
Stannyl-substituted metallocarboxylate complexes have
been observed previously, although they have been obtained
by different procedures.19-21 In those complexes, the tin
atom is typically bonded to both oxygen atoms of the car-
boxylate group, but even so these ligand groups are known to
(19) Senn, D. R.; Gladysz, J. A.; Emerson, K.; Larsen, R. D. Inorg.
Chem. 1987, 26, 2737–2739.
(20) (a) Gibson, D. H.; Ye, M.; Sleadd, B. A.; Mehta, J. M.; Mbadike,
O. P.; Richardson, J. F.; Mashuta, M. S. Organometallics 1995, 14,
1242–1255. (b) Gibson, D. H.; Mehta, J. M.; Ye, M.; Richardson, J. F.;
Mashuta, M. S. Organometallics 1994, 10, 1070–1072. (c) Gibson, D. H.;
Ong, T.-K.; Ye, M. Organometallics 1991, 10, 1811–1821.
(18) Garlaschelli, L.; Martinengo, S.; Chini, P.; Canziani, F.; Bau, R.
J. Organomet. Chem. 1981, 213, 379–388.
(21) Hirano, M.; Akita, M.; Tani, K.; Kumagai, K.; Kasuga, N.;
Fukuoka, A.; Komiya, S. Organometallics 1997, 16, 4206–4213.

664 Organometallics, Vol. 30, No. 4, 2011
Adams et al.
undergo decarboxylations that lead to the formation of
metal-tin bonds.19 A similar loss of CO2 from A and a
transfer of the SnPh3 group to an iridium atom should lead to
the anion 1. A second application of this process to 1 with a
subsequent proton addition would lead to 2, and a similar
process occurring with Ir4(CO)11(PPh3) would yield 3.
It has not yet been possible to synthesize the compounds
1-3 by other methods. We believe that reactions of [OSn-
R3]- anions with metal carbonyl complexes could be general
and lead to a variety of new tin-containing transition-metal
carbonyl complexes that may be useful as precursors to new
tin-containing homogeneous and heterogeneous transition-
metal catalysts. Further studies of the reactions of Ph3SnOH
with transition-metal carbonyl complexes in basic media are
in progress.
Acknowledgment. This research was supported by the
National Science Foundation under Grant No. CHE-
0743190. We thank the USC NanoCenter for partial
support of this work.
Supporting Information Available: Text, a table, figures, and
CIF files giving details for the synthesis of compounds 1-3 and
crystal data for the structural analyses of compounds 1-Et, 2,
and 3. This material is available free of charge via the Internet at
http://pubs.acs.org.